From 77e016e2704504594cd776ac897af1be5a99a56b Mon Sep 17 00:00:00 2001 From: Love Lysell Berglund Date: Thu, 25 Sep 2025 13:27:38 +0200 Subject: [PATCH] lab1.zip --- eng_stopwords.txt | 196 ++++++++++++++++++++ examples/article1.txt | 44 +++++ examples/article2.txt | 332 +++++++++++++++++++++++++++++++++ examples/article3.txt | 201 ++++++++++++++++++++ examples/article4.txt | 416 ++++++++++++++++++++++++++++++++++++++++++ examples/article5.txt | 398 ++++++++++++++++++++++++++++++++++++++++ examples/article6.txt | 367 +++++++++++++++++++++++++++++++++++++ examples/article7.txt | 78 ++++++++ test.py | 81 ++++++++ tokenize.py | 0 10 files changed, 2113 insertions(+) create mode 100644 eng_stopwords.txt create mode 100644 examples/article1.txt create mode 100644 examples/article2.txt create mode 100644 examples/article3.txt create mode 100644 examples/article4.txt create mode 100644 examples/article5.txt create mode 100644 examples/article6.txt create mode 100644 examples/article7.txt create mode 100644 test.py create mode 100644 tokenize.py diff --git a/eng_stopwords.txt b/eng_stopwords.txt new file mode 100644 index 0000000..281f884 --- /dev/null +++ b/eng_stopwords.txt @@ -0,0 +1,196 @@ +. +? +! +, +( +) +[ +] +{ +} +- +– +_ +" +' +’ +‘ +· +: +; +$ +£ +€ +% +# +@ +\ ++ +^ +/ += +± +& +— +* +0 +1 +2 +3 +4 +5 +6 +7 +8 +9 +the +a +an +and +or +nor +just +never +quite +am +is +are +was +were +be +been +do +did +does +may +might +can +must +should +shall +could +would +to +of +in +for +as +on +off +by +at +but +such +also +this +these +those +that +here +there +how +where +when +no +upon +out +up +down +into +i +me +my +myself +you +your +yourself +he +his +him +himself +she +her +herself +it +its +itself +we +our +us +they +their +them +themselves +s +t +d +n +o +with +all +not +from +so +now +which +whose +like +self +most +one +once +first +two +twice +second +three +last +have +has +had +then +what +some +more +if +other +only +yet +will +over +any +who +though +than +whom +very +about +still +before +after +again +while +away +go +went +goes +come +comes +came +say +says +said +see +sees +saw +let +give +gives +gave +take +takes +took +nothing +something +gutenberg +project diff --git a/examples/article1.txt b/examples/article1.txt new file mode 100644 index 0000000..08a5595 --- /dev/null +++ b/examples/article1.txt @@ -0,0 +1,44 @@ +The word count is the number of words in a document or passage of text. Word counting may be needed when a text is required to stay within certain numbers of words. This may particularly be the case in academia, legal proceedings, journalism and advertising. Word count is commonly used by translators to determine the price of a translation job. Word counts may also be used to calculate measures of readability and to measure typing and reading speeds (usually in words per minute). When converting character counts to words, a measure of 5 or 6 characters to a word is generally used for English.[1] + + +Contents +1 Details and variations of definition +2 Software +3 In fiction +4 In non-fiction +5 See also +6 References +7 Sources +Details and variations of definition + +This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. +Find sources: "Word count" – news · newspapers · books · scholar · JSTOR (July 2014) (Learn how and when to remove this template message) +Variations in the operational definitions of how to count the words can occur (namely, what "counts as" a word, and which words "don't count" toward the total). However, especially since the advent of widespread word processing, there is a broad consensus on these operational definitions (and hence the bottom-line integer result). The consensus is to accept the text segmentation rules generally found in most word processing software (including how word boundaries are determined, which depends on how word dividers are defined). The first trait of that definition is that a space (any of various whitespace characters, such as a "regular" word space, an em space, or a tab character) is a word divider. Usually a hyphen or a slash is, too. Different word counting programs may give varying results, depending on the text segmentation rule details, and on whether words outside the main text (such as footnotes, endnotes, or hidden text) are counted. But the behavior of most major word processing applications is broadly similar. + +However, during the era when school assignments were done in handwriting or with typewriters, the rules for these definitions often differed from today's consensus. Most importantly, many students were drilled on the rule that "certain words don't count", usually articles (namely, "a", "an", "the"), but sometimes also others, such as conjunctions (for example, "and", "or", "but") and some prepositions (usually "to", "of"). Hyphenated permanent compounds such as "follow-up" (noun) or "long-term" (adjective) were counted as one word. To save the time and effort of counting word-by-word, often a rule of thumb for the average number of words per line was used, such as 10 words per line. These "rules" have fallen by the wayside in the word processing era; the "word count" feature of such software (which follows the text segmentation rules mentioned earlier) is now the standard arbiter, because it is largely consistent (across documents and applications) and because it is fast, effortless, and costless (already included with the application). + +As for which sections of a document "count" toward the total (such as footnotes, endnotes, abstracts, reference lists and bibliographies, tables, figure captions, hidden text), the person in charge (teacher, client) can define their choice, and users (students, workers) can simply select (or exclude) the elements accordingly, and watch the word count automatically update. + +Software +Modern web browsers support word counting via extensions, via a JavaScript bookmarklet, or a script that is hosted in a website. Most word processors can also count words. Unix-like systems include a program, wc, specifically for word counting. There are a wide variety of word counting tools available online. + +As explained earlier, different word counting programs may give varying results, depending on the text segmentation rule details. The exact number of words often is not a strict requirement, thus the variation is acceptable. + +In fiction +Novelist Jane Smiley suggests that length is an important quality of the novel.[2] However, novels can vary tremendously in length; Smiley lists novels as typically being between 100,000 and 175,000 words,[3] while National Novel Writing Month requires its novels to be at least 50,000 words. There are no firm rules: for example, the boundary between a novella and a novel is arbitrary and a literary work may be difficult to categorise.[4] But while the length of a novel is to a large extent up to its writer,[5] lengths may also vary by subgenre; many chapter books for children start at a length of about 16,000 words,[6] and a typical mystery novel might be in the 60,000 to 80,000 word range while a thriller could be well over 100,000 words.[7] + +The Science Fiction and Fantasy Writers of America specifies word lengths for each category of its Nebula award categories:[8] + +Classification Word count +Novel 40,000 words or over +Novella 17,500 to 39,999 words +Novelette 7,500 to 17,499 words +Short story under 7,500 words +In non-fiction +The acceptable length of an academic dissertation varies greatly, dependent predominantly on the subject. Numerous American universities limit Ph.D. dissertations to 100,000 words, barring special permission for exceeding this limit.[9] + +See also +Flash fiction +List of longest novels +Twitterature +Word lists by frequency diff --git a/examples/article2.txt b/examples/article2.txt new file mode 100644 index 0000000..0ebe1f7 --- /dev/null +++ b/examples/article2.txt @@ -0,0 +1,332 @@ +The electron is a subatomic particle, symbol +e− + or +β− +, whose electric charge is negative one elementary charge.[9] Electrons belong to the first generation of the lepton particle family,[10] and are generally thought to be elementary particles because they have no known components or substructure.[1] The electron has a mass that is approximately 1/1836 that of the proton.[11] Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle.[10] Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy. + +Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism, chemistry and thermal conductivity, and they also participate in gravitational, electromagnetic and weak interactions.[12] Since an electron has charge, it has a surrounding electric field, and if that electron is moving relative to an observer, said observer will observe it to generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors and particle accelerators. + +Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms. Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.[13] In 1838, British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms.[3] Irish physicist George Johnstone Stoney named this charge 'electron' in 1891, and J. J. Thomson and his team of British physicists identified it as a particle in 1897.[5] Electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere. The antiparticle of the electron is called the positron; it is identical to the electron except that it carries electrical and other charges of the opposite sign. When an electron collides with a positron, both particles can be annihilated, producing gamma ray photons. + + +Contents +1 History +1.1 Discovery of effect of electric force +1.2 Discovery of two kinds of charges +1.3 Discovery of free electrons outside matter +1.4 Atomic theory +1.5 Quantum mechanics +1.6 Particle accelerators +1.7 Confinement of individual electrons +2 Characteristics +2.1 Classification +2.2 Fundamental properties +2.3 Quantum properties +2.4 Virtual particles +2.5 Interaction +2.6 Atoms and molecules +2.7 Conductivity +2.8 Motion and energy +3 Formation +4 Observation +5 Plasma applications +5.1 Particle beams +5.2 Imaging +5.3 Other applications +6 See also +7 Notes +8 References +9 External links +History +See also: History of electromagnetism +Discovery of effect of electric force +The ancient Greeks noticed that amber attracted small objects when rubbed with fur. Along with lightning, this phenomenon is one of humanity's earliest recorded experiences with electricity.[14] In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electrica, to refer to those substances with property similar to that of amber which attract small objects after being rubbed.[15] Both electric and electricity are derived from the Latin ēlectrum (also the root of the alloy of the same name), which came from the Greek word for amber, ἤλεκτρον (ēlektron). + +Discovery of two kinds of charges +In the early 1700s, French chemist Charles François du Fay found that if a charged gold-leaf is repulsed by glass rubbed with silk, then the same charged gold-leaf is attracted by amber rubbed with wool. From this and other results of similar types of experiments, du Fay concluded that electricity consists of two electrical fluids, vitreous fluid from glass rubbed with silk and resinous fluid from amber rubbed with wool. These two fluids can neutralize each other when combined.[15][16] American scientist Ebenezer Kinnersley later also independently reached the same conclusion.[17](p118) A decade later Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess (+) or deficit (−). He gave them the modern charge nomenclature of positive and negative respectively.[18] Franklin thought of the charge carrier as being positive, but he did not correctly identify which situation was a surplus of the charge carrier, and which situation was a deficit.[19] + +Between 1838 and 1851, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges.[2] Beginning in 1846, German physicist William Weber theorized that electricity was composed of positively and negatively charged fluids, and their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there existed a "single definite quantity of electricity", the charge of a monovalent ion. He was able to estimate the value of this elementary charge e by means of Faraday's laws of electrolysis.[20] However, Stoney believed these charges were permanently attached to atoms and could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".[3] + +Stoney initially coined the term electrolion in 1881. Ten years later, he switched to electron to describe these elementary charges, writing in 1894: "... an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name electron". A 1906 proposal to change to electrion failed because Hendrik Lorentz preferred to keep electron.[21][22] The word electron is a combination of the words electric and ion.[23] The suffix -on which is now used to designate other subatomic particles, such as a proton or neutron, is in turn derived from electron.[24][25] + +Discovery of free electrons outside matter +A round glass vacuum tube with a glowing circular beam inside +A beam of electrons deflected in a circle by a magnetic field[26] +The discovery of electrons by Joseph Thomson was closely tied with the experimental and theoretical research of cathode rays for decades by many physicists.[3] While studying electrical conductivity in rarefied gases in 1859, the German physicist Julius Plücker observed that the phosphorescent light, which was caused by radiation emitted from the cathode, appeared at the tube wall near the cathode, and the region of the phosphorescent light could be moved by application of a magnetic field. In 1869, Plucker's student Johann Wilhelm Hittorf found that a solid body placed in between the cathode and the phosphorescence would cast a shadow upon the phosphorescent region of the tube. Hittorf inferred that there are straight rays emitted from the cathode and that the phosphorescence was caused by the rays striking the tube walls. In 1876, the German physicist Eugen Goldstein showed that the rays were emitted perpendicular to the cathode surface, which distinguished between the rays that were emitted from the cathode and the incandescent light. Goldstein dubbed the rays cathode rays.[27][28]:393 + +During the 1870s, the English chemist and physicist Sir William Crookes developed the first cathode ray tube to have a high vacuum inside.[29] He then showed in 1874 that the cathode rays can turn a small paddle wheel when placed in their path. Therefore, he concluded that the rays carried momentum. Furthermore, by applying a magnetic field, he was able to deflect the rays, thereby demonstrating that the beam behaved as though it were negatively charged.[27] In 1879, he proposed that these properties could be explained by regarding cathode rays as composed of negatively charged gaseous molecules in fourth state of matter in which the mean free path of the particles is so long that collisions may be ignored.[28]:394–395 + +The German-born British physicist Arthur Schuster expanded upon Crookes' experiments by placing metal plates parallel to the cathode rays and applying an electric potential between the plates. The field deflected the rays toward the positively charged plate, providing further evidence that the rays carried negative charge. By measuring the amount of deflection for a given level of current, in 1890 Schuster was able to estimate the charge-to-mass ratio[c] of the ray components. However, this produced a value that was more than a thousand times greater than what was expected, so little credence was given to his calculations at the time.[27] + +In 1892 Hendrik Lorentz suggested that the mass of these particles (electrons) could be a consequence of their electric charge.[30] + + +J. J. Thomson +While studying naturally fluorescing minerals in 1896, the French physicist Henri Becquerel discovered that they emitted radiation without any exposure to an external energy source. These radioactive materials became the subject of much interest by scientists, including the New Zealand physicist Ernest Rutherford who discovered they emitted particles. He designated these particles alpha and beta, on the basis of their ability to penetrate matter.[31] In 1900, Becquerel showed that the beta rays emitted by radium could be deflected by an electric field, and that their mass-to-charge ratio was the same as for cathode rays.[32] This evidence strengthened the view that electrons existed as components of atoms.[33][34] + +In 1897, the British physicist J. J. Thomson, with his colleagues John S. Townsend and H. A. Wilson, performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier.[5] Thomson made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles," had perhaps one thousandth of the mass of the least massive ion known: hydrogen.[5] He showed that their charge-to-mass ratio, e/m, was independent of cathode material. He further showed that the negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal.[5][35] The name electron was adopted for these particles by the scientific community, mainly due to the advocation by G. F. Fitzgerald, J. Larmor, and H. A. Lorenz.[36](p273) + + +Robert Millikan +The electron's charge was more carefully measured by the American physicists Robert Millikan and Harvey Fletcher in their oil-drop experiment of 1909, the results of which were published in 1911. This experiment used an electric field to prevent a charged droplet of oil from falling as a result of gravity. This device could measure the electric charge from as few as 1–150 ions with an error margin of less than 0.3%. Comparable experiments had been done earlier by Thomson's team,[5] using clouds of charged water droplets generated by electrolysis, and in 1911 by Abram Ioffe, who independently obtained the same result as Millikan using charged microparticles of metals, then published his results in 1913.[37] However, oil drops were more stable than water drops because of their slower evaporation rate, and thus more suited to precise experimentation over longer periods of time.[38] + +Around the beginning of the twentieth century, it was found that under certain conditions a fast-moving charged particle caused a condensation of supersaturated water vapor along its path. In 1911, Charles Wilson used this principle to devise his cloud chamber so he could photograph the tracks of charged particles, such as fast-moving electrons.[39] + +Atomic theory +See also: The proton–electron model of the nucleus +Three concentric circles about a nucleus, with an electron moving from the second to the first circle and releasing a photon +The Bohr model of the atom, showing states of electron with energy quantized by the number n. An electron dropping to a lower orbit emits a photon equal to the energy difference between the orbits. +By 1914, experiments by physicists Ernest Rutherford, Henry Moseley, James Franck and Gustav Hertz had largely established the structure of an atom as a dense nucleus of positive charge surrounded by lower-mass electrons.[40] In 1913, Danish physicist Niels Bohr postulated that electrons resided in quantized energy states, with their energies determined by the angular momentum of the electron's orbit about the nucleus. The electrons could move between those states, or orbits, by the emission or absorption of photons of specific frequencies. By means of these quantized orbits, he accurately explained the spectral lines of the hydrogen atom.[41] However, Bohr's model failed to account for the relative intensities of the spectral lines and it was unsuccessful in explaining the spectra of more complex atoms.[40] + +Chemical bonds between atoms were explained by Gilbert Newton Lewis, who in 1916 proposed that a covalent bond between two atoms is maintained by a pair of electrons shared between them.[42] Later, in 1927, Walter Heitler and Fritz London gave the full explanation of the electron-pair formation and chemical bonding in terms of quantum mechanics.[43] In 1919, the American chemist Irving Langmuir elaborated on the Lewis' static model of the atom and suggested that all electrons were distributed in successive "concentric (nearly) spherical shells, all of equal thickness".[44] In turn, he divided the shells into a number of cells each of which contained one pair of electrons. With this model Langmuir was able to qualitatively explain the chemical properties of all elements in the periodic table,[43] which were known to largely repeat themselves according to the periodic law.[45] + +In 1924, Austrian physicist Wolfgang Pauli observed that the shell-like structure of the atom could be explained by a set of four parameters that defined every quantum energy state, as long as each state was occupied by no more than a single electron. This prohibition against more than one electron occupying the same quantum energy state became known as the Pauli exclusion principle.[46] The physical mechanism to explain the fourth parameter, which had two distinct possible values, was provided by the Dutch physicists Samuel Goudsmit and George Uhlenbeck. In 1925, they suggested that an electron, in addition to the angular momentum of its orbit, possesses an intrinsic angular momentum and magnetic dipole moment.[40][47] This is analogous to the rotation of the Earth on its axis as it orbits the Sun. The intrinsic angular momentum became known as spin, and explained the previously mysterious splitting of spectral lines observed with a high-resolution spectrograph; this phenomenon is known as fine structure splitting.[48] + +Quantum mechanics +See also: History of quantum mechanics +In his 1924 dissertation Recherches sur la théorie des quanta (Research on Quantum Theory), French physicist Louis de Broglie hypothesized that all matter can be represented as a de Broglie wave in the manner of light.[49] That is, under the appropriate conditions, electrons and other matter would show properties of either particles or waves. The corpuscular properties of a particle are demonstrated when it is shown to have a localized position in space along its trajectory at any given moment.[50] The wave-like nature of light is displayed, for example, when a beam of light is passed through parallel slits thereby creating interference patterns. In 1927, George Paget Thomson discovered the interference effect was produced when a beam of electrons was passed through thin metal foils and by American physicists Clinton Davisson and Lester Germer by the reflection of electrons from a crystal of nickel.[51] + +A symmetrical blue cloud that decreases in intensity from the center outward +In quantum mechanics, the behavior of an electron in an atom is described by an orbital, which is a probability distribution rather than an orbit. In the figure, the shading indicates the relative probability to "find" the electron, having the energy corresponding to the given quantum numbers, at that point. +De Broglie's prediction of a wave nature for electrons led Erwin Schrödinger to postulate a wave equation for electrons moving under the influence of the nucleus in the atom. In 1926, this equation, the Schrödinger equation, successfully described how electron waves propagated.[52] Rather than yielding a solution that determined the location of an electron over time, this wave equation also could be used to predict the probability of finding an electron near a position, especially a position near where the electron was bound in space, for which the electron wave equations did not change in time. This approach led to a second formulation of quantum mechanics (the first by Heisenberg in 1925), and solutions of Schrödinger's equation, like Heisenberg's, provided derivations of the energy states of an electron in a hydrogen atom that were equivalent to those that had been derived first by Bohr in 1913, and that were known to reproduce the hydrogen spectrum.[53] Once spin and the interaction between multiple electrons were describable, quantum mechanics made it possible to predict the configuration of electrons in atoms with atomic numbers greater than hydrogen.[54] + +In 1928, building on Wolfgang Pauli's work, Paul Dirac produced a model of the electron – the Dirac equation, consistent with relativity theory, by applying relativistic and symmetry considerations to the hamiltonian formulation of the quantum mechanics of the electro-magnetic field.[55] In order to resolve some problems within his relativistic equation, Dirac developed in 1930 a model of the vacuum as an infinite sea of particles with negative energy, later dubbed the Dirac sea. This led him to predict the existence of a positron, the antimatter counterpart of the electron.[56] This particle was discovered in 1932 by Carl Anderson, who proposed calling standard electrons negatons and using electron as a generic term to describe both the positively and negatively charged variants. + +In 1947, Willis Lamb, working in collaboration with graduate student Robert Retherford, found that certain quantum states of the hydrogen atom, which should have the same energy, were shifted in relation to each other; the difference came to be called the Lamb shift. About the same time, Polykarp Kusch, working with Henry M. Foley, discovered the magnetic moment of the electron is slightly larger than predicted by Dirac's theory. This small difference was later called anomalous magnetic dipole moment of the electron. This difference was later explained by the theory of quantum electrodynamics, developed by Sin-Itiro Tomonaga, Julian Schwinger and Richard Feynman in the late 1940s.[57] + +Particle accelerators +With the development of the particle accelerator during the first half of the twentieth century, physicists began to delve deeper into the properties of subatomic particles.[58] The first successful attempt to accelerate electrons using electromagnetic induction was made in 1942 by Donald Kerst. His initial betatron reached energies of 2.3 MeV, while subsequent betatrons achieved 300 MeV. In 1947, synchrotron radiation was discovered with a 70 MeV electron synchrotron at General Electric. This radiation was caused by the acceleration of electrons through a magnetic field as they moved near the speed of light.[59] + +With a beam energy of 1.5 GeV, the first high-energy particle collider was ADONE, which began operations in 1968.[60] This device accelerated electrons and positrons in opposite directions, effectively doubling the energy of their collision when compared to striking a static target with an electron.[61] The Large Electron–Positron Collider (LEP) at CERN, which was operational from 1989 to 2000, achieved collision energies of 209 GeV and made important measurements for the Standard Model of particle physics.[62][63] + +Confinement of individual electrons +Individual electrons can now be easily confined in ultra small (L = 20 nm, W = 20 nm) CMOS transistors operated at cryogenic temperature over a range of −269 °C (4 K) to about −258 °C (15 K).[64] The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in the single particle formalism, by replacing its mass with the effective mass tensor. + +Characteristics +Classification +A table with four rows and four columns, with each cell containing a particle identifier +Standard Model of elementary particles. The electron (symbol e) is on the left. +In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons, which are believed to be fundamental or elementary particles. Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first-generation of fundamental particles.[65] The second and third generation contain charged leptons, the muon and the tau, which are identical to the electron in charge, spin and interactions, but are more massive. Leptons differ from the other basic constituent of matter, the quarks, by their lack of strong interaction. All members of the lepton group are fermions, because they all have half-odd integer spin; the electron has spin +1 +/ +2 +.[66] + +Fundamental properties +The invariant mass of an electron is approximately 9.109×10−31 kilograms,[67] or 5.489×10−4 atomic mass units. On the basis of Einstein's principle of mass–energy equivalence, this mass corresponds to a rest energy of 0.511 MeV. The ratio between the mass of a proton and that of an electron is about 1836.[11][68] Astronomical measurements show that the proton-to-electron mass ratio has held the same value, as is predicted by the Standard Model, for at least half the age of the universe.[69] + +Electrons have an electric charge of −1.602176634×10−19 coulombs,[67] which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge. Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign.[70] As the symbol e is used for the elementary charge, the electron is commonly symbolized by +e− +, where the minus sign indicates the negative charge. The positron is symbolized by +e+ + because it has the same properties as the electron but with a positive rather than negative charge.[66][67] + +The electron has an intrinsic angular momentum or spin of +1 +/ +2 +.[67] This property is usually stated by referring to the electron as a spin- +1 +/ +2 + particle.[66] For such particles the spin magnitude is +ħ +/ +2 +,[71][d] while the result of the measurement of a projection of the spin on any axis can only be ± +ħ +/ +2 +. In addition to spin, the electron has an intrinsic magnetic moment along its spin axis.[67] It is approximately equal to one Bohr magneton,[72][e] which is a physical constant equal to 9.27400915(23)×10−24 joules per tesla.[67] The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity.[73] + +The electron has no known substructure.[1][74] + +The issue of the radius of the electron is a challenging problem of modern theoretical physics. The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity. On the other hand, a point-like electron (zero radius) generates serious mathematical difficulties due to the self-energy of the electron tending to infinity.[75] Observation of a single electron in a Penning trap suggests the upper limit of the particle's radius to be 10−22 meters.[76] The upper bound of the electron radius of 10−18 meters[77] can be derived using the uncertainty relation in energy. There is also a physical constant called the "classical electron radius", with the much larger value of 2.8179×10−15 m, greater than the radius of the proton. However, the terminology comes from a simplistic calculation that ignores the effects of quantum mechanics; in reality, the so-called classical electron radius has little to do with the true fundamental structure of the electron.[78][79][f] + +There are elementary particles that spontaneously decay into less massive particles. An example is the muon, with a mean lifetime of 2.2×10−6 seconds, which decays into an electron, a muon neutrino and an electron antineutrino. The electron, on the other hand, is thought to be stable on theoretical grounds: the electron is the least massive particle with non-zero electric charge, so its decay would violate charge conservation.[80] The experimental lower bound for the electron's mean lifetime is 6.6×1028 years, at a 90% confidence level.[8][81][82] + +Quantum properties +As with all particles, electrons can act as waves. This is called the wave–particle duality and can be demonstrated using the double-slit experiment. + +The wave-like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle. In quantum mechanics, the wave-like property of one particle can be described mathematically as a complex-valued function, the wave function, commonly denoted by the Greek letter psi (ψ). When the absolute value of this function is squared, it gives the probability that a particle will be observed near a location—a probability density.[83]:162–218 + +A three dimensional projection of a two dimensional plot. There are symmetric hills along one axis and symmetric valleys along the other, roughly giving a saddle-shape +Example of an antisymmetric wave function for a quantum state of two identical fermions in a 1-dimensional box. If the particles swap position, the wave function inverts its sign. +Electrons are identical particles because they cannot be distinguished from each other by their intrinsic physical properties. In quantum mechanics, this means that a pair of interacting electrons must be able to swap positions without an observable change to the state of the system. The wave function of fermions, including electrons, is antisymmetric, meaning that it changes sign when two electrons are swapped; that is, ψ(r1, r2) = −ψ(r2, r1), where the variables r1 and r2 correspond to the first and second electrons, respectively. Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities. Bosons, such as the photon, have symmetric wave functions instead.[83]:162–218 + +In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a zero probability that each pair will occupy the same location or state. This is responsible for the Pauli exclusion principle, which precludes any two electrons from occupying the same quantum state. This principle explains many of the properties of electrons. For example, it causes groups of bound electrons to occupy different orbitals in an atom, rather than all overlapping each other in the same orbit.[83]:162–218 + +Virtual particles +Main article: Virtual particle +In a simplified picture, every photon spends some time as a combination of a virtual electron plus its antiparticle, the virtual positron, which rapidly annihilate each other shortly thereafter.[84] The combination of the energy variation needed to create these particles, and the time during which they exist, fall under the threshold of detectability expressed by the Heisenberg uncertainty relation, ΔE · Δt ≥ ħ. In effect, the energy needed to create these virtual particles, ΔE, can be "borrowed" from the vacuum for a period of time, Δt, so that their product is no more than the reduced Planck constant, ħ ≈ 6.6×10−16 eV·s. Thus, for a virtual electron, Δt is at most 1.3×10−21 s.[85] + +A sphere with a minus sign at lower left symbolizes the electron, while pairs of spheres with plus and minus signs show the virtual particles +A schematic depiction of virtual electron–positron pairs appearing at random near an electron (at lower left) +While an electron–positron virtual pair is in existence, the coulomb force from the ambient electric field surrounding an electron causes a created positron to be attracted to the original electron, while a created electron experiences a repulsion. This causes what is called vacuum polarization. In effect, the vacuum behaves like a medium having a dielectric permittivity more than unity. Thus the effective charge of an electron is actually smaller than its true value, and the charge decreases with increasing distance from the electron.[86][87] This polarization was confirmed experimentally in 1997 using the Japanese TRISTAN particle accelerator.[88] Virtual particles cause a comparable shielding effect for the mass of the electron.[89] + +The interaction with virtual particles also explains the small (about 0.1%) deviation of the intrinsic magnetic moment of the electron from the Bohr magneton (the anomalous magnetic moment).[72][90] The extraordinarily precise agreement of this predicted difference with the experimentally determined value is viewed as one of the great achievements of quantum electrodynamics.[91] + +The apparent paradox in classical physics of a point particle electron having intrinsic angular momentum and magnetic moment can be explained by the formation of virtual photons in the electric field generated by the electron. These photons cause the electron to shift about in a jittery fashion (known as zitterbewegung),[92] which results in a net circular motion with precession. This motion produces both the spin and the magnetic moment of the electron.[10][93] In atoms, this creation of virtual photons explains the Lamb shift observed in spectral lines.[86] The Compton Wavelength shows that near elementary particles such as the electron, the uncertainty of the energy allows for the creation of virtual particles near the electron. This wavelength explains the "static" of virtual particles around elementary particles at a close distance. + +Interaction +An electron generates an electric field that exerts an attractive force on a particle with a positive charge, such as the proton, and a repulsive force on a particle with a negative charge. The strength of this force in nonrelativistic approximation is determined by Coulomb's inverse square law.[94](pp58–61) When an electron is in motion, it generates a magnetic field.[83](p140) The Ampère-Maxwell law relates the magnetic field to the mass motion of electrons (the current) with respect to an observer. This property of induction supplies the magnetic field that drives an electric motor.[95] The electromagnetic field of an arbitrary moving charged particle is expressed by the Liénard–Wiechert potentials, which are valid even when the particle's speed is close to that of light (relativistic).[94](pp429–434) + +A graph with arcs showing the motion of charged particles +A particle with charge q (at left) is moving with velocity v through a magnetic field B that is oriented toward the viewer. For an electron, q is negative so it follows a curved trajectory toward the top. +When an electron is moving through a magnetic field, it is subject to the Lorentz force that acts perpendicularly to the plane defined by the magnetic field and the electron velocity. This centripetal force causes the electron to follow a helical trajectory through the field at a radius called the gyroradius. The acceleration from this curving motion induces the electron to radiate energy in the form of synchrotron radiation.[96][g][83](p160) The energy emission in turn causes a recoil of the electron, known as the Abraham–Lorentz–Dirac Force, which creates a friction that slows the electron. This force is caused by a back-reaction of the electron's own field upon itself.[97] + +A curve shows the motion of the electron, a red dot shows the nucleus, and a wiggly line the emitted photon +Here, Bremsstrahlung is produced by an electron e deflected by the electric field of an atomic nucleus. The energy change E2 − E1 determines the frequency f of the emitted photon. +Photons mediate electromagnetic interactions between particles in quantum electrodynamics. An isolated electron at a constant velocity cannot emit or absorb a real photon; doing so would violate conservation of energy and momentum. Instead, virtual photons can transfer momentum between two charged particles. This exchange of virtual photons, for example, generates the Coulomb force.[98] Energy emission can occur when a moving electron is deflected by a charged particle, such as a proton. The acceleration of the electron results in the emission of Bremsstrahlung radiation.[99] + +An inelastic collision between a photon (light) and a solitary (free) electron is called Compton scattering. This collision results in a transfer of momentum and energy between the particles, which modifies the wavelength of the photon by an amount called the Compton shift.[h] The maximum magnitude of this wavelength shift is h/mec, which is known as the Compton wavelength.[100] For an electron, it has a value of 2.43×10−12 m.[67] When the wavelength of the light is long (for instance, the wavelength of the visible light is 0.4–0.7 μm) the wavelength shift becomes negligible. Such interaction between the light and free electrons is called Thomson scattering or linear Thomson scattering.[101] + +The relative strength of the electromagnetic interaction between two charged particles, such as an electron and a proton, is given by the fine-structure constant. This value is a dimensionless quantity formed by the ratio of two energies: the electrostatic energy of attraction (or repulsion) at a separation of one Compton wavelength, and the rest energy of the charge. It is given by α ≈ 7.297353×10−3, which is approximately equal to +1 +/ +137 +.[67] + +When electrons and positrons collide, they annihilate each other, giving rise to two or more gamma ray photons. If the electron and positron have negligible momentum, a positronium atom can form before annihilation results in two or three gamma ray photons totalling 1.022 MeV.[102][103] On the other hand, a high-energy photon can transform into an electron and a positron by a process called pair production, but only in the presence of a nearby charged particle, such as a nucleus.[104][105] + +In the theory of electroweak interaction, the left-handed component of electron's wavefunction forms a weak isospin doublet with the electron neutrino. This means that during weak interactions, electron neutrinos behave like electrons. Either member of this doublet can undergo a charged current interaction by emitting or absorbing a +W + and be converted into the other member. Charge is conserved during this reaction because the W boson also carries a charge, canceling out any net change during the transmutation. Charged current interactions are responsible for the phenomenon of beta decay in a radioactive atom. Both the electron and electron neutrino can undergo a neutral current interaction via a +Z0 + exchange, and this is responsible for neutrino-electron elastic scattering.[106] + +Atoms and molecules +Main article: Atom +A table of five rows and five columns, with each cell portraying a color-coded probability density +Probability densities for the first few hydrogen atom orbitals, seen in cross-section. The energy level of a bound electron determines the orbital it occupies, and the color reflects the probability of finding the electron at a given position. +An electron can be bound to the nucleus of an atom by the attractive Coulomb force. A system of one or more electrons bound to a nucleus is called an atom. If the number of electrons is different from the nucleus' electrical charge, such an atom is called an ion. The wave-like behavior of a bound electron is described by a function called an atomic orbital. Each orbital has its own set of quantum numbers such as energy, angular momentum and projection of angular momentum, and only a discrete set of these orbitals exist around the nucleus. According to the Pauli exclusion principle each orbital can be occupied by up to two electrons, which must differ in their spin quantum number. + +Electrons can transfer between different orbitals by the emission or absorption of photons with an energy that matches the difference in potential.[107]:159–160 Other methods of orbital transfer include collisions with particles, such as electrons, and the Auger effect.[108] To escape the atom, the energy of the electron must be increased above its binding energy to the atom. This occurs, for example, with the photoelectric effect, where an incident photon exceeding the atom's ionization energy is absorbed by the electron.[107]:127–132 + +The orbital angular momentum of electrons is quantized. Because the electron is charged, it produces an orbital magnetic moment that is proportional to the angular momentum. The net magnetic moment of an atom is equal to the vector sum of orbital and spin magnetic moments of all electrons and the nucleus. The magnetic moment of the nucleus is negligible compared with that of the electrons. The magnetic moments of the electrons that occupy the same orbital (so called, paired electrons) cancel each other out.[109] + +The chemical bond between atoms occurs as a result of electromagnetic interactions, as described by the laws of quantum mechanics.[110] The strongest bonds are formed by the sharing or transfer of electrons between atoms, allowing the formation of molecules.[13] Within a molecule, electrons move under the influence of several nuclei, and occupy molecular orbitals; much as they can occupy atomic orbitals in isolated atoms.[111] A fundamental factor in these molecular structures is the existence of electron pairs. These are electrons with opposed spins, allowing them to occupy the same molecular orbital without violating the Pauli exclusion principle (much like in atoms). Different molecular orbitals have different spatial distribution of the electron density. For instance, in bonded pairs (i.e. in the pairs that actually bind atoms together) electrons can be found with the maximal probability in a relatively small volume between the nuclei. By contrast, in non-bonded pairs electrons are distributed in a large volume around nuclei.[112] + +Conductivity +Four bolts of lightning strike the ground +A lightning discharge consists primarily of a flow of electrons.[113] The electric potential needed for lightning can be generated by a triboelectric effect.[114][115] +If a body has more or fewer electrons than are required to balance the positive charge of the nuclei, then that object has a net electric charge. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than the number of protons in nuclei, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel each other and the object is said to be electrically neutral. A macroscopic body can develop an electric charge through rubbing, by the triboelectric effect.[116] + +Independent electrons moving in vacuum are termed free electrons. Electrons in metals also behave as if they were free. In reality the particles that are commonly termed electrons in metals and other solids are quasi-electrons—quasiparticles, which have the same electrical charge, spin, and magnetic moment as real electrons but might have a different mass.[117] When free electrons—both in vacuum and metals—move, they produce a net flow of charge called an electric current, which generates a magnetic field. Likewise a current can be created by a changing magnetic field. These interactions are described mathematically by Maxwell's equations.[118] + +At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric potential is applied. Examples of good conductors include metals such as copper and gold, whereas glass and Teflon are poor conductors. In any dielectric material, the electrons remain bound to their respective atoms and the material behaves as an insulator. Most semiconductors have a variable level of conductivity that lies between the extremes of conduction and insulation.[119] On the other hand, metals have an electronic band structure containing partially filled electronic bands. The presence of such bands allows electrons in metals to behave as if they were free or delocalized electrons. These electrons are not associated with specific atoms, so when an electric field is applied, they are free to move like a gas (called Fermi gas)[120] through the material much like free electrons. + +Because of collisions between electrons and atoms, the drift velocity of electrons in a conductor is on the order of millimeters per second. However, the speed at which a change of current at one point in the material causes changes in currents in other parts of the material, the velocity of propagation, is typically about 75% of light speed.[121] This occurs because electrical signals propagate as a wave, with the velocity dependent on the dielectric constant of the material.[122] + +Metals make relatively good conductors of heat, primarily because the delocalized electrons are free to transport thermal energy between atoms. However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature. This is expressed mathematically by the Wiedemann–Franz law,[120] which states that the ratio of thermal conductivity to the electrical conductivity is proportional to the temperature. The thermal disorder in the metallic lattice increases the electrical resistivity of the material, producing a temperature dependence for electric current.[123] + +When cooled below a point called the critical temperature, materials can undergo a phase transition in which they lose all resistivity to electric current, in a process known as superconductivity. In BCS theory, pairs of electrons called Cooper pairs have their motion coupled to nearby matter via lattice vibrations called phonons, thereby avoiding the collisions with atoms that normally create electrical resistance.[124] (Cooper pairs have a radius of roughly 100 nm, so they can overlap each other.)[125] However, the mechanism by which higher temperature superconductors operate remains uncertain. + +Electrons inside conducting solids, which are quasi-particles themselves, when tightly confined at temperatures close to absolute zero, behave as though they had split into three other quasiparticles: spinons, orbitons and holons.[126][127] The former carries spin and magnetic moment, the next carries its orbital location while the latter electrical charge. + +Motion and energy +According to Einstein's theory of special relativity, as an electron's speed approaches the speed of light, from an observer's point of view its relativistic mass increases, thereby making it more and more difficult to accelerate it from within the observer's frame of reference. The speed of an electron can approach, but never reach, the speed of light in a vacuum, c. However, when relativistic electrons—that is, electrons moving at a speed close to c—are injected into a dielectric medium such as water, where the local speed of light is significantly less than c, the electrons temporarily travel faster than light in the medium. As they interact with the medium, they generate a faint light called Cherenkov radiation.[128] + +The plot starts at zero and curves sharply upward toward the right +Lorentz factor as a function of velocity. It starts at value 1 and goes to infinity as v approaches c. +The effects of special relativity are based on a quantity known as the Lorentz factor, defined as {\displaystyle \scriptstyle \gamma =1/{\sqrt {1-{v^{2}}/{c^{2}}}}}\scriptstyle \gamma =1/{\sqrt {1-{v^{2}}/{c^{2}}}} where v is the speed of the particle. The kinetic energy Ke of an electron moving with velocity v is: + +{\displaystyle \displaystyle K_{\mathrm {e} }=(\gamma -1)m_{\mathrm {e} }c^{2},}\displaystyle K_{\mathrm {e} }=(\gamma -1)m_{\mathrm {e} }c^{2}, +where me is the mass of electron. For example, the Stanford linear accelerator can accelerate an electron to roughly 51 GeV.[129] Since an electron behaves as a wave, at a given velocity it has a characteristic de Broglie wavelength. This is given by λe = h/p where h is the Planck constant and p is the momentum.[49] For the 51 GeV electron above, the wavelength is about 2.4×10−17 m, small enough to explore structures well below the size of an atomic nucleus.[130] + +Formation +A photon approaches the nucleus from the left, with the resulting electron and positron moving off to the right +Pair production of an electron and positron, caused by the close approach of a photon with an atomic nucleus. The lightning symbol represents an exchange of a virtual photon, thus an electric force acts. The angle between the particles is very small.[131] +The Big Bang theory is the most widely accepted scientific theory to explain the early stages in the evolution of the Universe.[132] For the first millisecond of the Big Bang, the temperatures were over 10 billion kelvins and photons had mean energies over a million electronvolts. These photons were sufficiently energetic that they could react with each other to form pairs of electrons and positrons. Likewise, positron-electron pairs annihilated each other and emitted energetic photons: + + +γ + + +γ + ↔ +e+ + + +e− +An equilibrium between electrons, positrons and photons was maintained during this phase of the evolution of the Universe. After 15 seconds had passed, however, the temperature of the universe dropped below the threshold where electron-positron formation could occur. Most of the surviving electrons and positrons annihilated each other, releasing gamma radiation that briefly reheated the universe.[133] + +For reasons that remain uncertain, during the annihilation process there was an excess in the number of particles over antiparticles. Hence, about one electron for every billion electron-positron pairs survived. This excess matched the excess of protons over antiprotons, in a condition known as baryon asymmetry, resulting in a net charge of zero for the universe.[134][135] The surviving protons and neutrons began to participate in reactions with each other—in the process known as nucleosynthesis, forming isotopes of hydrogen and helium, with trace amounts of lithium. This process peaked after about five minutes.[136] Any leftover neutrons underwent negative beta decay with a half-life of about a thousand seconds, releasing a proton and electron in the process, + + +n + → +p + + +e− + + +ν +e +For about the next 300000–400000 years, the excess electrons remained too energetic to bind with atomic nuclei.[137] What followed is a period known as recombination, when neutral atoms were formed and the expanding universe became transparent to radiation.[138] + +Roughly one million years after the big bang, the first generation of stars began to form.[138] Within a star, stellar nucleosynthesis results in the production of positrons from the fusion of atomic nuclei. These antimatter particles immediately annihilate with electrons, releasing gamma rays. The net result is a steady reduction in the number of electrons, and a matching increase in the number of neutrons. However, the process of stellar evolution can result in the synthesis of radioactive isotopes. Selected isotopes can subsequently undergo negative beta decay, emitting an electron and antineutrino from the nucleus.[139] An example is the cobalt-60 (60Co) isotope, which decays to form nickel-60 (60 +Ni +).[140] + +A branching tree representing the particle production +An extended air shower generated by an energetic cosmic ray striking the Earth's atmosphere +At the end of its lifetime, a star with more than about 20 solar masses can undergo gravitational collapse to form a black hole.[141] According to classical physics, these massive stellar objects exert a gravitational attraction that is strong enough to prevent anything, even electromagnetic radiation, from escaping past the Schwarzschild radius. However, quantum mechanical effects are believed to potentially allow the emission of Hawking radiation at this distance. Electrons (and positrons) are thought to be created at the event horizon of these stellar remnants. + +When a pair of virtual particles (such as an electron and positron) is created in the vicinity of the event horizon, random spatial positioning might result in one of them to appear on the exterior; this process is called quantum tunnelling. The gravitational potential of the black hole can then supply the energy that transforms this virtual particle into a real particle, allowing it to radiate away into space.[142] In exchange, the other member of the pair is given negative energy, which results in a net loss of mass-energy by the black hole. The rate of Hawking radiation increases with decreasing mass, eventually causing the black hole to evaporate away until, finally, it explodes.[143] + +Cosmic rays are particles traveling through space with high energies. Energy events as high as 3.0×1020 eV have been recorded.[144] When these particles collide with nucleons in the Earth's atmosphere, a shower of particles is generated, including pions.[145] More than half of the cosmic radiation observed from the Earth's surface consists of muons. The particle called a muon is a lepton produced in the upper atmosphere by the decay of a pion. + + +π− + → +μ− + + +ν +μ +A muon, in turn, can decay to form an electron or positron.[146] + + +μ− + → +e− + + +ν +e + +ν +μ +Observation +A swirling green glow in the night sky above snow-covered ground +Aurorae are mostly caused by energetic electrons precipitating into the atmosphere.[147] +Remote observation of electrons requires detection of their radiated energy. For example, in high-energy environments such as the corona of a star, free electrons form a plasma that radiates energy due to Bremsstrahlung radiation. Electron gas can undergo plasma oscillation, which is waves caused by synchronized variations in electron density, and these produce energy emissions that can be detected by using radio telescopes.[148] + +The frequency of a photon is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it absorbs or emits photons at characteristic frequencies. For instance, when atoms are irradiated by a source with a broad spectrum, distinct dark lines appear in the spectrum of transmitted radiation in places where the corresponding frequency is absorbed by the atom's electrons. Each element or molecule displays a characteristic set of spectral lines, such as the hydrogen spectral series. When detected, spectroscopic measurements of the strength and width of these lines allow the composition and physical properties of a substance to be determined.[149][150] + +In laboratory conditions, the interactions of individual electrons can be observed by means of particle detectors, which allow measurement of specific properties such as energy, spin and charge.[151] The development of the Paul trap and Penning trap allows charged particles to be contained within a small region for long durations. This enables precise measurements of the particle properties. For example, in one instance a Penning trap was used to contain a single electron for a period of 10 months.[152] The magnetic moment of the electron was measured to a precision of eleven digits, which, in 1980, was a greater accuracy than for any other physical constant.[153] + +The first video images of an electron's energy distribution were captured by a team at Lund University in Sweden, February 2008. The scientists used extremely short flashes of light, called attosecond pulses, which allowed an electron's motion to be observed for the first time.[154][155] + +The distribution of the electrons in solid materials can be visualized by angle-resolved photoemission spectroscopy (ARPES). This technique employs the photoelectric effect to measure the reciprocal space—a mathematical representation of periodic structures that is used to infer the original structure. ARPES can be used to determine the direction, speed and scattering of electrons within the material.[156] + +Plasma applications +Particle beams +A violet beam from above produces a blue glow about a Space shuttle model +During a NASA wind tunnel test, a model of the Space Shuttle is targeted by a beam of electrons, simulating the effect of ionizing gases during re-entry.[157] +Electron beams are used in welding.[158] They allow energy densities up to 107 W·cm−2 across a narrow focus diameter of 0.1–1.3 mm and usually require no filler material. This welding technique must be performed in a vacuum to prevent the electrons from interacting with the gas before reaching their target, and it can be used to join conductive materials that would otherwise be considered unsuitable for welding.[159][160] + +Electron-beam lithography (EBL) is a method of etching semiconductors at resolutions smaller than a micrometer.[161] This technique is limited by high costs, slow performance, the need to operate the beam in the vacuum and the tendency of the electrons to scatter in solids. The last problem limits the resolution to about 10 nm. For this reason, EBL is primarily used for the production of small numbers of specialized integrated circuits.[162] + +Electron beam processing is used to irradiate materials in order to change their physical properties or sterilize medical and food products.[163] Electron beams fluidise or quasi-melt glasses without significant increase of temperature on intensive irradiation: e.g. intensive electron radiation causes a many orders of magnitude decrease of viscosity and stepwise decrease of its activation energy.[164] + +Linear particle accelerators generate electron beams for treatment of superficial tumors in radiation therapy. Electron therapy can treat such skin lesions as basal-cell carcinomas because an electron beam only penetrates to a limited depth before being absorbed, typically up to 5 cm for electron energies in the range 5–20 MeV. An electron beam can be used to supplement the treatment of areas that have been irradiated by X-rays.[165][166] + +Particle accelerators use electric fields to propel electrons and their antiparticles to high energies. These particles emit synchrotron radiation as they pass through magnetic fields. The dependency of the intensity of this radiation upon spin polarizes the electron beam—a process known as the Sokolov–Ternov effect.[i] Polarized electron beams can be useful for various experiments. Synchrotron radiation can also cool the electron beams to reduce the momentum spread of the particles. Electron and positron beams are collided upon the particles' accelerating to the required energies; particle detectors observe the resulting energy emissions, which particle physics studies .[167] + +Imaging +Low-energy electron diffraction (LEED) is a method of bombarding a crystalline material with a collimated beam of electrons and then observing the resulting diffraction patterns to determine the structure of the material. The required energy of the electrons is typically in the range 20–200 eV.[168] The reflection high-energy electron diffraction (RHEED) technique uses the reflection of a beam of electrons fired at various low angles to characterize the surface of crystalline materials. The beam energy is typically in the range 8–20 keV and the angle of incidence is 1–4°.[169][170] + +The electron microscope directs a focused beam of electrons at a specimen. Some electrons change their properties, such as movement direction, angle, and relative phase and energy as the beam interacts with the material. Microscopists can record these changes in the electron beam to produce atomically resolved images of the material.[171] In blue light, conventional optical microscopes have a diffraction-limited resolution of about 200 nm.[172] By comparison, electron microscopes are limited by the de Broglie wavelength of the electron. This wavelength, for example, is equal to 0.0037 nm for electrons accelerated across a 100,000-volt potential.[173] The Transmission Electron Aberration-Corrected Microscope is capable of sub-0.05 nm resolution, which is more than enough to resolve individual atoms.[174] This capability makes the electron microscope a useful laboratory instrument for high resolution imaging. However, electron microscopes are expensive instruments that are costly to maintain. + +Two main types of electron microscopes exist: transmission and scanning. Transmission electron microscopes function like overhead projectors, with a beam of electrons passing through a slice of material then being projected by lenses on a photographic slide or a charge-coupled device. Scanning electron microscopes rasteri a finely focused electron beam, as in a TV set, across the studied sample to produce the image. Magnifications range from 100× to 1,000,000× or higher for both microscope types. The scanning tunneling microscope uses quantum tunneling of electrons from a sharp metal tip into the studied material and can produce atomically resolved images of its surface.[175][176][177] + +Other applications +In the free-electron laser (FEL), a relativistic electron beam passes through a pair of undulators that contain arrays of dipole magnets whose fields point in alternating directions. The electrons emit synchrotron radiation that coherently interacts with the same electrons to strongly amplify the radiation field at the resonance frequency. FEL can emit a coherent high-brilliance electromagnetic radiation with a wide range of frequencies, from microwaves to soft X-rays. These devices are used in manufacturing, communication, and in medical applications, such as soft tissue surgery.[178] + +Electrons are important in cathode ray tubes, which have been extensively used as display devices in laboratory instruments, computer monitors and television sets.[179] In a photomultiplier tube, every photon striking the photocathode initiates an avalanche of electrons that produces a detectable current pulse.[180] Vacuum tubes use the flow of electrons to manipulate electrical signals, and they played a critical role in the development of electronics technology. However, they have been largely supplanted by solid-state devices such as the transistor.[181] diff --git a/examples/article3.txt b/examples/article3.txt new file mode 100644 index 0000000..be5a510 --- /dev/null +++ b/examples/article3.txt @@ -0,0 +1,201 @@ +A proton is a subatomic particle, symbol +p + or +p+ +, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons" (particles present in atomic nuclei). + +One or more protons are present in the nucleus of every atom; they are a necessary part of the nucleus. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z). Since each element has a unique number of protons, each element has its own unique atomic number. + +The word proton is Greek for "first", and this name was given to the hydrogen nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen by atomic collisions.[3] Protons were therefore a candidate to be a fundamental particle, and hence a building block of nitrogen and all other heavier atomic nuclei. + +Although protons were originally considered fundamental or elementary particles, in the modern Standard Model of particle physics, protons are classified as hadrons, like neutrons, the other nucleon. Protons are composite particles composed of three valence quarks: two up quarks of charge + +2 +/ +3 +e and one down quark of charge – +1 +/ +3 +e. The rest masses of quarks contribute only about 1% of a proton's mass.[4] The remainder of a proton's mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. Because protons are not fundamental particles, they possess a measurable size; the root mean square charge radius of a proton is about 0.84–0.87 fm (or 0.84×10−15 to 0.87×10−15 m).[5][6] In 2019, two different studies, using different techniques, have found the radius of the proton to be 0.833 fm, with an uncertainty of ±0.010 fm.[7][8] + +At sufficiently low temperatures, free protons will bind to electrons. However, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, until it is captured by the electron cloud of an atom. The result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when free electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom, which is chemically a free radical. Such "free hydrogen atoms" tend to react chemically with many other types of atoms at sufficiently low energies. When free hydrogen atoms react with each other, they form neutral hydrogen molecules (H2), which are the most common molecular component of molecular clouds in interstellar space. + + +Contents +1 Description +2 History +3 Stability +4 Quarks and the mass of a proton +5 Charge radius +5.1 Pressure inside the proton +5.2 Charge radius in solvated proton, hydronium +6 Interaction of free protons with ordinary matter +7 Proton in chemistry +7.1 Atomic number +7.2 Hydrogen ion +7.3 Proton nuclear magnetic resonance (NMR) +8 Human exposure +9 Antiproton +10 See also +11 References +12 External links +Description +Nuclear physics +NuclearReaction.svg +Nucleus · Nucleons (p, n) · Nuclear matter · Nuclear force · Nuclear structure · Nuclear reaction +Models of the nucleus[show] +Nuclides' classification[show] +Nuclear stability[show] +Radioactive decay[show] +Nuclear fission[show] +Capturing processes[show] +High-energy processes[show] +Nucleosynthesis and +nuclear astrophysics[show] +High-energy nuclear physics[show] +Scientists[show] +vte +Question, Web Fundamentals.svg Unsolved problem in physics: +How do the quarks and gluons carry the spin of protons? +(more unsolved problems in physics) +Protons are spin-½ fermions and are composed of three valence quarks,[9] making them baryons (a sub-type of hadrons). The two up quarks and one down quark of a proton are held together by the strong force, mediated by gluons.[10]:21–22 A modern perspective has a proton composed of the valence quarks (up, up, down), the gluons, and transitory pairs of sea quarks. Protons have a positive charge distribution which decays approximately exponentially, with a mean square radius of about 0.8 fm.[11] + +Protons and neutrons are both nucleons, which may be bound together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the hydrogen atom (with the chemical symbol "H") is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium and tritium contain one proton bound to one and two neutrons, respectively. All other types of atomic nuclei are composed of two or more protons and various numbers of neutrons. + +History +The concept of a hydrogen-like particle as a constituent of other atoms was developed over a long period. As early as 1815, William Prout proposed that all atoms are composed of hydrogen atoms (which he called "protyles"), based on a simplistic interpretation of early values of atomic weights (see Prout's hypothesis), which was disproved when more accurate values were measured.[12]:39–42 + + +Ernest Rutherford at the first Solvay Conference, 1911 + +Proton detected in an isopropanol cloud chamber +In 1886, Eugen Goldstein discovered canal rays (also known as anode rays) and showed that they were positively charged particles (ions) produced from gases. However, since particles from different gases had different values of charge-to-mass ratio (e/m), they could not be identified with a single particle, unlike the negative electrons discovered by J. J. Thomson. Wilhelm Wien in 1898 identified the hydrogen ion as particle with highest charge-to-mass ratio in ionized gases.[13] + +Following the discovery of the atomic nucleus by Ernest Rutherford in 1911, Antonius van den Broek proposed that the place of each element in the periodic table (its atomic number) is equal to its nuclear charge. This was confirmed experimentally by Henry Moseley in 1913 using X-ray spectra. + +In 1917 (in experiments reported in 1919 and 1925), Rutherford proved that the hydrogen nucleus is present in other nuclei, a result usually described as the discovery of protons.[14] These experiments began after Rutherford had noticed that, when alpha particles were shot into air (mostly nitrogen), his scintillation detectors showed the signatures of typical hydrogen nuclei as a product. After experimentation Rutherford traced the reaction to the nitrogen in air and found that when alpha particles were introduced into pure nitrogen gas, the effect was larger. In 1919 Rutherford assumed that the alpha particle knocked a proton out of nitrogen, turning it into carbon. After observing Blackett's cloud chamber images in 1925, Rutherford realized that the opposite was the case: after capture of the alpha particle, a proton is ejected, so that heavy oxygen, not carbon, is the end result i.e. Z is not decremented but incremented. This was the first reported nuclear reaction, 14N + α → 17O + p. Depending on one's perspective, either 1919 or 1925 may be regarded as the moment when the proton was 'discovered'. + +Rutherford knew hydrogen to be the simplest and lightest element and was influenced by Prout's hypothesis that hydrogen was the building block of all elements. Discovery that the hydrogen nucleus is present in all other nuclei as an elementary particle led Rutherford to give the hydrogen nucleus a special name as a particle, since he suspected that hydrogen, the lightest element, contained only one of these particles. He named this new fundamental building block of the nucleus the proton, after the neuter singular of the Greek word for "first", πρῶτον. However, Rutherford also had in mind the word protyle as used by Prout. Rutherford spoke at the British Association for the Advancement of Science at its Cardiff meeting beginning 24 August 1920.[15] Rutherford was asked by Oliver Lodge for a new name for the positive hydrogen nucleus to avoid confusion with the neutral hydrogen atom. He initially suggested both proton and prouton (after Prout).[16] Rutherford later reported that the meeting had accepted his suggestion that the hydrogen nucleus be named the "proton", following Prout's word "protyle".[17] The first use of the word "proton" in the scientific literature appeared in 1920.[18] + +Recent research has shown that thunderstorms can produce protons with energies of up to several tens of MeV.[19][20] + +Protons are routinely used for accelerators for proton therapy or various particle physics experiments, with the most powerful example being the Large Hadron Collider. + +In a July 2017 paper, researchers measured the mass of a proton to be 1.007276466583+15 +−29 atomic mass units (the values in parentheses being the statistical and systematic uncertainties, respectively), which is lower than measurements from the CODATA 2014 value by three standard deviations.[21][22] + +Stability +Main article: Proton decay +Question, Web Fundamentals.svg Unsolved problem in physics: +Are protons fundamentally stable? Or do they decay with a finite lifetime as predicted by some extensions to the standard model? +(more unsolved problems in physics) +The free proton (a proton not bound to nucleons or electrons) is a stable particle that has not been observed to break down spontaneously to other particles. Free protons are found naturally in a number of situations in which energies or temperatures are high enough to separate them from electrons, for which they have some affinity. Free protons exist in plasmas in which temperatures are too high to allow them to combine with electrons. Free protons of high energy and velocity make up 90% of cosmic rays, which propagate in vacuum for interstellar distances. Free protons are emitted directly from atomic nuclei in some rare types of radioactive decay. Protons also result (along with electrons and antineutrinos) from the radioactive decay of free neutrons, which are unstable. + +The spontaneous decay of free protons has never been observed, and protons are therefore considered stable particles according to the Standard Model. However, some grand unified theories (GUTs) of particle physics predict that proton decay should take place with lifetimes between 1031 to 1036 years and experimental searches have established lower bounds on the mean lifetime of a proton for various assumed decay products.[23][24][25] + +Experiments at the Super-Kamiokande detector in Japan gave lower limits for proton mean lifetime of 6.6×1033 years for decay to an antimuon and a neutral pion, and 8.2×1033 years for decay to a positron and a neutral pion.[26] Another experiment at the Sudbury Neutrino Observatory in Canada searched for gamma rays resulting from residual nuclei resulting from the decay of a proton from oxygen-16. This experiment was designed to detect decay to any product, and established a lower limit to a proton lifetime of 2.1×1029 years.[27] + +However, protons are known to transform into neutrons through the process of electron capture (also called inverse beta decay). For free protons, this process does not occur spontaneously but only when energy is supplied. The equation is: + + +p+ + + +e− + → +n + + +ν +e +The process is reversible; neutrons can convert back to protons through beta decay, a common form of radioactive decay. In fact, a free neutron decays this way, with a mean lifetime of about 15 minutes. + +Quarks and the mass of a proton +In quantum chromodynamics, the modern theory of the nuclear force, most of the mass of protons and neutrons is explained by special relativity. The mass of a proton is about 80–100 times greater than the sum of the rest masses of the quarks that make it up, while the gluons have zero rest mass. The extra energy of the quarks and gluons in a region within a proton, as compared to the rest energy of the quarks alone in the QCD vacuum, accounts for almost 99% of the mass. The rest mass of a proton is, thus, the invariant mass of the system of moving quarks and gluons that make up the particle, and, in such systems, even the energy of massless particles is still measured as part of the rest mass of the system. + +Two terms are used in referring to the mass of the quarks that make up protons: current quark mass refers to the mass of a quark by itself, while constituent quark mass refers to the current quark mass plus the mass of the gluon particle field surrounding the quark.[28]:285–286 [29]:150–151 These masses typically have very different values. As noted, most of a proton's mass comes from the gluons that bind the current quarks together, rather than from the quarks themselves. While gluons are inherently massless, they possess energy—to be more specific, quantum chromodynamics binding energy (QCBE)—and it is this that contributes so greatly to the overall mass of protons (see mass in special relativity). A proton has a mass of approximately 938 MeV/c2, of which the rest mass of its three valence quarks contributes only about 9.4 MeV/c2; much of the remainder can be attributed to the gluons' QCBE.[30][31][32] + +The constituent quark model wavefunction for the proton is + +{\displaystyle |p_{\uparrow }\rangle ={\frac {1}{\sqrt {18}}}[2|u_{\uparrow }d_{\downarrow }u_{\uparrow }\rangle +2|u_{\uparrow }u_{\uparrow }d_{\downarrow }\rangle +2|d_{\downarrow }u_{\uparrow }u_{\uparrow }\rangle -|u_{\uparrow }u_{\downarrow }d_{\uparrow }\rangle -|u_{\uparrow }d_{\uparrow }u_{\downarrow }\rangle -|u_{\downarrow }d_{\uparrow }u_{\uparrow }\rangle -|d_{\uparrow }u_{\downarrow }u_{\uparrow }\rangle -|d_{\uparrow }u_{\uparrow }u_{\downarrow }\rangle -|u_{\downarrow }u_{\uparrow }d_{\uparrow }\rangle ].}{\displaystyle |p_{\uparrow }\rangle ={\frac {1}{\sqrt {18}}}[2|u_{\uparrow }d_{\downarrow }u_{\uparrow }\rangle +2|u_{\uparrow }u_{\uparrow }d_{\downarrow }\rangle +2|d_{\downarrow }u_{\uparrow }u_{\uparrow }\rangle -|u_{\uparrow }u_{\downarrow }d_{\uparrow }\rangle -|u_{\uparrow }d_{\uparrow }u_{\downarrow }\rangle -|u_{\downarrow }d_{\uparrow }u_{\uparrow }\rangle -|d_{\uparrow }u_{\downarrow }u_{\uparrow }\rangle -|d_{\uparrow }u_{\uparrow }u_{\downarrow }\rangle -|u_{\downarrow }u_{\uparrow }d_{\uparrow }\rangle ].} +The internal dynamics of protons are complicated, because they are determined by the quarks' exchanging gluons, and interacting with various vacuum condensates. Lattice QCD provides a way of calculating the mass of a proton directly from the theory to any accuracy, in principle. The most recent calculations[33][34] claim that the mass is determined to better than 4% accuracy, even to 1% accuracy (see Figure S5 in Dürr et al.[34]). These claims are still controversial, because the calculations cannot yet be done with quarks as light as they are in the real world. This means that the predictions are found by a process of extrapolation, which can introduce systematic errors.[35] It is hard to tell whether these errors are controlled properly, because the quantities that are compared to experiment are the masses of the hadrons, which are known in advance. + +These recent calculations are performed by massive supercomputers, and, as noted by Boffi and Pasquini: "a detailed description of the nucleon structure is still missing because ... long-distance behavior requires a nonperturbative and/or numerical treatment..."[36] More conceptual approaches to the structure of protons are: the topological soliton approach originally due to Tony Skyrme and the more accurate AdS/QCD approach that extends it to include a string theory of gluons,[37] various QCD-inspired models like the bag model and the constituent quark model, which were popular in the 1980s, and the SVZ sum rules, which allow for rough approximate mass calculations.[38] These methods do not have the same accuracy as the more brute-force lattice QCD methods, at least not yet. + +Charge radius +Ambox current red.svg +This section needs to be updated. The reason given is: as reported in Science, the proton radius puzzle has possibly been solved. A new measurement using the Lamb shift in ordinary hydrogen agrees with that using muonic hydrogen.. Please update this article to reflect recent events or newly available information. (September 2019) +Main article: Proton radius puzzle +The problem of defining a radius for an atomic nucleus (proton) is similar to the problem of atomic radius, in that neither atoms nor their nuclei have definite boundaries. However, the nucleus can be modeled as a sphere of positive charge for the interpretation of electron scattering experiments: because there is no definite boundary to the nucleus, the electrons "see" a range of cross-sections, for which a mean can be taken. The qualification of "rms" (for "root mean square") arises because it is the nuclear cross-section, proportional to the square of the radius, which is determining for electron scattering. + +The internationally accepted value of a proton's charge radius is 0.8768 fm (see orders of magnitude for comparison to other sizes). This value is based on measurements involving a proton and an electron (namely, electron scattering measurements and complex calculation involving scattering cross section based on Rosenbluth equation for momentum-transfer cross section), and studies of the atomic energy levels of hydrogen and deuterium. + +However, in 2010 an international research team published a proton charge radius measurement via the Lamb shift in muonic hydrogen (an exotic atom made of a proton and a negatively charged muon). As a muon is 200 times heavier than an electron, its de Broglie wavelength is correspondingly shorter. This smaller atomic orbital is much more sensitive to the proton's charge radius, so allows more precise measurement. Their measurement of the root-mean-square charge radius of a proton is "0.84184(67) fm, which differs by 5.0 standard deviations from the CODATA value of 0.8768(69) fm".[39] In January 2013, an updated value for the charge radius of a proton—0.84087(39) fm—was published. The precision was improved by 1.7 times, increasing the significance of the discrepancy to 7σ.[6] The 2014 CODATA adjustment slightly reduced the recommended value for the proton radius (computed using electron measurements only) to 0.8751(61) fm, but this leaves the discrepancy at 5.6σ. + +The international research team that obtained this result at the Paul Scherrer Institut in Villigen includes scientists from the Max Planck Institute of Quantum Optics, Ludwig-Maximilians-Universität, the Institut für Strahlwerkzeuge of Universität Stuttgart, and the University of Coimbra, Portugal.[40][41] The team is now attempting to explain the discrepancy, and re-examining the results of both previous high-precision measurements and complex calculations involving scattering cross section. If no errors are found in the measurements or calculations, it could be necessary to re-examine the world's most precise and best-tested fundamental theory: quantum electrodynamics.[40] The proton radius remains a puzzle as of 2017.[42] Perhaps the discrepancy is due to new physics, or the explanation may be an ordinary physics effect that has been missed.[43] + +The radius is linked to the form factor and momentum transfer cross section. The atomic form factor G modifies the cross section corresponding to point-like proton. + +{\displaystyle {\begin{aligned}R_{e}^{2}&=-6{{\frac {dG_{e}}{dq^{2}}}\,{\Bigg \vert }\,}_{q^{2}=0}\\{\frac {d\sigma }{d\Omega }}\ &={{\frac {d\sigma }{d\Omega }}\,{\Bigg \vert }\,}_{\text{point}}G^{2}(q^{2})\end{aligned}}}{\displaystyle {\begin{aligned}R_{e}^{2}&=-6{{\frac {dG_{e}}{dq^{2}}}\,{\Bigg \vert }\,}_{q^{2}=0}\\{\frac {d\sigma }{d\Omega }}\ &={{\frac {d\sigma }{d\Omega }}\,{\Bigg \vert }\,}_{\text{point}}G^{2}(q^{2})\end{aligned}}} +The atomic form factor is related to the wave function density of the target: + +{\displaystyle G(q^{2})=\int e^{iqr}\psi (r)^{2}\,dr^{3}}{\displaystyle G(q^{2})=\int e^{iqr}\psi (r)^{2}\,dr^{3}} +The form factor can be split in electric and magnetic form factors. These can be further written as linear combinations of Dirac and Pauli form factors.[43] + +{\displaystyle {\begin{aligned}G_{m}&=F_{D}+F_{P}\\G_{e}&=F_{D}-\tau F_{P}\\{\frac {d\sigma }{d\Omega }}&={{\frac {d\sigma }{d\Omega }}\,{\Bigg \vert }\,}_{NS}{\frac {1}{1+\tau }}\left(G_{e}^{2}\left(q^{2}\right)+{\frac {\tau }{\epsilon }}G_{m}^{2}\left(q^{2}\right)\right)\end{aligned}}}{\displaystyle {\begin{aligned}G_{m}&=F_{D}+F_{P}\\G_{e}&=F_{D}-\tau F_{P}\\{\frac {d\sigma }{d\Omega }}&={{\frac {d\sigma }{d\Omega }}\,{\Bigg \vert }\,}_{NS}{\frac {1}{1+\tau }}\left(G_{e}^{2}\left(q^{2}\right)+{\frac {\tau }{\epsilon }}G_{m}^{2}\left(q^{2}\right)\right)\end{aligned}}} +Pressure inside the proton +Since the proton is composed of quarks confined by gluons, an equivalent pressure which acts on the quarks can be defined. This allows calculation of their distribution as a function of distance from the centre using Compton scattering of high-energy electrons (DVCS, for deeply virtual Compton scattering). The pressure is maximum at the centre, about 1035 Pa which is greater than the pressure inside a neutron star.[44] It is positive (repulsive) to a radial distance of about 0.6 fm, negative (attractive) at greater distances, and very weak beyond about 2 fm. + +Charge radius in solvated proton, hydronium +The radius of hydrated proton appears in the Born equation for calculating the hydration enthalpy of hydronium. + +Interaction of free protons with ordinary matter +Although protons have affinity for oppositely charged electrons, this is a relatively low-energy interaction and so free protons must lose sufficient velocity (and kinetic energy) in order to become closely associated and bound to electrons. High energy protons, in traversing ordinary matter, lose energy by collisions with atomic nuclei, and by ionization of atoms (removing electrons) until they are slowed sufficiently to be captured by the electron cloud in a normal atom. + +However, in such an association with an electron, the character of the bound proton is not changed, and it remains a proton. The attraction of low-energy free protons to any electrons present in normal matter (such as the electrons in normal atoms) causes free protons to stop and to form a new chemical bond with an atom. Such a bond happens at any sufficiently "cold" temperature (i.e., comparable to temperatures at the surface of the Sun) and with any type of atom. Thus, in interaction with any type of normal (non-plasma) matter, low-velocity free protons are attracted to electrons in any atom or molecule with which they come in contact, causing the proton and molecule to combine. Such molecules are then said to be "protonated", and chemically they often, as a result, become so-called Brønsted acids. + +Proton in chemistry +Atomic number +In chemistry, the number of protons in the nucleus of an atom is known as the atomic number, which determines the chemical element to which the atom belongs. For example, the atomic number of chlorine is 17; this means that each chlorine atom has 17 protons and that all atoms with 17 protons are chlorine atoms. The chemical properties of each atom are determined by the number of (negatively charged) electrons, which for neutral atoms is equal to the number of (positive) protons so that the total charge is zero. For example, a neutral chlorine atom has 17 protons and 17 electrons, whereas a Cl− anion has 17 protons and 18 electrons for a total charge of −1. + +All atoms of a given element are not necessarily identical, however. The number of neutrons may vary to form different isotopes, and energy levels may differ, resulting in different nuclear isomers. For example, there are two stable isotopes of chlorine: 35 +17Cl + with 35 − 17 = 18 neutrons and 37 +17Cl + with 37 − 17 = 20 neutrons. + +Hydrogen ion +See also: Hydron (chemistry) + +Protium, the most common isotope of hydrogen, consists of one proton and one electron (it has no neutrons). The term "hydrogen ion" (H+ +) implies that that H-atom has lost its one electron, causing only a proton to remain. Thus, in chemistry, the terms "proton" and "hydrogen ion" (for the protium isotope) are used synonymously +The proton is a unique chemical species, being a bare nucleus. As a consequence it has no independent existence in the condensed state and is invariably found bound by a pair of electrons to another atom. +Ross Stewart, The Proton: Application to Organic Chemistry (1985, p. 1) +In chemistry, the term proton refers to the hydrogen ion, H+ +. Since the atomic number of hydrogen is 1, a hydrogen ion has no electrons and corresponds to a bare nucleus, consisting of a proton (and 0 neutrons for the most abundant isotope protium 1 +1H +). The proton is a "bare charge" with only about 1/64,000 of the radius of a hydrogen atom, and so is extremely reactive chemically. The free proton, thus, has an extremely short lifetime in chemical systems such as liquids and it reacts immediately with the electron cloud of any available molecule. In aqueous solution, it forms the hydronium ion, H3O+, which in turn is further solvated by water molecules in clusters such as [H5O2]+ and [H9O4]+.[45] + +The transfer of H+ + in an acid–base reaction is usually referred to as "proton transfer". The acid is referred to as a proton donor and the base as a proton acceptor. Likewise, biochemical terms such as proton pump and proton channel refer to the movement of hydrated H+ + ions. + +The ion produced by removing the electron from a deuterium atom is known as a deuteron, not a proton. Likewise, removing an electron from a tritium atom produces a triton. + +Proton nuclear magnetic resonance (NMR) +Also in chemistry, the term "proton NMR" refers to the observation of hydrogen-1 nuclei in (mostly organic) molecules by nuclear magnetic resonance. This method uses the spin of the proton, which has the value one-half. The name refers to examination of protons as they occur in protium (hydrogen-1 atoms) in compounds, and does not imply that free protons exist in the compound being studied. + +Human exposure +Main article: Effect of spaceflight on the body +See also: Proton therapy +The Apollo Lunar Surface Experiments Packages (ALSEP) determined that more than 95% of the particles in the solar wind are electrons and protons, in approximately equal numbers.[46][47] + +Because the Solar Wind Spectrometer made continuous measurements, it was possible to measure how the Earth's magnetic field affects arriving solar wind particles. For about two-thirds of each orbit, the Moon is outside of the Earth's magnetic field. At these times, a typical proton density was 10 to 20 per cubic centimeter, with most protons having velocities between 400 and 650 kilometers per second. For about five days of each month, the Moon is inside the Earth's geomagnetic tail, and typically no solar wind particles were detectable. For the remainder of each lunar orbit, the Moon is in a transitional region known as the magnetosheath, where the Earth's magnetic field affects the solar wind, but does not completely exclude it. In this region, the particle flux is reduced, with typical proton velocities of 250 to 450 kilometers per second. During the lunar night, the spectrometer was shielded from the solar wind by the Moon and no solar wind particles were measured.[46] + +Protons also have extrasolar origin from galactic cosmic rays, where they make up about 90% of the total particle flux. These protons often have higher energy than solar wind protons, and their intensity is far more uniform and less variable than protons coming from the Sun, the production of which is heavily affected by solar proton events such as coronal mass ejections. + +Research has been performed on the dose-rate effects of protons, as typically found in space travel, on human health.[47][48] To be more specific, there are hopes to identify what specific chromosomes are damaged, and to define the damage, during cancer development from proton exposure.[47] Another study looks into determining "the effects of exposure to proton irradiation on neurochemical and behavioral endpoints, including dopaminergic functioning, amphetamine-induced conditioned taste aversion learning, and spatial learning and memory as measured by the Morris water maze.[48] Electrical charging of a spacecraft due to interplanetary proton bombardment has also been proposed for study.[49] There are many more studies that pertain to space travel, including galactic cosmic rays and their possible health effects, and solar proton event exposure. + +The American Biostack and Soviet Biorack space travel experiments have demonstrated the severity of molecular damage induced by heavy ions on microorganisms including Artemia cysts.[50] + +Antiproton +Main article: Antiproton +CPT-symmetry puts strong constraints on the relative properties of particles and antiparticles and, therefore, is open to stringent tests. For example, the charges of a proton and antiproton must sum to exactly zero. This equality has been tested to one part in 108. The equality of their masses has also been tested to better than one part in 108. By holding antiprotons in a Penning trap, the equality of the charge-to-mass ratio of protons and antiprotons has been tested to one part in 6×109.[51] The magnetic moment of antiprotons has been measured with error of 8×10−3 nuclear Bohr magnetons, and is found to be equal and opposite to that of a proton. diff --git a/examples/article4.txt b/examples/article4.txt new file mode 100644 index 0000000..2117064 --- /dev/null +++ b/examples/article4.txt @@ -0,0 +1,416 @@ +The Higgs boson is an elementary particle in the Standard Model of particle physics, produced by the quantum excitation of the Higgs field,[8][9] one of the fields in particle physics theory.[9] It is named after physicist Peter Higgs, who in 1964, along with five other scientists, proposed the Higgs mechanism to explain why particles have mass. This mechanism implies the existence of the Higgs boson. The Higgs boson was initially discovered as a new particle in 2012 by the ATLAS and CMS collaborations based on collisions in the LHC at CERN, and the new particle was subsequently confirmed to match the expected properties of a Higgs boson over the following years. + +On December 10, 2013, two of the physicists, Peter Higgs and François Englert, were awarded the Nobel Prize in Physics for their theoretical predictions. Although Higgs's name has come to be associated with this theory (the Higgs mechanism), several researchers between about 1960 and 1972 independently developed different parts of it. + +In mainstream media the Higgs boson has often been called the "God particle", from a 1993 book on the topic,[10] although the nickname is strongly disliked by many physicists, including Higgs himself, who regard it as sensationalism.[11][12] + + +Contents +1 Introduction +1.1 The Standard Model +1.2 The problem of gauge boson mass +1.3 Symmetry breaking +1.4 Higgs mechanism +1.5 Higgs field +1.6 The "central problem" +1.7 Search and discovery +1.8 Interpretation +1.9 Overview of properties +2 Significance +2.1 Particle physics +2.2 Cosmology +2.3 Practical and technological impact +3 History +3.1 Theorization +3.2 Experimental search +4 Theoretical issues +4.1 Theoretical need for the Higgs +4.2 Alternative models +4.3 Further theoretical issues and hierarchy problem +5 Properties +5.1 Properties of the Higgs field +5.2 Properties of the Higgs boson +5.3 Production +5.4 Decay +6 Public discussion +6.1 Naming +6.2 Educational explanations and analogies +6.3 Recognition and awards +7 Technical aspects and mathematical formulation +8 See also +9 Notes +10 References +11 Further reading +12 External links +12.1 Popular science, mass media, and general coverage +12.2 Significant papers and other +12.3 Introductions to the field +Introduction +Standard Model of particle physics +Standard Model of Elementary Particles.svg +Elementary particles of the Standard Model +Background[show] +Constituents[show] +Limitations[show] +Scientists[show] +vte +The Standard Model +Physicists explain the properties of forces between elementary particles in terms of the Standard Model – a widely accepted framework for understanding almost everything in physics in the known universe, other than gravity. (A separate theory, general relativity, is used for gravity.) In this model, the fundamental forces in nature arise from properties of our universe called gauge invariance and symmetries. The forces are transmitted by particles known as gauge bosons.[13][14] + +The problem of gauge boson mass +Field theories had been used with great success in understanding the electromagnetic field and the strong force, but by around 1960 all attempts to create a gauge invariant theory for the weak force (and its combination with fundamental force electromagnetism, the electroweak interaction) had consistently failed, with gauge theories thereby starting to fall into disrepute as a result. The problem was that gauge invariant theory contains symmetry requirements, and these incorrectly predicted that the weak force's gauge bosons (W and Z) should have zero mass. It is known from experiments that they have non-zero mass.[15] This meant that either gauge invariance was an incorrect approach, or something else – unknown – was giving these particles their mass. By the late 1950s, physicists had not resolved these issues and were still unable to create a comprehensive theory for particle physics, because all attempts to solve this problem just created more theoretical problems. + +Symmetry breaking +In the late 1950s, Yoichiro Nambu recognized that spontaneous symmetry breaking, a process where a symmetric system ends up in an asymmetric state, could occur under certain conditions.[c] In 1962 physicist Philip Anderson, working in the field of condensed matter physics, observed that symmetry breaking played a role in superconductivity, and may have relevance to the problem of gauge invariance in particle physics. In 1963, this was shown to be theoretically possible, at least for some limited (non-relativistic) cases. + +Higgs mechanism +Main articles: Higgs mechanism and Standard Model +Following the 1962 and 1963 papers, three groups of researchers independently published the 1964 PRL symmetry breaking papers with similar conclusions and for all cases, not just some limited cases. They showed that the conditions for electroweak symmetry would be "broken" if an unusual type of field existed throughout the universe, and indeed, some fundamental particles would acquire mass. The field required for this to happen (which was purely hypothetical at the time) became known as the Higgs field (after Peter Higgs, one of the researchers) and the mechanism by which it led to symmetry breaking, known as the Higgs mechanism. A key feature of the necessary field is that it would take less energy for the field to have a non-zero value than a zero value, unlike all other known fields, therefore, the Higgs field has a non-zero value (or vacuum expectation) everywhere. This non-zero value could in theory break electroweak symmetry. It was the first proposal capable of showing how the weak force gauge bosons could have mass despite their governing symmetry, within a gauge invariant theory. + +Although these ideas did not gain much initial support or attention, by 1972 they had been developed into a comprehensive theory and proved capable of giving "sensible" results that accurately described particles known at the time, and which, with exceptional accuracy, predicted several other particles discovered during the following years.[d] During the 1970s these theories rapidly became the Standard Model of particle physics. + +Higgs field +The Standard Model includes a field of the kind needed to "break" electroweak symmetry and give particles their correct mass. This field, called the "Higgs Field", exists throughout space, and it breaks some symmetry laws of the electroweak interaction, triggering the Higgs mechanism. It therefore causes the W and Z gauge bosons of the weak force to be massive at all temperatures below an extreme high value.[e] When the weak force bosons acquire mass, this affects the distance they can freely travel, which becomes very small, also matching experimental findings.[f] Furthermore, it was later realised that the same field would also explain, in a different way, why other fundamental constituents of matter (including electrons and quarks) have mass. + +Unlike all other known fields such as the electromagnetic field, the Higgs field is a scalar field, and has a non-zero constant value in vacuum. + +The "central problem" +There was not yet any direct evidence that the Higgs field existed, but even without proof of the field, the accuracy of its predictions led scientists to believe the theory might be true. By the 1980s the question of whether or not the Higgs field existed, and therefore whether or not the entire Standard Model was correct, had come to be regarded as one of the most important unanswered questions in particle physics. + +For many decades, scientists had no way to determine whether or not the Higgs field existed, because the technology needed for its detection did not exist at that time. If the Higgs field did exist, then it would be unlike any other known fundamental field, but it also was possible that these key ideas, or even the entire Standard Model, were somehow incorrect.[g] + +The hypothesised Higgs mechanism made several accurate predictions.[d][17]:22 One crucial prediction was that a matching particle called the "Higgs boson" should also exist. Proving the existence of the Higgs boson could prove whether the Higgs field existed, and therefore finally prove whether the Standard Model's explanation was correct. Therefore there was an extensive search for the Higgs boson, as a way to prove the Higgs field itself existed.[8][9] + +The existence of the Higgs field became the last unverified part of the Standard Model of particle physics, and for several decades was considered "the central problem in particle physics".[18][19] + +Search and discovery +Although the Higgs field exists everywhere, proving its existence was far from easy. In principle, it can be proved to exist by detecting its excitations, which manifest as Higgs particles (the Higgs boson), but these are extremely difficult to produce and detect, due to the energy required to produce them and their very rare production even if the energy is sufficient. It was therefore several decades before the first evidence of the Higgs boson was found. Particle colliders, detectors, and computers capable of looking for Higgs bosons took more than 30 years (c. 1980–2010) to develop. + +The importance of this fundamental question led to a 40-year search, and the construction of one of the world's most expensive and complex experimental facilities to date, CERN's Large Hadron Collider,[20] in an attempt to create Higgs bosons and other particles for observation and study. On 4 July 2012, the discovery of a new particle with a mass between 125 and 127 GeV/c2 was announced; physicists suspected that it was the Higgs boson.[21][22][23] Since then, the particle has been shown to behave, interact, and decay in many of the ways predicted for Higgs particles by the Standard Model, as well as having even parity and zero spin,[6][7] two fundamental attributes of a Higgs boson. This also means it is the first elementary scalar particle discovered in nature.[24] + +By March 2013, the existence of the Higgs boson was confirmed, and therefore, the concept of some type of Higgs field throughout space is strongly supported.[21][23][6] + +The presence of the field, now confirmed by experimental investigation, explains why some fundamental particles have mass, despite the symmetries controlling their interactions implying that they should be massless. It also resolves several other long-standing puzzles, such as the reason for the extremely short distance travelled by the weak force bosons, and therefore the weak force's extremely short range. + +As of 2018, in-depth research shows the particle continuing to behave in line with predictions for the Standard Model Higgs boson. More studies are needed to verify with higher precision that the discovered particle has all of the properties predicted, or whether, as described by some theories, multiple Higgs bosons exist.[25] + +The nature and properties of this field are now being investigated further, using more data collected at the LHC.[1] + +Interpretation +Various analogies have been used to describe the Higgs field and boson, including analogies with well-known symmetry-breaking effects such as the rainbow and prism, electric fields, and ripples on the surface of water. + +Other analogies based on resistance of macro objects moving through media (such as people moving through crowds, or some objects moving through syrup or molasses) are commonly used but misleading, since the Higgs field does not actually resist particles, and the effect of mass is not caused by resistance. + +Overview of properties +In the Standard Model, the Higgs particle is a massive scalar boson with zero spin, no electric charge, and no colour charge. It is also very unstable, decaying into other particles almost immediately. The Higgs field is a scalar field, with two neutral and two electrically charged components that form a complex doublet of the weak isospin SU(2) symmetry. The Higgs field is a scalar field with a "Mexican hat-shaped" potential. In its ground state, this causes the field to have a nonzero value everywhere (including otherwise empty space), and as a result, below a very high energy it breaks the weak isospin symmetry of the electroweak interaction. (Technically the non-zero expectation value converts the Lagrangian's Yukawa coupling terms into mass terms.) When this happens, three components of the Higgs field are "absorbed" by the SU(2) and U(1) gauge bosons (the "Higgs mechanism") to become the longitudinal components of the now-massive W and Z bosons of the weak force. The remaining electrically neutral component either manifests as a Higgs particle, or may couple separately to other particles known as fermions (via Yukawa couplings), causing these to acquire mass as well.[26] + +Significance + +This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. +Find sources: "Higgs boson" – news · newspapers · books · scholar · JSTOR (January 2015) (Learn how and when to remove this template message) + +This section possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. (January 2015) (Learn how and when to remove this template message) +Evidence of the Higgs field and its properties has been extremely significant for many reasons. The importance of the Higgs boson is largely that it is able to be examined using existing knowledge and experimental technology, as a way to confirm and study the entire Higgs field theory.[8][9] Conversely, proof that the Higgs field and boson do not exist would have also been significant. + +Particle physics +Validation of the Standard Model +The Higgs boson validates the Standard Model through the mechanism of mass generation. As more precise measurements of its properties are made, more advanced extensions may be suggested or excluded. As experimental means to measure the field's behaviours and interactions are developed, this fundamental field may be better understood. If the Higgs field had not been discovered, the Standard Model would have needed to be modified or superseded. + +Related to this, a belief generally exists among physicists that there is likely to be "new" physics beyond the Standard Model, and the Standard Model will at some point be extended or superseded. The Higgs discovery, as well as the many measured collisions occurring at the LHC, provide physicists a sensitive tool to search their data for any evidence that the Standard Model seems to fail, and could provide considerable evidence guiding researchers into future theoretical developments. + +Symmetry breaking of the electroweak interaction +Below an extremely high temperature, electroweak symmetry breaking causes the electroweak interaction to manifest in part as the short-ranged weak force, which is carried by massive gauge bosons. In the history of the universe, electroweak symmetry breaking is believed to have happened shortly after the hot big bang, when the universe was at a temperature 159.5±1.5 GeV.[27] This symmetry breaking is required for atoms and other structures to form, as well as for nuclear reactions in stars, such as our Sun. The Higgs field is responsible for this symmetry breaking. + +Particle mass acquisition +The Higgs field is pivotal in generating the masses of quarks and charged leptons (through Yukawa coupling) and the W and Z gauge bosons (through the Higgs mechanism). + +It is worth noting that the Higgs field does not "create" mass out of nothing (which would violate the law of conservation of energy), nor is the Higgs field responsible for the mass of all particles. For example, approximately 99% of the mass of baryons (composite particles such as the proton and neutron), is due instead to quantum chromodynamic binding energy, which is the sum of the kinetic energies of quarks and the energies of the massless gluons mediating the strong interaction inside the baryons.[28] In Higgs-based theories, the property of "mass" is a manifestation of potential energy transferred to fundamental particles when they interact ("couple") with the Higgs field, which had contained that mass in the form of energy.[29] + +Scalar fields and extension of the Standard Model +The Higgs field is the only scalar (spin 0) field to be detected; all the other fields in the Standard Model are spin ½ fermions or spin 1 bosons. According to Rolf-Dieter Heuer, director general of CERN when the Higgs boson was discovered, this existence proof of a scalar field is almost as important as the Higgs's role in determining the mass of other particles. It suggests that other hypothetical scalar fields suggested by other theories, from the inflaton to quintessence, could perhaps exist as well.[30][31] + +Cosmology +Inflaton +There has been considerable scientific research on possible links between the Higgs field and the inflaton – a hypothetical field suggested as the explanation for the expansion of space during the first fraction of a second of the universe (known as the "inflationary epoch"). Some theories suggest that a fundamental scalar field might be responsible for this phenomenon; the Higgs field is such a field, and its existence has led to papers analysing whether it could also be the inflaton responsible for this exponential expansion of the universe during the Big Bang. Such theories are highly tentative and face significant problems related to unitarity, but may be viable if combined with additional features such as large non-minimal coupling, a Brans–Dicke scalar, or other "new" physics, and they have received treatments suggesting that Higgs inflation models are still of interest theoretically. + +Nature of the universe, and its possible fates + +Diagram showing the Higgs boson and top quark masses, which could indicate whether our universe is stable, or a long-lived 'bubble'. As of 2012, the 2 σ ellipse based on Tevatron and LHC data still allows for both possibilities.[32] +In the Standard Model, there exists the possibility that the underlying state of our universe – known as the "vacuum" – is long-lived, but not completely stable. In this scenario, the universe as we know it could effectively be destroyed by collapsing into a more stable vacuum state.[33][34][35][36][37] This was sometimes misreported as the Higgs boson "ending" the universe.[h] If the masses of the Higgs boson and top quark are known more precisely, and the Standard Model provides an accurate description of particle physics up to extreme energies of the Planck scale, then it is possible to calculate whether the vacuum is stable or merely long-lived.[40][41][42] A 125–127 GeV Higgs mass seems to be extremely close to the boundary for stability, but a definitive answer requires much more precise measurements of the pole mass of the top quark.[32] New physics can change this picture.[43] + +If measurements of the Higgs boson suggest that our universe lies within a false vacuum of this kind, then it would imply – more than likely in many billions of years.[44][i] – that the universe's forces, particles, and structures could cease to exist as we know them (and be replaced by different ones), if a true vacuum happened to nucleate.[44][j] It also suggests that the Higgs self-coupling λ and its βλ function could be very close to zero at the Planck scale, with "intriguing" implications, including theories of gravity and Higgs-based inflation.[32]:218[46][47] A future electron–positron collider would be able to provide the precise measurements of the top quark needed for such calculations.[32] + +Vacuum energy and the cosmological constant +Further information: Zero-point energy and Vacuum state +More speculatively, the Higgs field has also been proposed as the energy of the vacuum, which at the extreme energies of the first moments of the Big Bang caused the universe to be a kind of featureless symmetry of undifferentiated, extremely high energy. In this kind of speculation, the single unified field of a Grand Unified Theory is identified as (or modelled upon) the Higgs field, and it is through successive symmetry breakings of the Higgs field, or some similar field, at phase transitions that the presently known forces and fields of the universe arise.[48] + +The relationship (if any) between the Higgs field and the presently observed vacuum energy density of the universe has also come under scientific study. As observed, the present vacuum energy density is extremely close to zero, but the energy density expected from the Higgs field, supersymmetry, and other current theories are typically many orders of magnitude larger. It is unclear how these should be reconciled. This cosmological constant problem remains a major unanswered problem in physics. + +Practical and technological impact +As yet, there are no known immediate technological benefits of finding the Higgs particle. However, a common pattern for fundamental discoveries is for practical applications to follow later, and once the discovery has been explored further, perhaps becoming the basis for new technologies of importance to society.[49][50][51] + +The challenges in particle physics have furthered major technological progress of widespread importance. For example, the World Wide Web began as a project to improve CERN's communication system. CERN's requirement to process massive amounts of data produced by the Large Hadron Collider also led to contributions to the fields of distributed and cloud computing[citation needed]. + +History +AIP-Sakurai-best.JPG Higgs, Peter (1929) cropped.jpg +The six authors of the 1964 PRL papers, who received the 2010 J.J. Sakurai Prize for their work; from left to right: Kibble, Guralnik, Hagen, Englert, Brout; right: Higgs. + + +Nobel Prize Laureate Peter Higgs in Stockholm, December 2013 +Theorization +See also: 1964 PRL symmetry breaking papers, Higgs mechanism, and History of quantum field theory +Particle physicists study matter made from fundamental particles whose interactions are mediated by exchange particles – gauge bosons – acting as force carriers. At the beginning of the 1960s a number of these particles had been discovered or proposed, along with theories suggesting how they relate to each other, some of which had already been reformulated as field theories in which the objects of study are not particles and forces, but quantum fields and their symmetries.[52]:150 However, attempts to produce quantum field models for two of the four known fundamental forces – the electromagnetic force and the weak nuclear force – and then to unify these interactions, were still unsuccessful. + +One known problem was that gauge invariant approaches, including non-abelian models such as Yang–Mills theory (1954), which held great promise for unified theories, also seemed to predict known massive particles as massless.[53] Goldstone's theorem, relating to continuous symmetries within some theories, also appeared to rule out many obvious solutions,[54] since it appeared to show that zero-mass particles also would have to exist that simply were "not seen".[55] According to Guralnik, physicists had "no understanding" how these problems could be overcome.[55] + +Particle physicist and mathematician Peter Woit summarised the state of research at the time: +Yang and Mills work on non-abelian gauge theory had one huge problem: in perturbation theory it has massless particles which don’t correspond to anything we see. One way of getting rid of this problem is now fairly well understood, the phenomenon of confinement realized in QCD, where the strong interactions get rid of the massless “gluon” states at long distances. By the very early sixties, people had begun to understand another source of massless particles: spontaneous symmetry breaking of a continuous symmetry. What Philip Anderson realized and worked out in the summer of 1962 was that, when you have both gauge symmetry and spontaneous symmetry breaking, the massless Nambu–Goldstone mode can combine with the massless gauge field modes to produce a physical massive vector field. This is what happens in superconductivity, a subject about which Anderson was (and is) one of the leading experts.[53] [text condensed] + +The Higgs mechanism is a process by which vector bosons can acquire rest mass without explicitly breaking gauge invariance, as a byproduct of spontaneous symmetry breaking.[56][57] Initially, the mathematical theory behind spontaneous symmetry breaking was conceived and published within particle physics by Yoichiro Nambu in 1960,[58] and the concept that such a mechanism could offer a possible solution for the "mass problem" was originally suggested in 1962 by Philip Anderson (who had previously written papers on broken symmetry and its outcomes in superconductivity.[59] Anderson concluded in his 1963 paper on the Yang-Mills theory, that "considering the superconducting analog... [t]hese two types of bosons seem capable of canceling each other out... leaving finite mass bosons"),[60][61] and in March 1964, Abraham Klein and Benjamin Lee showed that Goldstone's theorem could be avoided this way in at least some non-relativistic cases, and speculated it might be possible in truly relativistic cases.[62] + +These approaches were quickly developed into a full relativistic model, independently and almost simultaneously, by three groups of physicists: by François Englert and Robert Brout in August 1964;[63] by Peter Higgs in October 1964;[64] and by Gerald Guralnik, Carl Hagen, and Tom Kibble (GHK) in November 1964.[65] Higgs also wrote a short, but important,[56] response published in September 1964 to an objection by Gilbert,[66] which showed that if calculating within the radiation gauge, Goldstone's theorem and Gilbert's objection would become inapplicable.[k] Higgs later described Gilbert's objection as prompting his own paper.[67] Properties of the model were further considered by Guralnik in 1965,[68] by Higgs in 1966,[69] by Kibble in 1967,[70] and further by GHK in 1967.[71] The original three 1964 papers demonstrated that when a gauge theory is combined with an additional field that spontaneously breaks the symmetry, the gauge bosons may consistently acquire a finite mass.[56][57][72] In 1967, Steven Weinberg [73] and Abdus Salam[74] independently showed how a Higgs mechanism could be used to break the electroweak symmetry of Sheldon Glashow's unified model for the weak and electromagnetic interactions,[75] (itself an extension of work by Schwinger), forming what became the Standard Model of particle physics. Weinberg was the first to observe that this would also provide mass terms for the fermions.[76][l] + +At first, these seminal papers on spontaneous breaking of gauge symmetries were largely ignored, because it was widely believed that the (non-Abelian gauge) theories in question were a dead-end, and in particular that they could not be renormalised. In 1971–72, Martinus Veltman and Gerard 't Hooft proved renormalisation of Yang–Mills was possible in two papers covering massless, and then massive, fields.[76] Their contribution, and the work of others on the renormalisation group – including "substantial" theoretical work by Russian physicists Ludvig Faddeev, Andrei Slavnov, Efim Fradkin, and Igor Tyutin[77] – was eventually "enormously profound and influential",[78] but even with all key elements of the eventual theory published there was still almost no wider interest. For example, Coleman found in a study that "essentially no-one paid any attention" to Weinberg's paper prior to 1971[79] and discussed by David Politzer in his 2004 Nobel speech.[78] – now the most cited in particle physics [80] – and even in 1970 according to Politzer, Glashow's teaching of the weak interaction contained no mention of Weinberg's, Salam's, or Glashow's own work.[78] In practice, Politzer states, almost everyone learned of the theory due to physicist Benjamin Lee, who combined the work of Veltman and 't Hooft with insights by others, and popularised the completed theory.[78] In this way, from 1971, interest and acceptance "exploded"[78] and the ideas were quickly absorbed in the mainstream.[76][78] + +The resulting electroweak theory and Standard Model have accurately predicted (among other things) weak neutral currents, three bosons, the top and charm quarks, and with great precision, the mass and other properties of some of these.[d] Many of those involved eventually won Nobel Prizes or other renowned awards. A 1974 paper and comprehensive review in Reviews of Modern Physics commented that "while no one doubted the [mathematical] correctness of these arguments, no one quite believed that nature was diabolically clever enough to take advantage of them",[81] adding that the theory had so far produced accurate answers that accorded with experiment, but it was unknown whether the theory was fundamentally correct.[82] By 1986 and again in the 1990s it became possible to write that understanding and proving the Higgs sector of the Standard Model was "the central problem today in particle physics".[18][19] + +Summary and impact of the PRL papers + Wikinews has news related to: +2010 Sakurai Prize awarded for 1964 Higgs Boson theory work +Prospective Nobel Prize for Higgs boson work disputed +The three papers written in 1964 were each recognised as milestone papers during Physical Review Letters's 50th anniversary celebration.[72] Their six authors were also awarded the 2010 J. J. Sakurai Prize for Theoretical Particle Physics for this work.[83] (A controversy also arose the same year, because in the event of a Nobel Prize only up to three scientists could be recognised, with six being credited for the papers.[84]) Two of the three PRL papers (by Higgs and by GHK) contained equations for the hypothetical field that eventually would become known as the Higgs field and its hypothetical quantum, the Higgs boson.[64][65] Higgs' subsequent 1966 paper showed the decay mechanism of the boson; only a massive boson can decay and the decays can prove the mechanism.[citation needed] + +In the paper by Higgs the boson is massive, and in a closing sentence Higgs writes that "an essential feature" of the theory "is the prediction of incomplete multiplets of scalar and vector bosons".[64] (Frank Close comments that 1960s gauge theorists were focused on the problem of massless vector bosons, and the implied existence of a massive scalar boson was not seen as important; only Higgs directly addressed it.[85]:154, 166, 175) In the paper by GHK the boson is massless and decoupled from the massive states.[65] In reviews dated 2009 and 2011, Guralnik states that in the GHK model the boson is massless only in a lowest-order approximation, but it is not subject to any constraint and acquires mass at higher orders, and adds that the GHK paper was the only one to show that there are no massless Goldstone bosons in the model and to give a complete analysis of the general Higgs mechanism.[55][86] All three reached similar conclusions, despite their very different approaches: Higgs' paper essentially used classical techniques, Englert and Brout's involved calculating vacuum polarisation in perturbation theory around an assumed symmetry-breaking vacuum state, and GHK used operator formalism and conservation laws to explore in depth the ways in which Goldstone's theorem may be worked around.[56] Some versions of the theory predicted more than one kind of Higgs fields and bosons, and alternative "Higgsless" models were considered until the discovery of the Higgs boson. + +Experimental search +Main article: Search for the Higgs boson +To produce Higgs bosons, two beams of particles are accelerated to very high energies and allowed to collide within a particle detector. Occasionally, although rarely, a Higgs boson will be created fleetingly as part of the collision byproducts. Because the Higgs boson decays very quickly, particle detectors cannot detect it directly. Instead the detectors register all the decay products (the decay signature) and from the data the decay process is reconstructed. If the observed decay products match a possible decay process (known as a decay channel) of a Higgs boson, this indicates that a Higgs boson may have been created. In practice, many processes may produce similar decay signatures. Fortunately, the Standard Model precisely predicts the likelihood of each of these, and each known process, occurring. So, if the detector detects more decay signatures consistently matching a Higgs boson than would otherwise be expected if Higgs bosons did not exist, then this would be strong evidence that the Higgs boson exists. + +Because Higgs boson production in a particle collision is likely to be very rare (1 in 10 billion at the LHC),[m] and many other possible collision events can have similar decay signatures, the data of hundreds of trillions of collisions needs to be analysed and must "show the same picture" before a conclusion about the existence of the Higgs boson can be reached. To conclude that a new particle has been found, particle physicists require that the statistical analysis of two independent particle detectors each indicate that there is lesser than a one-in-a-million chance that the observed decay signatures are due to just background random Standard Model events – i.e., that the observed number of events is more than 5 standard deviations (sigma) different from that expected if there was no new particle. More collision data allows better confirmation of the physical properties of any new particle observed, and allows physicists to decide whether it is indeed a Higgs boson as described by the Standard Model or some other hypothetical new particle. + +To find the Higgs boson, a powerful particle accelerator was needed, because Higgs bosons might not be seen in lower-energy experiments. The collider needed to have a high luminosity in order to ensure enough collisions were seen for conclusions to be drawn. Finally, advanced computing facilities were needed to process the vast amount of data (25 petabytes per year as of 2012) produced by the collisions.[89] For the announcement of 4 July 2012, a new collider known as the Large Hadron Collider was constructed at CERN with a planned eventual collision energy of 14 TeV – over seven times any previous collider – and over 300 trillion (3×1014) LHC proton–proton collisions were analysed by the LHC Computing Grid, the world's largest computing grid (as of 2012), comprising over 170 computing facilities in a worldwide network across 36 countries.[89][90][91] + +Search before 4 July 2012 +The first extensive search for the Higgs boson was conducted at the Large Electron–Positron Collider (LEP) at CERN in the 1990s. At the end of its service in 2000, LEP had found no conclusive evidence for the Higgs.[n] This implied that if the Higgs boson were to exist it would have to be heavier than 114.4 GeV/c2.[92] + +The search continued at Fermilab in the United States, where the Tevatron – the collider that discovered the top quark in 1995 – had been upgraded for this purpose. There was no guarantee that the Tevatron would be able to find the Higgs, but it was the only supercollider that was operational since the Large Hadron Collider (LHC) was still under construction and the planned Superconducting Super Collider had been cancelled in 1993 and never completed. The Tevatron was only able to exclude further ranges for the Higgs mass, and was shut down on 30 September 2011 because it no longer could keep up with the LHC. The final analysis of the data excluded the possibility of a Higgs boson with a mass between 147 GeV/c2 and 180 GeV/c2. In addition, there was a small (but not significant) excess of events possibly indicating a Higgs boson with a mass between 115 GeV/c2 and 140 GeV/c2.[93] + +The Large Hadron Collider at CERN in Switzerland, was designed specifically to be able to either confirm or exclude the existence of the Higgs boson. Built in a 27 km tunnel under the ground near Geneva originally inhabited by LEP, it was designed to collide two beams of protons, initially at energies of 3.5 TeV per beam (7 TeV total), or almost 3.6 times that of the Tevatron, and upgradeable to 2 × 7 TeV (14 TeV total) in future. Theory suggested if the Higgs boson existed, collisions at these energy levels should be able to reveal it. As one of the most complicated scientific instruments ever built, its operational readiness was delayed for 14 months by a magnet quench event nine days after its inaugural tests, caused by a faulty electrical connection that damaged over 50 superconducting magnets and contaminated the vacuum system.[94][95][96] + +Data collection at the LHC finally commenced in March 2010.[97] By December 2011 the two main particle detectors at the LHC, ATLAS and CMS, had narrowed down the mass range where the Higgs could exist to around 116-130 GeV (ATLAS) and 115-127 GeV (CMS).[98][99] There had also already been a number of promising event excesses that had "evaporated" and proven to be nothing but random fluctuations. However, from around May 2011,[100] both experiments had seen among their results, the slow emergence of a small yet consistent excess of gamma and 4-lepton decay signatures and several other particle decays, all hinting at a new particle at a mass around 125 GeV.[100] By around November 2011, the anomalous data at 125 GeV was becoming "too large to ignore" (although still far from conclusive), and the team leaders at both ATLAS and CMS each privately suspected they might have found the Higgs.[100] On November 28, 2011, at an internal meeting of the two team leaders and the director general of CERN, the latest analyses were discussed outside their teams for the first time, suggesting both ATLAS and CMS might be converging on a possible shared result at 125 GeV, and initial preparations commenced in case of a successful finding.[100] While this information was not known publicly at the time, the narrowing of the possible Higgs range to around 115–130 GeV and the repeated observation of small but consistent event excesses across multiple channels at both ATLAS and CMS in the 124-126 GeV region (described as "tantalising hints" of around 2-3 sigma) were public knowledge with "a lot of interest".[101] It was therefore widely anticipated around the end of 2011, that the LHC would provide sufficient data to either exclude or confirm the finding of a Higgs boson by the end of 2012, when their 2012 collision data (with slightly higher 8 TeV collision energy) had been examined.[101][102] + +Discovery of candidate boson at CERN +2-photon Higgs decay.svg 4-lepton Higgs decay.svg +Feynman diagrams showing the cleanest channels associated with the low-mass (~125 GeV) Higgs boson candidate observed by ATLAS and CMS at the LHC. The dominant production mechanism at this mass involves two gluons from each proton fusing to a Top-quark Loop, which couples strongly to the Higgs field to produce a Higgs boson. +Left: Diphoton channel: Boson subsequently decays into 2 gamma ray photons by virtual interaction with a W boson loop or top quark loop. + +Right: 4-Lepton "golden channel": Boson emits 2 Z bosons, which each decay into 2 leptons (electrons, muons). + +Experimental analysis of these channels reached a significance of more than 5 sigma in both experiments.[103][104][105] + +On 22 June 2012 CERN announced an upcoming seminar covering tentative findings for 2012,[106][107] and shortly afterwards (from around 1 July 2012 according to an analysis of the spreading rumour in social media[108]) rumours began to spread in the media that this would include a major announcement, but it was unclear whether this would be a stronger signal or a formal discovery.[109][110] Speculation escalated to a "fevered" pitch when reports emerged that Peter Higgs, who proposed the particle, was to be attending the seminar,[111][112] and that "five leading physicists" had been invited – generally believed to signify the five living 1964 authors – with Higgs, Englert, Guralnik, Hagen attending and Kibble confirming his invitation (Brout having died in 2011).[113] + +On 4 July 2012 both of the CERN experiments announced they had independently made the same discovery:[114] CMS of a previously unknown boson with mass 125.3 ± 0.6 GeV/c2[115][116] and ATLAS of a boson with mass 126.0 ± 0.6 GeV/c2.[117][118] Using the combined analysis of two interaction types (known as 'channels'), both experiments independently reached a local significance of 5 sigma – implying that the probability of getting at least as strong a result by chance alone is less than 1 in 3 million. When additional channels were taken into account, the CMS significance was reduced to 4.9 sigma.[116] + +The two teams had been working 'blinded' from each other from around late 2011 or early 2012,[100] meaning they did not discuss their results with each other, providing additional certainty that any common finding was genuine validation of a particle.[89] This level of evidence, confirmed independently by two separate teams and experiments, meets the formal level of proof required to announce a confirmed discovery. + +On 31 July 2012, the ATLAS collaboration presented additional data analysis on the "observation of a new particle", including data from a third channel, which improved the significance to 5.9 sigma (1 in 588 million chance of obtaining at least as strong evidence by random background effects alone) and mass 126.0 ± 0.4 (stat) ± 0.4 (sys) GeV/c2,[118] and CMS improved the significance to 5-sigma and mass 125.3 ± 0.4 (stat) ± 0.5 (sys) GeV/c2.[115] + +The new particle tested as a possible Higgs boson +Following the 2012 discovery, it was still unconfirmed whether or not the 125 GeV/c2 particle was a Higgs boson. On one hand, observations remained consistent with the observed particle being the Standard Model Higgs boson, and the particle decayed into at least some of the predicted channels. Moreover, the production rates and branching ratios for the observed channels broadly matched the predictions by the Standard Model within the experimental uncertainties. However, the experimental uncertainties currently still left room for alternative explanations, meaning an announcement of the discovery of a Higgs boson would have been premature.[119] To allow more opportunity for data collection, the LHC's proposed 2012 shutdown and 2013–14 upgrade were postponed by 7 weeks into 2013.[120] + +In November 2012, in a conference in Kyoto researchers said evidence gathered since July was falling into line with the basic Standard Model more than its alternatives, with a range of results for several interactions matching that theory's predictions.[121] Physicist Matt Strassler highlighted "considerable" evidence that the new particle is not a pseudoscalar negative parity particle (consistent with this required finding for a Higgs boson), "evaporation" or lack of increased significance for previous hints of non-Standard Model findings, expected Standard Model interactions with W and Z bosons, absence of "significant new implications" for or against supersymmetry, and in general no significant deviations to date from the results expected of a Standard Model Higgs boson.[122] However some kinds of extensions to the Standard Model would also show very similar results;[123] so commentators noted that based on other particles that are still being understood long after their discovery, it may take years to be sure, and decades to fully understand the particle that has been found.[121][122] + +These findings meant that as of January 2013, scientists were very sure they had found an unknown particle of mass ~ 125 GeV/c2, and had not been misled by experimental error or a chance result. They were also sure, from initial observations, that the new particle was some kind of boson. The behaviours and properties of the particle, so far as examined since July 2012, also seemed quite close to the behaviours expected of a Higgs boson. Even so, it could still have been a Higgs boson or some other unknown boson, since future tests could show behaviours that do not match a Higgs boson, so as of December 2012 CERN still only stated that the new particle was "consistent with" the Higgs boson,[21][23] and scientists did not yet positively say it was the Higgs boson.[124] Despite this, in late 2012, widespread media reports announced (incorrectly) that a Higgs boson had been confirmed during the year.[o] + +In January 2013, CERN director-general Rolf-Dieter Heuer stated that based on data analysis to date, an answer could be possible 'towards' mid-2013,[130] and the deputy chair of physics at Brookhaven National Laboratory stated in February 2013 that a "definitive" answer might require "another few years" after the collider's 2015 restart.[131] In early March 2013, CERN Research Director Sergio Bertolucci stated that confirming spin-0 was the major remaining requirement to determine whether the particle is at least some kind of Higgs boson.[132] + + +Confirmation of existence and current status +On 14 March 2013 CERN confirmed that: + +"CMS and ATLAS have compared a number of options for the spin-parity of this particle, and these all prefer no spin and even parity [two fundamental criteria of a Higgs boson consistent with the Standard Model]. This, coupled with the measured interactions of the new particle with other particles, strongly indicates that it is a Higgs boson."[6] +This also makes the particle the first elementary scalar particle to be discovered in nature.[24] + +Examples of tests used to validate that the discovered particle is the Higgs boson:[122][133] + +Requirement How tested / explanation Current status (As of July 2017) +Zero spin Examining decay patterns. Spin-1 had been ruled out at the time of initial discovery by the observed decay to two photons (γ γ), leaving spin-0 and spin-2 as remaining candidates. Spin-0 confirmed.[7][6][134][135] The spin-2 hypothesis is excluded with a confidence level exceeding 99.9%.[135] +Even (Positive) parity Studying the angles at which decay products fly apart. Negative parity was also disfavoured if spin-0 was confirmed.[136] Even parity tentatively confirmed.[6][134][135] The spin-0 negative parity hypothesis is excluded with a confidence level exceeding 99.9%.[134][7] +Decay channels (outcomes of particle decaying) are as predicted The Standard Model predicts the decay patterns of a 125 GeV Higgs boson. Are these all being seen, and at the right rates? +Particularly significant, we should observe decays into pairs of photons (γ γ), W and Z bosons (WW and ZZ), bottom quarks (bb), and tau leptons (τ τ), among the possible outcomes. + +bb, γ γ, τ τ, WW and ZZ observed. All observed signal strengths are consistent with the Standard Model prediction.[137][1] +Couples to mass (i.e., strength of interaction with Standard Model particles proportional to their mass) Particle physicist Adam Falkowski states that the essential qualities of a Higgs boson are that it is a spin-0 (scalar) particle which also couples to mass (W and Z bosons); proving spin-0 alone is insufficient.[133] Couplings to mass strongly evidenced ("At 95% confidence level cV is within 15% of the standard model value cV=1").[133] +Higher energy results remain consistent After the LHC's 2015 restart at the higher energy of 13 TeV, searches for multiple Higgs particles (as predicted in some theories) and tests targeting other versions of particle theory continued. These higher energy results must continue to give results consistent with Higgs theories. Analysis of collisions up to July 2017 do not show deviations from the Standard Model, with experimental precisions better than results at lower energies.[1] +Findings since 2013 +In July 2017, CERN confirmed that all measurements still agree with the predictions of the Standard Model, and called the discovered particle simply "the Higgs boson".[1] As of 2019, the Large Hadron Collider has continued to produce findings that confirm the 2013 understanding of the Higgs field and particle.[138][139] + +The LHC's experimental work since restarting in 2015 has included probing the Higgs field and boson to a greater level of detail, and confirming whether or not less common predictions were correct. In particular, exploration since 2015 has provided strong evidence of the predicted direct decay into fermions such as pairs of bottom quarks (3.6 σ) – described as an "important milestone" in understanding its short lifetime and other rare decays – and also to confirm decay into pairs of tau leptons (5.9 σ). This was described by CERN as being "of paramount importance to establishing the coupling of the Higgs boson to leptons and represents an important step towards measuring its couplings to third generation fermions, the very heavy copies of the electrons and quarks, whose role in nature is a profound mystery".[1] Published results as of 19 Mar 2018 at 13 TeV for ATLAS and CMS had their measurements of the Higgs mass at 124.98±0.28 GeV and 125.26±0.21 GeV respectively. + +In July 2018, the ATLAS and CMS experiments reported observing the Higgs boson decay into a pair of bottom quarks, which makes up approximately 60% of all of its decays.[140][141][142] + +Theoretical issues +Main article: Higgs mechanism +Theoretical need for the Higgs + +"Symmetry breaking illustrated": – At high energy levels (left) the ball settles in the centre, and the result is symmetrical. At lower energy levels (right), the overall "rules" remain symmetrical, but the "Mexican hat" potential comes into effect: "local" symmetry inevitably becomes broken since eventually the ball must at random roll one way or another. +Gauge invariance is an important property of modern particle theories such as the Standard Model, partly due to its success in other areas of fundamental physics such as electromagnetism and the strong interaction (quantum chromodynamics). However, before Sheldon L. Glashow extended the electroweak unification models in 1961, there were great difficulties in developing gauge theories for the weak nuclear force or a possible unified electroweak interaction. Fermions with a mass term would violate gauge symmetry and therefore cannot be gauge invariant. (This can be seen by examining the Dirac Lagrangian for a fermion in terms of left and right handed components; we find none of the spin-half particles could ever flip helicity as required for mass, so they must be massless.[p]) W and Z bosons are observed to have mass, but a boson mass term contains terms which clearly depend on the choice of gauge, and therefore these masses too cannot be gauge invariant. Therefore, it seems that none of the standard model fermions or bosons could "begin" with mass as an inbuilt property except by abandoning gauge invariance. If gauge invariance were to be retained, then these particles had to be acquiring their mass by some other mechanism or interaction. Additionally, whatever was giving these particles their mass had to not "break" gauge invariance as the basis for other parts of the theories where it worked well, and had to not require or predict unexpected massless particles or long-range forces (seemingly an inevitable consequence of Goldstone's theorem) which did not actually seem to exist in nature. + +A solution to all of these overlapping problems came from the discovery of a previously unnoticed borderline case hidden in the mathematics of Goldstone's theorem,[k] that under certain conditions it might theoretically be possible for a symmetry to be broken without disrupting gauge invariance and without any new massless particles or forces, and having "sensible" (renormalisable) results mathematically. This became known as the Higgs mechanism. + + +Summary of interactions between certain particles described by the Standard Model. +The Standard Model hypothesises a field which is responsible for this effect, called the Higgs field (symbol: {\displaystyle \phi }\phi ), which has the unusual property of a non-zero amplitude in its ground state; i.e., a non-zero vacuum expectation value. It can have this effect because of its unusual "Mexican hat" shaped potential whose lowest "point" is not at its "centre". In simple terms, unlike all other known fields, the Higgs field requires less energy to have a non-zero value than a zero value, so it ends up having a non-zero value everywhere. Below a certain extremely high energy level the existence of this non-zero vacuum expectation spontaneously breaks electroweak gauge symmetry which in turn gives rise to the Higgs mechanism and triggers the acquisition of mass by those particles interacting with the field. This effect occurs because scalar field components of the Higgs field are "absorbed" by the massive bosons as degrees of freedom, and couple to the fermions via Yukawa coupling, thereby producing the expected mass terms. When symmetry breaks under these conditions, the Goldstone bosons that arise interact with the Higgs field (and with other particles capable of interacting with the Higgs field) instead of becoming new massless particles. The intractable problems of both underlying theories "neutralise" each other, and the residual outcome is that elementary particles acquire a consistent mass based on how strongly they interact with the Higgs field. It is the simplest known process capable of giving mass to the gauge bosons while remaining compatible with gauge theories.[143] Its quantum would be a scalar boson, known as the Higgs boson.[144] + +Alternative models +Main article: Alternatives to the Standard Model Higgs +The Minimal Standard Model as described above is the simplest known model for the Higgs mechanism with just one Higgs field. However, an extended Higgs sector with additional Higgs particle doublets or triplets is also possible, and many extensions of the Standard Model have this feature. The non-minimal Higgs sector favoured by theory are the two-Higgs-doublet models (2HDM), which predict the existence of a quintet of scalar particles: two CP-even neutral Higgs bosons h0 and H0, a CP-odd neutral Higgs boson A0, and two charged Higgs particles H±. Supersymmetry ("SUSY") also predicts relations between the Higgs-boson masses and the masses of the gauge bosons, and could accommodate a 125 GeV/c2 neutral Higgs boson. + +The key method to distinguish between these different models involves study of the particles' interactions ("coupling") and exact decay processes ("branching ratios"), which can be measured and tested experimentally in particle collisions. In the Type-I 2HDM model one Higgs doublet couples to up and down quarks, while the second doublet does not couple to quarks. This model has two interesting limits, in which the lightest Higgs couples to just fermions ("gauge-phobic") or just gauge bosons ("fermiophobic"), but not both. In the Type-II 2HDM model, one Higgs doublet only couples to up-type quarks, the other only couples to down-type quarks.[145] The heavily researched Minimal Supersymmetric Standard Model (MSSM) includes a Type-II 2HDM Higgs sector, so it could be disproven by evidence of a Type-I 2HDM Higgs.[citation needed] + +In other models the Higgs scalar is a composite particle. For example, in technicolor the role of the Higgs field is played by strongly bound pairs of fermions called techniquarks. Other models, feature pairs of top quarks (see top quark condensate). In yet other models, there is no Higgs field at all and the electroweak symmetry is broken using extra dimensions.[146][147] + +Further theoretical issues and hierarchy problem +Main articles: Hierarchy problem and Hierarchy problem § The Higgs mass + +A one-loop Feynman diagram of the first-order correction to the Higgs mass. In the Standard Model the effects of these corrections are potentially enormous, giving rise to the so-called hierarchy problem. +The Standard Model leaves the mass of the Higgs boson as a parameter to be measured, rather than a value to be calculated. This is seen as theoretically unsatisfactory, particularly as quantum corrections (related to interactions with virtual particles) should apparently cause the Higgs particle to have a mass immensely higher than that observed, but at the same time the Standard Model requires a mass of the order of 100 to 1000 GeV to ensure unitarity (in this case, to unitarise longitudinal vector boson scattering).[148] Reconciling these points appears to require explaining why there is an almost-perfect cancellation resulting in the visible mass of ~ 125 GeV, and it is not clear how to do this. Because the weak force is about 1032 times stronger than gravity, and (linked to this) the Higgs boson's mass is so much less than the Planck mass or the grand unification energy, it appears that either there is some underlying connection or reason for these observations which is unknown and not described by the Standard Model, or some unexplained and extremely precise fine-tuning of parameters – however at present neither of these explanations is proven. This is known as a hierarchy problem.[149] More broadly, the hierarchy problem amounts to the worry that a future theory of fundamental particles and interactions should not have excessive fine-tunings or unduly delicate cancellations, and should allow masses of particles such as the Higgs boson to be calculable. The problem is in some ways unique to spin-0 particles (such as the Higgs boson), which can give rise to issues related to quantum corrections that do not affect particles with spin.[148] A number of solutions have been proposed, including supersymmetry, conformal solutions and solutions via extra dimensions such as braneworld models. + +There are also issues of quantum triviality, which suggests that it may not be possible to create a consistent quantum field theory involving elementary scalar particles.[150] However, if quantum triviality is avoided, triviality constraints may set bounds on the Higgs Boson mass. + +Properties +Properties of the Higgs field +In the Standard Model, the Higgs field is a scalar tachyonic field – scalar meaning it does not transform under Lorentz transformations, and tachyonic meaning the field (but not the particle) has imaginary mass, and in certain configurations must undergo symmetry breaking. It consists of four components: Two neutral ones and two charged component fields. Both of the charged components and one of the neutral fields are Goldstone bosons, which act as the longitudinal third-polarisation components of the massive W+, W−, and Z bosons. The quantum of the remaining neutral component corresponds to (and is theoretically realised as) the massive Higgs boson.[151] This component can interact with fermions via Yukawa coupling to give them mass as well. + +Mathematically, the Higgs field has imaginary mass and is therefore a tachyonic field.[152] While tachyons (particles that move faster than light) are a purely hypothetical concept, fields with imaginary mass have come to play an important role in modern physics.[153][154] Under no circumstances do any excitations ever propagate faster than light in such theories – the presence or absence of a tachyonic mass has no effect whatsoever on the maximum velocity of signals (there is no violation of causality).[155] Instead of faster-than-light particles, the imaginary mass creates an instability: Any configuration in which one or more field excitations are tachyonic must spontaneously decay, and the resulting configuration contains no physical tachyons. This process is known as tachyon condensation, and is now believed to be the explanation for how the Higgs mechanism itself arises in nature, and therefore the reason behind electroweak symmetry breaking. + +Although the notion of imaginary mass might seem troubling, it is only the field, and not the mass itself, that is quantised. Therefore, the field operators at spacelike separated points still commute (or anticommute), and information and particles still do not propagate faster than light.[156] Tachyon condensation drives a physical system that has reached a local limit – and might naively be expected to produce physical tachyons – to an alternate stable state where no physical tachyons exist. Once a tachyonic field such as the Higgs field reaches the minimum of the potential, its quanta are not tachyons any more but rather are ordinary particles such as the Higgs boson.[157] + +Properties of the Higgs boson +Ambox current red.svg +This section needs to be updated. The reason given is: With the Higgs boson now empirically confirmed, the paragraphs on the mass should be rephrased to make it clear that they are about what could be predicted before that observation. Please update this article to reflect recent events or newly available information. (July 2018) +Since the Higgs field is scalar, the Higgs boson has no spin. The Higgs boson is also its own antiparticle, is CP-even, and has zero electric and colour charge.[158] + +The Standard Model does not predict the mass of the Higgs boson.[159] If that mass is between 115 and 180 GeV/c2 (consistent with empirical observations of 125 GeV/c2), then the Standard Model can be valid at energy scales all the way up to the Planck scale (1019 GeV).[160] Many theorists expect new physics beyond the Standard Model to emerge at the TeV-scale, based on unsatisfactory properties of the Standard Model.[161] The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetry breaking mechanism) is 1.4 TeV; beyond this point, the Standard Model becomes inconsistent without such a mechanism, because unitarity is violated in certain scattering processes.[162] + +It is also possible, although experimentally difficult, to estimate the mass of the Higgs boson indirectly. In the Standard Model, the Higgs boson has a number of indirect effects; most notably, Higgs loops result in tiny corrections to masses of the W and Z bosons. Precision measurements of electroweak parameters, such as the Fermi constant and masses of the W and Z bosons, can be used to calculate constraints on the mass of the Higgs. As of July 2011, the precision electroweak measurements tell us that the mass of the Higgs boson is likely to be less than about 161 GeV/c2 at 95% confidence level.[q] These indirect constraints rely on the assumption that the Standard Model is correct. It may still be possible to discover a Higgs boson above these masses, if it is accompanied by other particles beyond those accommodated by the Standard Model.[164] + +Production +Feynman diagrams for Higgs production +Gluon fusion +Gluon fusion Higgs Strahlung +Higgs Strahlung +Vector boson fusion +Vector boson fusion Top fusion +Top fusion +If Higgs particle theories are valid, then a Higgs particle can be produced much like other particles that are studied, in a particle collider. This involves accelerating a large number of particles to extremely high energies and extremely close to the speed of light, then allowing them to smash together. Protons and lead ions (the bare nuclei of lead atoms) are used at the LHC. In the extreme energies of these collisions, the desired esoteric particles will occasionally be produced and this can be detected and studied; any absence or difference from theoretical expectations can also be used to improve the theory. The relevant particle theory (in this case the Standard Model) will determine the necessary kinds of collisions and detectors. The Standard Model predicts that Higgs bosons could be formed in a number of ways,[87][165][166] although the probability of producing a Higgs boson in any collision is always expected to be very small – for example, only 1 Higgs boson per 10 billion collisions in the Large Hadron Collider.[m] The most common expected processes for Higgs boson production are: + +Gluon fusion. If the collided particles are hadrons such as the proton or antiproton – as is the case in the LHC and Tevatron – then it is most likely that two of the gluons binding the hadron together collide. The easiest way to produce a Higgs particle is if the two gluons combine to form a loop of virtual quarks. Since the coupling of particles to the Higgs boson is proportional to their mass, this process is more likely for heavy particles. In practice it is enough to consider the contributions of virtual top and bottom quarks (the heaviest quarks). This process is the dominant contribution at the LHC and Tevatron being about ten times more likely than any of the other processes.[87][165] +Higgs Strahlung. If an elementary fermion collides with an anti-fermion – e.g., a quark with an anti-quark or an electron with a positron – the two can merge to form a virtual W or Z boson which, if it carries sufficient energy, can then emit a Higgs boson. This process was the dominant production mode at the LEP, where an electron and a positron collided to form a virtual Z boson, and it was the second largest contribution for Higgs production at the Tevatron. At the LHC this process is only the third largest, because the LHC collides protons with protons, making a quark-antiquark collision less likely than at the Tevatron. Higgs Strahlung is also known as associated production.[87][165][166] +Weak boson fusion. Another possibility when two (anti-)fermions collide is that the two exchange a virtual W or Z boson, which emits a Higgs boson. The colliding fermions do not need to be the same type. So, for example, an up quark may exchange a Z boson with an anti-down quark. This process is the second most important for the production of Higgs particle at the LHC and LEP.[87][166] +Top fusion. The final process that is commonly considered is by far the least likely (by two orders of magnitude). This process involves two colliding gluons, which each decay into a heavy quark–antiquark pair. A quark and antiquark from each pair can then combine to form a Higgs particle.[87][165] +Decay + +The Standard Model prediction for the decay width of the Higgs particle depends on the value of its mass. +Quantum mechanics predicts that if it is possible for a particle to decay into a set of lighter particles, then it will eventually do so.[167] This is also true for the Higgs boson. The likelihood with which this happens depends on a variety of factors including: the difference in mass, the strength of the interactions, etc. Most of these factors are fixed by the Standard Model, except for the mass of the Higgs boson itself. For a Higgs boson with a mass of 125 GeV/c2 the SM predicts a mean life time of about 1.6×10−22 s.[b] + + +The Standard Model prediction for the branching ratios of the different decay modes of the Higgs particle depends on the value of its mass. +Since it interacts with all the massive elementary particles of the SM, the Higgs boson has many different processes through which it can decay. Each of these possible processes has its own probability, expressed as the branching ratio; the fraction of the total number decays that follows that process. The SM predicts these branching ratios as a function of the Higgs mass (see plot). + +One way that the Higgs can decay is by splitting into a fermion–antifermion pair. As general rule, the Higgs is more likely to decay into heavy fermions than light fermions, because the mass of a fermion is proportional to the strength of its interaction with the Higgs.[119] By this logic the most common decay should be into a top–antitop quark pair. However, such a decay would only be possible if the Higgs were heavier than ~346 GeV/c2, twice the mass of the top quark. For a Higgs mass of 125 GeV/c2 the SM predicts that the most common decay is into a bottom–antibottom quark pair, which happens 57.7% of the time.[3] The second most common fermion decay at that mass is a tau–antitau pair, which happens only about 6.3% of the time.[3] + +Another possibility is for the Higgs to split into a pair of massive gauge bosons. The most likely possibility is for the Higgs to decay into a pair of W bosons (the light blue line in the plot), which happens about 21.5% of the time for a Higgs boson with a mass of 125 GeV/c2.[3] The W bosons can subsequently decay either into a quark and an antiquark or into a charged lepton and a neutrino. The decays of W bosons into quarks are difficult to distinguish from the background, and the decays into leptons cannot be fully reconstructed (because neutrinos are impossible to detect in particle collision experiments). A cleaner signal is given by decay into a pair of Z-bosons (which happens about 2.6% of the time for a Higgs with a mass of 125 GeV/c2),[3] if each of the bosons subsequently decays into a pair of easy-to-detect charged leptons (electrons or muons). + +Decay into massless gauge bosons (i.e., gluons or photons) is also possible, but requires intermediate loop of virtual heavy quarks (top or bottom) or massive gauge bosons.[119] The most common such process is the decay into a pair of gluons through a loop of virtual heavy quarks. This process, which is the reverse of the gluon fusion process mentioned above, happens approximately 8.6% of the time for a Higgs boson with a mass of 125 GeV/c2.[3] Much rarer is the decay into a pair of photons mediated by a loop of W bosons or heavy quarks, which happens only twice for every thousand decays.[3] However, this process is very relevant for experimental searches for the Higgs boson, because the energy and momentum of the photons can be measured very precisely, giving an accurate reconstruction of the mass of the decaying particle.[119] + +Public discussion +Naming +Names used by physicists +The name most strongly associated with the particle and field is the Higgs boson[85]:168 and Higgs field. For some time the particle was known by a combination of its PRL author names (including at times Anderson), for example the Brout–Englert–Higgs particle, the Anderson-Higgs particle, or the Englert–Brout–Higgs–Guralnik–Hagen–Kibble mechanism,[r] and these are still used at times.[56][169] Fuelled in part by the issue of recognition and a potential shared Nobel Prize,[169][170] the most appropriate name was still occasionally a topic of debate until 2013.[169] Higgs himself prefers to call the particle either by an acronym of all those involved, or "the scalar boson", or "the so-called Higgs particle".[170] + +A considerable amount has been written on how Higgs' name came to be exclusively used. Two main explanations are offered. The first is that Higgs undertook a step which was either unique, clearer or more explicit in his paper in formally predicting and examining the particle. Of the PRL papers' authors, only the paper by Higgs explicitly offered as a prediction that a massive particle would exist and calculated some of its properties;[85]:167[171] he was therefore "the first to postulate the existence of a massive particle" according to Nature.[169] Physicist and author Frank Close and physicist-blogger Peter Woit both comment that the paper by GHK was also completed after Higgs and Brout–Englert were submitted to Physical Review Letters,[85]:167[172] and that Higgs alone had drawn attention to a predicted massive scalar boson, while all others had focused on the massive vector bosons;[85]:154, 166, 175[172] In this way, Higgs' contribution also provided experimentalists with a crucial "concrete target" needed to test the theory.[173] However, in Higgs' view, Brout and Englert did not explicitly mention the boson since its existence is plainly obvious in their work,[60]:6 while according to Guralnik the GHK paper was a complete analysis of the entire symmetry breaking mechanism whose mathematical rigour is absent from the other two papers, and a massive particle may exist in some solutions.[86]:9 Higgs' paper also provided an "especially sharp" statement of the challenge and its solution according to science historian David Kaiser.[170] + +The alternative explanation is that the name was popularised in the 1970s due to its use as a convenient shorthand or because of a mistake in citing. Many accounts (including Higgs' own[60]:7) credit the "Higgs" name to physicist Benjamin Lee (in Korean: Lee Whi-soh). Lee was a significant populist for the theory in its early stages, and habitually attached the name "Higgs" as a "convenient shorthand" for its components from 1972[11][169][174][175][176] and in at least one instance from as early as 1966.[177] Although Lee clarified in his footnotes that "'Higgs' is an abbreviation for Higgs, Kibble, Guralnik, Hagen, Brout, Englert",[174] his use of the term (and perhaps also Steven Weinberg's mistaken cite of Higgs' paper as the first in his seminal 1967 paper[85][178][177]) meant that by around 1975–1976 others had also begun to use the name 'Higgs' exclusively as a shorthand.[s] + +Nickname +The Higgs boson is often referred to as the "God particle" in popular media outside the scientific community.[179][180][181][182][183] The nickname comes from the title of the 1993 book on the Higgs boson and particle physics, The God Particle: If the Universe Is the Answer, What Is the Question? by Physics Nobel Prize winner and Fermilab director Leon Lederman.[17] Lederman wrote it in the context of failing US government support for the Superconducting Super Collider,[184] a partially constructed titanic[185][186] competitor to the Large Hadron Collider with planned collision energies of 2 × 20 TeV that was championed by Lederman since its 1983 inception[184][187][188] and shut down in 1993. The book sought in part to promote awareness of the significance and need for such a project in the face of its possible loss of funding.[189] Lederman, a leading researcher in the field, writes that he wanted to title his book The Goddamn Particle: If the Universe is the Answer, What is the Question? Lederman's editor decided that the title was too controversial and convinced him to change the title to The God Particle: If the Universe is the Answer, What is the Question?[190] + +While media use of this term may have contributed to wider awareness and interest,[191] many scientists feel the name is inappropriate[11][12][192] since it is sensational hyperbole and misleads readers;[193] the particle also has nothing to do with any God, leaves open numerous questions in fundamental physics, and does not explain the ultimate origin of the universe. Higgs, an atheist, was reported to be displeased and stated in a 2008 interview that he found it "embarrassing" because it was "the kind of misuse... which I think might offend some people".[193][194][195] The nickname has been satirised in mainstream media as well.[196] Science writer Ian Sample stated in his 2010 book on the search that the nickname is "universally hate[d]" by physicists and perhaps the "worst derided" in the history of physics, but that (according to Lederman) the publisher rejected all titles mentioning "Higgs" as unimaginative and too unknown.[197] + +Lederman begins with a review of the long human search for knowledge, and explains that his tongue-in-cheek title draws an analogy between the impact of the Higgs field on the fundamental symmetries at the Big Bang, and the apparent chaos of structures, particles, forces and interactions that resulted and shaped our present universe, with the biblical story of Babel in which the primordial single language of early Genesis was fragmented into many disparate languages and cultures.[198] + +Today ... we have the standard model, which reduces all of reality to a dozen or so particles and four forces. ... It's a hard-won simplicity [...and...] remarkably accurate. But it is also incomplete and, in fact, internally inconsistent... This boson is so central to the state of physics today, so crucial to our final understanding of the structure of matter, yet so elusive, that I have given it a nickname: the God Particle. Why God Particle? Two reasons. One, the publisher wouldn't let us call it the Goddamn Particle, though that might be a more appropriate title, given its villainous nature and the expense it is causing. And two, there is a connection, of sorts, to another book, a much older one... + +— Leon M. Lederman and Dick Teresi, The God Particle: If the Universe is the Answer, What is the Question[17] p. 22 +Lederman asks whether the Higgs boson was added just to perplex and confound those seeking knowledge of the universe, and whether physicists will be confounded by it as recounted in that story, or ultimately surmount the challenge and understand "how beautiful is the universe [God has] made".[199] + +Other proposals +A renaming competition by British newspaper The Guardian in 2009 resulted in their science correspondent choosing the name "the champagne bottle boson" as the best submission: "The bottom of a champagne bottle is in the shape of the Higgs potential and is often used as an illustration in physics lectures. So it's not an embarrassingly grandiose name, it is memorable, and [it] has some physics connection too."[200] The name Higgson was suggested as well, in an opinion piece in the Institute of Physics' online publication physicsworld.com.[201] + +Educational explanations and analogies + +Photograph of light passing through a dispersive prism: the rainbow effect arises because photons are not all affected to the same degree by the dispersive material of the prism. +There has been considerable public discussion of analogies and explanations for the Higgs particle and how the field creates mass,[202][203] including coverage of explanatory attempts in their own right and a competition in 1993 for the best popular explanation by then-UK Minister for Science Sir William Waldegrave[204] and articles in newspapers worldwide. + +An educational collaboration involving an LHC physicist and a High School Teachers at CERN educator suggests that dispersion of light – responsible for the rainbow and dispersive prism – is a useful analogy for the Higgs field's symmetry breaking and mass-causing effect.[205] + +Symmetry breaking +in optics In a vacuum, light of all colours (or photons of all wavelengths) travels at the same velocity, a symmetrical situation. In some substances such as glass, water or air, this symmetry is broken (See: Photons in matter). The result is that light of different wavelengths have different velocities. +Symmetry breaking +in particle physics In 'naive' gauge theories, gauge bosons and other fundamental particles are all massless – also a symmetrical situation. In the presence of the Higgs field this symmetry is broken. The result is that particles of different types will have different masses. +Matt Strassler uses electric fields as an analogy:[206] + +Some particles interact with the Higgs field while others don’t. Those particles that feel the Higgs field act as if they have mass. Something similar happens in an electric field – charged objects are pulled around and neutral objects can sail through unaffected. So you can think of the Higgs search as an attempt to make waves in the Higgs field [create Higgs bosons] to prove it’s really there. + +A similar explanation was offered by The Guardian:[207] + +The Higgs boson is essentially a ripple in a field said to have emerged at the birth of the universe and to span the cosmos to this day ... The particle is crucial however: It is the smoking gun, the evidence required to show the theory is right. + +The Higgs field's effect on particles was famously described by physicist David Miller as akin to a room full of political party workers spread evenly throughout a room: The crowd gravitates to and slows down famous people but does not slow down others.[t] He also drew attention to well-known effects in solid state physics where an electron's effective mass can be much greater than usual in the presence of a crystal lattice.[208] + +Analogies based on drag effects, including analogies of "syrup" or "molasses" are also well known, but can be somewhat misleading since they may be understood (incorrectly) as saying that the Higgs field simply resists some particles' motion but not others' – a simple resistive effect could also conflict with Newton's third law.[210] + +Recognition and awards +There was considerable discussion prior to late 2013 of how to allocate the credit if the Higgs boson is proven, made more pointed as a Nobel prize had been expected, and the very wide basis of people entitled to consideration. These include a range of theoreticians who made the Higgs mechanism theory possible, the theoreticians of the 1964 PRL papers (including Higgs himself), the theoreticians who derived from these a working electroweak theory and the Standard Model itself, and also the experimentalists at CERN and other institutions who made possible the proof of the Higgs field and boson in reality. The Nobel prize has a limit of 3 persons to share an award, and some possible winners are already prize holders for other work, or are deceased (the prize is only awarded to persons in their lifetime). Existing prizes for works relating to the Higgs field, boson, or mechanism include: + +Nobel Prize in Physics (1979) – Glashow, Salam, and Weinberg, for contributions to the theory of the unified weak and electromagnetic interaction between elementary particles[211] +Nobel Prize in Physics (1999) – 't Hooft and Veltman, for elucidating the quantum structure of electroweak interactions in physics[212] +J. J. Sakurai Prize for Theoretical Particle Physics (2010) – Hagen, Englert, Guralnik, Higgs, Brout, and Kibble, for elucidation of the properties of spontaneous symmetry breaking in four-dimensional relativistic gauge theory and of the mechanism for the consistent generation of vector boson masses[83] (for the 1964 papers described above) +Wolf Prize (2004) – Englert, Brout, and Higgs +Breakthrough Prize in Fundamental Physics (2013) – Fabiola Gianotti and Peter Jenni, spokespersons of the ATLAS Collaboration and Michel Della Negra, Tejinder Singh Virdee, Guido Tonelli, and Joseph Incandela spokespersons, past and present, of the CMS collaboration, "For [their] leadership role in the scientific endeavour that led to the discovery of the new Higgs-like particle by the ATLAS and CMS collaborations at CERN's Large Hadron Collider."[213] +Nobel Prize in Physics (2013) – Peter Higgs and François Englert, for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider[214] Englert's co-researcher Robert Brout had died in 2011 and the Nobel Prize is not ordinarily given posthumously.[215] +Additionally Physical Review Letters' 50-year review (2008) recognised the 1964 PRL symmetry breaking papers and Weinberg's 1967 paper A model of Leptons (the most cited paper in particle physics, as of 2012) "milestone Letters".[80] + +Following reported observation of the Higgs-like particle in July 2012, several Indian media outlets reported on the supposed neglect of credit to Indian physicist Satyendra Nath Bose after whose work in the 1920s the class of particles "bosons" is named[216][217] (although physicists have described Bose's connection to the discovery as tenuous).[218] + +Technical aspects and mathematical formulation +See also: Standard Model (mathematical formulation) + +The potential for the Higgs field, plotted as function of {\displaystyle \phi ^{0}}\phi ^{0} and {\displaystyle \phi ^{3}}\phi ^{3}. It has a Mexican-hat or champagne-bottle profile at the ground. +In the Standard Model, the Higgs field is a four-component scalar field that forms a complex doublet of the weak isospin SU(2) symmetry: + +{\displaystyle \phi ={\frac {1}{\sqrt {2}}}\left({\begin{array}{c}\phi ^{1}+i\phi ^{2}\\\phi ^{0}+i\phi ^{3}\end{array}}\right)\;,}\phi ={\frac {1}{\sqrt {2}}}\left({\begin{array}{c}\phi ^{1}+i\phi ^{2}\\\phi ^{0}+i\phi ^{3}\end{array}}\right)\;, +while the field has charge +½ under the weak hypercharge U(1) symmetry.[219] +Note: This article uses the scaling convention where the electric charge, Q, the weak isospin, T3, and the weak hypercharge, YW, are related by Q = T3 + YW. A different convention used in most other Wikipedia articles is Q = T3 + ½ YW.[220][221][222] + +The Higgs part of the Lagrangian is[219] + +{\displaystyle {\mathcal {L}}_{\text{H}}=\left|\left(\partial _{\mu }-igW_{\mu \ a}{\tfrac {1}{2}}\sigma ^{a}-i{\tfrac {1}{2}}g'B_{\mu }\right)\phi \right|^{2}+\mu _{\text{H}}^{2}\phi ^{\dagger }\phi -\lambda (\phi ^{\dagger }\phi )^{2},}{\displaystyle {\mathcal {L}}_{\text{H}}=\left|\left(\partial _{\mu }-igW_{\mu \ a}{\tfrac {1}{2}}\sigma ^{a}-i{\tfrac {1}{2}}g'B_{\mu }\right)\phi \right|^{2}+\mu _{\text{H}}^{2}\phi ^{\dagger }\phi -\lambda (\phi ^{\dagger }\phi )^{2},} +where {\displaystyle W_{\mu \ a}}{\displaystyle W_{\mu \ a}} and {\displaystyle B_{\mu }}B_{\mu } are the gauge bosons of the SU(2) and U(1) symmetries, {\displaystyle g}g and {\displaystyle g'}g' their respective coupling constants, {\displaystyle \sigma ^{a}}\sigma ^{a} are the Pauli matrices (a complete set generators of the SU(2) symmetry), and {\displaystyle \lambda >0}\lambda >0 and {\displaystyle \mu _{\text{H}}^{2}>0}{\displaystyle \mu _{\text{H}}^{2}>0}, so that the ground state breaks the SU(2) symmetry (see figure). + +The ground state of the Higgs field (the bottom of the potential) is degenerate with different ground states related to each other by a SU(2) gauge transformation. It is always possible to pick a gauge such that in the ground state {\displaystyle \phi ^{1}=\phi ^{2}=\phi ^{3}=0}{\displaystyle \phi ^{1}=\phi ^{2}=\phi ^{3}=0}. The expectation value of {\displaystyle \phi ^{0}}\phi ^{0} in the ground state (the vacuum expectation value or VEV) is then {\displaystyle \langle \phi ^{0}\rangle ={\tfrac {1}{\ {\sqrt {2\ }}\ }}v}{\displaystyle \langle \phi ^{0}\rangle ={\tfrac {1}{\ {\sqrt {2\ }}\ }}v}, where {\displaystyle v={\tfrac {1}{\,{\sqrt {\lambda }}\,}}\left|\mu _{\text{H}}\right|}{\displaystyle v={\tfrac {1}{\,{\sqrt {\lambda }}\,}}\left|\mu _{\text{H}}\right|}. The measured value of this parameter is ~246 GeV/c2.[119] It has units of mass, and is the only free parameter of the Standard Model that is not a dimensionless number. Quadratic terms in {\displaystyle W_{\mu }}W_{\mu } and {\displaystyle B_{\mu }}B_{\mu } arise, which give masses to the W and Z bosons:[219] + +{\displaystyle m_{\text{W}}={\tfrac {1}{2}}v\left|g\right|,}{\displaystyle m_{\text{W}}={\tfrac {1}{2}}v\left|g\right|,} +{\displaystyle m_{\text{Z}}={\tfrac {1}{2}}v{\sqrt {g^{2}+{g'}^{2}\ }},}{\displaystyle m_{\text{Z}}={\tfrac {1}{2}}v{\sqrt {g^{2}+{g'}^{2}\ }},} +with their ratio determining the Weinberg angle, {\displaystyle \cos \theta _{\text{W}}={\frac {m_{\text{W}}}{\ m_{\text{Z}}\ }}={\frac {|g|}{\ {\sqrt {g^{2}+{g'}^{2}\ }}\ }}}{\displaystyle \cos \theta _{\text{W}}={\frac {m_{\text{W}}}{\ m_{\text{Z}}\ }}={\frac {|g|}{\ {\sqrt {g^{2}+{g'}^{2}\ }}\ }}}, and leave a massless U(1) photon, {\displaystyle \gamma }\gamma . The mass of the Higgs boson itself is given by + +{\displaystyle m_{\text{H}}={\sqrt {2\mu _{\text{H}}^{2}\ }}\equiv {\sqrt {2\lambda v^{2}\ }}.}{\displaystyle m_{\text{H}}={\sqrt {2\mu _{\text{H}}^{2}\ }}\equiv {\sqrt {2\lambda v^{2}\ }}.} +The quarks and the leptons interact with the Higgs field through Yukawa interaction terms: + +{\displaystyle {\begin{aligned}{\mathcal {L}}_{\text{Y}}=&-\lambda _{u}^{ij}{\frac {\phi ^{0}-i\phi ^{3}}{\sqrt {2\ }}}{\overline {u}}_{\text{L}}^{i}u_{\text{R}}^{j}+\lambda _{u}^{ij}{\frac {\phi ^{1}-i\phi ^{2}}{\sqrt {2\ }}}{\overline {d}}_{\text{L}}^{i}u_{\text{R}}^{j}\\&-\lambda _{d}^{ij}{\frac {\phi ^{0}+i\phi ^{3}}{\sqrt {2\ }}}{\overline {d}}_{\text{L}}^{i}d_{\text{R}}^{j}-\lambda _{d}^{ij}{\frac {\phi ^{1}+i\phi ^{2}}{\sqrt {2\ }}}{\overline {u}}_{\text{L}}^{i}d_{\text{R}}^{j}\\&-\lambda _{e}^{ij}{\frac {\phi ^{0}+i\phi ^{3}}{\sqrt {2\ }}}{\overline {e}}_{\text{L}}^{i}e_{\text{R}}^{j}-\lambda _{e}^{ij}{\frac {\phi ^{1}+i\phi ^{2}}{\sqrt {2\ }}}{\overline {\nu }}_{\text{L}}^{i}e_{\text{R}}^{j}+{\textrm {h.c.}},\end{aligned}}}{\displaystyle {\begin{aligned}{\mathcal {L}}_{\text{Y}}=&-\lambda _{u}^{ij}{\frac {\phi ^{0}-i\phi ^{3}}{\sqrt {2\ }}}{\overline {u}}_{\text{L}}^{i}u_{\text{R}}^{j}+\lambda _{u}^{ij}{\frac {\phi ^{1}-i\phi ^{2}}{\sqrt {2\ }}}{\overline {d}}_{\text{L}}^{i}u_{\text{R}}^{j}\\&-\lambda _{d}^{ij}{\frac {\phi ^{0}+i\phi ^{3}}{\sqrt {2\ }}}{\overline {d}}_{\text{L}}^{i}d_{\text{R}}^{j}-\lambda _{d}^{ij}{\frac {\phi ^{1}+i\phi ^{2}}{\sqrt {2\ }}}{\overline {u}}_{\text{L}}^{i}d_{\text{R}}^{j}\\&-\lambda _{e}^{ij}{\frac {\phi ^{0}+i\phi ^{3}}{\sqrt {2\ }}}{\overline {e}}_{\text{L}}^{i}e_{\text{R}}^{j}-\lambda _{e}^{ij}{\frac {\phi ^{1}+i\phi ^{2}}{\sqrt {2\ }}}{\overline {\nu }}_{\text{L}}^{i}e_{\text{R}}^{j}+{\textrm {h.c.}},\end{aligned}}} +where {\displaystyle (d,u,e,\nu )_{\text{L,R}}^{i}}{\displaystyle (d,u,e,\nu )_{\text{L,R}}^{i}} are left-handed and right-handed quarks and leptons of the ith generation, {\displaystyle \lambda _{u,d,e}^{ij}}\lambda _{u,d,e}^{ij} are matrices of Yukawa couplings where h.c. denotes the hermitian conjugate of all the preceding terms. In the symmetry breaking ground state, only the terms containing {\displaystyle \phi ^{0}}\phi ^{0} remain, giving rise to mass terms for the fermions. Rotating the quark and lepton fields to the basis where the matrices of Yukawa couplings are diagonal, one gets + +{\displaystyle {\mathcal {L}}_{m}=-m_{u}^{i}{\overline {u}}_{\text{L}}^{i}u_{\text{R}}^{i}-m_{d}^{i}{\overline {d}}_{\text{L}}^{i}d_{\text{R}}^{i}-m_{e}^{i}{\overline {e}}_{\text{L}}^{i}e_{\text{R}}^{i}+{\textrm {h.c.}},}{\displaystyle {\mathcal {L}}_{m}=-m_{u}^{i}{\overline {u}}_{\text{L}}^{i}u_{\text{R}}^{i}-m_{d}^{i}{\overline {d}}_{\text{L}}^{i}d_{\text{R}}^{i}-m_{e}^{i}{\overline {e}}_{\text{L}}^{i}e_{\text{R}}^{i}+{\textrm {h.c.}},} +where the masses of the fermions are {\displaystyle m_{u,d,e}^{i}={\tfrac {1}{{\sqrt {2}}\ }}\lambda _{u,d,e}^{i}v}{\displaystyle m_{u,d,e}^{i}={\tfrac {1}{{\sqrt {2}}\ }}\lambda _{u,d,e}^{i}v}, and {\displaystyle \lambda _{u,d,e}^{i}}\lambda _{u,d,e}^{i} denote the eigenvalues of the Yukawa matrices.[219] diff --git a/examples/article5.txt b/examples/article5.txt new file mode 100644 index 0000000..b655a83 --- /dev/null +++ b/examples/article5.txt @@ -0,0 +1,398 @@ +A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat, may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity. + +Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds and forms. Resistors are also implemented within integrated circuits. + +The electrical function of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. The nominal value of the resistance falls within the manufacturing tolerance, indicated on the component. + + +Contents +1 Electronic symbols and notation +2 Theory of operation +2.1 Ohm's law +2.2 Series and parallel resistors +2.3 Power dissipation +3 Nonideal properties +4 Fixed resistor +4.1 Lead arrangements +4.2 Carbon composition +4.3 Carbon pile +4.4 Carbon film +4.5 Printed carbon resistor +4.6 Thick and thin film +4.7 Metal film +4.8 Metal oxide film +4.9 Wire wound +4.10 Foil resistor +4.11 Ammeter shunts +4.12 Grid resistor +4.13 Special varieties +5 Variable resistors +5.1 Adjustable resistors +5.2 Potentiometers +5.3 Resistance decade boxes +5.4 Special devices +6 Measurement +7 Standards +7.1 Production resistors +7.2 Resistance standards +8 Resistor marking +8.1 Preferred values +8.2 SMT resistors +8.3 Industrial type designation +9 Electrical and thermal noise +10 Failure modes +11 See also +12 References +13 External links +Electronic symbols and notation +Main articles: Electronic symbol and RKM code +Two typical schematic diagram symbols are as follows: + + +(a) resistor, (b) rheostat (variable resistor), and (c) potentiometer + + + +IEC resistor symbol + +The notation to state a resistor's value in a circuit diagram varies. + +One common scheme is the RKM code following IEC 60062. It avoids using a decimal separator and replaces the decimal separator with a letter loosely associated with SI prefixes corresponding with the part's resistance. For example, 8K2 as part marking code, in a circuit diagram or in a bill of materials (BOM) indicates a resistor value of 8.2 kΩ. Additional zeros imply a tighter tolerance, for example 15M0 for three significant digits. When the value can be expressed without the need for a prefix (that is, multiplicator 1), an "R" is used instead of the decimal separator. For example, 1R2 indicates 1.2 Ω, and 18R indicates 18 Ω. + +Theory of operation + +The hydraulic analogy compares electric current flowing through circuits to water flowing through pipes. When a pipe (left) is clogged with hair (right), it takes a larger pressure to achieve the same flow of water. Pushing electric current through a large resistance is like pushing water through a pipe clogged with hair: It requires a larger push (voltage) to drive the same flow (electric current).[1] +Ohm's law +Main article: Ohm's law +The behaviour of an ideal resistor is dictated by the relationship specified by Ohm's law: + +{\displaystyle V=I\cdot R.}V=I \cdot R. +Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the constant of proportionality is the resistance (R). For example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a current of 12 / 300 = 0.04 amperes flows through that resistor. + +Practical resistors also have some inductance and capacitance which affect the relation between voltage and current in alternating current circuits. + +The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 mΩ = 10−3 Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 106 Ω) are also in common usage. + +Series and parallel resistors +Main article: Series and parallel circuits + +The total resistance of resistors connected in series is the sum of their individual resistance values. + +A diagram of several resistors, connected end to end, with the same amount of current going through each +{\displaystyle R_{\mathrm {eq} }=R_{1}+R_{2}+\cdots +R_{n}.} +R_\mathrm{eq} = R_1 + R_2 + \cdots + R_n. +The total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual resistors. + +A diagram of several resistors, side by side, both leads of each connected to the same wires +{\displaystyle {\frac {1}{R_{\mathrm {eq} }}}={\frac {1}{R_{1}}}+{\frac {1}{R_{2}}}+\cdots +{\frac {1}{R_{n}}}.} +\frac{1}{R_\mathrm{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + \cdots + \frac{1}{R_n}. +For example, a 10 ohm resistor connected in parallel with a 5 ohm resistor and a 15 ohm resistor produces +1 +/ +1/10 + 1/5 + 1/15 + ohms of resistance, or +30 +/ +11 + = 2.727 ohms. + +A resistor network that is a combination of parallel and series connections can be broken up into smaller parts that are either one or the other. Some complex networks of resistors cannot be resolved in this manner, requiring more sophisticated circuit analysis. Generally, the Y-Δ transform, or matrix methods can be used to solve such problems.[2][3][4] + +Power dissipation +At any instant, the power P (watts) consumed by a resistor of resistance R (ohms) is calculated as: {\displaystyle P=I^{2}R=IV={\frac {V^{2}}{R}}} +P =I^2 R = I V = \frac{V^2}{R} + where V (volts) is the voltage across the resistor and I (amps) is the current flowing through it. Using Ohm's law, the two other forms can be derived. This power is converted into heat which must be dissipated by the resistor's package before its temperature rises excessively. + +Resistors are rated according to their maximum power dissipation. Discrete resistors in solid-state electronic systems are typically rated as 1/10, 1/8, or 1/4 watt. They usually absorb much less than a watt of electrical power and require little attention to their power rating. + + +An aluminium-encased power resistor rated for dissipation of 50 W when mounted on a heat-sink +Resistors required to dissipate substantial amounts of power, particularly used in power supplies, power conversion circuits, and power amplifiers, are generally referred to as power resistors; this designation is loosely applied to resistors with power ratings of 1 watt or greater. Power resistors are physically larger and may not use the preferred values, color codes, and external packages described below. + +If the average power dissipated by a resistor is more than its power rating, damage to the resistor may occur, permanently altering its resistance; this is distinct from the reversible change in resistance due to its temperature coefficient when it warms. Excessive power dissipation may raise the temperature of the resistor to a point where it can burn the circuit board or adjacent components, or even cause a fire. There are flameproof resistors that fail (open circuit) before they overheat dangerously. + +Since poor air circulation, high altitude, or high operating temperatures may occur, resistors may be specified with higher rated dissipation than is experienced in service. + +All resistors have a maximum voltage rating; this may limit the power dissipation for higher resistance values. + + +VZR power resistor 1.5kΩ 12W, manufactured in 1963 in the Soviet Union +Nonideal properties +Practical resistors have a series inductance and a small parallel capacitance; these specifications can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise characteristics of a resistor may be an issue. + +The temperature coefficient of the resistance may also be of concern in some precision applications. + +The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology.[5] A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and the position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them. + +Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor. While there is no minimum working voltage for a given resistor, failure to account for a resistor's maximum rating may cause the resistor to incinerate when current is run through it. + +Fixed resistor + +A single in line (SIL) resistor package with 8 individual 47 ohm resistors. This package is also known as a SIP-9. One end of each resistor is connected to a separate pin and the other ends are all connected together to the remaining (common) pin – pin 1, at the end identified by the white dot. +Lead arrangements + +Axial resistors with wire leads for through-hole mounting +Through-hole components typically have "leads" (pronounced /liːdz/) leaving the body "axially," that is, on a line parallel with the part's longest axis. Others have leads coming off their body "radially" instead. Other components may be SMT (surface mount technology), while high power resistors may have one of their leads designed into the heat sink. + +Carbon composition + +Old Style "Dog Bone" resistors + +Three carbon composition resistors in a 1960s valve (vacuum tube) radio +Carbon composition resistors (CCR) consist of a solid cylindrical resistive element with embedded wire leads or metal end caps to which the lead wires are attached. The body of the resistor is protected with paint or plastic. Early 20th-century carbon composition resistors had uninsulated bodies; the lead wires were wrapped around the ends of the resistance element rod and soldered. The completed resistor was painted for color-coding of its value. + +The resistive element is made from a mixture of finely powdered carbon and an insulating material, usually ceramic. A resin holds the mixture together. The resistance is determined by the ratio of the fill material (the powdered ceramic) to the carbon. Higher concentrations of carbon, which is a good conductor, result in lower resistance. Carbon composition resistors were commonly used in the 1960s and earlier, but are not popular for general use now as other types have better specifications, such as tolerance, voltage dependence, and stress. Carbon composition resistors change value when stressed with over-voltages. Moreover, if internal moisture content, from exposure for some length of time to a humid environment, is significant, soldering heat creates a non-reversible change in resistance value. Carbon composition resistors have poor stability with time and were consequently factory sorted to, at best, only 5% tolerance.[6] These resistors are non-inductive, which provides benefits when used in voltage pulse reduction and surge protection applications.[7] Carbon composition resistors have higher capability to withstand overload relative to the component's size.[8] + +Carbon composition resistors are still available, but relatively expensive. Values ranged from fractions of an ohm to 22 megohms. Due to their high price, these resistors are no longer used in most applications. However, they are used in power supplies and welding controls.[8] They are also in demand for repair of vintage electronic equipment where authenticity is a factor. + +Carbon pile +A carbon pile resistor is made of a stack of carbon disks compressed between two metal contact plates. Adjusting the clamping pressure changes the resistance between the plates. These resistors are used when an adjustable load is required, for example in testing automotive batteries or radio transmitters. A carbon pile resistor can also be used as a speed control for small motors in household appliances (sewing machines, hand-held mixers) with ratings up to a few hundred watts.[9] A carbon pile resistor can be incorporated in automatic voltage regulators for generators, where the carbon pile controls the field current to maintain relatively constant voltage.[10] The principle is also applied in the carbon microphone. + +Carbon film + +Carbon film resistor with exposed carbon spiral (Tesla TR-212 1 kΩ) +A carbon film is deposited on an insulating substrate, and a helix is cut in it to create a long, narrow resistive path. Varying shapes, coupled with the resistivity of amorphous carbon (ranging from 500 to 800 μΩ m), can provide a wide range of resistance values. Compared to carbon composition they feature low noise, because of the precise distribution of the pure graphite without binding.[11] Carbon film resistors feature a power rating range of 0.125 W to 5 W at 70 °C. Resistances available range from 1 ohm to 10 megohm. The carbon film resistor has an operating temperature range of −55 °C to 155 °C. It has 200 to 600 volts maximum working voltage range. Special carbon film resistors are used in applications requiring high pulse stability.[8] + +Printed carbon resistor + +A carbon resistor printed directly onto the SMD pads on a PCB. Inside a 1989 vintage Psion II Organiser +Carbon composition resistors can be printed directly onto printed circuit board (PCB) substrates as part of the PCB manufacturing process. Although this technique is more common on hybrid PCB modules, it can also be used on standard fibreglass PCBs. Tolerances are typically quite large, and can be in the order of 30%. A typical application would be non-critical pull-up resistors. + +Thick and thin film + +Laser Trimmed Precision Thin Film Resistor Network from Fluke, used in the Keithley DMM7510 multimeter. Ceramic backed with glass hermetic seal cover. +Thick film resistors became popular during the 1970s, and most SMD (surface mount device) resistors today are of this type. The resistive element of thick films is 1000 times thicker than thin films,[12] but the principal difference is how the film is applied to the cylinder (axial resistors) or the surface (SMD resistors). + +Thin film resistors are made by sputtering (a method of vacuum deposition) the resistive material onto an insulating substrate. The film is then etched in a similar manner to the old (subtractive) process for making printed circuit boards; that is, the surface is coated with a photo-sensitive material, then covered by a pattern film, irradiated with ultraviolet light, and then the exposed photo-sensitive coating is developed, and underlying thin film is etched away. + +Thick film resistors are manufactured using screen and stencil printing processes.[8] + +Because the time during which the sputtering is performed can be controlled, the thickness of the thin film can be accurately controlled. The type of material is also usually different consisting of one or more ceramic (cermet) conductors such as tantalum nitride (TaN), ruthenium oxide (RuO +2), lead oxide (PbO), bismuth ruthenate (Bi +2Ru +2O +7), nickel chromium (NiCr), or bismuth iridate (Bi +2Ir +2O +7). + +The resistance of both thin and thick film resistors after manufacture is not highly accurate; they are usually trimmed to an accurate value by abrasive or laser trimming. Thin film resistors are usually specified with tolerances of 1% and 5%, and with temperature coefficients of 5 to 50 ppm/K. They also have much lower noise levels, on the level of 10–100 times less than thick film resistors.[13] Thick film resistors may use the same conductive ceramics, but they are mixed with sintered (powdered) glass and a carrier liquid so that the composite can be screen-printed. This composite of glass and conductive ceramic (cermet) material is then fused (baked) in an oven at about 850 °C. + +Thick film resistors, when first manufactured, had tolerances of 5%, but standard tolerances have improved to 2% or 1% in the last few decades. Temperature coefficients of thick film resistors are high, typically ±200 or ±250 ppm/K; a 40-kelvin (70 °F) temperature change can change the resistance by 1%. + +Thin film resistors are usually far more expensive than thick film resistors. For example, SMD thin film resistors, with 0.5% tolerances, and with 25 ppm/K temperature coefficients, when bought in full size reel quantities, are about twice the cost of 1%, 250 ppm/K thick film resistors. + +Metal film +A common type of axial-leaded resistor today is the metal-film resistor. Metal Electrode Leadless Face (MELF) resistors often use the same technology. + +Metal film resistors are usually coated with nickel chromium (NiCr), but might be coated with any of the cermet materials listed above for thin film resistors. Unlike thin film resistors, the material may be applied using different techniques than sputtering (though this is one of the techniques). Also, unlike thin-film resistors, the resistance value is determined by cutting a helix through the coating rather than by etching. (This is similar to the way carbon resistors are made.) The result is a reasonable tolerance (0.5%, 1%, or 2%) and a temperature coefficient that is generally between 50 and 100 ppm/K.[14] Metal film resistors possess good noise characteristics and low non-linearity due to a low voltage coefficient. Also beneficial are their tight tolerance, low temperature coefficient and long-term stability.[8] + +Metal oxide film +Metal-oxide film resistors are made of metal oxides which results in a higher operating temperature and greater stability and reliability than metal film. They are used in applications with high endurance demands. + +Wire wound + +High-power wire wound resistors used for dynamic braking on an electric railway car. Such resistors may dissipate many kilowatts for an extended length of time. + +Types of windings in wire resistors: +common +bifilar +common on a thin former +Ayrton–Perry +Wirewound resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core. The ends of the wire are soldered or welded to two caps or rings, attached to the ends of the core. The assembly is protected with a layer of paint, molded plastic, or an enamel coating baked at high temperature. These resistors are designed to withstand unusually high temperatures of up to 450 °C.[8] Wire leads in low power wirewound resistors are usually between 0.6 and 0.8 mm in diameter and tinned for ease of soldering. For higher power wirewound resistors, either a ceramic outer case or an aluminum outer case on top of an insulating layer is used – if the outer case is ceramic, such resistors are sometimes described as "cement" resistors, though they do not actually contain any traditional cement. The aluminum-cased types are designed to be attached to a heat sink to dissipate the heat; the rated power is dependent on being used with a suitable heat sink, e.g., a 50 W power rated resistor overheats at a fraction of the power dissipation if not used with a heat sink. Large wirewound resistors may be rated for 1,000 watts or more. + +Because wirewound resistors are coils they have more undesirable inductance than other types of resistor, although winding the wire in sections with alternately reversed direction can minimize inductance. Other techniques employ bifilar winding, or a flat thin former (to reduce cross-section area of the coil). For the most demanding circuits, resistors with Ayrton–Perry winding are used. + +Applications of wirewound resistors are similar to those of composition resistors with the exception of the high frequency. The high frequency response of wirewound resistors is substantially worse than that of a composition resistor.[8] + +Foil resistor + +Metal foil resistor +In 1960 Felix Zandman and Sidney J. Stein[15] presented a development of resistor film of very high stability. + +The primary resistance element of a foil resistor is a chromium nickel alloy foil several micrometers thick. Chromium nickel alloys are characterized by having a large electrical resistance (about 58 times that of copper), a small temperature coefficient and high resistance to oxidation. Examples are Chromel A and Nichrome V, whose typical composition is 80 Ni and 20 Cr, with a melting point of 1420° C. When iron is added, the chromium nickel alloy becomes more ductile. The Nichrome and Chromel C are examples of an alloy containing iron. The composition typical of Nichrome is 60 Ni, 12 Cr, 26 Fe, 2 Mn and Chromel C, 64 Ni, 11 Cr, Fe 25. The melting temperature of these alloys are 1350° and 1390 ° C, respectively. [16] + +Since their introduction in the 1960s, foil resistors have had the best precision and stability of any resistor available. One of the important parameters of stability is the temperature coefficient of resistance (TCR). The TCR of foil resistors is extremely low, and has been further improved over the years. One range of ultra-precision foil resistors offers a TCR of 0.14 ppm/°C, tolerance ±0.005%, long-term stability (1 year) 25 ppm, (3 years) 50 ppm (further improved 5-fold by hermetic sealing), stability under load (2000 hours) 0.03%, thermal EMF 0.1 μV/°C, noise −42 dB, voltage coefficient 0.1 ppm/V, inductance 0.08 μH, capacitance 0.5 pF.[17] + +The thermal stability of this type of resistor also has to do with the opposing effects of the metal's electrical resistance increasing with temperature, and being reduced by thermal expansion leading to an increase in thickness of the foil, whose other dimensions are constrained by a ceramic substrate.[citation needed] + +Ammeter shunts +An ammeter shunt is a special type of current-sensing resistor, having four terminals and a value in milliohms or even micro-ohms. Current-measuring instruments, by themselves, can usually accept only limited currents. To measure high currents, the current passes through the shunt across which the voltage drop is measured and interpreted as current. A typical shunt consists of two solid metal blocks, sometimes brass, mounted on an insulating base. Between the blocks, and soldered or brazed to them, are one or more strips of low temperature coefficient of resistance (TCR) manganin alloy. Large bolts threaded into the blocks make the current connections, while much smaller screws provide volt meter connections. Shunts are rated by full-scale current, and often have a voltage drop of 50 mV at rated current. Such meters are adapted to the shunt full current rating by using an appropriately marked dial face; no change need to be made to the other parts of the meter. + +Grid resistor +In heavy-duty industrial high-current applications, a grid resistor is a large convection-cooled lattice of stamped metal alloy strips connected in rows between two electrodes. Such industrial grade resistors can be as large as a refrigerator; some designs can handle over 500 amperes of current, with a range of resistances extending lower than 0.04 ohms. They are used in applications such as dynamic braking and load banking for locomotives and trams, neutral grounding for industrial AC distribution, control loads for cranes and heavy equipment, load testing of generators and harmonic filtering for electric substations.[18] + +The term grid resistor is sometimes used to describe a resistor of any type connected to the control grid of a vacuum tube. This is not a resistor technology; it is an electronic circuit topology. + +Special varieties +Cermet +Phenolic +Tantalum +Water resistor +Variable resistors +Adjustable resistors +A resistor may have one or more fixed tapping points so that the resistance can be changed by moving the connecting wires to different terminals. Some wirewound power resistors have a tapping point that can slide along the resistance element, allowing a larger or smaller part of the resistance to be used. + +Where continuous adjustment of the resistance value during operation of equipment is required, the sliding resistance tap can be connected to a knob accessible to an operator. Such a device is called a rheostat and has two terminals. + +Potentiometers + +Typical panel mount potentiometer + +Drawing of potentiometer with case cut away, showing parts: (A) shaft, (B) stationary carbon composition resistance element, (C) phosphor bronze wiper, (D) shaft attached to wiper, (E, G) terminals connected to ends of resistance element, (F) terminal connected to wiper. + +An assortment of small through-hole potentiometers designed for mounting on printed circuit boards. +A potentiometer (colloquially, pot) is a three-terminal resistor with a continuously adjustable tapping point controlled by rotation of a shaft or knob or by a linear slider.[19] The name potentiometer comes from its function as an adjustable voltage divider to provide a variable potential at the terminal connected to the tapping point. Volume control in an audio device is a common application of a potentiometer. A typical low power potentiometer (see drawing) is constructed of a flat resistance element (B) of carbon composition, metal film, or conductive plastic, with a springy phosphor bronze wiper contact (C) which moves along the surface. An alternate construction is resistance wire wound on a form, with the wiper sliding axially along the coil.[19] These have lower resolution, since as the wiper moves the resistance changes in steps equal to the resistance of a single turn.[19] + +High-resolution multiturn potentiometers are used in precision applications. These have wire-wound resistance elements typically wound on a helical mandrel, with the wiper moving on a helical track as the control is turned, making continuous contact with the wire. Some include a conductive-plastic resistance coating over the wire to improve resolution. These typically offer ten turns of their shafts to cover their full range. They are usually set with dials that include a simple turns counter and a graduated dial, and can typically achieve three digit resolution. Electronic analog computers used them in quantity for setting coefficients, and delayed-sweep oscilloscopes of recent decades included one on their panels. + +Resistance decade boxes +Main article: Decade box + +Resistance decade box "Kurbelwiderstand", made in former East Germany. +A resistance decade box or resistor substitution box is a unit containing resistors of many values, with one or more mechanical switches which allow any one of various discrete resistances offered by the box to be dialed in. Usually the resistance is accurate to high precision, ranging from laboratory/calibration grade accuracy of 20 parts per million, to field grade at 1%. Inexpensive boxes with lesser accuracy are also available. All types offer a convenient way of selecting and quickly changing a resistance in laboratory, experimental and development work without needing to attach resistors one by one, or even stock each value. The range of resistance provided, the maximum resolution, and the accuracy characterize the box. For example, one box offers resistances from 0 to 100 megohms, maximum resolution 0.1 ohm, accuracy 0.1%.[20] + +Special devices +There are various devices whose resistance changes with various quantities. The resistance of NTC thermistors exhibit a strong negative temperature coefficient, making them useful for measuring temperatures. Since their resistance can be large until they are allowed to heat up due to the passage of current, they are also commonly used to prevent excessive current surges when equipment is powered on. Similarly, the resistance of a humistor varies with humidity. One sort of photodetector, the photoresistor, has a resistance which varies with illumination. + +The strain gauge, invented by Edward E. Simmons and Arthur C. Ruge in 1938, is a type of resistor that changes value with applied strain. A single resistor may be used, or a pair (half bridge), or four resistors connected in a Wheatstone bridge configuration. The strain resistor is bonded with adhesive to an object that is subjected to mechanical strain. With the strain gauge and a filter, amplifier, and analog/digital converter, the strain on an object can be measured. + +A related but more recent invention uses a Quantum Tunnelling Composite to sense mechanical stress. It passes a current whose magnitude can vary by a factor of 1012 in response to changes in applied pressure. + +Measurement +The value of a resistor can be measured with an ohmmeter, which may be one function of a multimeter. Usually, probes on the ends of test leads connect to the resistor. A simple ohmmeter may apply a voltage from a battery across the unknown resistor (with an internal resistor of a known value in series) producing a current which drives a meter movement. The current, in accordance with Ohm's law, is inversely proportional to the sum of the internal resistance and the resistor being tested, resulting in an analog meter scale which is very non-linear, calibrated from infinity to 0 ohms. A digital multimeter, using active electronics, may instead pass a specified current through the test resistance. The voltage generated across the test resistance in that case is linearly proportional to its resistance, which is measured and displayed. In either case the low-resistance ranges of the meter pass much more current through the test leads than do high-resistance ranges, in order for the voltages present to be at reasonable levels (generally below 10 volts) but still measurable. + +Measuring low-value resistors, such as fractional-ohm resistors, with acceptable accuracy requires four-terminal connections. One pair of terminals applies a known, calibrated current to the resistor, while the other pair senses the voltage drop across the resistor. Some laboratory quality ohmmeters, especially milliohmmeters, and even some of the better digital multimeters sense using four input terminals for this purpose, which may be used with special test leads. Each of the two so-called Kelvin clips has a pair of jaws insulated from each other. One side of each clip applies the measuring current, while the other connections are only to sense the voltage drop. The resistance is again calculated using Ohm's Law as the measured voltage divided by the applied current. + +Standards +Production resistors +Resistor characteristics are quantified and reported using various national standards. In the US, MIL-STD-202[21] contains the relevant test methods to which other standards refer. + +There are various standards specifying properties of resistors for use in equipment: + +IEC 60062 (IEC 62) / DIN 40825 / BS 1852 / IS 8186 / JIS C 5062 etc. (Resistor color code, RKM code, date code) +EIA RS-279 / DIN 41429 (Resistor color code) +IEC 60063 (IEC 63) / JIS C 5063 (Standard E series values) +MIL-PRF-26 +MIL-PRF-39007 (Fixed power, established reliability) +MIL-PRF-55342 (Surface-mount thick and thin film) +MIL-PRF-914 +MIL-R-11 Standard Canceled +MIL-R-39017 (Fixed, General Purpose, Established Reliability) +MIL-PRF-32159 (zero ohm jumpers) +UL 1412 (fusing and temperature limited resistors)[22] +There are other United States military procurement MIL-R- standards. + +Resistance standards +The primary standard for resistance, the "mercury ohm" was initially defined in 1884 in as a column of mercury 106.3 cm long and 1 square millimeter in cross-section, at 0 degrees Celsius. Difficulties in precisely measuring the physical constants to replicate this standard result in variations of as much as 30 ppm. From 1900 the mercury ohm was replaced with a precision machined plate of manganin.[23] Since 1990 the international resistance standard has been based on the quantized Hall effect discovered by Klaus von Klitzing, for which he won the Nobel Prize in Physics in 1985.[24] + +Resistors of extremely high precision are manufactured for calibration and laboratory use. They may have four terminals, using one pair to carry an operating current and the other pair to measure the voltage drop; this eliminates errors caused by voltage drops across the lead resistances, because no charge flows through voltage sensing leads. It is important in small value resistors (100–0.0001 ohm) where lead resistance is significant or even comparable with respect to resistance standard value.[25] + +Resistor marking + +Wheel-based RMA Resistor Color Code guide. Circa 1945-1955. +Main article: Electronic color code +Axial resistors' cases are usually tan, brown, blue, or green (though other colors are occasionally found as well, such as dark red or dark gray), and display 3–6 colored stripes that indicate resistance (and by extension tolerance), and may be extended to indicate the temperature coefficient and reliability class. The first two stripes represent the first two digits of the resistance in ohms, the third represents a multiplier, and the fourth the tolerance (which if absent, denotes ±20%). For five- and six- striped resistors the third is the third digit, the fourth the multiplier and the fifth is the tolerance; a sixth stripe represents the temperature coefficient. The power rating of the resistor is usually not marked and is deduced from the size. + +Surface-mount resistors are marked numerically. + +Early 20th century resistors, essentially uninsulated, were dipped in paint to cover their entire body for color-coding. A second color of paint was applied to one end of the element, and a color dot (or band) in the middle provided the third digit. The rule was "body, tip, dot", providing two significant digits for value and the decimal multiplier, in that sequence. Default tolerance was ±20%. Closer-tolerance resistors had silver (±10%) or gold-colored (±5%) paint on the other end. + +Preferred values +See also: E-series of preferred numbers +Early resistors were made in more or less arbitrary round numbers; a series might have 100, 125, 150, 200, 300, etc.[26] Resistors as manufactured are subject to a certain percentage tolerance, and it makes sense to manufacture values that correlate with the tolerance, so that the actual value of a resistor overlaps slightly with its neighbors. Wider spacing leaves gaps; narrower spacing increases manufacturing and inventory costs to provide resistors that are more or less interchangeable. + +A logical scheme is to produce resistors in a range of values which increase in a geometric progression, so that each value is greater than its predecessor by a fixed multiplier or percentage, chosen to match the tolerance of the range. For example, for a tolerance of ±20% it makes sense to have each resistor about 1.5 times its predecessor, covering a decade in 6 values. In practice the factor used is 1.4678, giving values of 1.47, 2.15, 3.16, 4.64, 6.81, 10 for the 1–10-decade (a decade is a range increasing by a factor of 10; 0.1–1 and 10–100 are other examples); these are rounded in practice to 1.5, 2.2, 3.3, 4.7, 6.8, 10; followed by 15, 22, 33, … and preceded by … 0.47, 0.68, 1. This scheme has been adopted as the E48 series of the IEC 60063 preferred number values. There are also E12, E24, E48, E96 and E192 series for components of progressively finer resolution, with 12, 24, 96, and 192 different values within each decade. The actual values used are in the IEC 60063 lists of preferred numbers. + +A resistor of 100 ohms ±20% would be expected to have a value between 80 and 120 ohms; its E6 neighbors are 68 (54–82) and 150 (120–180) ohms. A sensible spacing, E6 is used for ±20% components; E12 for ±10%; E24 for ±5%; E48 for ±2%, E96 for ±1%; E192 for ±0.5% or better. Resistors are manufactured in values from a few milliohms to about a gigaohm in IEC60063 ranges appropriate for their tolerance. Manufacturers may sort resistors into tolerance-classes based on measurement. Accordingly, a selection of 100 ohms resistors with a tolerance of ±10%, might not lie just around 100 ohm (but no more than 10% off) as one would expect (a bell-curve), but rather be in two groups – either between 5 and 10% too high or 5 to 10% too low (but not closer to 100 ohm than that) because any resistors the factory had measured as being less than 5% off would have been marked and sold as resistors with only ±5% tolerance or better. When designing a circuit, this may become a consideration. This process of sorting parts based on post-production measurement is known as "binning", and can be applied to other components than resistors (such as speed grades for CPUs). + +Earlier power wirewound resistors, such as brown vitreous-enameled types, however, were made with a different system of preferred values, such as some of those mentioned in the first sentence of this section. + +SMT resistors + +This image shows four surface-mount resistors (the component at the upper left is a capacitor) including two zero-ohm resistors. Zero-ohm links are often used instead of wire links, so that they can be inserted by a resistor-inserting machine. Their resistance is negligible. +Surface mounted resistors of larger sizes (metric 1608 and above) are printed with numerical values in a code related to that used on axial resistors. Standard-tolerance surface-mount technology (SMT) resistors are marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten (the number of zeroes). For example: + +334 = 33 × 104 Ω = 330 kΩ +222 = 22 × 102 Ω = 2.2 kΩ +473 = 47 × 103 Ω = 47 kΩ +105 = 10 × 105 Ω = 1 MΩ +Resistances less than 100 Ω are written: 100, 220, 470. The final zero represents ten to the power zero, which is 1. For example: + +100 = 10 × 100 Ω = 10 Ω +220 = 22 × 100 Ω = 22 Ω +Sometimes these values are marked as 10 or 22 to prevent a mistake. + +Resistances less than 10 Ω have 'R' to indicate the position of the decimal point (radix point). For example: + +4R7 = 4.7 Ω +R300 = 0.30 Ω +0R22 = 0.22 Ω +0R01 = 0.01 Ω +Precision resistors are marked with a four-digit code, in which the first three digits are the significant figures and the fourth is the power of ten. For example: + +1001 = 100 × 101 Ω = 1.00 kΩ +4992 = 499 × 102 Ω = 49.9 kΩ +1000 = 100 × 100 Ω = 100 Ω +000 and 0000 sometimes appear as values on surface-mount zero-ohm links, since these have (approximately) zero resistance. + +More recent surface-mount resistors are too small, physically, to permit practical markings to be applied. + +Industrial type designation +Format: [two letters][resistance value (three digit)][tolerance code(numerical – one digit)] [27] +Power Rating at 70 °C +Type No. Power +rating +(watts) MIL-R-11 +Style MIL-R-39008 +Style +BB ​1⁄8 RC05 RCR05 +CB ​1⁄4 RC07 RCR07 +EB ​1⁄2 RC20 RCR20 +GB 1 RC32 RCR32 +HB 2 RC42 RCR42 +GM 3 - - +HM 4 - - +Tolerance Code +Industrial type designation Tolerance MIL Designation +5 ±5% J +2 ±20% M +1 ±10% K +- ±2% G +- ±1% F +- ±0.5% D +- ±0.25% C +- ±0.1% B +Steps to find out the resistance or capacitance values: + +First two letters gives the power dissipation capacity. +Next three digits gives the resistance value. +First two digits are the significant values +Third digit is the multiplier. +Final digit gives the tolerance. +If a resistor is coded: + +EB1041: power dissipation capacity = 1/2 watts, resistance value = 10×10^4±10% = between 9×10^4 ohms and 11×10^4 ohms. +CB3932: power dissipation capacity = 1/4 watts, resistance value = 39×10^3±20% = between 46.8×10^3 ohms and 31.2×10^3 ohms. +Electrical and thermal noise +Main article: Noise (electronics) +In amplifying faint signals, it is often necessary to minimize electronic noise, particularly in the first stage of amplification. As a dissipative element, even an ideal resistor naturally produces a randomly fluctuating voltage, or noise, across its terminals. This Johnson–Nyquist noise is a fundamental noise source which depends only upon the temperature and resistance of the resistor, and is predicted by the fluctuation–dissipation theorem. Using a larger value of resistance produces a larger voltage noise, whereas a smaller value of resistance generates more current noise, at a given temperature. + +The thermal noise of a practical resistor may also be larger than the theoretical prediction and that increase is typically frequency-dependent. Excess noise of a practical resistor is observed only when current flows through it. This is specified in unit of μV/V/decade – μV of noise per volt applied across the resistor per decade of frequency. The μV/V/decade value is frequently given in dB so that a resistor with a noise index of 0 dB exhibits 1 μV (rms) of excess noise for each volt across the resistor in each frequency decade. Excess noise is thus an example of 1/f noise. Thick-film and carbon composition resistors generate more excess noise than other types at low frequencies. Wire-wound and thin-film resistors are often used for their better noise characteristics. Carbon composition resistors can exhibit a noise index of 0 dB while bulk metal foil resistors may have a noise index of −40 dB, usually making the excess noise of metal foil resistors insignificant.[28] Thin film surface mount resistors typically have lower noise and better thermal stability than thick film surface mount resistors. Excess noise is also size-dependent: in general excess noise is reduced as the physical size of a resistor is increased (or multiple resistors are used in parallel), as the independently fluctuating resistances of smaller components tend to average out. + +While not an example of "noise" per se, a resistor may act as a thermocouple, producing a small DC voltage differential across it due to the thermoelectric effect if its ends are at different temperatures. This induced DC voltage can degrade the precision of instrumentation amplifiers in particular. Such voltages appear in the junctions of the resistor leads with the circuit board and with the resistor body. Common metal film resistors show such an effect at a magnitude of about 20 µV/°C. Some carbon composition resistors can exhibit thermoelectric offsets as high as 400 µV/°C, whereas specially constructed resistors can reduce this number to 0.05 µV/°C. In applications where the thermoelectric effect may become important, care has to be taken to mount the resistors horizontally to avoid temperature gradients and to mind the air flow over the board.[29] + +Failure modes +The failure rate of resistors in a properly designed circuit is low compared to other electronic components such as semiconductors and electrolytic capacitors. Damage to resistors most often occurs due to overheating when the average power delivered to it greatly exceeds its ability to dissipate heat (specified by the resistor's power rating). This may be due to a fault external to the circuit, but is frequently caused by the failure of another component (such as a transistor that shorts out) in the circuit connected to the resistor. Operating a resistor too close to its power rating can limit the resistor's lifespan or cause a significant change in its resistance. A safe design generally uses overrated resistors in power applications to avoid this danger. + +Low-power thin-film resistors can be damaged by long-term high-voltage stress, even below maximum specified voltage and below maximum power rating. This is often the case for the startup resistors feeding the SMPS integrated circuit.[citation needed] + +When overheated, carbon-film resistors may decrease or increase in resistance.[30] Carbon film and composition resistors can fail (open circuit) if running close to their maximum dissipation. This is also possible but less likely with metal film and wirewound resistors. + +There can also be failure of resistors due to mechanical stress and adverse environmental factors including humidity. If not enclosed, wirewound resistors can corrode. + +Surface mount resistors have been known to fail due to the ingress of sulfur into the internal makeup of the resistor. This sulfur chemically reacts with the silver layer to produce non-conductive silver sulfide. The resistor's impedance goes to infinity. Sulfur resistant and anti-corrosive resistors are sold into automotive, industrial, and military applications. ASTM B809 is an industry standard that tests a part's susceptibility to sulfur. + +An alternative failure mode can be encountered where large value resistors are used (hundreds of kilohms and higher). Resistors are not only specified with a maximum power dissipation, but also for a maximum voltage drop. Exceeding this voltage causes the resistor to degrade slowly reducing in resistance. The voltage dropped across large value resistors can be exceeded before the power dissipation reaches its limiting value. Since the maximum voltage specified for commonly encountered resistors is a few hundred volts, this is a problem only in applications where these voltages are encountered. + +Variable resistors can also degrade in a different manner, typically involving poor contact between the wiper and the body of the resistance. This may be due to dirt or corrosion and is typically perceived as "crackling" as the contact resistance fluctuates; this is especially noticed as the device is adjusted. This is similar to crackling caused by poor contact in switches, and like switches, potentiometers are to some extent self-cleaning: running the wiper across the resistance may improve the contact. Potentiometers which are seldom adjusted, especially in dirty or harsh environments, are most likely to develop this problem. When self-cleaning of the contact is insufficient, improvement can usually be obtained through the use of contact cleaner (also known as "tuner cleaner") spray. The crackling noise associated with turning the shaft of a dirty potentiometer in an audio circuit (such as the volume control) is greatly accentuated when an undesired DC voltage is present, often indicating the failure of a DC blocking capacitor in the circuit. diff --git a/examples/article6.txt b/examples/article6.txt new file mode 100644 index 0000000..ebb5579 --- /dev/null +++ b/examples/article6.txt @@ -0,0 +1,367 @@ +A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits. + +Austro-Hungarian physicist Julius Edgar Lilienfeld proposed the concept of a field-effect transistor in 1926, but it was not possible to actually construct a working device at that time.[1] The first working device to be built was a point-contact transistor invented in 1947 by American physicists John Bardeen and Walter Brattain while working under William Shockley at Bell Labs. They shared the 1956 Nobel Prize in Physics for their achievement.[2] The most widely used transistor is the MOSFET (metal–oxide–semiconductor field-effect transistor), also known as the MOS transistor, which was invented by Egyptian engineer Mohamed Atalla with Korean engineer Dawon Kahng at Bell Labs in 1959.[3][4][5] The MOSFET was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses.[6] + +Transistors revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The first transistor and the MOSFET are on the list of IEEE milestones in electronics.[7][8] The MOSFET is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems.[9] An estimated total of 13 sextillion MOSFETs have been manufactured between 1960 and 2018 (at least 99.9% of all transistors), making the MOSFET the most widely manufactured device in history.[10] + +Most transistors are made from very pure silicon, and some from germanium, but certain other semiconductor materials are sometimes used. A transistor may have only one kind of charge carrier, in a field-effect transistor, or may have two kinds of charge carriers in bipolar junction transistor devices. Compared with the vacuum tube, transistors are generally smaller, and require less power to operate. Certain vacuum tubes have advantages over transistors at very high operating frequencies or high operating voltages. Many types of transistors are made to standardized specifications by multiple manufacturers. + + +Contents +1 History +1.1 Bipolar transistors +1.2 MOSFET (MOS transistor) +2 Importance +3 Simplified operation +3.1 Transistor as a switch +3.2 Transistor as an amplifier +4 Comparison with vacuum tubes +4.1 Advantages +4.2 Limitations +5 Types +5.1 Field-effect transistor (FET) +5.1.1 Metal-oxide-semiconductor FET (MOSFET) +5.2 Bipolar junction transistor (BJT) +5.3 Usage of MOSFETs and BJTs +5.4 Other transistor types +6 Part numbering standards/specifications +6.1 Japanese Industrial Standard (JIS) +6.2 European Electronic Component Manufacturers Association (EECA) +6.3 Joint Electron Device Engineering Council (JEDEC) +6.4 Proprietary +6.5 Naming problems +7 Construction +7.1 Semiconductor material +7.2 Packaging +7.2.1 Flexible transistors +8 See also +9 References +10 Further reading +11 External links +History +Main article: History of the transistor + +Julius Edgar Lilienfeld proposed the concept of a field-effect transistor in 1925. +The thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony. The triode, however, was a fragile device that consumed a substantial amount of power. In 1909, physicist William Eccles discovered the crystal diode oscillator.[11] Austro-Hungarian physicist Julius Edgar Lilienfeld filed a patent for a field-effect transistor (FET) in Canada in 1925,[12] which was intended to be a solid-state replacement for the triode.[13][14] Lilienfeld also filed identical patents in the United States in 1926[15] and 1928.[16][17] However, Lilienfeld did not publish any research articles about his devices nor did his patents cite any specific examples of a working prototype. Because the production of high-quality semiconductor materials was still decades away, Lilienfeld's solid-state amplifier ideas would not have found practical use in the 1920s and 1930s, even if such a device had been built.[18] In 1934, German inventor Oskar Heil patented a similar device in Europe.[19] + +Bipolar transistors + +John Bardeen, William Shockley and Walter Brattain at Bell Labs in 1948. They invented the point-contact transistor in 1947 and bipolar junction transistor in 1948. + +A replica of the first working transistor, a point-contact transistor invented in 1947. +Further information: Point-contact transistor and Bipolar junction transistor +From November 17, 1947, to December 23, 1947, John Bardeen and Walter Brattain at AT&T's Bell Labs in Murray Hill, New Jersey, performed experiments and observed that when two gold point contacts were applied to a crystal of germanium, a signal was produced with the output power greater than the input.[20] Solid State Physics Group leader William Shockley saw the potential in this, and over the next few months worked to greatly expand the knowledge of semiconductors. The term transistor was coined by John R. Pierce as a contraction of the term transresistance.[21][22][23] According to Lillian Hoddeson and Vicki Daitch, authors of a biography of John Bardeen, Shockley had proposed that Bell Labs' first patent for a transistor should be based on the field-effect and that he be named as the inventor. Having unearthed Lilienfeld's patents that went into obscurity years earlier, lawyers at Bell Labs advised against Shockley's proposal because the idea of a field-effect transistor that used an electric field as a "grid" was not new. Instead, what Bardeen, Brattain, and Shockley invented in 1947 was the first point-contact transistor.[18] In acknowledgement of this accomplishment, Shockley, Bardeen, and Brattain were jointly awarded the 1956 Nobel Prize in Physics "for their researches on semiconductors and their discovery of the transistor effect".[24][25] + +Shockley's research team initially attempted to build a field-effect transistor (FET), by trying to modulate the conductivity of a semiconductor, but was unsuccessful, mainly due to problems with the surface states, the dangling bond, and the germanium and copper compound materials. In the course of trying to understand the mysterious reasons behind their failure to build a working FET, this led them instead to invent the bipolar point-contact and junction transistors.[26][27] + + +Herbert Mataré in 1950. He independently invented a point-contact transistor in June 1948. +In 1948, the point-contact transistor was independently invented by German physicists Herbert Mataré and Heinrich Welker while working at the Compagnie des Freins et Signaux, a Westinghouse subsidiary located in Paris. Mataré had previous experience in developing crystal rectifiers from silicon and germanium in the German radar effort during World War II. Using this knowledge, he began researching the phenomenon of "interference" in 1947. By June 1948, witnessing currents flowing through point-contacts, Mataré produced consistent results using samples of germanium produced by Welker, similar to what Bardeen and Brattain had accomplished earlier in December 1947. Realizing that Bell Labs' scientists had already invented the transistor before them, the company rushed to get its "transistron" into production for amplified use in France's telephone network and filed his first transistor patent application on August 13, 1948.[28][29][30] + +The first bipolar junction transistors were invented by Bell Labs' William Shockley, which applied for patent (2,569,347) on June 26, 1948. On April 12, 1950, Bell Labs chemists Gordon Teal and Morgan Sparks had successfully produced a working bipolar NPN junction amplifying germanium transistor. Bell Labs had announced the discovery of this new "sandwich" transistor in a press release on July 4, 1951.[31][32] + + +Philco surface-barrier transistor developed and produced in 1953 +The first high-frequency transistor was the surface-barrier germanium transistor developed by Philco in 1953, capable of operating up to 60 MHz.[33] These were made by etching depressions into an N-type germanium base from both sides with jets of Indium(III) sulfate until it was a few ten-thousandths of an inch thick. Indium electroplated into the depressions formed the collector and emitter.[34][35] + +The first "prototype" pocket transistor radio was shown by INTERMETALL (a company founded by Herbert Mataré in 1952) at the Internationale Funkausstellung Düsseldorf between August 29, 1953 and September 6, 1953.[36][37] The first "production" pocket transistor radio was the Regency TR-1, released in October 1954.[25] Produced as a joint venture between the Regency Division of Industrial Development Engineering Associates, I.D.E.A. and Texas Instruments of Dallas Texas, the TR-1 was manufactured in Indianapolis, Indiana. It was a near pocket-sized radio featuring 4 transistors and one germanium diode. The industrial design was outsourced to the Chicago firm of Painter, Teague and Petertil. It was initially released in one of four different colours: black, bone white, red, and gray. Other colours were to shortly follow.[38][39][40] + +The first "production" all-transistor car radio was developed by Chrysler and Philco corporations and it was announced in the April 28, 1955 edition of the Wall Street Journal. Chrysler had made the all-transistor car radio, Mopar model 914HR, available as an option starting in fall 1955 for its new line of 1956 Chrysler and Imperial cars which first hit the dealership showroom floors on October 21, 1955.[41][42][43] + +The Sony TR-63, released in 1957, was the first mass-produced transistor radio, leading to the mass-market penetration of transistor radios.[44] The TR-63 went on to sell seven million units worldwide by the mid-1960s.[45] Sony's success with transistor radios led to transistors replacing vacuum tubes as the dominant electronic technology in the late 1950s.[46] + +The first working silicon transistor was developed at Bell Labs on January 26, 1954 by Morris Tanenbaum. The first commercial silicon transistor was produced by Texas Instruments in 1954. This was the work of Gordon Teal, an expert in growing crystals of high purity, who had previously worked at Bell Labs.[47][48][49] + +MOSFET (MOS transistor) +Main article: MOSFET + + +Mohamed Atalla (left) and Dawon Kahng (right) invented the MOSFET (MOS transistor) at Bell Labs in 1959. +Semiconductor companies initially focused on junction transistors in the early years of the semiconductor industry. However, the junction transistor was a relatively bulky device that was difficult to manufacture on a mass-production basis, which limited it to a number of specialised applications. Field-effect transistors (FETs) were theorized as potential alternatives to junction transistors, but researchers could not get FETs to work properly, largely due to the troublesome surface state barrier that prevented the external electric field from penetrating into the material.[6] + +In the 1950s, Egyptian engineer Mohamed Atalla investigated the surface properties of silicon semiconductors at Bell Labs, where he proposed a new method of semiconductor device fabrication, coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below, overcoming the surface states that prevented electricity from reaching the semiconducting layer. This is known as surface passivation, a method that became critical to the semiconductor industry as it later made possible the mass-production of silicon integrated circuits.[50][51] He presented his findings in 1957.[52] Building on his surface passivation method, he developed the metal–oxide–semiconductor (MOS) process.[50] He proposed the MOS process could be used to build the first working silicon FET, which he began working on building with the help of his Korean colleague Dawon Kahng.[50] + +The metal–oxide–semiconductor field-effect transistor (MOSFET), also known as the MOS transistor, was invented by Mohamed Atalla and Dawon Kahng in 1959.[3][4] The MOSFET was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses.[6] With its high scalability,[53] and much lower power consumption and higher density than bipolar junction transistors,[54] the MOSFET made it possible to build high-density integrated circuits,[5] allowing the integration of more than 10,000 transistors in a single IC.[55] + +CMOS (complementary MOS) was invented by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor in 1963.[56] The first report of a floating-gate MOSFET was made by Dawon Kahng and Simon Sze in 1967.[57] A double-gate MOSFET was first demonstrated in 1984 by Electrotechnical Laboratory researchers Toshihiro Sekigawa and Yutaka Hayashi.[58][59] FinFET (fin field-effect transistor), a type of 3D non-planar multi-gate MOSFET, originated from the research of Digh Hisamoto and his team at Hitachi Central Research Laboratory in 1989.[60][61] + +Importance +Transistors are the key active components in practically all modern electronics. Many thus consider the transistor to be one of the greatest inventions of the 20th century.[62] + +The MOSFET (metal–oxide–semiconductor field-effect transistor), also known as the MOS transistor, is by far the most widely used transistor, used in applications ranging from computers and electronics[51] to communications technology such as smartphones.[63] The MOSFET has been considered to be the most important transistor,[64] possibly the most important invention in electronics,[65] and the birth of modern electronics.[66] The MOS transistor has been the fundamental building block of modern digital electronics since the late 20th century, paving the way for the digital age.[9] The US Patent and Trademark Office calls it a "groundbreaking invention that transformed life and culture around the world".[63] Its importance in today's society rests on its ability to be mass-produced using a highly automated process (semiconductor device fabrication) that achieves astonishingly low per-transistor costs. + +The invention of the first transistor at Bell Labs was named an IEEE Milestone in 2009.[67] The list of IEEE Milestones also includes the inventions of the junction transistor in 1948 and the MOSFET in 1959.[68] + +Although several companies each produce over a billion individually packaged (known as discrete) MOS transistors every year,[69] the vast majority of transistors are now produced in integrated circuits (often shortened to IC, microchips or simply chips), along with diodes, resistors, capacitors and other electronic components, to produce complete electronic circuits. A logic gate consists of up to about twenty transistors whereas an advanced microprocessor, as of 2009, can use as many as 3 billion transistors (MOSFETs).[70] "About 60 million transistors were built in 2002… for [each] man, woman, and child on Earth."[71] + +The MOS transistor is the most widely manufactured device in history.[10] As of 2013, billions of transistors are manufactured every day, nearly all of which are MOSFET devices.[5] Between 1960 and 2018, an estimated total of 13 sextillion MOS transistors have been manufactured, accounting for at least 99.9% of all transistors.[10] + +The transistor's low cost, flexibility, and reliability have made it a ubiquitous device. Transistorized mechatronic circuits have replaced electromechanical devices in controlling appliances and machinery. It is often easier and cheaper to use a standard microcontroller and write a computer program to carry out a control function than to design an equivalent mechanical system to control that same function. + +Simplified operation + +A Darlington transistor opened up so the actual transistor chip (the small square) can be seen inside. A Darlington transistor is effectively two transistors on the same chip. One transistor is much larger than the other, but both are large in comparison to transistors in large-scale integration because this particular example is intended for power applications. + +A simple circuit diagram to show the labels of a n–p–n bipolar transistor. +The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. It can produce a stronger output signal, a voltage or current, which is proportional to a weaker input signal and thus, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.[72] + +There are two types of transistors, which have slight differences in how they are used in a circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals. For a field-effect transistor, the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current between source and drain.[73] + +The image represents a typical bipolar transistor in a circuit. Charge will flow between emitter and collector terminals depending on the current in the base. Because internally the base and emitter connections behave like a semiconductor diode, a voltage drop develops between base and emitter while the base current exists. The amount of this voltage depends on the material the transistor is made from, and is referred to as VBE.[73] + +Transistor as a switch + +BJT used as an electronic switch, in grounded-emitter configuration. +Transistors are commonly used in digital circuits as electronic switches which can be either in an "on" or "off" state, both for high-power applications such as switched-mode power supplies and for low-power applications such as logic gates. Important parameters for this application include the current switched, the voltage handled, and the switching speed, characterised by the rise and fall times.[73] + +In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the base voltage rises, the emitter and collector currents rise exponentially. The collector voltage drops because of reduced resistance from collector to emitter. If the voltage difference between the collector and emitter were zero (or near zero), the collector current would be limited only by the load resistance (light bulb) and the supply voltage. This is called saturation because current is flowing from collector to emitter freely. When saturated, the switch is said to be on.[74] + +Providing sufficient base drive current is a key problem in the use of bipolar transistors as switches. The transistor provides current gain, allowing a relatively large current in the collector to be switched by a much smaller current into the base terminal. The ratio of these currents varies depending on the type of transistor, and even for a particular type, varies depending on the collector current. In the example light-switch circuit shown, the resistor is chosen to provide enough base current to ensure the transistor will be saturated.[73] + +In a switching circuit, the idea is to simulate, as near as possible, the ideal switch having the properties of open circuit when off, short circuit when on, and an instantaneous transition between the two states. Parameters are chosen such that the "off" output is limited to leakage currents too small to affect connected circuitry, the resistance of the transistor in the "on" state is too small to affect circuitry, and the transition between the two states is fast enough not to have a detrimental effect.[73] + +Transistor as an amplifier + +Amplifier circuit, common-emitter configuration with a voltage-divider bias circuit. +The common-emitter amplifier is designed so that a small change in voltage (Vin) changes the small current through the base of the transistor whose current amplification combined with the properties of the circuit means that small swings in Vin produce large changes in Vout.[73] + +Various configurations of single transistor amplifier are possible, with some providing current gain, some voltage gain, and some both. + +From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing. The first discrete-transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved.[73] + +Modern transistor audio amplifiers of up to a few hundred watts are common and relatively inexpensive. + +Comparison with vacuum tubes +Before transistors were developed, vacuum (electron) tubes (or in the UK "thermionic valves" or just "valves") were the main active components in electronic equipment. + +Advantages +The key advantages that have allowed transistors to replace vacuum tubes in most applications are + +No cathode heater (which produces the characteristic orange glow of tubes), reducing power consumption, eliminating delay as tube heaters warm up, and immune from cathode poisoning and depletion. +Very small size and weight, reducing equipment size. +Large numbers of extremely small transistors can be manufactured as a single integrated circuit. +Low operating voltages compatible with batteries of only a few cells. +Circuits with greater energy efficiency are usually possible. For low-power applications (for example, voltage amplification) in particular, energy consumption can be very much less than for tubes. +Complementary devices available, providing design flexibility including complementary-symmetry circuits, not possible with vacuum tubes. +Very low sensitivity to mechanical shock and vibration, providing physical ruggedness and virtually eliminating shock-induced spurious signals (for example, microphonics in audio applications). +Not susceptible to breakage of a glass envelope, leakage, outgassing, and other physical damage. +Limitations +Transistors have the following limitations: + +They lack the higher electron mobility afforded by the vacuum of vacuum tubes, which is desirable for high-power, high-frequency operation — such as that used in over-the-air television broadcasting. +Transistors and other solid-state devices are susceptible to damage from very brief electrical and thermal events, including electrostatic discharge in handling. Vacuum tubes are electrically much more rugged. +They are sensitive to radiation and cosmic rays (special radiation-hardened chips are used for spacecraft devices). +In audio applications, transistors lack the lower-harmonic distortion — the so-called tube sound — which is characteristic of vacuum tubes, and is preferred by some.[75] +Types +BJT PNP symbol.svg PNP JFET P-Channel Labelled.svg P-channel +BJT NPN symbol.svg NPN JFET N-Channel Labelled.svg N-channel +BJT JFET +BJT and JFET symbols +JFET P-Channel Labelled.svg IGFET P-Ch Enh Labelled.svg IGFET P-Ch Enh Labelled simplified.svg IGFET P-Ch Dep Labelled.svg P-channel +JFET N-Channel Labelled.svg IGFET N-Ch Enh Labelled.svg IGFET N-Ch Enh Labelled simplified.svg IGFET N-Ch Dep Labelled.svg N-channel +JFET MOSFET enh MOSFET dep +JFET and MOSFET symbols +Transistors are categorized by + +Structure: MOSFET (IGFET), BJT, JFET, insulated-gate bipolar transistor (IGBT), "other types". +semiconductor material: the metalloids germanium (first used in 1947) and silicon (first used in 1954)—in amorphous, polycrystalline and monocrystalline form—, the compounds gallium arsenide (1966) and silicon carbide (1997), the alloy silicon-germanium (1989), the allotrope of carbon graphene (research ongoing since 2004), etc. (see Semiconductor material). +Electrical polarity (positive and negative): n–p–n, p–n–p (BJTs), n-channel, p-channel (FETs). +Maximum power rating: low, medium, high. +Maximum operating frequency: low, medium, high, radio (RF), microwave frequency (the maximum effective frequency of a transistor in a common-emitter or common-source circuit is denoted by the term fT, an abbreviation for transition frequency—the frequency of transition is the frequency at which the transistor yields unity voltage gain) +Application: switch, general purpose, audio, high voltage, super-beta, matched pair. +Physical packaging: through-hole metal, through-hole plastic, surface mount, ball grid array, power modules (see Packaging). +Amplification factor hFE, βF (transistor beta)[76] or gm (transconductance). +temperature: Extreme temperature transistors and traditional temperature transistors (−55°C to +150°C). Extreme temperature transistors include high-temperature transistors (above +150°C) and low-temperature transistors (below −55°C). The high-temperature transistors that operate thermally stable up to 220°C, can be developed by a general strategy of blending interpenetrating semi-crystalline conjugated polymers and high glass-transition temperature insulating polymers.[77] +Hence, a particular transistor may be described as silicon, surface-mount, BJT, n–p–n, low-power, high-frequency switch. + +A popular way to remember which symbol represents which type of transistor is to look at the arrow and how it is arranged. Within an NPN transistor symbol, the arrow will Not Point iN. Conversely, within the PNP symbol you see that the arrow Points iN Proudly. + +Field-effect transistor (FET) +Main article: Field-effect transistor +See also: JFET + +Operation of a FET and its Id-Vg curve. At first, when no gate voltage is applied, there are no inversion electrons in the channel, so the device is turned off. As gate voltage increases, the inversion electron density in the channel increases, current increases, and thus the device turns on. +The field-effect transistor, sometimes called a unipolar transistor, uses either electrons (in n-channel FET) or holes (in p-channel FET) for conduction. The four terminals of the FET are named source, gate, drain, and body (substrate). On most FETs, the body is connected to the source inside the package, and this will be assumed for the following description. + +In a FET, the drain-to-source current flows via a conducting channel that connects the source region to the drain region. The conductivity is varied by the electric field that is produced when a voltage is applied between the gate and source terminals, hence the current flowing between the drain and source is controlled by the voltage applied between the gate and source. As the gate–source voltage (VGS) is increased, the drain–source current (IDS) increases exponentially for VGS below threshold, and then at a roughly quadratic rate (IDS ∝ (VGS − VT)2) (where VT is the threshold voltage at which drain current begins)[78] in the "space-charge-limited" region above threshold. A quadratic behavior is not observed in modern devices, for example, at the 65 nm technology node.[79] + +For low noise at narrow bandwidth the higher input resistance of the FET is advantageous. + +FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET). The IGFET is more commonly known as a metal–oxide–semiconductor FET (MOSFET), reflecting its original construction from layers of metal (the gate), oxide (the insulation), and semiconductor. Unlike IGFETs, the JFET gate forms a p–n diode with the channel which lies between the source and drain. Functionally, this makes the n-channel JFET the solid-state equivalent of the vacuum tube triode which, similarly, forms a diode between its grid and cathode. Also, both devices operate in the depletion mode, they both have a high input impedance, and they both conduct current under the control of an input voltage. + +Metal–semiconductor FETs (MESFETs) are JFETs in which the reverse biased p–n junction is replaced by a metal–semiconductor junction. These, and the HEMTs (high-electron-mobility transistors, or HFETs), in which a two-dimensional electron gas with very high carrier mobility is used for charge transport, are especially suitable for use at very high frequencies (several GHz). + +FETs are further divided into depletion-mode and enhancement-mode types, depending on whether the channel is turned on or off with zero gate-to-source voltage. For enhancement mode, the channel is off at zero bias, and a gate potential can "enhance" the conduction. For the depletion mode, the channel is on at zero bias, and a gate potential (of the opposite polarity) can "deplete" the channel, reducing conduction. For either mode, a more positive gate voltage corresponds to a higher current for n-channel devices and a lower current for p-channel devices. Nearly all JFETs are depletion-mode because the diode junctions would forward bias and conduct if they were enhancement-mode devices, while most IGFETs are enhancement-mode types. + +Metal-oxide-semiconductor FET (MOSFET) +Main article: MOSFET +The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS transistor, or MOS),[5] is a type of field-effect transistor that is fabricated by the controlled oxidation of a semiconductor, typically silicon. It has an insulated gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The MOSFET is by far the most common transistor, and the basic building block of most modern electronics.[9] The MOSFET accounts for 99.9% of all transistors in the world.[10] + +Bipolar junction transistor (BJT) +Main article: Bipolar junction transistor +Bipolar transistors are so named because they conduct by using both majority and minority carriers. The bipolar junction transistor, the first type of transistor to be mass-produced, is a combination of two junction diodes, and is formed of either a thin layer of p-type semiconductor sandwiched between two n-type semiconductors (an n–p–n transistor), or a thin layer of n-type semiconductor sandwiched between two p-type semiconductors (a p–n–p transistor). This construction produces two p–n junctions: a base–emitter junction and a base–collector junction, separated by a thin region of semiconductor known as the base region. (Two junction diodes wired together without sharing an intervening semiconducting region will not make a transistor). + +BJTs have three terminals, corresponding to the three layers of semiconductor—an emitter, a base, and a collector. They are useful in amplifiers because the currents at the emitter and collector are controllable by a relatively small base current.[80] In an n–p–n transistor operating in the active region, the emitter–base junction is forward biased (electrons and holes recombine at the junction), and the base-collector junction is reverse biased (electrons and holes are formed at, and move away from the junction), and electrons are injected into the base region. Because the base is narrow, most of these electrons will diffuse into the reverse-biased base–collector junction and be swept into the collector; perhaps one-hundredth of the electrons will recombine in the base, which is the dominant mechanism in the base current. As well, as the base is lightly doped (in comparison to the emitter and collector regions), recombination rates are low, permitting more carriers to diffuse across the base region. By controlling the number of electrons that can leave the base, the number of electrons entering the collector can be controlled.[80] Collector current is approximately β (common-emitter current gain) times the base current. It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for high-power applications. + +Unlike the field-effect transistor (see below), the BJT is a low-input-impedance device. Also, as the base–emitter voltage (VBE) is increased the base–emitter current and hence the collector–emitter current (ICE) increase exponentially according to the Shockley diode model and the Ebers-Moll model. Because of this exponential relationship, the BJT has a higher transconductance than the FET. + +Bipolar transistors can be made to conduct by exposure to light, because absorption of photons in the base region generates a photocurrent that acts as a base current; the collector current is approximately β times the photocurrent. Devices designed for this purpose have a transparent window in the package and are called phototransistors. + +Usage of MOSFETs and BJTs +The MOSFET is by far the most widely used transistor for both digital circuits as well as analog circuits,[81] accounting for 99.9% of all transistors in the world.[10] The bipolar junction transistor (BJT) was previously the most commonly used transistor during the 1950s to 1960s. Even after MOSFETs became widely available in the 1970s, the BJT remained the transistor of choice for many analog circuits such as amplifiers because of their greater linearity, up until MOSFET devices (such as power MOSFETs, LDMOS and RF CMOS) replaced them for most power electronic applications in the 1980s. In integrated circuits, the desirable properties of MOSFETs allowed them to capture nearly all market share for digital circuits in the 1970s. Discrete MOSFETs (typically power MOSFETs) can be applied in transistor applications, including analog circuits, voltage regulators, amplifiers, power transmitters and motor drivers. + +Other transistor types + +Transistor symbol created on Portuguese pavement in the University of Aveiro. +For early bipolar transistors, see Bipolar junction transistor § Bipolar transistors. +Field-effect transistor (FET): +Metal–oxide–semiconductor field-effect transistor (MOSFET), where the gate is insulated by a shallow layer of insulator +p-type MOS (PMOS) +n-type MOS (NMOS) +complementary MOS (CMOS) +RF CMOS, for power electronics +Multi-gate field-effect transistor (MuGFET) +Fin field-effect transistor (FinFET), source/drain region shapes fins on the silicon surface +Thin-film transistor, used in LCD and OLED displays +Floating-gate MOSFET (FGMOS), for non-volatile storage +Power MOSFET, for power electronics +lateral diffused MOS (LDMOS) +Carbon nanotube field-effect transistor (CNFET), where the channel material is replaced by a carbon nanotube +Junction gate field-effect transistor (JFET), where the gate is insulated by a reverse-biased p–n junction +Metal–semiconductor field-effect transistor (MESFET), similar to JFET with a Schottky junction instead of a p–n junction +High-electron-mobility transistor (HEMT) +Inverted-T field-effect transistor (ITFET) +Fast-reverse epitaxial diode field-effect transistor (FREDFET) +Organic field-effect transistor (OFET), in which the semiconductor is an organic compound +Ballistic transistor (disambiguation) +FETs used to sense environment +Ion-sensitive field-effect transistor (IFSET), to measure ion concentrations in solution, +Electrolyte–oxide–semiconductor field-effect transistor (EOSFET), neurochip, +Deoxyribonucleic acid field-effect transistor (DNAFET). +Bipolar junction transistor (BJT): +Heterojunction bipolar transistor, up to several hundred GHz, common in modern ultrafast and RF circuits +Schottky transistor +avalanche transistor +Darlington transistors are two BJTs connected together to provide a high current gain equal to the product of the current gains of the two transistors +Insulated-gate bipolar transistors (IGBTs) use a medium-power IGFET, similarly connected to a power BJT, to give a high input impedance. Power diodes are often connected between certain terminals depending on specific use. IGBTs are particularly suitable for heavy-duty industrial applications. The ASEA Brown Boveri (ABB) 5SNA2400E170100 ,[82] intended for three-phase power supplies, houses three n–p–n IGBTs in a case measuring 38 by 140 by 190 mm and weighing 1.5 kg. Each IGBT is rated at 1,700 volts and can handle 2,400 amperes +Phototransistor. +Emitter-switched bipolar transistor (ESBT) is a monolithic configuration of a high-voltage bipolar transistor and a low-voltage power MOSFET in cascode topology. It was introduced by STMicroelectronics in the 2000s,[83] and abandoned a few years later around 2012.[84] +Multiple-emitter transistor, used in transistor–transistor logic and integrated current mirrors +Multiple-base transistor, used to amplify very-low-level signals in noisy environments such as the pickup of a record player or radio front ends. Effectively, it is a very large number of transistors in parallel where, at the output, the signal is added constructively, but random noise is added only stochastically.[85] +Tunnel field-effect transistor, where it switches by modulating quantum tunnelling through a barrier. +Diffusion transistor, formed by diffusing dopants into semiconductor substrate; can be both BJT and FET. +Unijunction transistor, can be used as simple pulse generators. It comprise a main body of either P-type or N-type semiconductor with ohmic contacts at each end (terminals Base1 and Base2). A junction with the opposite semiconductor type is formed at a point along the length of the body for the third terminal (Emitter). +Single-electron transistors (SET), consist of a gate island between two tunneling junctions. The tunneling current is controlled by a voltage applied to the gate through a capacitor.[86] +Nanofluidic transistor, controls the movement of ions through sub-microscopic, water-filled channels.[87] +Multigate devices: +Tetrode transistor +Pentode transistor +Trigate transistor (prototype by Intel) +Dual-gate field-effect transistors have a single channel with two gates in cascode, a configuration optimized for high-frequency amplifiers, mixers, and oscillators. +Junctionless nanowire transistor (JNT), uses a simple nanowire of silicon surrounded by an electrically isolated "wedding ring" that acts to gate the flow of electrons through the wire. +Vacuum-channel transistor, when in 2012, NASA and the National Nanofab Center in South Korea were reported to have built a prototype vacuum-channel transistor in only 150 nanometers in size, can be manufactured cheaply using standard silicon semiconductor processing, can operate at high speeds even in hostile environments, and could consume just as much power as a standard transistor.[88] +Organic electrochemical transistor. +Solaristor (from solar cell transistor), a two-terminal gate-less self-powered phototransistor. +Part numbering standards/specifications +The types of some transistors can be parsed from the part number. There are three major semiconductor naming standards. In each, the alphanumeric prefix provides clues to type of the device. + +Japanese Industrial Standard (JIS) +JIS transistor prefix table +Prefix Type of transistor +2SA high-frequency p–n–p BJT +2SB audio-frequency p–n–p BJT +2SC high-frequency n–p–n BJT +2SD audio-frequency n–p–n BJT +2SJ P-channel FET (both JFET and MOSFET) +2SK N-channel FET (both JFET and MOSFET) +The JIS-C-7012 specification for transistor part numbers starts with "2S",[89] e.g. 2SD965, but sometimes the "2S" prefix is not marked on the package – a 2SD965 might only be marked "D965"; a 2SC1815 might be listed by a supplier as simply "C1815". This series sometimes has suffixes (such as "R", "O", "BL", standing for "red", "orange", "blue", etc.) to denote variants, such as tighter hFE (gain) groupings. + +European Electronic Component Manufacturers Association (EECA) +The Pro Electron standard, the European Electronic Component Manufacturers Association part numbering scheme, begins with two letters: the first gives the semiconductor type (A for germanium, B for silicon, and C for materials like GaAs); the second letter denotes the intended use (A for diode, C for general-purpose transistor, etc.). A 3-digit sequence number (or one letter then two digits, for industrial types) follows. With early devices this indicated the case type. Suffixes may be used, with a letter (e.g. "C" often means high hFE, such as in: BC549C[90]) or other codes may follow to show gain (e.g. BC327-25) or voltage rating (e.g. BUK854-800A[91]). The more common prefixes are: + +Pro Electron / EECA transistor prefix table +Prefix class Type and usage Example Equivalent Reference +AC Germanium small-signal AF transistor AC126 NTE102A Datasheet +AD Germanium AF power transistor AD133 NTE179 Datasheet +AF Germanium small-signal RF transistor AF117 NTE160 Datasheet +AL Germanium RF power transistor ALZ10 NTE100 Datasheet +AS Germanium switching transistor ASY28 NTE101 Datasheet +AU Germanium power switching transistor AU103 NTE127 Datasheet +BC Silicon, small-signal transistor ("general purpose") BC548 2N3904 Datasheet +BD Silicon, power transistor BD139 NTE375 Datasheet +BF Silicon, RF (high frequency) BJT or FET BF245 NTE133 Datasheet +BS Silicon, switching transistor (BJT or MOSFET) BS170 2N7000 Datasheet +BL Silicon, high frequency, high power (for transmitters) BLW60 NTE325 Datasheet +BU Silicon, high voltage (for CRT horizontal deflection circuits) BU2520A NTE2354 Datasheet +CF Gallium arsenide small-signal microwave transistor (MESFET) CF739 — Datasheet +CL Gallium arsenide microwave power transistor (FET) CLY10 — Datasheet +Joint Electron Device Engineering Council (JEDEC) +The JEDEC EIA370 transistor device numbers usually start with "2N", indicating a three-terminal device (dual-gate field-effect transistors are four-terminal devices, so begin with 3N), then a 2, 3 or 4-digit sequential number with no significance as to device properties (although early devices with low numbers tend to be germanium). For example, 2N3055 is a silicon n–p–n power transistor, 2N1301 is a p–n–p germanium switching transistor. A letter suffix (such as "A") is sometimes used to indicate a newer variant, but rarely gain groupings. + +Proprietary +Manufacturers of devices may have their own proprietary numbering system, for example CK722. Since devices are second-sourced, a manufacturer's prefix (like "MPF" in MPF102, which originally would denote a Motorola FET) now is an unreliable indicator of who made the device. Some proprietary naming schemes adopt parts of other naming schemes, for example a PN2222A is a (possibly Fairchild Semiconductor) 2N2222A in a plastic case (but a PN108 is a plastic version of a BC108, not a 2N108, while the PN100 is unrelated to other xx100 devices). + +Military part numbers sometimes are assigned their own codes, such as the British Military CV Naming System. + +Manufacturers buying large numbers of similar parts may have them supplied with "house numbers", identifying a particular purchasing specification and not necessarily a device with a standardized registered number. For example, an HP part 1854,0053 is a (JEDEC) 2N2218 transistor[92][93] which is also assigned the CV number: CV7763[94] + +Naming problems +With so many independent naming schemes, and the abbreviation of part numbers when printed on the devices, ambiguity sometimes occurs. For example, two different devices may be marked "J176" (one the J176 low-power JFET, the other the higher-powered MOSFET 2SJ176). + +As older "through-hole" transistors are given surface-mount packaged counterparts, they tend to be assigned many different part numbers because manufacturers have their own systems to cope with the variety in pinout arrangements and options for dual or matched n–p–n + p–n–p devices in one pack. So even when the original device (such as a 2N3904) may have been assigned by a standards authority, and well known by engineers over the years, the new versions are far from standardized in their naming. + +Construction +Semiconductor material +Semiconductor material characteristics +Semiconductor +material Junction forward +voltage +V @ 25 °C Electron mobility +m2/(V·s) @ 25 °C Hole mobility +m2/(V·s) @ 25 °C Max. +junction temp. +°C +Ge 0.27 0.39 0.19 70 to 100 +Si 0.71 0.14 0.05 150 to 200 +GaAs 1.03 0.85 0.05 150 to 200 +Al-Si junction 0.3 — — 150 to 200 +The first BJTs were made from germanium (Ge). Silicon (Si) types currently predominate but certain advanced microwave and high-performance versions now employ the compound semiconductor material gallium arsenide (GaAs) and the semiconductor alloy silicon germanium (SiGe). Single element semiconductor material (Ge and Si) is described as elemental. + +Rough parameters for the most common semiconductor materials used to make transistors are given in the adjacent table. These parameters will vary with increase in temperature, electric field, impurity level, strain, and sundry other factors. + +The junction forward voltage is the voltage applied to the emitter–base junction of a BJT in order to make the base conduct a specified current. The current increases exponentially as the junction forward voltage is increased. The values given in the table are typical for a current of 1 mA (the same values apply to semiconductor diodes). The lower the junction forward voltage the better, as this means that less power is required to "drive" the transistor. The junction forward voltage for a given current decreases with increase in temperature. For a typical silicon junction the change is −2.1 mV/°C.[95] In some circuits special compensating elements (sensistors) must be used to compensate for such changes. + +The density of mobile carriers in the channel of a MOSFET is a function of the electric field forming the channel and of various other phenomena such as the impurity level in the channel. Some impurities, called dopants, are introduced deliberately in making a MOSFET, to control the MOSFET electrical behavior. + +The electron mobility and hole mobility columns show the average speed that electrons and holes diffuse through the semiconductor material with an electric field of 1 volt per meter applied across the material. In general, the higher the electron mobility the faster the transistor can operate. The table indicates that Ge is a better material than Si in this respect. However, Ge has four major shortcomings compared to silicon and gallium arsenide: + +Its maximum temperature is limited. +It has relatively high leakage current. +It cannot withstand high voltages. +It is less suitable for fabricating integrated circuits. +Because the electron mobility is higher than the hole mobility for all semiconductor materials, a given bipolar n–p–n transistor tends to be swifter than an equivalent p–n–p transistor. GaAs has the highest electron mobility of the three semiconductors. It is for this reason that GaAs is used in high-frequency applications. A relatively recent[when?] FET development, the high-electron-mobility transistor (HEMT), has a heterostructure (junction between different semiconductor materials) of aluminium gallium arsenide (AlGaAs)-gallium arsenide (GaAs) which has twice the electron mobility of a GaAs-metal barrier junction. Because of their high speed and low noise, HEMTs are used in satellite receivers working at frequencies around 12 GHz. HEMTs based on gallium nitride and aluminium gallium nitride (AlGaN/GaN HEMTs) provide a still higher electron mobility and are being developed for various applications. + +'Max. junction temperature' values represent a cross section taken from various manufacturers' data sheets. This temperature should not be exceeded or the transistor may be damaged. + +'Al–Si junction' refers to the high-speed (aluminum–silicon) metal–semiconductor barrier diode, commonly known as a Schottky diode. This is included in the table because some silicon power IGFETs have a parasitic reverse Schottky diode formed between the source and drain as part of the fabrication process. This diode can be a nuisance, but sometimes it is used in the circuit. + +Packaging +See also: Semiconductor package and Chip carrier + +Assorted discrete transistors + +Soviet KT315b transistors +Discrete transistors can be individually packaged transistors or unpackaged transistor chips (dice). + +Transistors come in many different semiconductor packages (see image). The two main categories are through-hole (or leaded), and surface-mount, also known as surface-mount device (SMD). The ball grid array (BGA) is the latest surface-mount package (currently only for large integrated circuits). It has solder "balls" on the underside in place of leads. Because they are smaller and have shorter interconnections, SMDs have better high-frequency characteristics but lower power rating. + +Transistor packages are made of glass, metal, ceramic, or plastic. The package often dictates the power rating and frequency characteristics. Power transistors have larger packages that can be clamped to heat sinks for enhanced cooling. Additionally, most power transistors have the collector or drain physically connected to the metal enclosure. At the other extreme, some surface-mount microwave transistors are as small as grains of sand. + +Often a given transistor type is available in several packages. Transistor packages are mainly standardized, but the assignment of a transistor's functions to the terminals is not: other transistor types can assign other functions to the package's terminals. Even for the same transistor type the terminal assignment can vary (normally indicated by a suffix letter to the part number, q.e. BC212L and BC212K). + +Nowadays most transistors come in a wide range of SMT packages, in comparison the list of available through-hole packages is relatively small, here is a short list of the most common through-hole transistors packages in alphabetical order: ATV, E-line, MRT, HRT, SC-43, SC-72, TO-3, TO-18, TO-39, TO-92, TO-126, TO220, TO247, TO251, TO262, ZTX851. + +Unpackaged transistor chips (die) may be assembled into hybrid devices.[96] The IBM SLT module of the 1960s is one example of such a hybrid circuit module using glass passivated transistor (and diode) die. Other packaging techniques for discrete transistors as chips include Direct Chip Attach (DCA) and Chip On Board (COB).[96] + +Flexible transistors +Researchers have made several kinds of flexible transistors, including organic field-effect transistors.[97][98][99] Flexible transistors are useful in some kinds of flexible displays and other flexible electronics. diff --git a/examples/article7.txt b/examples/article7.txt new file mode 100644 index 0000000..10adfd9 --- /dev/null +++ b/examples/article7.txt @@ -0,0 +1,78 @@ +Tomography is imaging by sections or sectioning through the use of any kind of penetrating wave. The method is used in radiology, archaeology, biology, atmospheric science, geophysics, oceanography, plasma physics, materials science, astrophysics, quantum information, and other areas of science. The word tomography is derived from Ancient Greek τόμος tomos, "slice, section" and γράφω graphō, "to write" or, in this context as well, " to describe." A device used in tomography is called a tomograph, while the image produced is a tomogram. + +In many cases, the production of these images is based on the mathematical procedure tomographic reconstruction, such as X-ray computed tomography technically being produced from multiple projectional radiographs. Many different reconstruction algorithms exist. Most algorithms fall into one of two categories: filtered back projection (FBP) and iterative reconstruction (IR). These procedures give inexact results: they represent a compromise between accuracy and computation time required. FBP demands fewer computational resources, while IR generally produces fewer artifacts (errors in the reconstruction) at a higher computing cost.[1] + +Although MRI and ultrasound are transmission methods, they typically do not require movement of the transmitter to acquire data from different directions. In MRI, both projections and higher spatial harmonics are sampled by applying spatially-varying magnetic fields; no moving parts are necessary to generate an image. On the other hand, since ultrasound uses time-of-flight to spatially encode the received signal, it is not strictly a tomographic method and does not require multiple acquisitions at all. + + +Contents +1 Types of tomography +1.1 Synchrotron X-ray tomographic microscopy +2 Volume rendering +3 History +4 See also +5 References +6 External links +Types of tomography +Name Source of data Abbreviation Year of introduction +Aerial tomography Electromagnetic radiation AT 2020 +Atom probe tomography Atom probe APT +Computed tomography imaging spectrometer[2] Visible light spectral imaging CTIS +Computed tomography of chemiluminescence[3][4][5] Chemiluminescence Flames CTC 2009 +Confocal microscopy (Laser scanning confocal microscopy) Laser scanning confocal microscopy LSCM +Cryogenic electron tomography Cryogenic transmission electron microscopy CryoET +Electrical capacitance tomography Electrical capacitance ECT 1988[6] +Electrical capacitance volume tomography Electrical capacitance ECVT +Electrical resistivity tomography Electrical resistivity ERT +Electrical impedance tomography Electrical impedance EIT 1984 +Electron tomography Transmission electron microscopy ET 1968[7][8] +Focal plane tomography X-ray 1930s +Functional magnetic resonance imaging Magnetic resonance fMRI 1992 +Hydraulic tomography fluid flow HT 2000 +Infrared microtomographic imaging[9] Mid-infrared 2013 +Laser Ablation Tomography Laser Ablation & Fluorescent Microscopy LAT 2013 +Magnetic induction tomography Magnetic induction MIT +Magnetic particle imaging Superparamagnetism MPI 2005 +Magnetic resonance imaging or nuclear magnetic resonance tomography Nuclear magnetic moment MRI or MRT +Muon tomography Muon +Microwave tomography[10] Microwave (1-10 GHz electromagnetic radiation) +Neutron tomography Neutron +Ocean acoustic tomography Sonar OAT +Optical coherence tomography Interferometry OCT +Optical diffusion tomography Absorption of light ODT +Optical projection tomography Optical microscope OPT +Photoacoustic imaging in biomedicine Photoacoustic spectroscopy PAT +Positron emission tomography Positron emission PET +Positron emission tomography - computed tomography Positron emission & X-ray PET-CT +Quantum tomography Quantum state QST +Single photon emission computed tomography Gamma ray SPECT +Seismic tomography Seismic waves +Terahertz tomography Terahertz radiation THz-CT +Thermoacoustic imaging Photoacoustic spectroscopy TAT +Ultrasound-modulated optical tomography Ultrasound UOT +Ultrasound computer tomography Ultrasound USCT +Ultrasound transmission tomography Ultrasound +X-ray computed tomography X-ray CT, CATScan 1971 +X-ray microtomography X-ray microCT +Zeeman-Doppler imaging Zeeman effect +Some recent advances rely on using simultaneously integrated physical phenomena, e.g. X-rays for both CT and angiography, combined CT/MRI and combined CT/PET. + +Discrete tomography and Geometric tomography, on the other hand, are research areas[citation needed] that deal with the reconstruction of objects that are discrete (such as crystals) or homogeneous. They are concerned with reconstruction methods, and as such they are not restricted to any of the particular (experimental) tomography methods listed above. + +Synchrotron X-ray tomographic microscopy +A new technique called synchrotron X-ray tomographic microscopy (SRXTM) allows for detailed three-dimensional scanning of fossils.[11] + +The construction of third-generation synchrotron sources combined with the tremendous improvement of detector technology, data storage and processing capabilities since the 1990s has led to a boost of high-end synchrotron tomography in materials research with a wide range of different applications, e.g. the visualization and quantitative analysis of differently absorbing phases, microporosities, cracks, precipitates or grains in a specimen. Synchrotron radiation is created by accelerating free particles in high vacuum. By the laws of electrodynamics this acceleration leads to the emission of electromagnetic radiation (Jackson, 1975). Linear particle acceleration is one possibility, but apart from the very high electric fields one would need it is more practical to hold the charged particles on a closed trajectory in order to obtain a source of continuous radiation. Magnetic fields are used to force the particles onto the desired orbit and prevent them from flying in a straight line. The radial acceleration associated with the change of direction then generates radiation.[12] + +Volume rendering +Main article: Volume rendering + +Multiple X-ray computed tomographs (with quantitative mineral density calibration) stacked to form a 3D model. +Volume rendering is a set of techniques used to display a 2D projection of a 3D discretely sampled data set, typically a 3D scalar field. A typical 3D data set is a group of 2D slice images acquired, for example, by a CT, MRI, or MicroCT scanner. These are usually acquired in a regular pattern (e.g., one slice every millimeter) and usually have a regular number of image pixels in a regular pattern. This is an example of a regular volumetric grid, with each volume element, or voxel represented by a single value that is obtained by sampling the immediate area surrounding the voxel. + +To render a 2D projection of the 3D data set, one first needs to define a camera in space relative to the volume. Also, one needs to define the opacity and color of every voxel. This is usually defined using an RGBA (for red, green, blue, alpha) transfer function that defines the RGBA value for every possible voxel value. + +For example, a volume may be viewed by extracting isosurfaces (surfaces of equal values) from the volume and rendering them as polygonal meshes or by rendering the volume directly as a block of data. The marching cubes algorithm is a common technique for extracting an isosurface from volume data. Direct volume rendering is a computationally intensive task that may be performed in several ways. + +History +Focal plane tomography was developed in the 1930s by the radiologist Alessandro Vallebona, and proved useful in reducing the problem of superimposition of structures in projectional radiography. In a 1953 article in the medical journal Chest, B. Pollak of the Fort William Sanatorium described the use of planography, another term for tomography.[13] Focal plane tomography remained the conventional form of tomography until being largely replaced by mainly computed tomography the late-1970s.[14] Focal plane tomography uses the fact that the focal plane appears sharper, while structures in other planes appear blurred. By moving an X-ray source and the film in opposite directions during the exposure, and modifying the direction and extent of the movement, operators can select different focal planes which contain the structures of interest. diff --git a/test.py b/test.py new file mode 100644 index 0000000..b7cb47d --- /dev/null +++ b/test.py @@ -0,0 +1,81 @@ +import io +import sys +import importlib.util + +def test(fun,x,y): + global pass_tests, fail_tests + if type(x) == tuple: + z = fun(*x) + else: + z = fun(x) + if y == z: + pass_tests = pass_tests + 1 + else: + if type(x) == tuple: + s = repr(x) + else: + s = "("+repr(x)+")" + print("Condition failed:") + print(" "+fun.__name__+s+" == "+repr(y)) + print(fun.__name__+" returned/printed:") + print(str(z)) + fail_tests = fail_tests + 1 + +def run(src_path=None): + global pass_tests, fail_tests + + if src_path == None: + import wordfreq + else: + spec = importlib.util.spec_from_file_location("wordfreq", src_path+"/wordfreq.py") + wordfreq = importlib.util.module_from_spec(spec) + spec.loader.exec_module(wordfreq) + + pass_tests = 0 + fail_tests = 0 + fun_count = 0 + + def printTopMost(freq,n): + saved = sys.stdout + sys.stdout = io.StringIO() + wordfreq.printTopMost(freq,n) + out = sys.stdout.getvalue() + sys.stdout = saved + return out + + if hasattr(wordfreq, "tokenize"): + fun_count = fun_count + 1 + test(wordfreq.tokenize, [], []) + test(wordfreq.tokenize, [""], []) + test(wordfreq.tokenize, [" "], []) + test(wordfreq.tokenize, ["This is a simple sentence"], ["this","is","a","simple","sentence"]) + test(wordfreq.tokenize, ["I told you!"], ["i","told","you","!"]) + test(wordfreq.tokenize, ["The 10 little chicks"], ["the","10","little","chicks"]) + test(wordfreq.tokenize, ["15th anniversary"], ["15","th","anniversary"]) + test(wordfreq.tokenize, ["He is in the room, she said."], ["he","is","in","the","room",",","she","said","."]) + else: + print("tokenize is not implemented yet!") + + if hasattr(wordfreq, "countWords"): + fun_count = fun_count + 1 + test(wordfreq.countWords, ([],[]), {}) + test(wordfreq.countWords, (["clean","water"],[]), {"clean":1,"water":1}) + test(wordfreq.countWords, (["clean","water","is","drinkable","water"],[]), {"clean":1,"water":2,"is":1,"drinkable":1}) + test(wordfreq.countWords, (["clean","water","is","drinkable","water"],["is"]), {"clean":1,"water":2,"drinkable":1}) + else: + print("countWords is not implemented yet!") + + if hasattr(wordfreq, "printTopMost"): + fun_count = fun_count + 1 + test(printTopMost,({},10),"") + test(printTopMost,({"horror": 5, "happiness": 15},0),"") + test(printTopMost,({"C": 3, "python": 5, "haskell": 2, "java": 1},3),"python 5\nC 3\nhaskell 2\n") + else: + print("printTopMost is not implemented yet!") + + print(str(pass_tests)+" out of "+str(pass_tests+fail_tests)+" passed.") + + return (fun_count == 3 and fail_tests == 0) + +if __name__ == "__main__": + run() diff --git a/tokenize.py b/tokenize.py new file mode 100644 index 0000000..e69de29