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In northwestern Africa (the Maghrib or Maghreb), including Morocco, Algeria, and Tunisia, madrasas began to be constructed in the 13th century under the Marinid and Hafsid dynasties. In Tunisia (or Ifriqiya), the earliest Hafsid madrasa was the Madrasa al-Shamma'iyya founded in 1238: 209 (or in 1249 according to some sources: 296 ). In Morocco, the first madrasa was the Madrasa as-Saffarin built in Fes in 1271, followed by many others constructed around the country. The main architectural highlights among these are the Madrasa as-Sahrij (built in 1321–1328), the Madrasa al-Attarin (built in 1323–1325), and the Madrasa of Salé (completed in 1341), all of which are lavishly decorated with sculpted wood, carved stucco, and zellij mosaic tilework. | https://en.wikipedia.org/wiki/Koran_school |
The Bou Inania Madrasa in Fes, built in 1350–1355, distinguished itself from other madrasas by its size and by being the only madrasa which also officially functioned as a public Friday mosque. The Marinids also built madrasas in Algeria, particularly in Tlemcen.In Morocco, madrasas were generally built in brick and wood and were still centered around a main internal courtyard with a central fountain or water basin, around which student dorms were distributed across one or two floors. A prayer hall or mosque chamber usually stood opposite the entrance on one side of the courtyard. | https://en.wikipedia.org/wiki/Koran_school |
The Bou Inania Madrasa in Fes also contained two side-chambers opening off the lateral sides of its courtyard, which may reflect an influence of the older four-iwan layout. : 293 However, most other Moroccan madrasas did not have this feature and the courtyards were instead flanked by ornate galleries. By contrast with Mamluk structures to the east, Moroccan and Maghrebi madrasas were not prominently distinguishable from the outside except for an ornate entrance portal decorated with carved wood and stucco. This model continued to be found in later madrasas like the Ben Youssef Madrasa of the 16th century in Marrakesh. | https://en.wikipedia.org/wiki/Koran_school |
In northwestern Africa (the Maghrib or Maghreb), including Morocco, Algeria, and Tunisia, the appearance of madrasas was delayed until after the fall of the Almohad dynasty, who espoused a reformist doctrine generally considered unorthodox by other Sunnis. As such, it only came to flourish in the region in the 13th century, under the Marinid and Hafsid dynasties which succeeded them. In Tunisia (or Ifriqiya), the earliest Hafsid madrasa was the Madrasat al-Ma'raḍ, founded in Tunis in 1252 and followed by many others. In Morocco, the first madrasa was the Madrasa as-Saffarin built in Fes in 1271, followed by many others constructed around the country. | https://en.wikipedia.org/wiki/Koran_school |
The Marinids also built madrasas in Algeria, particularly in Tlemcen.As elsewhere, rulers in the Maghreb built madrasas to bolster their political legitimacy and that of their dynasty. The Marinids used their patronage of madrasas to cultivate the loyalty of Morocco's influential but independent religious elites and also to portray themselves to the general population as protectors and promoters of orthodox Sunni Islam. Madrasas also served to train the scholars and educated elites who generally operated the state bureaucracy. | https://en.wikipedia.org/wiki/Koran_school |
A number of madrasas also played a supporting role to major learning institutions like the older Qarawiyyin Mosque-University and the al-Andalusiyyin Mosque (both located in Fes) because they provided accommodations for students coming from other cities. : 137: 110 Many of these students were poor, seeking sufficient education to gain a higher position in their home towns, and the madrasas provided them with basic necessities such as lodging and bread. : 463 However, the madrasas were also teaching institutions in their own right and offered their own courses, but usually with much narrower and more limited curriculums than the Qarawiyyin. : 141 The Bou Inania Madrasa in Fes, distinguished itself from other madrasas by its size and by being the only madrasa which also officially functioned as a public Friday mosque.While some historical madrasas in Morocco remained in use well into the 20th century, most are no longer used for their original purpose following the reorganization of the Moroccan education system under French colonial rule and in the period following independence in 1956. Likewise, while some madrasas are still used for learning in Tunisia, many have since been converted to other uses in modern times. | https://en.wikipedia.org/wiki/Koran_school |
In northwestern Mexico, the Seri people continue to "sew" baskets using splints of the limberbush plant, Jatropha cuneata. | https://en.wikipedia.org/wiki/Basket_weaving |
In northwestern Sichuan, China, Volemys millicens is found in the Wolong National Nature Reserve, and likely also occurs in Wenchuan Caopo, Heishuihe, Fengtongzhai, Anzihe, and Longhixihongkou Nature Reserves. | https://en.wikipedia.org/wiki/Szechuan_vole |
In nosological literature relating to the symptom or disorder of apathy, clinicians have used cognitive inertia as one of the three main criteria for diagnosis. The description of cognitive inertia differs from its use in cognitive and industrial psychology in that lack of motivation plays a key role. As a clinical diagnostic criterion, Thant and Yager described it as "impaired abilities to elaborate and sustain goals and plans of actions, to shift mental sets, and to use working memory". This definition of apathy is frequently applied to onset of apathy due to neurodegenerative disorders such as Alzheimer's and Parkinson's disease but has also been applied to individuals who have gone through extreme trauma or abuse. | https://en.wikipedia.org/wiki/Cognitive_inertia |
In notation, a grace note is distinguished from a standard note by print size. A grace note is indicated by printing a note much smaller than an ordinary note, sometimes with a slash through the note stem (if two or more grace notes, there might be a slash through the note stem of the first note but not the subsequent grace notes). The presence or absence of a slash through a note stem is often interpreted to indicate the intention of an acciaccatura or an appoggiatura, respectively. The works of some composers, especially Frédéric Chopin, may contain long series of notes printed in the small type reserved for grace notes simply to show that the amount of time to be taken up by those notes as a whole unit is a subjective matter to be decided by the performer. Such a group of small printed notes may or may not have an accompanying principal note, and so may or may not be considered as grace notes in analysis. | https://en.wikipedia.org/wiki/Grace_notes |
In notes dating to 1779, Darwin made a sketch of a simple hydrogen-oxygen rocket engine, with gas tanks connected by plumbing and pumps to an elongated combustion chamber and expansion nozzle, a concept not to be seen again until one century later. | https://en.wikipedia.org/wiki/Erasmus_Darwin |
In nouns, the thematic vowel is almost always *o, and only becomes *e when there is no ending or when followed by *h₂ in the neuter nominative/accusative plural. Here is an example paradigm for *h₂ŕ̥tḱos 'bear', a thematic animate noun, supplemented by the neuter *h₂érh₃trom 'plough' for the nominative/accusative: Again, athematic nouns show ablaut and accent shifts, mainly between the "strong" cases (nominative and vocative in all numbers, and accusative singular/dual) and the "weak" cases (all others). A few endings are also different from the thematic paradigm; for example, the nominative/accusative neuter has *-∅ instead of *-m. See Athematic accent/ablaut classes of PIE nouns for examples. | https://en.wikipedia.org/wiki/Thematic_vowel |
In nozzle governing the flow rate of steam is regulated by opening and shutting of sets of nozzles rather than regulating its pressure. In this method groups of two, three or more nozzles form a set and each set is controlled by a separate valve. The actuation of individual valve closes the corresponding set of nozzle thereby controlling the flow rate. | https://en.wikipedia.org/wiki/Steam_turbine_governing |
In actual turbine, nozzle governing is applied only to the first stage whereas the subsequent stages remain unaffected. Since no regulation to the pressure is applied, the advantage of this method lies in the exploitation of full boiler pressure and temperature. Figure 2 shows the mechanism of nozzle governing applied to steam turbines. As shown in the figure the three sets of nozzles are controlled by means of three separate valves. | https://en.wikipedia.org/wiki/Steam_turbine_governing |
In nuclear EMP all of the components of the electromagnetic pulse are generated outside of the weapon.For high-altitude nuclear explosions, much of the EMP is generated far from the detonation (where the gamma radiation from the explosion hits the upper atmosphere). This electric field from the EMP is remarkably uniform over the large area affected.According to the standard reference text on nuclear weapons effects published by the U.S. Department of Defense, "The peak electric field (and its amplitude) at the Earth's surface from a high-altitude burst will depend upon the explosion yield, the height of the burst, the location of the observer, and the orientation with respect to the geomagnetic field. As a general rule, however, the field strength may be expected to be tens of kilovolts per metre over most of the area receiving the EMP radiation. | https://en.wikipedia.org/wiki/Nuclear_EMP |
"The text also states that, "... over most of the area affected by the EMP the electric field strength on the ground would exceed 0.5Emax. For yields of less than a few hundred kilotons, this would not necessarily be true because the field strength at the Earth's tangent could be substantially less than 0.5Emax. | https://en.wikipedia.org/wiki/Nuclear_EMP |
"(Emax refers to the maximum electric field strength in the affected area.) In other words, the electric field strength in the entire area that is affected by the EMP will be fairly uniform for weapons with a large gamma-ray output. For smaller weapons, the electric field may fall at a faster rate as distance increases. | https://en.wikipedia.org/wiki/Nuclear_EMP |
In nuclear and materials physics, stopping power is the retarding force acting on charged particles, typically alpha and beta particles, due to interaction with matter, resulting in loss of particle kinetic energy. Its application is important in areas such as radiation protection, ion implantation and nuclear medicine. | https://en.wikipedia.org/wiki/Stopping_power_(particle_radiation) |
In nuclear and particle physics, the energy profile of a resonance is described by the relativistic Breit–Wigner distribution, while the Cauchy distribution is the (non-relativistic) Breit–Wigner distribution. | https://en.wikipedia.org/wiki/Lorentzian_distribution |
In nuclear and particle physics, σ is used to denote cross sections in general (see also RCS), while Σ represents macroscopic cross sections . The symbol is to denote the Stefan–Boltzmann constant. In relation to fundamental properties of material, σ is often used to signify electrical conductivity. In electrostatics, σ represents surface charge density. | https://en.wikipedia.org/wiki/Final_sigma |
In continuum mechanics, σ is used to signify stress. In condensed matter physics, Σ denotes self-energy. The symbol can be used to signify surface tension (alternatively, γ or T are also used instead). | https://en.wikipedia.org/wiki/Final_sigma |
In quantum mechanics, σ is used to indicate Pauli matrices. In astronomy, σ represents velocity dispersion. In astronomy, the prefix Σ is used to designate double stars of the Catalogus Novus Stellarum Duplicium by Friedrich Georg Wilhelm von Struve. In particle physics, Σ represents a class of baryons. | https://en.wikipedia.org/wiki/Final_sigma |
In nuclear astrophysics, the rapid neutron-capture process, also known as the r-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", with the other half produced by the p-process and s-process. The r-process usually synthesizes the most neutron-rich stable isotopes of each heavy element. The r-process can typically synthesize the heaviest four isotopes of every heavy element, and the two heaviest isotopes, which are referred to as r-only nuclei, can be created via the r-process only. Abundance peaks for the r-process occur near mass numbers A = 82 (elements Se, Br, and Kr), A = 130 (elements Te, I, and Xe) and A = 196 (elements Os, Ir, and Pt). | https://en.wikipedia.org/wiki/R_process |
The r-process entails a succession of rapid neutron captures (hence the name) by one or more heavy seed nuclei, typically beginning with nuclei in the abundance peak centered on 56Fe. The captures must be rapid in the sense that the nuclei must not have time to undergo radioactive decay (typically via β− decay) before another neutron arrives to be captured. This sequence can continue up to the limit of stability of the increasingly neutron-rich nuclei (the neutron drip line) to physically retain neutrons as governed by the short range nuclear force. | https://en.wikipedia.org/wiki/R_process |
The r-process therefore must occur in locations where there exists a high density of free neutrons. Early studies theorized that 1024 free neutrons per cm3 would be required, for temperatures about 1 GK, in order to match the waiting points, at which no more neutrons can be captured, with the mass numbers of the abundance peaks for r-process nuclei. This amounts to almost a gram of free neutrons in every cubic centimeter, an astonishing number requiring extreme locations. | https://en.wikipedia.org/wiki/R_process |
Traditionally this suggested the material ejected from the reexpanded core of a core-collapse supernova, as part of supernova nucleosynthesis, or decompression of neutron-star matter thrown off by a binary neutron star merger in a kilonova. The relative contribution of each of these sources to the astrophysical abundance of r-process elements is a matter of ongoing research.A limited r-process-like series of neutron captures occurs to a minor extent in thermonuclear weapon explosions. These led to the discovery of the elements einsteinium (element 99) and fermium (element 100) in nuclear weapon fallout. | https://en.wikipedia.org/wiki/R_process |
The r-process contrasts with the s-process, the other predominant mechanism for the production of heavy elements, which is nucleosynthesis by means of slow captures of neutrons. In general, isotopes involved in the s-process have half-lives long enough to enable their study in laboratory experiments, but this is not typically true for isotopes involved in the r-process. The s-process primarily occurs within ordinary stars, particularly AGB stars, where the neutron flux is sufficient to cause neutron captures to recur every 10–100 years, much too slow for the r-process, which requires 100 captures per second. | https://en.wikipedia.org/wiki/R_process |
The s-process is secondary, meaning that it requires pre-existing heavy isotopes as seed nuclei to be converted into other heavy nuclei by a slow sequence of captures of free neutrons. The r-process scenarios create their own seed nuclei, so they might proceed in massive stars that contain no heavy seed nuclei. Taken together, the r- and s-processes account for almost the entire abundance of chemical elements heavier than iron. The historical challenge has been to locate physical settings appropriate for their time scales. | https://en.wikipedia.org/wiki/R_process |
In nuclear chemistry and nuclear physics, J-couplings (also called spin-spin coupling or indirect dipole–dipole coupling) are mediated through chemical bonds connecting two spins. It is an indirect interaction between two nuclear spins that arises from hyperfine interactions between the nuclei and local electrons. In NMR spectroscopy, J-coupling contains information about relative bond distances and angles. Most importantly, J-coupling provides information on the connectivity of chemical bonds. It is responsible for the often complex splitting of resonance lines in the NMR spectra of fairly simple molecules. J-coupling is a frequency difference that is not affected by the strength of the magnetic field, so is always stated in Hz. | https://en.wikipedia.org/wiki/Spin_coupling |
In nuclear chemistry, the actinide concept (also known as actinide hypothesis) proposed that the actinides form a second inner transition series homologous to the lanthanides. Its origins stem from observation of lanthanide-like properties in transuranic elements in contrast to the distinct complex chemistry of previously known actinides. Glenn Theodore Seaborg, one of the researchers who synthesized transuranic elements, proposed the actinide concept in 1944 as an explanation for observed deviations and a hypothesis to guide future experiments. It was accepted shortly thereafter, resulting in the placement of a new actinide series comprising elements 89 (actinium) to 103 (lawrencium) below the lanthanides in Dmitri Mendeleev's periodic table of the elements. | https://en.wikipedia.org/wiki/Actinide_concept |
In nuclear electronics, a microstrip detector is a particle detector that consists of a large number of identical semiconductor strips laid out along one axis of a two-dimensional structure, generally by lithography. The geometrical layout of the components allows to accurately reconstruct the track of an incoming particle of ionizing radiation. Silicon microstrip detectors are a common design used in various particle physics experiments. The detection mechanism consists of the production of electron-hole pairs in a layer of silicon a few hundreds of micrometers thick. The free electrons are drifted by an electric field created by a pattern of anodes and cathodes interdigitated on the surface of the silicon and separated by a SiO2 insulator. | https://en.wikipedia.org/wiki/Microstrip_detector |
In nuclear energy studies, xenon is used in bubble chambers, probes, and in other areas where a high molecular weight and inert chemistry is desirable. A by-product of nuclear weapon testing is the release of radioactive xenon-133 and xenon-135. These isotopes are monitored to ensure compliance with nuclear test ban treaties, and to confirm nuclear tests by states such as North Korea. Liquid xenon is used in calorimeters to measure gamma rays, and as a detector of hypothetical weakly interacting massive particles, or WIMPs. | https://en.wikipedia.org/wiki/Xenon_compounds |
When a WIMP collides with a xenon nucleus, theory predicts it will impart enough energy to cause ionization and scintillation. Liquid xenon is useful for these experiments because its density makes dark matter interaction more likely and it permits a quiet detector through self-shielding. | https://en.wikipedia.org/wiki/Xenon_compounds |
Xenon is the preferred propellant for ion propulsion of spacecraft because it has low ionization potential per atomic weight and can be stored as a liquid at near room temperature (under high pressure), yet easily evaporated to feed the engine. Xenon is inert, environmentally friendly, and less corrosive to an ion engine than other fuels such as mercury or caesium. Xenon was first used for satellite ion engines during the 1970s. | https://en.wikipedia.org/wiki/Xenon_compounds |
It was later employed as a propellant for JPL's Deep Space 1 probe, Europe's SMART-1 spacecraft and for the three ion propulsion engines on NASA's Dawn Spacecraft.Chemically, the perxenate compounds are used as oxidizing agents in analytical chemistry. Xenon difluoride is used as an etchant for silicon, particularly in the production of microelectromechanical systems (MEMS). The anticancer drug 5-fluorouracil can be produced by reacting xenon difluoride with uracil. Xenon is also used in protein crystallography. Applied at pressures from 0.5 to 5 MPa (5 to 50 atm) to a protein crystal, xenon atoms bind in predominantly hydrophobic cavities, often creating a high-quality, isomorphous, heavy-atom derivative that can be used for solving the phase problem. | https://en.wikipedia.org/wiki/Xenon_compounds |
In nuclear engineering and astrophysics contexts, the shake is sometimes used as a conveniently short period of time. 1 shake is defined as 10 nanoseconds. | https://en.wikipedia.org/wiki/List_of_unusual_units_of_measurement |
In nuclear engineering and nuclear safety, all safety activities, whether organizational, behavioural or equipment related, are subject to layers of overlapping provisions, so that if a failure should occur it would be compensated for or corrected without causing harm to individuals or the public at large. Defence in depth consists in a hierarchical deployment of different levels of equipment and procedures in order to maintain the effectiveness of physical barriers placed between radioactive materials and workers, the public or the environment, in normal operation, anticipated operational occurrences and, for some barriers, in accidents at the plant. Defence in depth is implemented through design and operation to provide a graded protection against a wide variety of transients, incidents and accidents, including equipment failures and human errors within the plant and events initiated outside the plan. | https://en.wikipedia.org/wiki/Defence_in_depth_(non-military) |
In nuclear engineering, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fission cross-section), density, shape, enrichment, purity, temperature, and surroundings. The concept is important in nuclear weapon design. | https://en.wikipedia.org/wiki/Critical_mass_(nuclear) |
In nuclear engineering, a delayed neutron is a neutron emitted after a nuclear fission event, by one of the fission products (or actually, a fission product daughter after beta decay), any time from a few milliseconds to a few minutes after the fission event. Neutrons born within 10−14 seconds of the fission are termed "prompt neutrons". In a nuclear reactor large nuclides fission into two neutron-rich fission products (i.e. unstable nuclides) and free neutrons (prompt neutrons). Many of these fission products then undergo radioactive decay (usually beta decay) and the resulting nuclides are unstable with respect to beta decay. | https://en.wikipedia.org/wiki/Delayed_neutrons |
A small fraction of them are excited enough to be able to beta-decay by emitting a delayed neutron in addition to the beta. The moment of beta decay of the precursor nuclides - which are the precursors of the delayed neutrons - happens orders of magnitude later compared to the emission of the prompt neutrons. Hence the neutron that originates from the precursor's decay is termed a delayed neutron. | https://en.wikipedia.org/wiki/Delayed_neutrons |
However, the "delay" in the neutron emission is due to the delay in beta decay (which is slower since controlled by the weak force), since neutron emission, like gamma emission, is controlled by the strong nuclear force and thus either happens at fission, or nearly simultaneously with the beta decay, immediately after it. The various half lives of these decays that finally result in neutron emission, are thus the beta decay half lives of the precursor radionuclides. Delayed neutrons play an important role in nuclear reactor control and safety analysis. | https://en.wikipedia.org/wiki/Delayed_neutrons |
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal (thermal) kinetic energy. These thermal neutrons are immensely more susceptible than fast neutrons to propagate a nuclear chain reaction of uranium-235 or other fissile isotope by colliding with their atomic nucleus. Water (sometimes called "light water" in this context) is the most commonly used moderator (roughly 75% of the world's reactors). Solid graphite (20% of reactors) and heavy water (5% of reactors) are the main alternatives. Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility. | https://en.wikipedia.org/wiki/Neutron_moderator |
In nuclear engineering, a prompt neutron is a neutron immediately emitted (neutron emission) by a nuclear fission event, as opposed to a delayed neutron decay which can occur within the same context, emitted after beta decay of one of the fission products anytime from a few milliseconds to a few minutes later. Prompt neutrons emerge from the fission of an unstable fissionable or fissile heavy nucleus almost instantaneously. There are different definitions for how long it takes for a prompt neutron to emerge. For example, the United States Department of Energy defines a prompt neutron as a neutron born from fission within 10−13 seconds after the fission event. | https://en.wikipedia.org/wiki/Prompt_neutron |
The U.S. Nuclear Regulatory Commission defines a prompt neutron as a neutron emerging from fission within 10−14 seconds. This emission is controlled by the nuclear force and is extremely fast. By contrast, so-called delayed neutrons are delayed by the time delay associated with beta decay (mediated by the weak force) to the precursor excited nuclide, after which neutron emission happens on a prompt time scale (i.e., almost immediately). | https://en.wikipedia.org/wiki/Prompt_neutron |
In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal chain reaction can only be achieved with fissile material. The predominant neutron energy in a system may be typified by either slow neutrons (i.e., a thermal system) or fast neutrons. Fissile material can be used to fuel thermal-neutron reactors, fast-neutron reactors and nuclear explosives. | https://en.wikipedia.org/wiki/Fissionable_material |
In nuclear engineering, prompt criticality describes a nuclear fission event in which criticality (the threshold for an exponentially growing nuclear fission chain reaction) is achieved with prompt neutrons alone and does not rely on delayed neutrons. As a result, prompt supercriticality causes a much more rapid growth in the rate of energy release than other forms of criticality. Nuclear weapons are based on prompt criticality, while nuclear reactors rely on delayed neutrons or external neutrons to achieve criticality. | https://en.wikipedia.org/wiki/Prompt_critical |
In nuclear engineering, the temperature coefficient of reactivity is a measure of the change in reactivity (resulting in a change in power), brought about by a change in temperature of the reactor components or the reactor coolant. This may be defined as α T = ∂ ρ ∂ T {\displaystyle \alpha _{T}={\frac {\partial \rho }{\partial T}}} Where ρ {\displaystyle \rho } is reactivity and T is temperature. The relationship shows that α T {\displaystyle \alpha _{T}} is the value of the partial differential of reactivity with respect to temperature and is referred to as the "temperature coefficient of reactivity". As a result, the temperature feedback provided by α T {\displaystyle \alpha _{T}} has an intuitive application to passive nuclear safety. | https://en.wikipedia.org/wiki/Negative_temperature_coefficient |
A negative α T {\displaystyle \alpha _{T}} is broadly cited as important for reactor safety, but wide temperature variations across real reactors (as opposed to a theoretical homogeneous reactor) limit the usability of a single metric as a marker of reactor safety. In water moderated nuclear reactors, the bulk of reactivity changes with respect to temperature are brought about by changes in the temperature of the water. | https://en.wikipedia.org/wiki/Negative_temperature_coefficient |
However each element of the core has a specific temperature coefficient of reactivity (e.g. the fuel or cladding). The mechanisms which drive fuel temperature coefficients of reactivity are different from water temperature coefficients. While water expands as temperature increases, causing longer neutron travel times during moderation, fuel material will not expand appreciably. Changes in reactivity in fuel due to temperature stem from a phenomenon known as doppler broadening, where resonance absorption of fast neutrons in fuel filler material prevents those neutrons from thermalizing (slowing down). | https://en.wikipedia.org/wiki/Negative_temperature_coefficient |
In nuclear engineering, the void coefficient (more properly called void coefficient of reactivity) is a number that can be used to estimate how much the reactivity of a nuclear reactor changes as voids (typically steam bubbles) form in the reactor moderator or coolant. Net reactivity in a reactor is the sum total of multiple contributions, of which the void coefficient is but one. Reactors in which either the moderator or the coolant is a liquid typically will have a void coefficient value that is either negative (if the reactor is under-moderated) or positive (if the reactor is over-moderated). Reactors in which neither the moderator nor the coolant is a liquid (e.g., a graphite-moderated, gas-cooled reactor) will have a void coefficient value equal to zero. It is unclear how the definition of "void" coefficient applies to reactors in which the moderator/coolant is neither liquid nor gas (supercritical water reactor). | https://en.wikipedia.org/wiki/Void_coefficient |
In nuclear fusion power research, the plasma-facing material (or materials) (PFM) is any material used to construct the plasma-facing components (PFC), those components exposed to the plasma within which nuclear fusion occurs, and particularly the material used for the lining the first wall or divertor region of the reactor vessel. Plasma-facing materials for fusion reactor designs must support the overall steps for energy generation, these include: Generating heat through fusion, Capturing heat in the first wall, Transferring heat at a faster rate than capturing heat. Generating electricity.In addition PFMs have to operate over the lifetime of a fusion reactor vessel by handling the harsh environmental conditions, such as: Ion bombardment causing physical and chemical sputtering and therefore erosion. | https://en.wikipedia.org/wiki/Plasma_facing_material |
Ion implantation causing displacement damage and chemical composition changes High-heat fluxes (e.g. 10 MW/m 2 {\displaystyle ^{2}} ) due to ELMS and other transients. Limited tritium codeposition and sequestration. Stable thermomechanical properties under operation. | https://en.wikipedia.org/wiki/Plasma_facing_material |
Limited number of negative nuclear transmutation effectsCurrently, fusion reactor research focuses on improving efficiency and reliability in heat generation and capture and on raising the rate of transfer. Generating electricity from heat is beyond the scope of current research, due to existing efficient heat-transfer cycles, such as heating water to operate steam turbines that drive electrical generators. Current reactor designs are fueled by deuterium-tritium (D-T) fusion reactions, which produce high-energy neutrons that can damage the first wall, however, high-energy neutrons (14.1 MeV) are needed for blanket and Tritium breeder operation. Tritium is not a naturally abundant isotope due to its short half-life, therefore for a fusion D-T reactor it will need to be bred by the nuclear reaction of lithium (Li), boron (B), or beryllium (Be) isotopes with high-energy neutrons that collide within the first wall. | https://en.wikipedia.org/wiki/Plasma_facing_material |
In nuclear fusion, there are two types of reactors stable enough to conduct fusion: magnetic confinement reactors and inertial confinement reactors. The former method of fusion seeks to lengthen the time that ions spend close together in order to fuse them together, while the latter aims to fuse the ions so fast that they do not have time to move apart. Inertial confinement reactors, unlike magnetic confinement reactors, use laser fusion and ion-beam fusion in order to conduct fusion. | https://en.wikipedia.org/wiki/Tokamak_Fusion_Test_Reactor |
However, with magnetic confinement reactors you avoid the problem of having to find a material that can withstand the high temperatures of nuclear fusion reactions. The heating current is induced by the changing magnetic fields in central induction coils and exceeds a million amperes. Magnetic fusion devices keep the hot plasma out of contact with the walls of its container by keeping it moving in circular or helical paths by means of the magnetic force on charged particles and by a centripetal force acting on the moving particles. | https://en.wikipedia.org/wiki/Tokamak_Fusion_Test_Reactor |
In nuclear fusion, two low-mass nuclei come into very close contact with each other so that the strong force fuses them. It requires a large amount of energy for the strong or nuclear forces to overcome the electrical repulsion between the nuclei in order to fuse them; therefore nuclear fusion can only take place at very high temperatures or high pressures. When nuclei fuse, a very large amount of energy is released and the combined nucleus assumes a lower energy level. The binding energy per nucleon increases with mass number up to nickel-62. | https://en.wikipedia.org/wiki/Nuclear_research |
Stars like the Sun are powered by the fusion of four protons into a helium nucleus, two positrons, and two neutrinos. The uncontrolled fusion of hydrogen into helium is known as thermonuclear runaway. A frontier in current research at various institutions, for example the Joint European Torus (JET) and ITER, is the development of an economically viable method of using energy from a controlled fusion reaction. Nuclear fusion is the origin of the energy (including in the form of light and other electromagnetic radiation) produced by the core of all stars including our own Sun. | https://en.wikipedia.org/wiki/Nuclear_research |
In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of a molecule. Chemical shifts are also used to describe signals in other forms of spectroscopy such as photoemission spectroscopy. | https://en.wikipedia.org/wiki/Chemical_shift_anisotropy |
Some atomic nuclei possess a magnetic moment (nuclear spin), which gives rise to different energy levels and resonance frequencies in a magnetic field. The total magnetic field experienced by a nucleus includes local magnetic fields induced by currents of electrons in the molecular orbitals (electrons have a magnetic moment themselves). The electron distribution of the same type of nucleus (e.g. 1H, 13C, 15N) usually varies according to the local geometry (binding partners, bond lengths, angles between bonds, and so on), and with it the local magnetic field at each nucleus. | https://en.wikipedia.org/wiki/Chemical_shift_anisotropy |
This is reflected in the spin energy levels (and resonance frequencies). The variations of nuclear magnetic resonance frequencies of the same kind of nucleus, due to variations in the electron distribution, is called the chemical shift. The size of the chemical shift is given with respect to a reference frequency or reference sample (see also chemical shift referencing), usually a molecule with a barely distorted electron distribution. | https://en.wikipedia.org/wiki/Chemical_shift_anisotropy |
In nuclear magnetic resonance (NMR) spectroscopy, three prominent nuclear magnetic interactions, dipolar coupling, chemical shift anisotropy (CSA), and first-order quadrupolar coupling, depend on the orientation of the interaction tensor with the external magnetic field. By spinning the sample around a given axis, their average angular dependence becomes: ⟨ 3 cos 2 θ − 1 ⟩ = ( 3 cos 2 θ r − 1 ) ( 3 cos 2 β − 1 ) , {\displaystyle \left\langle 3\cos ^{2}\theta -1\right\rangle =\left(3\cos ^{2}\theta _{\mathrm {r} }-1\right)\left(3\cos ^{2}\beta -1\right)\!,} where θ is the angle between the principal axis of the interaction and the magnetic field, θr is the angle of the axis of rotation relative to the magnetic field and β is the (arbitrary) angle between the axis of rotation and principal axis of the interaction. For dipolar couplings, the principal axis corresponds to the internuclear vector between the coupled spins; for the CSA, it corresponds to the direction with the largest deshielding; for the quadrupolar coupling, it corresponds to the z-axis of the electric-field gradient tensor. The angle β cannot be manipulated as it depends on the orientation of the interaction relative to the molecular frame and on the orientation of the molecule relative to the external field. | https://en.wikipedia.org/wiki/Magic_angle |
The angle θr, however, can be decided by the experimenter. If one sets θr = θm ≈ 54.7°, then the average angular dependence goes to zero. | https://en.wikipedia.org/wiki/Magic_angle |
Magic angle spinning is a technique in solid-state NMR spectroscopy which employs this principle to remove or reduce the influence of anisotropic interactions, thereby increasing spectral resolution. For a time-independent interaction, i.e. heteronuclear dipolar couplings, CSA and first-order quadrupolar couplings, the anisotropic component is greatly reduced and almost suppressed in the limit of fast spinning, i.e. when the spinning frequency is greater than the width of the interaction. The averaging is only close to zero in a first-order perturbation theory treatment; higher order terms cause allowed frequencies at multiples of the spinning frequency to appear, creating spinning side-bands in the spectra. Time-dependent interactions, such as homonuclear dipolar couplings, are more difficult to average to their isotropic values by magic angle spinning; a network of strongly coupled spins will produce a mixing of spin states during the course of the sample rotation, interfering with the averaging process. | https://en.wikipedia.org/wiki/Magic_angle |
In nuclear magnetic resonance (NMR), various relaxations are the properties that it measures. | https://en.wikipedia.org/wiki/Dynamical_relaxation |
In nuclear magnetic resonance spectroscopy and magnetic resonance imaging, the Ernst angle is the flip angle (a.k.a. "tip" or "nutation" angle) for excitation of a particular spin that gives the maximal signal intensity in the least amount of time when signal averaging over many transients. In other words, the highest signal-to-noise ratio can be achieved in a given amount of time. This relationship was described by Richard R. Ernst, winner of the 1991 Nobel Prize in Chemistry.Consider a single pulse sequence consisting of (1) an excitation pulse with flip angle θ E {\displaystyle \theta _{E}} , (2) the recording of the time domain signal (Free induction decay, FID) for a duration known as acquisition time a t {\displaystyle a_{t}} , and (3) a delay until the next excitation pulse (here called interpulse delay d 1 {\displaystyle d_{1}} ). | https://en.wikipedia.org/wiki/Ernst_angle |
This sequence is repeated back-to-back many times and the sum or the average of all recorded FIDs ("transients") is calculated. If the longitudinal relaxation time T 1 {\displaystyle T_{1}} of the specific spin in question is short compared to the sum of a t {\displaystyle a_{t}} and d 1 {\displaystyle d_{1}} , the spins (or the spin ensembles) are fully or close to fully relaxed. Then a 90° flip angle will yield the maximum signal intensity (or signal-to-noise ratio) per number of averaged FIDs. | https://en.wikipedia.org/wiki/Ernst_angle |
For shorter intervals between excitation pulses compared to the longitudinal relaxation, partial longitudinal relaxation until the next excitation pulse leads to signal loss in the subsequent FID. This signal loss can be minimized by reducing the flip angle. The optimal signal-to-noise ratio for a given combination of longitudinal relaxation time and delay between excitation pulses is obtained at the Ernst angle: cos ( θ E ) = e − ( d 1 + a t ) / T 1 {\displaystyle \cos(\theta _{E})=e^{-(d_{1}+a_{t})/T_{1}}} . | https://en.wikipedia.org/wiki/Ernst_angle |
For example, to obtain the highest signal-to-noise ratio for a signal with d 1 + a t {\displaystyle d_{1}+a_{t}} set to match the signal's T 1 {\displaystyle T_{1}} , the optimal flip angle is 68°. An NMR spectrum or an in vivo MR spectrum most of the time consists of signals of more than one spin species which can exhibit different longitudinal relaxation times. Therefore, the calculated Ernst angle may apply only to the selected one of the many signals in the spectrum and other signals may be less intense than at their own Ernst angle. | https://en.wikipedia.org/wiki/Ernst_angle |
In contrast in standard MRI, the detected signal of interest is predominantly that of a single spin species, the water 1H spins. This relationship is especially important in magnetic resonance imaging where the sum of interscan delay d 1 {\displaystyle d_{1}} and acquisition time a t {\displaystyle a_{t}} is often short relative to the signal's T 1 {\displaystyle T_{1}} value. | https://en.wikipedia.org/wiki/Ernst_angle |
In the MRI community, this sum is often known as repetition time T R = d 1 + a t {\displaystyle T_{R}=d_{1}+a_{t}} , thus cos ( θ E ) = e − T R / T 1 {\displaystyle \cos(\theta _{E})=e^{-T_{R}/T_{1}}} , and, consequently, θ E = arccos ( e − T R T 1 ) . {\displaystyle \theta _{E}=\arccos \left(e^{-{\frac {T_{R}}{T_{1}}}}\right).} == References == | https://en.wikipedia.org/wiki/Ernst_angle |
In nuclear magnetic resonance spectroscopy, the highly abundant 12C isotope does not produce any signal whereas the comparably rare 13C isotope is easily detected. As a result, carbon isotopomers of a compound can be studied by carbon-13 NMR to learn about the different carbon atoms in the structure. Each individual structure that contains a single 13C isotope provides data about the structure in its immediate vicinity. A large sample of a chemical contains a mixture of all such isotopomers, so a single spectrum of the sample contains data about all carbons in it. | https://en.wikipedia.org/wiki/Isotopomer |
Nearly all of the carbon in normal samples of carbon-based chemicals is 12C, with only about 1% abundance of 13C, so there is only about a 1% abundance of the total of the singly-substituted isotopologues, and exponentially smaller amounts of structures having two or more 13C in them. The rare case where two adjacent carbon atoms in a single structure are both 13C causes a detectable coupling effect between them as well as signals for each one itself. The INADEQUATE correlation experiment uses this effect to provide evidence for which carbon atoms in a structure are attached to each other, which can be useful for determining the actual structure of an unknown chemical. | https://en.wikipedia.org/wiki/Isotopomer |
In nuclear medicine imaging, radiopharmaceuticals are taken internally, for example, through inhalation, intravenously or orally. Then, external detectors (gamma cameras) capture and form images from the radiation emitted by the radiopharmaceuticals. This process is unlike a diagnostic X-ray, where external radiation is passed through the body to form an image.There are several techniques of diagnostic nuclear medicine. 2D: Scintigraphy ("scint") is the use of internal radionuclides to create two-dimensional images. | https://en.wikipedia.org/wiki/Nuclear_cardiology |
3D: SPECT is a 3D tomographic technique that uses gamma camera data from many projections and can be reconstructed in different planes. Positron emission tomography (PET) uses coincidence detection to image functional processes. Nuclear medicine tests differ from most other imaging modalities in that diagnostic tests primarily show the physiological function of the system being investigated as opposed to traditional anatomical imaging such as CT or MRI. | https://en.wikipedia.org/wiki/Nuclear_cardiology |
Nuclear medicine imaging studies are generally more organ-, tissue- or disease-specific (e.g.: lungs scan, heart scan, bone scan, brain scan, tumor, infection, Parkinson etc.) than those in conventional radiology imaging, which focus on a particular section of the body (e.g.: chest X-ray, abdomen/pelvis CT scan, head CT scan, etc.). In addition, there are nuclear medicine studies that allow imaging of the whole body based on certain cellular receptors or functions. Examples are whole body PET scans or PET/CT scans, gallium scans, indium white blood cell scans, MIBG and octreotide scans. | https://en.wikipedia.org/wiki/Nuclear_cardiology |
While the ability of nuclear metabolism to image disease processes from differences in metabolism is unsurpassed, it is not unique. Certain techniques such as fMRI image tissues (particularly cerebral tissues) by blood flow and thus show metabolism. Also, contrast-enhancement techniques in both CT and MRI show regions of tissue that are handling pharmaceuticals differently, due to an inflammatory process. | https://en.wikipedia.org/wiki/Nuclear_cardiology |
Diagnostic tests in nuclear medicine exploit the way that the body handles substances differently when there is disease or pathology present. The radionuclide introduced into the body is often chemically bound to a complex that acts characteristically within the body; this is commonly known as a tracer. In the presence of disease, a tracer will often be distributed around the body and/or processed differently. | https://en.wikipedia.org/wiki/Nuclear_cardiology |
For example, the ligand methylene-diphosphonate (MDP) can be preferentially taken up by bone. By chemically attaching technetium-99m to MDP, radioactivity can be transported and attached to bone via the hydroxyapatite for imaging. Any increased physiological function, such as due to a fracture in the bone, will usually mean increased concentration of the tracer. | https://en.wikipedia.org/wiki/Nuclear_cardiology |
This often results in the appearance of a "hot spot", which is a focal increase in radio accumulation or a general increase in radio accumulation throughout the physiological system. Some disease processes result in the exclusion of a tracer, resulting in the appearance of a "cold spot". Many tracer complexes have been developed to image or treat many different organs, glands, and physiological processes. | https://en.wikipedia.org/wiki/Nuclear_cardiology |
In nuclear medicine, an atomic cocktail is also used to describe a real-life radioactive mixture that is drunk by patients with hyperthyroidism and was discovered in 1941 through the work of Dr. Saul Hertz and others. The "Atomic Cocktail" song was released by Slim Gaillard in 1945 and included the following lyrics:"It's the drink that you don't pour, now when you take one sip you won't need anymore You're small as a beetle or big as a whale, Boom! Atomic Cocktail" | https://en.wikipedia.org/wiki/Atomic_(cocktail) |
In nuclear physics a superdeformed nucleus is a nucleus that is very far from spherical, forming an ellipsoid with axes in ratios of approximately 2:1:1. Normal deformation is approximately 1.3:1:1. Only some nuclei can exist in superdeformed states. The first superdeformed states to be observed were the fission isomers, low-spin states of elements in the actinide series. | https://en.wikipedia.org/wiki/Superdeformation |
The strong force decays much faster than the Coulomb force, which becomes stronger when nucleons are greater than 2.5 femtometers apart. For this reason, these elements undergo spontaneous fission. | https://en.wikipedia.org/wiki/Superdeformation |
In the late 1980s, high-spin superdeformed rotational bands were observed in other regions of the periodic table. Specific elements include ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, and mercury. The existence of superdeformed states occurs because of a combination of macroscopic and microscopic factors, which together lower their energies, and make them stable minima of energy as a function of deformation. | https://en.wikipedia.org/wiki/Superdeformation |
Macroscopically, the nucleus can be described by the liquid drop model. The liquid drop's energy as a function of deformation is at a minimum for zero deformation, due to the surface tension term. However, the curve may become soft with respect to high deformations because of the Coulomb repulsion (especially for the fission isomers, which have high Z) and also, in the case of high-spin states, because of the increased moment of inertia. | https://en.wikipedia.org/wiki/Superdeformation |
Modulating this macroscopic behavior, the microscopic shell correction creates certain superdeformed magic numbers that are analogous to the spherical magic numbers. For nuclei near these magic numbers, the shell correction creates a second minimum in the energy as a function of deformation. Even more deformed states (3:1) are called hyperdeformed. | https://en.wikipedia.org/wiki/Superdeformation |
In nuclear physics and atomic physics, weak charge refers to the Standard Model weak interaction coupling of a particle to the Z boson. For example, for any given nuclear isotope, the total weak charge is approximately −0.99 per neutron, and +0.07 per proton. It also shows an effect of parity violation during electron scattering. This same term is sometimes also used to refer to other, distinct quantities, such as weak isospin, weak hypercharge, or the vector coupling of a fermion to the Z boson (i.e. the coupling strength of weak neutral currents). | https://en.wikipedia.org/wiki/Weak_charge |
In nuclear physics and chemistry, the Q value for a reaction is the amount of energy absorbed or released during the nuclear reaction. The value relates to the enthalpy of a chemical reaction or the energy of radioactive decay products. It can be determined from the masses of reactants and products. | https://en.wikipedia.org/wiki/Q_value_(nuclear_science) |
Q values affect reaction rates. In general, the larger the positive Q value for the reaction, the faster the reaction proceeds, and the more likely the reaction is to "favor" the products. Q = ( m r − m p ) × 0.9315 GeV {\displaystyle Q=(\,m_{\text{r}}-m_{\text{p}}\,)\times {\text{0.9315 GeV }}} where the masses are in atomic mass units. Also, both m r {\displaystyle \;m_{\text{r}}\;} and m p {\displaystyle \;m_{\text{p}}\;} are the sums of the reactant and product masses respectively. | https://en.wikipedia.org/wiki/Q_value_(nuclear_science) |
In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a transformation of at least one nuclide to another. If a nucleus interacts with another nucleus or particle and they then separate without changing the nature of any nuclide, the process is simply referred to as a type of nuclear scattering, rather than a nuclear reaction. In principle, a reaction can involve more than two particles colliding, but because the probability of three or more nuclei to meet at the same time at the same place is much less than for two nuclei, such an event is exceptionally rare (see triple alpha process for an example very close to a three-body nuclear reaction). | https://en.wikipedia.org/wiki/Nuclear_reactions |
The term "nuclear reaction" may refer either to a change in a nuclide induced by collision with another particle or to a spontaneous change of a nuclide without collision. Natural nuclear reactions occur in the interaction between cosmic rays and matter, and nuclear reactions can be employed artificially to obtain nuclear energy, at an adjustable rate, on-demand. Nuclear chain reactions in fissionable materials produce induced nuclear fission. Various nuclear fusion reactions of light elements power the energy production of the Sun and stars. | https://en.wikipedia.org/wiki/Nuclear_reactions |
In nuclear physics and nuclear chemistry, the fission barrier is the activation energy required for a nucleus of an atom to undergo fission. This barrier may also be defined as the minimum amount of energy required to deform the nucleus to the point where it is irretrievably committed to the fission process. The energy to overcome this barrier can come from either neutron bombardment of the nucleus, where the additional energy from the neutron brings the nucleus to an excited state and undergoes deformation, or through spontaneous fission, where the nucleus is already in an excited and deformed state. It is important to note that efforts to understand fission processes are still an ongoing and have been a very difficult problem to solve since fission was first discovered by Lise Meitner, Otto Hahn, and Fritz Strassmann in 1938. While nuclear physicists understand many aspects of the fission process, there is currently no encompassing theoretical framework that gives a satisfactory account of the basic observations. | https://en.wikipedia.org/wiki/Fission_barrier |
In nuclear physics and particle physics, isospin (I) is a quantum number related to the up- and down quark content of the particle. More specifically, isospin symmetry is a subset of the flavour symmetry seen more broadly in the interactions of baryons and mesons. The name of the concept contains the term spin because its quantum mechanical description is mathematically similar to that of angular momentum (in particular, in the way it couples; for example, a proton–neutron pair can be coupled either in a state of total isospin 1 or in one of 0). But unlike angular momentum, it is a dimensionless quantity and is not actually any type of spin. | https://en.wikipedia.org/wiki/Isospin |
Etymologically, the term was derived from isotopic spin, a confusing term to which nuclear physicists prefer isobaric spin, which is more precise in meaning. Before the concept of quarks was introduced, particles that are affected equally by the strong force but had different charges (e.g. protons and neutrons) were considered different states of the same particle, but having isospin values related to the number of charge states. A close examination of isospin symmetry ultimately led directly to the discovery and understanding of quarks and to the development of Yang–Mills theory. Isospin symmetry remains an important concept in particle physics. | https://en.wikipedia.org/wiki/Isospin |
In nuclear physics and particle physics, the strong interaction, which is also often called the strong force or strong nuclear force, is a fundamental interaction that confines quarks into proton, neutron, and other hadron particles. The strong interaction also binds neutrons and protons to create atomic nuclei, where it is called the nuclear force. Most of the mass of a common proton or neutron is the result of the strong interaction energy; the individual quarks provide only about 1% of the mass of a proton. At the range of 10−15 m (1 femtometer, slightly more than the radius of a nucleon), the strong force is approximately 100 times as strong as electromagnetism, 106 times as strong as the weak interaction, and 1038 times as strong as gravitation.The strong interaction is observable at two ranges and mediated by two force carriers. | https://en.wikipedia.org/wiki/Strong_nuclear_force |
On a larger scale (of about 1 to 3 fm), it is the force (carried by mesons) that binds protons and neutrons (nucleons) together to form the nucleus of an atom. On the smaller scale (less than about 0.8 fm, the radius of a nucleon), it is the force (carried by gluons) that holds quarks together to form protons, neutrons, and other hadron particles. In the latter context, it is often known as the color force. | https://en.wikipedia.org/wiki/Strong_nuclear_force |
The strong force inherently has such a high strength that hadrons bound by the strong force can produce new massive particles. Thus, if hadrons are struck by high-energy particles, they give rise to new hadrons instead of emitting freely moving radiation (gluons). This property of the strong force is called color confinement, and it prevents the free "emission" of the strong force: instead, in practice, jets of massive particles are produced. | https://en.wikipedia.org/wiki/Strong_nuclear_force |
In the context of atomic nuclei, the same strong interaction force (that binds quarks within a nucleon) also binds protons and neutrons together to form a nucleus. In this capacity it is called the nuclear force (or residual strong force). So the residuum from the strong interaction within protons and neutrons also binds nuclei together. | https://en.wikipedia.org/wiki/Strong_nuclear_force |
As such, the residual strong interaction obeys a distance-dependent behavior between nucleons that is quite different from that when it is acting to bind quarks within nucleons. Additionally, distinctions exist in the binding energies of the nuclear force of nuclear fusion vs nuclear fission. Nuclear fusion accounts for most energy production in the Sun and other stars. | https://en.wikipedia.org/wiki/Strong_nuclear_force |
Nuclear fission allows for decay of radioactive elements and isotopes, although it is often mediated by the weak interaction. Artificially, the energy associated with the nuclear force is partially released in nuclear power and nuclear weapons, both in uranium or plutonium-based fission weapons and in fusion weapons like the hydrogen bomb.The strong interaction is mediated by the exchange of massless particles called gluons that act between quarks, antiquarks, and other gluons. Gluons are thought to interact with quarks and other gluons by way of a type of charge called color charge. Color charge is analogous to electromagnetic charge, but it comes in three types (±red, ±green, and ±blue) rather than one, which results in a different type of force, with different rules of behavior. These rules are detailed in the theory of quantum chromodynamics (QCD), which is the theory of quark–gluon interactions. | https://en.wikipedia.org/wiki/Strong_nuclear_force |
In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, and gravitation. It is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms: The weak interaction participates in nuclear fission and nuclear fusion. The theory describing its behaviour and effects is sometimes called quantum flavourdynamics (QFD); however, the term QFD is rarely used, because the weak force is better understood by electroweak theory (EWT).The effective range of the weak force is limited to subatomic distances and is less than the diameter of a proton. | https://en.wikipedia.org/wiki/Nuclear_weak_force |
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