document_title: Wave–particle duality

question_text: who proposed that electrons behave like waves and particles

root

text: Wave–particle duality

text: Brief history of wave and particle viewpoints[edit]

text: Democritus—the original atomist—argued that all things in the universe, including light, are composed of indivisible sub-components (light being some form of solar atom).[8] At the beginning of the 11th Century, the Arabic scientist Alhazen wrote the first comprehensive treatise on optics; describing refraction, reflection, and the operation of a pinhole lens via rays of light traveling from the point of emission to the eye. He asserted that these rays were composed of particles of light. In 1630, René Descartes popularized and accredited the opposing wave description in his treatise on light, showing that the behavior of light could be re-created by modeling wave-like disturbances in a universal medium ("plenum"). Beginning in 1670 and progressing over three decades, Isaac Newton developed and championed his corpuscular hypothesis, arguing that the perfectly straight lines of reflection demonstrated light's particle nature; only particles could travel in such straight lines. He explained refraction by positing that particles of light accelerated laterally upon entering a denser medium. Around the same time, Newton's contemporaries Robert Hooke and Christiaan Huygens—and later Augustin-Jean Fresnel—mathematically refined the wave viewpoint, showing that if light traveled at different speeds in different media (such as water and air), refraction could be easily explained as the medium-dependent propagation of light waves. The resulting Huygens–Fresnel principle was extremely successful at reproducing light's behavior and was subsequently supported by Thomas Young's 1801 discovery of double-slit interference.[9][10] The wave view did not immediately displace the ray and particle view, but began to dominate scientific thinking about light in the mid 19th century, since it could explain polarization phenomena that the alternatives could not.[11]

tag: p

text: James Clerk Maxwell discovered that he could apply his equations for electromagnetism, which had been previously discovered, along with a slight modification to describe self-propagating waves of oscillating electric and magnetic fields. It quickly became apparent that visible light, ultraviolet light, and infrared light (phenomena thought previously to be unrelated) were all electromagnetic waves of differing frequency. The wave theory had prevailed—or at least it seemed to.

text: While the 19th century had seen the success of the wave theory at describing light, it had also witnessed the rise of the atomic theory at describing matter. Antoine Lavoisier deduced the law of conservation of mass and categorized many new chemical elements and compounds; and Joseph Louis Proust advanced chemistry towards the atom by showing that elements combined in definite proportions. This led John Dalton to propose that elements were invisible sub components; Amedeo Avogadro discovered diatomic gases and completed the basic atomic theory, allowing the correct molecular formulae of most known compounds—as well as the correct weights of atoms—to be deduced and categorized in a consistent manner. Dimitri Mendeleev saw an order in recurring chemical properties, and created a table presenting the elements in unprecedented order and symmetry.

text: Turn of the 20th century and the paradigm shift[edit]

text: Particles of electricity[edit]

text: At the close of the 19th century, the reductionism of atomic theory began to advance into the atom itself; determining, through physics, the nature of the atom and the operation of chemical reactions. Electricity, first thought to be a fluid, was now understood to consist of particles called electrons. This was first demonstrated by J. J. Thomson in 1897 when, using a cathode ray tube, he found that an electrical charge would travel across a vacuum (which would possess infinite resistance in classical theory). Since the vacuum offered no medium for an electric fluid to travel, this discovery could only be explained via a particle carrying a negative charge and moving through the vacuum. This electron flew in the face of classical electrodynamics, which had successfully treated electricity as a fluid for many years (leading to the invention of batteries, electric motors, dynamos, and arc lamps). More importantly, the intimate relation between electric charge and electromagnetism had been well documented following the discoveries of Michael Faraday and James Clerk Maxwell. Since electromagnetism was known to be a wave generated by a changing electric or magnetic field (a continuous, wave-like entity itself) an atomic/particle description of electricity and charge was a non sequitur. Furthermore, classical electrodynamics was not the only classical theory rendered incomplete.

text: Radiation quantization[edit]

text: In 1901, Max Planck published an analysis that succeeded in reproducing the observed spectrum of light emitted by a glowing object. To accomplish this, Planck had to make an ad hoc mathematical assumption of quantized energy of the oscillators (atoms of the black body) that emit radiation. Einstein later proposed that electromagnetic radiation itself is quantized, not the energy of radiating atoms.

text: Black-body radiation, the emission of electromagnetic energy due to an object's heat, could not be explained from classical arguments alone. The equipartition theorem of classical mechanics, the basis of all classical thermodynamic theories, stated that an object's energy is partitioned equally among the object's vibrational modes. But applying the same reasoning to the electromagnetic emission of such a thermal object was not so successful. That thermal objects emit light had been long known. Since light was known to be waves of electromagnetism, physicists hoped to describe this emission via classical laws. This became known as the black body problem. Since the equipartition theorem worked so well in describing the vibrational modes of the thermal object itself, it was natural to assume that it would perform equally well in describing the radiative emission of such objects. But a problem quickly arose: if each mode received an equal partition of energy, the short wavelength modes would consume all the energy. This became clear when plotting the Rayleigh–Jeans law which, while correctly predicting the intensity of long wavelength emissions, predicted infinite total energy as the intensity diverges to infinity for short wavelengths. This became known as the ultraviolet catastrophe.

text: In 1900, Max Planck hypothesized that the frequency of light emitted by the black body depended on the frequency of the oscillator that emitted it, and the energy of these oscillators increased linearly with frequency (according to his constant h, where E = hν). This was not an unsound proposal considering that macroscopic oscillators operate similarly: when studying five simple harmonic oscillators of equal amplitude but different frequency, the oscillator with the highest frequency possesses the highest energy (though this relationship is not linear like Planck's). By demanding that high-frequency light must be emitted by an oscillator of equal frequency, and further requiring that this oscillator occupy higher energy than one of a lesser frequency, Planck avoided any catastrophe; giving an equal partition to high-frequency oscillators produced successively fewer oscillators and less emitted light. And as in the Maxwell–Boltzmann distribution, the low-frequency, low-energy oscillators were suppressed by the onslaught of thermal jiggling from higher energy oscillators, which necessarily increased their energy and frequency.

text: The most revolutionary aspect of Planck's treatment of the black body is that it inherently relies on an integer number of oscillators in thermal equilibrium with the electromagnetic field. These oscillators give their entire energy to the electromagnetic field, creating a quantum of light, as often as they are excited by the electromagnetic field, absorbing a quantum of light and beginning to oscillate at the corresponding frequency. Planck had intentionally created an atomic theory of the black body, but had unintentionally generated an atomic theory of light, where the black body never generates quanta of light at a given frequency with an energy less than hν. However, once realizing that he had quantized the electromagnetic field, he denounced particles of light as a limitation of his approximation, not a property of reality.

text: Photoelectric effect illuminated[edit]

text: While Planck had solved the ultraviolet catastrophe by using atoms and a quantized electromagnetic field, most contemporary physicists agreed that Planck's "light quanta" represented only flaws in his model. A more-complete derivation of black body radiation would yield a fully continuous and 'wave-like' electromagnetic field with no quantization. However, in 1905 Albert Einstein took Planck's black body model to produce his solution to another outstanding problem of the day: the photoelectric effect, wherein electrons are emitted from atoms when they absorb energy from light. Since their existence was theorized eight years previously, phenomenon had been studied with the electron model in mind in physics laboratories worldwide.

text: In 1902 Philipp Lenard discovered that the energy of these ejected electrons did not depend on the intensity of the incoming light, but instead on its frequency. So if one shines a little low-frequency light upon a metal, a few low energy electrons are ejected. If one now shines a very intense beam of low-frequency light upon the same metal, a whole slew of electrons are ejected; however they possess the same low energy, there are merely more of them. The more light there is, the more electrons are ejected. Whereas in order to get high energy electrons, one must illuminate the metal with high-frequency light. Like blackbody radiation, this was at odds with a theory invoking continuous transfer of energy between radiation and matter. However, it can still be explained using a fully classical description of light, as long as matter is quantum mechanical in nature.[12]

text: If one used Planck's energy quanta, and demanded that electromagnetic radiation at a given frequency could only transfer energy to matter in integer multiples of an energy quantum hν, then the photoelectric effect could be explained very simply. Low-frequency light only ejects low-energy electrons because each electron is excited by the absorption of a single photon. Increasing the intensity of the low-frequency light (increasing the number of photons) only increases the number of excited electrons, not their energy, because the energy of each photon remains low. Only by increasing the frequency of the light, and thus increasing the energy of the photons, can one eject electrons with higher energy. Thus, using Planck's constant h to determine the energy of the photons based upon their frequency, the energy of ejected electrons should also increase linearly with frequency; the gradient of the line being Planck's constant. These results were not confirmed until 1915, when Robert Andrews Millikan, who had previously determined the charge of the electron, produced experimental results in perfect accord with Einstein's predictions. While the energy of ejected electrons reflected Planck's constant, the existence of photons was not explicitly proven until the discovery of the photon antibunching effect, of which a modern experiment can be performed in undergraduate-level labs.[13] This phenomenon could only be explained via photons, and not through any semi-classical theory (which could alternatively explain the photoelectric effect). When Einstein received his Nobel Prize in 1921, it was not for his more difficult and mathematically laborious special and general relativity, but for the simple, yet totally revolutionary, suggestion of quantized light. Einstein's "light quanta" would not be called photons until 1925, but even in 1905 they represented the quintessential example of wave-particle duality. Electromagnetic radiation propagates following linear wave equations, but can only be emitted or absorbed as discrete elements, thus acting as a wave and a particle simultaneously.

text: Einstein's explanation of the photoelectric effect[edit]

text: In 1905, Albert Einstein provided an explanation of the photoelectric effect, a hitherto troubling experiment that the wave theory of light seemed incapable of explaining. He did so by postulating the existence of photons, quanta of light energy with particulate qualities.

text: In the photoelectric effect, it was observed that shining a light on certain metals would lead to an electric current in a circuit. Presumably, the light was knocking electrons out of the metal, causing current to flow. However, using the case of potassium as an example, it was also observed that while a dim blue light was enough to cause a current, even the strongest, brightest red light available with the technology of the time caused no current at all. According to the classical theory of light and matter, the strength or amplitude of a light wave was in proportion to its brightness: a bright light should have been easily strong enough to create a large current. Yet, oddly, this was not so.

text: Einstein explained this enigma by postulating that the electrons can receive energy from electromagnetic field only in discrete portions (quanta that were called photons): an amount of energy E that was related to the frequency f of the light by

text: where h is Planck's constant (6.626 × 10−34 J seconds). Only photons of a high enough frequency (above a certain threshold value) could knock an electron free. For example, photons of blue light had sufficient energy to free an electron from the metal, but photons of red light did not. One photon of light above the threshold frequency could release only one electron; the higher the frequency of a photon, the higher the kinetic energy of the emitted electron, but no amount of light (using technology available at the time) below the threshold frequency could release an electron. To "violate" this law would require extremely high-intensity lasers which had not yet been invented. Intensity-dependent phenomena have now been studied in detail with such lasers.[14]

text: Einstein was awarded the Nobel Prize in Physics in 1921 for his discovery of the law of the photoelectric effect.

text: De Broglie's wavelength[edit]

text: In 1924, Louis-Victor de Broglie formulated the de Broglie hypothesis, claiming that all matter,[15][16] not just light, has a wave-like nature; he related wavelength (denoted as λ), and momentum (denoted as p):

text:
This is a generalization of Einstein's equation above, since the momentum of a photon is given by p =

E
c

{\displaystyle {\tfrac {E}{c}}}

 and the wavelength (in a vacuum) by λ =

c
f

{\displaystyle {\tfrac {c}{f}}}

, where c is the speed of light in vacuum.

text: De Broglie's formula was confirmed three years later for electrons (which differ from photons in having a rest mass) with the observation of electron diffraction in two independent experiments. At the University of Aberdeen, George Paget Thomson passed a beam of electrons through a thin metal film and observed the predicted interference patterns. At Bell Labs, Clinton Joseph Davisson and Lester Halbert Germer guided their beam through a crystalline grid.

text: De Broglie was awarded the Nobel Prize for Physics in 1929 for his hypothesis. Thomson and Davisson shared the Nobel Prize for Physics in 1937 for their experimental work.

text: Heisenberg's uncertainty principle[edit]

text: In his work on formulating quantum mechanics, Werner Heisenberg postulated his uncertainty principle, which states:

text: where

text: Heisenberg originally explained this as a consequence of the process of measuring: Measuring position accurately would disturb momentum and vice versa, offering an example (the "gamma-ray microscope") that depended crucially on the de Broglie hypothesis. The thought is now, however, that this only partly explains the phenomenon, but that the uncertainty also exists in the particle itself, even before the measurement is made.

text: In fact, the modern explanation of the uncertainty principle, extending the Copenhagen interpretation first put forward by Bohr and Heisenberg, depends even more centrally on the wave nature of a particle: Just as it is nonsensical to discuss the precise location of a wave on a string, particles do not have perfectly precise positions; likewise, just as it is nonsensical to discuss the wavelength of a "pulse" wave traveling down a string, particles do not have perfectly precise momenta (which corresponds to the inverse of wavelength). Moreover, when position is relatively well defined, the wave is pulse-like and has a very ill-defined wavelength (and thus momentum). And conversely, when momentum (and thus wavelength) is relatively well defined, the wave looks long and sinusoidal, and therefore it has a very ill-defined position.

text: de Broglie–Bohm theory[edit]

text: De Broglie himself had proposed a pilot wave construct to explain the observed wave-particle duality. In this view, each particle has a well-defined position and momentum, but is guided by a wave function derived from Schrödinger's equation. The pilot wave theory was initially rejected because it generated non-local effects when applied to systems involving more than one particle. Non-locality, however, soon became established as an integral feature of quantum theory (see EPR paradox), and David Bohm extended de Broglie's model to explicitly include it.

text: In the resulting representation, also called the de Broglie–Bohm theory or Bohmian mechanics,[18] the wave-particle duality vanishes, and explains the wave behaviour as a scattering with wave appearance, because the particle's motion is subject to a guiding equation or quantum potential. "This idea seems to me so natural and simple, to resolve the wave-particle dilemma in such a clear and ordinary way, that it is a great mystery to me that it was so generally ignored",[19] J.S.Bell.

text: The best illustration of the pilot-wave model was given by Couder's 2010 "walking droplets" experiments,[20] demonstrating the pilot-wave behaviour in a macroscopic mechanical analog.[17]

text: Wave behavior of large objects[edit]

text: Since the demonstrations of wave-like properties in photons and electrons, similar experiments have been conducted with neutrons and protons. Among the most famous experiments are those of Estermann and Otto Stern in 1929.[21] Authors of similar recent experiments with atoms and molecules, described below, claim that these larger particles also act like waves.

text: A dramatic series of experiments emphasizing the action of gravity in relation to wave–particle duality was conducted in the 1970s using the neutron interferometer.[22] Neutrons, one of the components of the atomic nucleus, provide much of the mass of a nucleus and thus of ordinary matter. In the neutron interferometer, they act as quantum-mechanical waves directly subject to the force of gravity. While the results were not surprising since gravity was known to act on everything, including light (see tests of general relativity and the Pound–Rebka falling photon experiment), the self-interference of the quantum mechanical wave of a massive fermion in a gravitational field had never been experimentally confirmed before.

text: In 1999, the diffraction of C60 fullerenes by researchers from the University of Vienna was reported.[23] Fullerenes are comparatively large and massive objects, having an atomic mass of about 720 u. The de Broglie wavelength of the incident beam was about 2.5 pm, whereas the diameter of the molecule is about 1 nm, about 400 times larger. In 2012, these far-field diffraction experiments could be extended to phthalocyanine molecules and their heavier derivatives, which are composed of 58 and 114 atoms respectively. In these experiments the build-up of such interference patterns could be recorded in real time and with single molecule sensitivity.[24][25]

text: In 2003, the Vienna group also demonstrated the wave nature of tetraphenylporphyrin[26]—a flat biodye with an extension of about 2 nm and a mass of 614 u. For this demonstration they employed a near-field Talbot Lau interferometer.[27][28] In the same interferometer they also found interference fringes for C60F48., a fluorinated buckyball with a mass of about 1600 u, composed of 108 atoms.[26] Large molecules are already so complex that they give experimental access to some aspects of the quantum-classical interface, i.e., to certain decoherence mechanisms.[29][30] In 2011, the interference of molecules as heavy as 6910 u could be demonstrated in a Kapitza–Dirac–Talbot–Lau interferometer.[31] In 2013, the interference of molecules beyond 10,000 u has been demonstrated.[32]

text: Whether objects heavier than the Planck mass (about the weight of a large bacterium) have a de Broglie wavelength is theoretically unclear and experimentally unreachable; above the Planck mass a particle's Compton wavelength would be smaller than the Planck length and its own Schwarzschild radius, a scale at which current theories of physics may break down or need to be replaced by more general ones.[33]

text: Recently Couder, Fort, et al. showed[34] that we can use macroscopic oil droplets on a vibrating surface as a model of wave–particle duality—localized droplet creates periodical waves around and interaction with them leads to quantum-like phenomena: interference in double-slit experiment,[35] unpredictable tunneling[36] (depending in complicated way on practically hidden state of field), orbit quantization[37] (that particle has to 'find a resonance' with field perturbations it creates—after one orbit, its internal phase has to return to the initial state) and Zeeman effect.[38]

text: Treatment in modern quantum mechanics[edit]

text: Wave–particle duality is deeply embedded into the foundations of quantum mechanics. In the formalism of the theory, all the information about a particle is encoded in its wave function, a complex-valued function roughly analogous to the amplitude of a wave at each point in space. This function evolves according to a differential equation (generically called the Schrödinger equation). For particles with mass this equation has solutions that follow the form of the wave equation. Propagation of such waves leads to wave-like phenomena such as interference and diffraction. Particles without mass, like photons, have no solutions of the Schrödinger equation so have another wave.

text: The particle-like behavior is most evident due to phenomena associated with measurement in quantum mechanics. Upon measuring the location of the particle, the particle will be forced into a more localized state as given by the uncertainty principle. When viewed through this formalism, the measurement of the wave function will randomly "collapse", or rather "decohere", to a sharply peaked function at some location. For particles with mass the likelihood of detecting the particle at any particular location is equal to the squared amplitude of the wave function there. The measurement will return a well-defined position, (subject to uncertainty), a property traditionally associated with particles. It is important to note that a measurement is only a particular type of interaction where some data is recorded and the measured quantity is forced into a particular eigenstate. The act of measurement is therefore not fundamentally different from any other interaction.

text: Following the development of quantum field theory the ambiguity disappeared. The field permits solutions that follow the wave equation, which are referred to as the wave functions. The term particle is used to label the irreducible representations of the Lorentz group that are permitted by the field. An interaction as in a Feynman diagram is accepted as a calculationally convenient approximation where the outgoing legs are known to be simplifications of the propagation and the internal lines are for some order in an expansion of the field interaction. Since the field is non-local and quantized, the phenomena which previously were thought of as paradoxes are explained. Within the limits of the wave-particle duality the quantum field theory gives the same results.

text: Visualization[edit]

text: There are two ways to visualize the wave-particle behaviour: by the "standard model", described below; and by the Broglie–Bohm model, where no duality is perceived.

text: Below is an illustration of wave–particle duality as it relates to De Broglie's hypothesis and Heisenberg's uncertainty principle (above), in terms of the position and momentum space wavefunctions for one spinless particle with mass in one dimension. These wavefunctions are Fourier transforms of each other.

text: The more localized the position-space wavefunction, the more likely the particle is to be found with the position coordinates in that region, and correspondingly the momentum-space wavefunction is less localized so the possible momentum components the particle could have are more widespread.

text: Conversely the more localized the momentum-space wavefunction, the more likely the particle is to be found with those values of momentum components in that region, and correspondingly the less localized the position-space wavefunction, so the position coordinates the particle could occupy are more widespread.

text: Alternative views[edit]

text: Wave–particle duality is an ongoing conundrum in modern physics. Most physicists accept wave-particle duality as the best explanation for a broad range of observed phenomena; however, it is not without controversy. Alternative views are also presented here. These views are not generally accepted by mainstream physics, but serve as a basis for valuable discussion within the community.

text: Both-particle-and-wave view[edit]

text: The pilot wave model, originally developed by Louis de Broglie and further developed by David Bohm into the hidden variable theory proposes that there is no duality, but rather a system exhibits both particle properties and wave properties simultaneously, and particles are guided, in a deterministic fashion, by the pilot wave (or its "quantum potential") which will direct them to areas of constructive interference in preference to areas of destructive interference. This idea is held by a significant minority within the physics community.[39]

text: At least one physicist considers the "wave-duality" as not being an incomprehensible mystery. L.E. Ballentine, Quantum Mechanics, A Modern Development, p. 4, explains:

text: When first discovered, particle diffraction was a source of great puzzlement. Are "particles" really "waves?" In the early experiments, the diffraction patterns were detected holistically by means of a photographic plate, which could not detect individual particles. As a result, the notion grew that particle and wave properties were mutually incompatible, or complementary, in the sense that different measurement apparatuses would be required to observe them. That idea, however, was only an unfortunate generalization from a technological limitation. Today it is possible to detect the arrival of individual electrons, and to see the diffraction pattern emerge as a statistical pattern made up of many small spots (Tonomura et al., 1989). Evidently, quantum particles are indeed particles, but whose behaviour is very different from classical physics would have us to expect.

text: The Afshar experiment[40] (2007) may suggest that it is possible to simultaneously observe both wave and particle properties of photons. This claim is, however, disputed by other scientists.[41][42][43][44]

text: Wave-only view[edit]

text: Carver Mead, an American scientist and professor at Caltech, proposes that the duality can be replaced by a "wave-only" view. In his book Collective Electrodynamics: Quantum Foundations of Electromagnetism (2000), Mead purports to analyze the behavior of electrons and photons purely in terms of electron wave functions, and attributes the apparent particle-like behavior to quantization effects and eigenstates. According to reviewer David Haddon:[45]

text: Mead has cut the Gordian knot of quantum complementarity. He claims that atoms, with their neutrons, protons, and electrons, are not particles at all but pure waves of matter. Mead cites as the gross evidence of the exclusively wave nature of both light and matter the discovery between 1933 and 1996 of ten examples of pure wave phenomena, including the ubiquitous laser of CD players, the self-propagating electrical currents of superconductors, and the Bose–Einstein condensate of atoms.

text: Albert Einstein, who, in his search for a Unified Field Theory, did not accept wave-particle duality, wrote:[46]

text: This double nature of radiation (and of material corpuscles) ... has been interpreted by quantum-mechanics in an ingenious and amazingly successful fashion. This interpretation ... appears to me as only a temporary way out...

text: The many-worlds interpretation (MWI) is sometimes presented as a waves-only theory, including by its originator, Hugh Everett who referred to MWI as "the wave interpretation".[47]

text: The three wave hypothesis of R. Horodecki relates the particle to wave.[48][49] The hypothesis implies that a massive particle is an intrinsically spatially, as well as temporally extended, wave phenomenon by a nonlinear law.

text: Particle-only view[edit]

text: Still in the days of the old quantum theory, a pre-quantum-mechanical version of wave–particle duality was pioneered by William Duane,[50] and developed by others including Alfred Landé.[51] Duane explained diffraction of x-rays by a crystal in terms solely of their particle aspect. The deflection of the trajectory of each diffracted photon was explained as due to quantized momentum transfer from the spatially regular structure of the diffracting crystal.[52]

text: Neither-wave-nor-particle view[edit]

text: It has been argued that there are never exact particles or waves, but only some compromise or intermediate between them. For this reason, in 1928 Arthur Eddington[53] coined the name "wavicle" to describe the objects although it is not regularly used today. One consideration is that zero-dimensional mathematical points cannot be observed. Another is that the formal representation of such points, the Dirac delta function is unphysical, because it cannot be normalized. Parallel arguments apply to pure wave states. Roger Penrose states:[54]

text: "Such 'position states' are idealized wavefunctions in the opposite sense from the momentum states. Whereas the momentum states are infinitely spread out, the position states are infinitely concentrated. Neither is normalizable [...]."

text: Relational approach to wave–particle duality[edit]

text: Relational quantum mechanics has been developed as a point of view that regards the event of particle detection as having established a relationship between the quantized field and the detector. The inherent ambiguity associated with applying Heisenberg’s uncertainty principle is consequently avoided; hence there is no wave-particle duality.[55]

text: Applications[edit]

text: Although it is difficult to draw a line separating wave–particle duality from the rest of quantum mechanics, it is nevertheless possible to list some applications of this basic idea.

text:
Wave–particle duality is exploited in electron microscopy, where the small wavelengths associated with the electron can be used to view objects much smaller than what is visible using visible light.
Similarly, neutron diffraction uses neutrons with a wavelength of about 0.1 nm, the typical spacing of atoms in a solid, to determine the structure of solids.
Photos are now able to show this dual nature, which may lead to new ways of examining and recording this behaviour.[56]

tag: ul


document_title: Deposition (phase transition)

question_text: phase change from gas to solid is called

text: Deposition (phase transition)

text: This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please help to improve this article by introducing more precise citations. (April 2011) (Learn how and when to remove this template message)

tag: table

text: Deposition is a thermodynamic process, a phase transition in which gas transforms into solid without passing through the liquid phase. The reverse of deposition is sublimation and hence sometimes deposition is called desublimation.

text: One example of deposition is the process by which, in sub-freezing air, water vapor changes directly to ice without first becoming a liquid. This is how snow forms in clouds, as well as how frost and hoar frost form on the ground or other surfaces. Another example is when frost forms on a leaf. For deposition to occur, thermal energy must be removed from a gas. When the air becomes cold enough, water vapor in the air surrounding the leaf loses enough thermal energy to change into a solid. Even though the air temperature may be below the dew point, the water vapor may not be able to condense spontaneously if there is no way to remove the latent heat. When the leaf is introduced, the supercooled water vapor immediately begins to condense, but by this point is already past the freezing point. This causes the water vapor to change directly into a solid.

text: Another example is the soot that is deposited on the walls of chimneys. Soot molecules rise from the fire in a hot and gaseous state. When they come into contact with the walls they cool, and change to the solid state, without formation of the liquid state. The process is made use of industrially in combustion chemical vapor deposition.

text: There is an industrial coatings process, known as evaporative deposition, whereby a solid material is heated to the gaseous state in a low-pressure chamber, the gas molecules travel across the chamber space and then condense to the solid state on a target surface, forming a smooth and thin layer on the target surface. Again, the molecules do not go through an intermediate liquid state when going from the gas to the solid. See also physical vapor deposition, which is a class of processes used to deposit thin films of various materials onto various surfaces.

text: Deposition releases energy and is an exothermic phase change.


document_title: Longest word in English

question_text: what is the longest english word in the dictionary

text: Longest word in English

text: Major dictionaries

text: The longest word in any of the major English language dictionaries is pneumonoultramicroscopicsilicovolcanoconiosis, a word that refers to a lung disease contracted from the inhalation of very fine silica particles,[8] specifically from a volcano; medically, it is the same as silicosis. The word was deliberately coined to be the longest word in English, and has since been used in a close approximation of its originally intended meaning, lending at least some degree of validity to its claim.[4]

text: The Oxford English Dictionary contains pseudopseudohypoparathyroidism (30 letters).

text: Merriam-Webster's Collegiate Dictionary does not contain antidisestablishmentarianism (28 letters), as the editors found no widespread, sustained usage of the word in its original meaning. The longest word in that dictionary is electroencephalographically (27 letters).[9]

text: The longest non-technical word in major dictionaries is floccinaucinihilipilification at 29 letters. Consisting of a series of Latin words meaning "nothing" and defined as "the act of estimating something as worthless"; its usage has been recorded as far back as 1741.[10][11][12]

text: Ross Eckler has noted that most of the longest English words are not likely to occur in general text, meaning non-technical present-day text seen by casual readers, in which the author did not specifically intend to use an unusually long word. According to Eckler, the longest words likely to be encountered in general text are deinstitutionalization and counterrevolutionaries, with 22 letters each.[13]

text: A computer study of over a million samples of normal English prose found that the longest word one is likely to encounter on an everyday basis is uncharacteristically, at 20 letters.[14]

text: The word internationalization is abbreviated "i18n", the embedded number representing the number of letters between the first and the last.[15][16][17]

text: Creations of long words

text: Coinages

text: In his play Assemblywomen (Ecclesiazousae), the ancient Greek comedic playwright Aristophanes created a word of 171 letters (183 in the transliteration below), which describes a dish by stringing together its ingredients:

text: Henry Carey's farce Chrononhotonthologos (1743) holds the opening line: "Aldiborontiphoscophornio! Where left you Chrononhotonthologos?"

text: Thomas Love Peacock put these creations into the mouth of the phrenologist Mr. Cranium in his 1816 romp Headlong Hall: osteosarchaematosplanchnochondroneuromuelous (44 characters) and osseocarnisanguineoviscericartilaginonervomedullary (51 characters).

text: James Joyce made up nine 100-letter words plus one 101-letter word in his novel Finnegans Wake, the most famous of which is Bababadalgharaghtakamminarronnkonnbronntonnerronntuonnthunntrovarrhounawnskawntoohoohoordenenthurnuk. Appearing on the first page, it allegedly represents the symbolic thunderclap associated with the fall of Adam and Eve. As it appears nowhere else except in reference to this passage, it is generally not accepted as a real word. Sylvia Plath made mention of it in her semi-autobiographical novel The Bell Jar, when the protagonist was reading Finnegans Wake.

text: "Supercalifragilisticexpialidocious", the 34-letter title of a song from the movie Mary Poppins, does appear in several dictionaries, but only as a proper noun defined in reference to the song title. The attributed meaning is "a word that you say when you don't know what to say." The idea and invention of the word is credited to songwriters Robert and Richard Sherman.

text: Agglutinative constructions

text: The English language permits the legitimate extension of existing words to serve new purposes by the addition of prefixes and suffixes. This is sometimes referred to as agglutinative construction. This process can create arbitrarily long words: for example, the prefixes pseudo (false, spurious) and anti (against, opposed to) can be added as many times as desired. A word like anti-aircraft (pertaining to the defense against aircraft) is easily extended to anti-anti-aircraft (pertaining to counteracting the defense against aircraft, a legitimate concept) and can from there be prefixed with an endless stream of "anti-"s, each time creating a new level of counteraction. More familiarly, the addition of numerous "great"s to a relative, e.g. great-great-great-grandfather, can produce words of arbitrary length. In musical notation, a 8192nd note may be called a semihemidemisemihemidemisemihemidemisemiquaver.

text: Antidisestablishmentarianism is the longest common example of a word formed by agglutinative construction.

text: Technical terms

text: A number of scientific naming schemes can be used to generate arbitrarily long words.

text: The IUPAC nomenclature for organic chemical compounds is open-ended, giving rise to the 189,819-letter chemical name Methionylthreonylthreonyl...isoleucine for the protein also known as titin, which is involved in striated muscle formation. In nature, DNA molecules can be much bigger than protein molecules and therefore potentially be referred to with much longer chemical names. For example, the wheat chromosome 3B contains almost 1 billion base pairs,[18] so the sequence of one of its strands, if written out in full like Adenilyladenilylguanilylcystidylthymidyl..., would be about 8 billion letters long. The longest published word, Acetylseryltyrosylseryliso...serine, referring to the coat protein of a certain strain of tobacco mosaic virus, was 1,185 letters long, and appeared in the American Chemical Society's Chemical Abstracts Service in 1964 and 1966.[19] In 1965, the Chemical Abstracts Service overhauled its naming system and started discouraging excessively long names.

text:
John Horton Conway and Landon Curt Noll developed an open-ended system for naming powers of 10, in which one sexmilliaquingentsexagintillion, coming from the Latin name for 6560, is the name for 103(6560+1) = 1019683. Under the long number scale, it would be 106(6560) = 1039360. Jonathan Bowers has developed a system for even larger numbers (enneenneconteennahecteika-enneenneconteennahectenedaka-enneenneconteennahecteyodaka-enneenneconteennahectezedaka-enneenneconteennahecteexdaka-enneenneconteennahectepedaka-enneennecontehectetedaka-enneenneconteennahectetradaka-enneenneconteennahectedoka-enneenneconteennahectehendaka-enneenneconteennahectedaka-enneenneconteennahectexenna-enneenneconteennahecteyotta-enneenneconteennahectezetta-enneenneconteennahecteexa-enneenneconteennahectepeta-enneenneconteennahectetera-enneenneconteennahectegiga-enneenneconteennahectemega-enneenneconteennahectekilla-enneenneconteennahectillion for

10

3
∗

10

3
∗

10

63

−
3

+
3

{\displaystyle 10^{3*10^{3*10^{63}-3}+3}}

).[20]

text: Gammaracanthuskytodermogammarus loricatobaicalensis is sometimes cited as the longest binomial name—it is a kind of amphipod. However, this name, proposed by B. Dybowski, was invalidated by the International Code of Zoological Nomenclature in 1929 after being petitioned by Mary J. Rathbun to take up the case.[21]

text: Parastratiosphecomyia stratiosphecomyioides is the longest accepted binomial name. It is a species of soldier fly.[22]

text: Aequeosalinocalcalinoceraceoaluminosocupreovitriolic, at 52 letters, describing the spa waters at Bath, England, is attributed to Dr. Edward Strother (1675–1737).[23] The word is composed of the following elements:

text:
Aequeo: equal (Latin, aequo[24])
Salino: containing salt (Latin, salinus)
Calcalino: calcium (Latin, calx)
Ceraceo: waxy (Latin, cera)
Aluminoso: alumina (Latin)
Cupreo: from "copper"
Vitriolic: resembling vitriol

text: Notable long words

text: Place names

text: The longest officially recognized place name in an English-speaking country is Taumatawhakatangihangakoauauotamateapokaiwhenuakitanatahu (57 letters), which is a hill in New Zealand. The name is in the Māori language. A longer and widely recognised version of the name is Taumatawhakatangihangakoauauotamateaturipukakapikimaungahoronukupokaiwhenuakitanatahu (85 letters), which appears on the signpost at the location (see the photo on this page). In Māori, the digraphs ng and wh are each treated as single letters.

text: In Canada, the longest place name is Dysart, Dudley, Harcourt, Guilford, Harburn, Bruton, Havelock, Eyre and Clyde, a township in Ontario, at 61 letters or 68 non-space characters.[25]

text: The longest non-contrived place name in the United Kingdom which is a single non-hyphenated word is Cottonshopeburnfoot (19 letters) and the longest which is hyphenated is Sutton-under-Whitestonecliffe (29 characters).

text: The longest place name in the United States (45 letters) is Chargoggagoggmanchauggagoggchaubunagungamaugg, a lake in Webster, Massachusetts. It means "Fishing Place at the Boundaries – Neutral Meeting Grounds" and is sometimes facetiously translated as "you fish your side of the water, I fish my side of the water, nobody fishes the middle". The lake is also known as Webster Lake.[26] The longest hyphenated names in the U.S. are Winchester-on-the-Severn, a town in Maryland, and Washington-on-the-Brazos, a notable place in Texas history.

text: The longest official geographical name in Australia is Mamungkukumpurangkuntjunya.[27] It has 26 letters and is a Pitjantjatjara word meaning "where the Devil urinates".[28]

text: In Ireland, the longest English placename at 19 letters is Newtownmountkennedy in County Wicklow.

text: Personal names

text: Guinness World Records formerly contained a category for longest personal name used.

text:
From about 1975 to 1985, the recordholder was Adolph Blaine Charles David Earl Frederick Gerald Hubert Irvin John Kenneth Lloyd Martin Nero Oliver Paul Quincy Randolph Sherman Thomas Uncas Victor William Xerxes Yancy Zeus Wolfeschlegelsteinhausenbergerdorffvoralternwarengewissenhaftschaferswessenschafewarenwohlgepflegeundsorgfaltigkeitbeschutzenvonangreifendurchihrraubgierigfeindewelchevoralternzwolftausendjahresvorandieerscheinenwanderersteerdemenschderraumschiffgebrauchlichtalsseinursprungvonkraftgestartseinlangefahrthinzwischensternartigraumaufdersuchenachdiesternwelchegehabtbewohnbarplanetenkreisedrehensichundwohinderneurassevonverstandigmenschlichkeitkonntefortplanzenundsicherfreuenanlebenslanglichfreudeundruhemitnichteinfurchtvorangreifenvonandererintelligentgeschopfsvonhinzwischensternartigraum, Senior (746 letters), also known as Wolfe+585, Senior.
After 1985 Guinness briefly awarded the record to a newborn girl with a longer name. The category was removed shortly afterward.

text: Long birth names are often coined in protest of naming laws or for other personal reasons.

text: The naming law in Sweden was challenged by parents Lasse Diding and Elisabeth Hallin, who proposed the given name "Brfxxccxxmnpcccclllmmnprxvclmnckssqlbb11116" for their child (pronounced [ˈalbɪn], 43 characters), which was rejected by a district court in Halmstad, southern Sweden.

text: Words with certain characteristics of notable length

text: 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. (August 2017) (Learn how and when to remove this template message)

text:
Schmaltzed and strengthed (10 letters) appear to be the longest monosyllabic words recorded in The Oxford English Dictionary, while scraunched and scroonched appear to be the longest monosyllabic words recorded in Webster's Third New International Dictionary; but squirrelled (11 letters) is the longest if pronounced as one syllable only (as permitted in The Shorter Oxford English Dictionary and Merriam-Webster Online Dictionary at squirrel, and in Longman Pronunciation Dictionary). Schtroumpfed (12 letters) was coined by Umberto Eco, while broughammed (11 letters) was coined by William Harmon after broughamed (10 letters) was coined by George Bernard Shaw.
Strengths is the longest word in the English language containing only one vowel.
Euouae, a medieval musical term, is the longest English word consisting only of vowels, and the word with the most consecutive vowels. However, the "word" itself is simply a mnemonic consisting of the vowels to be sung in the phrase "seculorum Amen" at the end of the lesser doxology. (Although u was often used interchangeably with v, and the variant "Evovae" is occasionally used, the v in these cases would still be a vowel.)
The longest words with no repeated letters are dermatoglyphics, misconjugatedly and uncopyrightables.[29]
The longest word whose letters are in alphabetical order is the eight-letter Aegilops, a grass genus. However, this is arguably both Latin and a proper noun. There are several six-letter English words with their letters in alphabetical order, including abhors, almost, begins, biopsy, chimps and chintz.[30]
The longest words recorded in OED with each vowel only once, and in order, are abstemiously, affectiously, and tragediously (OED). Fracedinously and gravedinously (constructed from adjectives in OED) have thirteen letters; Gadspreciously, constructed from Gadsprecious (in OED), has fourteen letters. Facetiously is among the few other words directly attested in OED with single occurrences of all five vowels and the semivowel y.
The longest single palindromic word in English is rotavator, another name for a rotary tiller for breaking and aerating soil.

text: Typed words

text:
The longest words typable with only the left hand using conventional hand placement on a QWERTY keyboard are tesseradecades, aftercataracts,[31] and the more common but sometimes hyphenated sweaterdresses.[30] Using the right hand alone, the longest word that can be typed is johnny-jump-up, or, excluding hyphens, monimolimnion[32] and phyllophyllin.
The longest English word typable using only the top row of letters has 11 letters: rupturewort. Similar words with 10 letters include: pepperwort, perpetuity, proprietor, requietory, repertoire, tripertite, pourriture and (fittingly) typewriter. The word teetertotter (used in North American English) is longer at 12 letters, although it is usually spelled with a hyphen.
The longest using only the middle row is shakalshas (10 letters). Nine-letter words include flagfalls, galahads and alfalfas.
Since the bottom row contains no vowels, no standard words can be formed. Exceptions might include Zzz, seen in some dictionaries to denote sleep, or m', the clitic form of my.[33]
The longest words typable by alternating left and right hands are antiskepticism and leucocytozoans respectively.[30]
On a Dvorak keyboard, the longest "left-handed" words are epopoeia, jipijapa, peekapoo, and quiaquia.[34] Other such long words are papaya, Kikuyu, opaque, and upkeep.[35] Kikuyu is typed entirely with the index finger, and so the longest one-fingered word on the Dvorak keyboard. There are no vowels on the right-hand side, and so the longest "right-handed" word is crwth.


document_title: NBA All-Star Game Most Valuable Player Award

question_text: who has the most all star mvp awards

question_tokens: who has the most all star mvp awards

text: Winners[edit]

text:
^
Denotes player who is still active in the NBA

*
Elected to the Naismith Memorial Basketball Hall of Fame

Player (X)
Denotes the number of times the player has been awarded the MVP award

Team (X)
Denotes the number of times a player from this team has won

text:
Season
Player
Position
Nationality
Team

1951
Macauley, EdEd Macauley*
Center/Forward
 United States
Boston Celtics

1952
Arizin, PaulPaul Arizin*
Forward/Guard
 United States
Philadelphia Warriors

1953
Mikan, GeorgeGeorge Mikan*
Center
 United States
Minneapolis Lakers

1954
Cousy, BobBob Cousy*
Guard
 United States
Boston Celtics (2)

1955
Sharman, BillBill Sharman*
Guard
 United States
Boston Celtics (3)

1956
Pettit, BobBob Pettit*
Forward/Center
 United States
St. Louis Hawks

1957
Cousy, BobBob Cousy* (2)
Guard
 United States
Boston Celtics (4)

1958
Pettit, BobBob Pettit* (2)
Forward/Center
 United States
St. Louis Hawks (2)

1959[b]
Baylor, ElginElgin Baylor*
Forward
 United States
Minneapolis Lakers (2)

Pettit, BobBob Pettit* (3)
Forward/Center
 United States
St. Louis Hawks (3)

1960
Chamberlain, WiltWilt Chamberlain*
Center
 United States
Philadelphia Warriors (2)

1961
Robertson, OscarOscar Robertson*
Guard
 United States
Cincinnati Royals

1962
Pettit, BobBob Pettit* (4)
Forward/Center
 United States
St. Louis Hawks (4)

1963
Russell, BillBill Russell*
Center
 United States
Boston Celtics (5)

1964
Robertson, OscarOscar Robertson* (2)
Guard
 United States
Cincinnati Royals (2)

1965
Lucas, JerryJerry Lucas*
Forward/Center
 United States
Cincinnati Royals (3)

1966
Smith, AdrianAdrian Smith
Guard
 United States
Cincinnati Royals (4)

1967
Barry, RickRick Barry*
Forward
 United States
San Francisco Warriors (3)

1968
Greer, HalHal Greer*
Guard/Forward
 United States
Philadelphia 76ers

1969
Robertson, OscarOscar Robertson* (3)
Guard
 United States
Cincinnati Royals (5)

1970
Reed, WillisWillis Reed*
Center/Forward
 United States
New York Knicks

1971
Wilkens, LennyLenny Wilkens*
Guard
 United States
Seattle SuperSonics

1972
West, JerryJerry West*
Guard
 United States
Los Angeles Lakers (3)

1973
Cowens, DaveDave Cowens*
Center/Forward
 United States
Boston Celtics (6)

1974
Lanier, BobBob Lanier*
Center
 United States
Detroit Pistons

1975
Frazier, WaltWalt Frazier*
Guard
 United States
New York Knicks (2)

1976
Bing, DaveDave Bing*
Guard
 United States
Washington Bullets

1977
Erving, JuliusJulius Erving*
Forward
 United States
Philadelphia 76ers (2)

1978
Smith, RandyRandy Smith
Guard/Forward
 United States
Buffalo Braves

1979
Thompson, DavidDavid Thompson*
Guard/Forward
 United States
Denver Nuggets

1980
Gervin, GeorgeGeorge Gervin*
Guard/Forward
 United States
San Antonio Spurs

1981
Archibald, NateNate Archibald*
Guard
 United States
Boston Celtics (7)

1982
Bird, LarryLarry Bird*
Forward
 United States
Boston Celtics (8)

1983
Erving, JuliusJulius Erving* (2)
Forward
 United States
Philadelphia 76ers (3)

1984
Thomas, IsiahIsiah Thomas*
Guard
 United States
Detroit Pistons (2)

1985
Sampson, RalphRalph Sampson*
Center/Forward
 United States
Houston Rockets

1986
Thomas, IsiahIsiah Thomas* (2)
Guard
 United States
Detroit Pistons (3)

1987
Chambers, TomTom Chambers
Forward/Center
 United States
Seattle SuperSonics (2)

1988
Jordan, MichaelMichael Jordan*
Guard
 United States
Chicago Bulls

1989
Malone, KarlKarl Malone*
Forward
 United States
Utah Jazz

1990
Johnson, MagicMagic Johnson*
Guard
 United States
Los Angeles Lakers (4)

1991
Barkley, CharlesCharles Barkley*
Forward
 United States
Philadelphia 76ers (4)

1992
Johnson, MagicMagic Johnson* (2)
Guard
 United States
Los Angeles Lakers (5)

1993[b]
Stockton, JohnJohn Stockton*
Guard
 United States
Utah Jazz (2)

Malone, KarlKarl Malone* (2)
Forward
 United States
Utah Jazz (3)

1994
Pippen, ScottieScottie Pippen*
Forward
 United States
Chicago Bulls (2)

1995
Richmond, MitchMitch Richmond*
Guard
 United States
Sacramento Kings (6)

1996
Jordan, MichaelMichael Jordan* (2)
Guard
 United States
Chicago Bulls (3)

1997
Rice, GlenGlen Rice
Forward
 United States
Charlotte Hornets

1998
Jordan, MichaelMichael Jordan* (3)
Guard
 United States
Chicago Bulls (4)

1999
Not awarded as the game was canceled due to the league's lockout.[3]

2000[b]
O'Neal, ShaquilleShaquille O'Neal*
Center
 United States
Los Angeles Lakers (6)

Duncan, TimTim Duncan
Forward/Center
 United States[c]
San Antonio Spurs (2)

2001
Iverson, AllenAllen Iverson*
Guard
 United States
Philadelphia 76ers (5)

2002
Bryant, KobeKobe Bryant
Guard
 United States
Los Angeles Lakers (7)

2003
Garnett, KevinKevin Garnett
Forward/Center
 United States
Minnesota Timberwolves

2004
O'Neal, ShaquilleShaquille O'Neal* (2)
Center
 United States
Los Angeles Lakers (8)

2005
Iverson, AllenAllen Iverson* (2)
Guard
 United States
Philadelphia 76ers (6)

2006
James, LeBronLeBron James^ [d]
Forward
 United States
Cleveland Cavaliers

2007
Bryant, KobeKobe Bryant (2)
Guard
 United States
Los Angeles Lakers (9)

2008
James, LeBronLeBron James^ (2)
Forward
 United States
Cleveland Cavaliers (2)

2009[b]
Bryant, KobeKobe Bryant (3)
Guard
 United States
Los Angeles Lakers (10)

O'Neal, ShaquilleShaquille O'Neal* (3) [e]
Center
 United States
Phoenix Suns

2010
Wade, DwyaneDwyane Wade^
Guard
 United States
Miami Heat

2011
Bryant, KobeKobe Bryant (4)
Guard
 United States
Los Angeles Lakers (11)

2012
Durant, KevinKevin Durant^
Forward
 United States
Oklahoma City Thunder (3)

2013
Paul, ChrisChris Paul^
Guard
 United States
Los Angeles Clippers (2)

2014
Irving, KyrieKyrie Irving^
Guard
 United States[a]
Cleveland Cavaliers (3)

2015
Westbrook, RussellRussell Westbrook^
Guard
 United States
Oklahoma City Thunder (4)

2016
Westbrook, RussellRussell Westbrook^ (2)
Guard
 United States
Oklahoma City Thunder (5)

2017
Davis, AnthonyAnthony Davis^
Forward/Center
 United States
New Orleans Pelicans

2018
James, LeBronLeBron James^ (3)
Forward
 United States
Cleveland Cavaliers (4)

text: Multi-time winners[edit]

text:
Player
Team
No.
Years

Pettit, BobBob Pettit
St. Louis Hawks
4
1956, 1958, 1959, 1962

Bryant, KobeKobe Bryant
Los Angeles Lakers
2002, 2007, 2009, 2011

Robertson, OscarOscar Robertson
Cincinnati Royals
3
1961, 1964, 1969

Jordan, MichaelMichael Jordan
Chicago Bulls
1988, 1996, 1998

O'Neal, ShaquilleShaquille O'Neal
Los Angeles Lakers
Phoenix Suns
2000, 2004, 2009

James, LeBronLeBron James
Cleveland Cavaliers
2006, 2008, 2018

Cousy, BobBob Cousy
Boston Celtics
2
1954, 1957

Erving, JuliusJulius Erving
Philadelphia 76ers
1977, 1983

Thomas, IsiahIsiah Thomas
Detroit Pistons
1984, 1986

Malone, KarlKarl Malone
Utah Jazz
1989, 1993

Johnson, MagicMagic Johnson
Los Angeles Lakers
1990, 1992

Iverson, AllenAllen Iverson
Philadelphia 76ers
2001, 2005

Westbrook, RussellRussell Westbrook
Oklahoma City Thunder
2015, 2016


document_title: Startup neutron source

question_text: where do the neutrons come from in nuclear fission

text: Startup neutron source

text: Startup neutron source is a neutron source used for stable and reliable initiation of nuclear chain reaction in nuclear reactors, when they are loaded with fresh nuclear fuel, whose neutron flux from spontaneous fission is insufficient for a reliable startup, or after prolonged shutdown periods. Neutron sources ensure a constant minimal population of neutrons in the reactor core, sufficient for a smooth startup. Without them, the reactor could suffer fast power excursions during startup from state with too few self-generated neutrons (new core or after extended shutdown).

text: The startup sources are typically inserted in regularly spaced positions inside the reactor core, in place of some of the fuel rods.

text: The sources are important for safe reactor startup. The spontaneous fission and cosmic rays serve as weak neutron sources, but these are too weak for the reactor instrumentation to detect; relying on them could lead to a "blind" start, which is an unsafe condition.[1] The sources are therefore positioned so the neutron flux they produce is always detectable by the reactor monitoring instruments. When the reactor is in shutdown state, the neutron sources serve to provide signals for neutron detectors monitoring the reactor, to ensure they are operable.[2] The equilibrium level of neutron flux in a subcritical reactor is dependent on the neutron source strength; a certain minimum level of source activity therefore has to be ensured in order to maintain control over the reactor when in strongly subcritical state, namely during startups.[3]

text: The sources can be of two types:[4]

text:
Primary sources, used for startup of a fresh reactor core; conventional neutron sources are used. The primary sources are removed from the reactor after the first fuel campaign, usually after few months, as neutron capture resulting from the thermal neutron flux in an operating reactor changes the composition of the isotopes used, and thus reduces their useful lifetime as neutron sources.

Californium-252 (spontaneous fission)
Plutonium-238 & beryllium, (α,n) reaction
americium-241 & beryllium, (α,n) reaction
polonium-210 & beryllium, (α,n) reaction
radium-226 & beryllium, (α,n) reaction[5]

text: When plutonium-238/beryllium primary sources are utilized, they can be either affixed to control rods which are removed from the reactor when it is powered, or clad in a cadmium alloy, which is opaque to thermal neutrons (reducing transmutation of the plutonium-238 by neutron capture) but transparent to fast neutrons produced by the source.[2]

text:
Secondary sources, originally inert, become radioactive and neutron-producing only after neutron activation in the reactor. Due to this, they tend to be less expensive. Exposure to thermal neutrons also serves to maintain the source activity (the radioactive isotopes are both burned and generated in neutron flux).

Sb-Be photoneutron source; antimony becomes radioactive in the reactor and its strong gamma emissions (1.7 MeV for 124Sb) interact with beryllium-9 by an (γ,n) reaction and provide photoneutrons. In a PWR reactor one neutron source rod contains 160 grams of antimony, and stay in the reactor for 5–7 years.[6] The sources are often constructed as an antimony rod surrounded by beryllium layer and clad in stainless steel.[5][7] Antimony-beryllium alloy can be also used.

text: The chain reaction in the first critical reactor, CP-1, was initiated by neutron sources generated during its prior subcritical test runs. The very first of those could have been initiated by ambient cosmic-ray neutrons. Similarly, in modern reactors (after startup), delayed neutron emission from fission products suffices to sustain the amplification reaction while yielding controllable growth times. (In comparison, a bomb is based on immediate neutrons and grows exponentially in nanoseconds.)


document_title: List of pig breeds

question_text: how many breeds of pigs are there in the uk

text: List of pig breeds

text: There are hundreds of breeds of the domestic pig (Sus scrofa domesticus).

text:
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
See also
References

text: List with classification and standards[edit]

text:
Breed
Origin
Height
Weight
Color
Image

Aksai Black Pied
Kazakhstan
167–182 cm
240–320 kg (530–710 lb)
Black & White
Red & Black

[1]

American Yorkshire
United States
---
---
White

Angeln Saddleback
Germany
---
300–350 kg (660–770 lb)
Black & White

Appalachian English
---
---
---
---
---

Arapawa Island
New Zealand
---
100–180 kg (220–400 lb)
Red & Black

[2]

Auckland Island Pig
New Zealand
---
---
Black, Black & Tan

[3]

Australian Yorkshire
Australia
---
---
---
---

Babi Kampung
---
---
---
---
---

Ba Xuyen
Vietnam
---
100 kg (220 lb)
Black & White
---

Bantu
---
---
---
---
---

Basque
France
---
---
---

Bazna
Romania
---
---
Black & White
---

Beijing Black
China
---
---
Black
---

Belarus Black Pied
Belarus
---
---
Black & White
---

Belgian Landrace
Belgium
---
---
White

Bengali Brown Shannaj
---
---
---
---
---

Bentheim Black Pied
Germany
70–75 cm (28–30 in)
180–250 kg (400–550 lb)
Black & White

Berkshire
United Kingdom
---
---
Black with some White markings

Bisaro
Portugal
---
---
Black & White
---

Bangur pig
Nepal
---
205–600 kg (452–1,323 lb)
Black and White
---

Black Slavonian
---
---
---
Black
---

Black Canarian Pig
---
---
---
Black
---

Breitovo
Russia
---
---
---
---

British Landrace
United Kingdom
---
---
White
---

British Lop
United Kingdom
---
---
White

British Saddleback
United Kingdom
---
---
Black & White

Bulgarian White
Bulgaria
21
---
White
---

Cantonese
---
---
---
---
---

Celtic pig
Galicia, Spain
80 cm (31 in)
---
Black & White

Chato Murciano
Spain
---
180 kg (400 lb)
Black or White or Black & White
---

Chester White
United States
---
---
White

Chiangmai Blackpig aka MooDum Chiangmai
Thailand
---
---
Black
---

Choctaw Hog
United States
---
60 kg (130 lb)
Black
---

Creole Pig
Haiti
---
---
---
---

Cumberland Pig
United Kingdom
---
---
White

Czech Improved White
---
---
---
White
---

Danish Landrace
Denmark
---
---
White
---

Danish Protest Pig
Germany
92 cm (36 in)
350 kg (770 lb)
Red & White

Dermantsi Pied
---
---
---
---
---

Li Yan Pig
---
Singapore Boon Lay
---
---
---

Dharane Kalo sungur
Dharan, Nepal
---
---
---
---

Duroc
United States
---
---
Red or Black

Dutch Landrace pig
Netherlands
---
---
---
---

East Balkan pig
---
---
---
---
---

Essex
United Kingdom
---
---
Black & White

Estonian Bacon
Estonia
---
---
---
---

Fengjing pig
China
---
---
---
---

Finnish Landrance
Finland
---
---
---
---

Forest Mountain
Armenia
---
165–260 kg (364–573 lb)
White
---

French Landrace
France
---
---
White

Gascon
France
---
---
Black

German Landrace
Germany
80–90 cm
250–320 kg (550–710 lb)
White

Gloucestershire Old Spot
United Kingdom
---
220–280 kg (490–620 lb)
White with Black spots

Göttingen minipig
Germany
35 cm
34 kg (75 lb)
White

Grice
United Kingdom
---
---
---
---

Guinea Hog
United States
---
200 kg (440 lb)
Black

Hampshire
United Kingdom
---
---
Black & White

Hante
---
---
---
---
---

Hereford
United States
---
200–370 kg (440–820 lb)
Red & White
---

Hezuo
---
---
---
---
---

Hogan Hog
Baraga, MI, United States
---
---
---
---

Huntingdon Black Hog
United Kingdom
---
---
Black with White socks
---

Iberian
Iberian Peninsula
---
---
Black, Red

Italian Landrace
Italy
---
---
White

Japanese Landrace
Japan
---
---
---
---

Jeju Black Pig
Jeju Island, South Korea
---
---
Black

Jinhua pig
---
---
---
---
---

Juliana
Europe
---
---
Tri-Colored
---

Kakhetian
Georgia
---
---
---

Kele pig
---
---
---
---
---

Kemerovo
Russia
---
---
---
---

Korean Native Pig
Korea
---
---
Black
---

Krskopolje
Slovenia
---
---
---
---

Kunekune
New Zealand
60 cm (24 in)
68–100 kg (150–220 lb)
Red, Black & White, Cream, Gold-tip, Black, Brown & Tri-colored

Lacombe
Canada
---
---
---
---

Large Black
United Kingdom
---
270–360 kg (600–790 lb)
Black

Large Black-white
---
---
---
Black & White
---

Large White
United Kingdom
---
---
White

Latvian White
Latvia
---
---
White
---

Leicoma
---
---
---
---
---

Lithuanian Native
Lithuania
---
---
Black & White, Red, Black & Tri-Colored
---

Lithuanian White
Lithuania
---
---
White
---

Lincolnshire Curly-Coated Pig
United Kingdom
---
---
White
---

Livny
Russia
---
---
---
---

Malhado de Alcobaça
Portugal
---
---
Black & White
---

Mangalitsa
Hungary
---
---
Blonde, Swallow-Bellied, Red

Meishan
China
---
---
Black

Middle White
United Kingdom
---
---
White

Minzhu
---
---
---
---
---

Minokawa Buta
---
---
---
---
---

Mong Cai
---
---
---
---
---

Mora Romagnola
---
---
---
---
---

Moura
---
---
---
---
---

Mukota
Zimbabwe
---
---
---
---

Mulefoot
Gulf Coast
---
---
---
---

Murom
---
---
---
---
---

Myrhorod
Ukraine
---
---
Black & White
---

Nero dei Nebrodi
Italy - Sicily
60–65 cm (24–26 in)
150 kg (330 lb)
Black

Neijiang
---
---
---
---
---

Ningxiang
---
---
---
---
---

North Caucasian
Russia & Uzbekistan
---
---
---
---

North Siberian
Russia
---
---
---
---

Norwegian Landrace
Norway
---
---
White

Norwegian Yorkshire
Norway
---
---
---
---

Ossabaw Island
Ossabaw Island
51 cm (20 in)
90 kg (200 lb)
Black, Spotted

Oxford Sandy and Black
United Kingdom
---
---
Red & Black spotted

Pakchong 5
Thailand
---
---
---
---

Philippine Native
---
---
---
---
---

Piétrain
Wallonia
---
---
White spotted

Poland China
United States
---
---
---

Red Wattle
United States
120 cm (47 in)
270–680 kg (600–1,500 lb)
Red

Semirechensk
Kazakhstan
---
---
---
---

Siberian Black Pied
Russia
---
---
Black & White
---

Small Black
United Kingdom
---
---
Black

Small White
United Kingdom
---
---
White

Spots
---
---
---
---
---

Surabaya Babi
---
---
---
---
---

Swabian-Hall
Germany
---
---
Black & White

Swedish Landrace
Sweden
---
---
White
---

Taihu pig
China
---
---
Black
---

Tamworth
United Kingdom
50–65 cm (20–26 in)
250–370 kg (550–820 lb)
Red

Thuoc Nhieu
---
---
---
---
---

Tibetan
---
---
---
---

Tokyo-X
Japan
---
---
---
---

Tsivilsk
Russia
---
---
White
---

Turopolje
Croatia
---
---
---

Ukrainian Spotted Steppe
Ukraine
---
---
---
---

Ukrainian White Steppe
Ukraine
---
---
White
---

Urzhum
Russia
---
---
---
---

Vietnamese Potbelly
Vietnam
40–66 cm (16–26 in)
45–90 kg (99–198 lb)
Black, Black with white markings

Welsh
United Kingdom
---
110–140 kg (240–310 lb)
White
---

Wessex Saddleback
United Kingdom
---
---
Black & White

West French White
France
---
---
White

Windsnyer
---
---
---
---
---

Wuzishan
---
---
---
---
---

Yanan
---
---
---
---
---

Yorkshire Blue and White
United Kingdom
---
---
---
---