1.
Fissility (geology)
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Fissility or fissibility refers to the property of rocks to split along planes of weakness into thin sheets. This is commonly observed in shales, which are sedimentary rocks, and in slates and phyllites, the fissility in these rocks is caused by the preferred alignment of platy phyllosilicate grains due to compaction, deformation or new mineral growth. A highly fissile rock splits easily along the cleavage
2.
Table of nuclides
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A table of nuclides or chart of nuclides is a two-dimensional graph in which one axis represents the number of neutrons and the other represents the number of protons in an atomic nucleus. Each point plotted on the graph represents the nuclide of a real or hypothetical chemical element. This system of ordering nuclides can offer an insight into the characteristics of isotopes than the better-known periodic table. A chart or table of nuclides is a map to the nuclear, or radioactive, behaviour of nuclides. It contrasts with a table, which only maps their chemical behavior. Nuclide charts organize isotopes along the X axis by their numbers of neutrons and along the Y axis by their numbers of protons and this representation was first published by Giorgio Fea in 1935, and expanded by Emilio Segrè in 1945 or G. Seaborg. In 1958, Walter Seelmann-Eggebert and Gerda Pfennig published the first edition of the Karlsruhe Nuclide Chart and its 7th edition was made available in 2006. It has become a tool of the nuclear community. The isotope table below shows isotopes of the elements, including all with half-life of at least one day. They are arranged with increasing numbers from left to right. Cell colour denotes the half-life of each isotope, if a border is present, in graphical browsers, each isotope also has a tool tip indicating its half-life. Each color represents certain range of length of half-life, and the color of border indicates the half-life of its nuclear isomer state, some nuclides have multiple nuclear isomers, and this table notes the longest one. Dotted borders mean it has a nuclear isomer, and its color is same as the normal counterpart, isotopes are nuclides with the same number of protons but differing numbers of neutrons, that is, they have the same atomic number and are therefore the same chemical element. Isotopes neighbor each other vertically, e. g. carbon-12, carbon-13, carbon-14 or oxygen-15, oxygen-16, isotones are nuclides with the same number of neutrons but differing number of protons. Example, carbon-14, nitrogen-15, oxygen-16 in the table above. Isobars are nuclides with the number of nucleons, i. e. mass number. Isobars neighbor each other diagonally from lower-left to upper-right, example, carbon-14, nitrogen-14, oxygen-14 in the sample table above. Isodiaphers are nuclides with the difference between neutrons and protons
3.
Thermal neutron
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The neutron detection temperature, also called the neutron energy, indicates a free neutrons kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature, the neutron energy distribution is then adopted to the Maxwellian distribution known for thermal motion. Qualitatively, the higher the temperature, the higher the energy of the free neutrons. Kinetic energy, speed and wavelength of the neutron are related through the De Broglie relation, but different ranges with different names are observed in other sources. After a number of collisions with nuclei in a medium at this temperature, neutrons arrive at about this energy level, Neutrons of energy greater than thermal Greater than 0.2 eV Neutrons which are strongly absorbed by cadmium Less than 0.4 eV. Neutrons which are not strongly absorbed by cadmium Greater than 0.6 eV, Neutrons of energy slightly greater than epicadmium neutrons. Refers to neutrons which are strongly susceptible non-fission capture by U-238,1 eV to 300 eV Neutrons that are between slow and fast Few hundred eV to 0.5 MeV. A fast neutron is a neutron with a kinetic energy level close to 1 MeV, hence a speed of 14,000 km/s. They are named fast neutrons to distinguish them from lower-energy thermal neutrons, fast neutrons are produced by nuclear processes, nuclear fission produces neutrons with a mean energy of 2 MeV, which qualifies as fast. Spontaneous fission is a type of decay that some heavy elements undergo. Nuclear fusion, deuterium–tritium fusion produces neutrons of 14.1 MeV that can easily fission uranium-238, neutron emission occurs in very rare situations in which a nucleus contains extra neutrons. Unstable nuclei of this sort will often decay rapidly, with half-lives of a fraction of a second, fast neutrons are usually undesirable in a steady-state nuclear reactor because most fissile fuel has a higher reaction rate with thermal neutrons. Fast neutrons can be changed into thermal neutrons via a process called moderation. This is done through numerous collisions with slower-moving and thus lower-temperature particles like atomic nuclei and these collisions will generally speed up the other particle and slow down the neutron and scatter it. Ideally, a room temperature neutron moderator is used for this process, in reactors heavy water, light water, or graphite are typically used to moderate neutrons. Relativistic Greater than 20 MeV Pile Neutrons of all present in nuclear reactors 0.001 eV to 15 MeV. Ultracold neutrons are free neutrons which can be stored in traps made from certain materials, most fission reactors are thermal reactors that use a neutron moderator to slow down the neutrons produced by nuclear fission. Moderation substantially increases the fission cross section for fissile nuclei such as uranium-235 or plutonium-239, the combination of these effects allows light water reactors to use low-enriched uranium
4.
Nuclear engineering
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In the sub-field of nuclear fission, it particularly includes the interaction and maintenance of systems and components like nuclear reactors, nuclear power plants, or nuclear weapons. The United States generates about 18% of its electricity from power plants. Nuclear engineers in this field work, directly or indirectly. Current research in the industry is directed at producing economical, proliferation-resistant reactor designs with passive safety features, a principal pipeline for trained personnel for US reactor facilities is the Navy Nuclear Power Program. An important field is medical physics, and its subfields nuclear medicine, radiation therapy, health physics, from x-ray machines to MRI to PET, among many others, medical physics provides most of modern medicines diagnostic capability along with providing many treatment options. Nuclear materials research focuses on two main areas, nuclear fuels and irradiation-induced modification of materials. Improvement of three nuclear fuels is crucial for obtaining increased efficiency from nuclear reactors, irradiation effects studies have many purposes, from studying structural changes to reactor components to studying nano-modification of metals using ion-beams or particle accelerators. This includes detector design, fabrication and analysis, measurements of atomic and nuclear parameters. American Nuclear Society Nuclear Institute International Atomic Energy Agency Gowing, Margaret, independence and Deterrence, Britain and Atomic Energy, Vol. I, Policy Making, 1945–52, Vol. II, Policy Execution, 1945–52 Johnston, Sean F
5.
Nuclear fission
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In nuclear physics and nuclear chemistry, nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts. The fission process often produces free neutrons and gamma photons, Frisch named the process by analogy with biological fission of living cells. It is a reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. In order for fission to produce energy, the binding energy of the resulting elements must be less negative than that of the starting element. Fission is a form of nuclear transmutation because the fragments are not the same element as the original atom. The two nuclei produced are most often of comparable but slightly different sizes, typically with a ratio of products of about 3 to 2. Most fissions are binary fissions, but occasionally, three positively charged fragments are produced, in a ternary fission, the smallest of these fragments in ternary processes ranges in size from a proton to an argon nucleus. Nuclear fission produces energy for power and drives the explosion of nuclear weapons. Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons and this makes possible a self-sustaining nuclear chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon. Nuclear fission can occur without neutron bombardment as a type of radioactive decay and this type of fission is rare except in a few heavy isotopes. In engineered nuclear devices, essentially all nuclear fission occurs as a nuclear reaction — a bombardment-driven process that results from the collision of two subatomic particles, in nuclear reactions, a subatomic particle collides with an atomic nucleus and causes changes to it. Nuclear reactions are driven by the mechanics of bombardment, not by the relatively constant exponential decay. Many types of reactions are currently known. Nuclear fission differs importantly from other types of reactions, in that it can be amplified. In such a reaction, free neutrons released by each fission event can trigger yet more events, the chemical element isotopes that can sustain a fission chain reaction are called nuclear fuels, and are said to be fissile. The most common nuclear fuels are 235U and 239Pu and these fuels break apart into a bimodal range of chemical elements with atomic masses centering near 95 and 135 u. Most nuclear fuels undergo spontaneous fission only very slowly, decaying instead mainly via an alpha-beta decay chain over periods of millennia to eons. In a nuclear reactor or nuclear weapon, the majority of fission events are induced by bombardment with another particle, a neutron
6.
Nuclear chain reaction
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The specific nuclear reaction may be the fission of heavy isotopes. The nuclear chain reaction releases several million times more energy per reaction than any chemical reaction, chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and were reasonably well understood before nuclear chain reactions were proposed. It was understood that chemical reactions were responsible for exponentially increasing rates in reactions. The concept of a chain reaction was reportedly first hypothesized by Hungarian scientist Leó Szilárd on September 12,1933. The neutron had been discovered in 1932, shortly before, Szilárd realized that if a nuclear reaction produced neutrons, which then caused further nuclear reactions, the process might be self-perpetuating. Szilárd, however, did not propose fission as the mechanism for his chain reaction, instead, Szilárd proposed using mixtures of lighter known isotopes which produced neutrons in copious amounts. He filed a patent for his idea of a nuclear reactor the following year. In 1936, Szilárd attempted to create a reaction using beryllium and indium. In 1956, Paul Kuroda of the University of Arkansas postulated that a fission reactor may have once existed. Since nuclear chain reactions only require natural materials, it is possible to have these chain reactions occur where there is the combination of materials within the Earths crust. Kurodas prediction was verified with the discovery of evidence of natural self-sustaining nuclear chain reactions in the past at Oklo in Gabon, fission chain reactions occur because of interactions between neutrons and fissile isotopes. The chain reaction requires both the release of neutrons from fissile isotopes undergoing nuclear fission and the subsequent absorption of some of these neutrons in fissile isotopes, when an atom undergoes nuclear fission, a few neutrons are ejected from the reaction. These free neutrons will interact with the surrounding medium, and if more fissile fuel is present, some may be absorbed. Thus, the repeats to give a reaction that is self-sustaining. Nuclear power plants operate by controlling the rate at which nuclear reactions occur. Moreover, the materials in a reactor core and the uranium enrichment level make a nuclear explosion impossible. On the other hand, nuclear weapons are specifically engineered to produce a reaction that is so fast, when properly designed, this uncontrolled reaction can lead to an explosive energy release. Nuclear weapons employ high quality, highly enriched fuel exceeding the critical size, the fuel for energy purposes, such as in a nuclear fission reactor, is very different, usually consisting of a low-enriched oxide material
7.
Neutron
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The neutron is a subatomic particle, symbol n or n0, with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with approximately one atomic mass unit, constitute the nucleus of an atom. Their properties and interactions are described by nuclear physics, the nucleus consists of Z protons, where Z is called the atomic number, and N neutrons, where N is the neutron number. The atomic number defines the properties of the atom. The terms isotope and nuclide are often used synonymously, but they are chemical and nuclear concepts, the atomic mass number, symbol A, equals Z+N. For example, carbon has atomic number 6, and its abundant carbon-12 isotope has 6 neutrons, some elements occur in nature with only one stable isotope, such as fluorine. Other elements occur with many stable isotopes, such as tin with ten stable isotopes, even though it is not a chemical element, the neutron is included in the table of nuclides. Within the nucleus, protons and neutrons are bound together through the nuclear force, neutrons are produced copiously in nuclear fission and fusion. They are a contributor to the nucleosynthesis of chemical elements within stars through fission, fusion. The neutron is essential to the production of nuclear power, in the decade after the neutron was discovered in 1932, neutrons were used to induce many different types of nuclear transmutations. These events and findings led to the first self-sustaining nuclear reactor, free neutrons, or individual neutrons free of the nucleus, are effectively a form of ionizing radiation, and as such, are a biological hazard, depending upon dose. A small natural background flux of free neutrons exists on Earth, caused by cosmic ray showers. Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation, neutrons and protons are both nucleons, which are attracted and bound together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton. The nuclei of the hydrogen isotopes deuterium and tritium contain one proton bound to one. All other types of nuclei are composed of two or more protons and various numbers of neutrons. The most common nuclide of the chemical element lead, 208Pb has 82 protons and 126 neutrons. The free neutron has a mass of about 1. 675×10−27 kg, the neutron has a mean square radius of about 0. 8×10−15 m, or 0.8 fm, and it is a spin-½ fermion
8.
Slow neutron
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The neutron detection temperature, also called the neutron energy, indicates a free neutrons kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature, the neutron energy distribution is then adopted to the Maxwellian distribution known for thermal motion. Qualitatively, the higher the temperature, the higher the energy of the free neutrons. Kinetic energy, speed and wavelength of the neutron are related through the De Broglie relation, but different ranges with different names are observed in other sources. After a number of collisions with nuclei in a medium at this temperature, neutrons arrive at about this energy level, Neutrons of energy greater than thermal Greater than 0.2 eV Neutrons which are strongly absorbed by cadmium Less than 0.4 eV. Neutrons which are not strongly absorbed by cadmium Greater than 0.6 eV, Neutrons of energy slightly greater than epicadmium neutrons. Refers to neutrons which are strongly susceptible non-fission capture by U-238,1 eV to 300 eV Neutrons that are between slow and fast Few hundred eV to 0.5 MeV. A fast neutron is a neutron with a kinetic energy level close to 1 MeV, hence a speed of 14,000 km/s. They are named fast neutrons to distinguish them from lower-energy thermal neutrons, fast neutrons are produced by nuclear processes, nuclear fission produces neutrons with a mean energy of 2 MeV, which qualifies as fast. Spontaneous fission is a type of decay that some heavy elements undergo. Nuclear fusion, deuterium–tritium fusion produces neutrons of 14.1 MeV that can easily fission uranium-238, neutron emission occurs in very rare situations in which a nucleus contains extra neutrons. Unstable nuclei of this sort will often decay rapidly, with half-lives of a fraction of a second, fast neutrons are usually undesirable in a steady-state nuclear reactor because most fissile fuel has a higher reaction rate with thermal neutrons. Fast neutrons can be changed into thermal neutrons via a process called moderation. This is done through numerous collisions with slower-moving and thus lower-temperature particles like atomic nuclei and these collisions will generally speed up the other particle and slow down the neutron and scatter it. Ideally, a room temperature neutron moderator is used for this process, in reactors heavy water, light water, or graphite are typically used to moderate neutrons. Relativistic Greater than 20 MeV Pile Neutrons of all present in nuclear reactors 0.001 eV to 15 MeV. Ultracold neutrons are free neutrons which can be stored in traps made from certain materials, most fission reactors are thermal reactors that use a neutron moderator to slow down the neutrons produced by nuclear fission. Moderation substantially increases the fission cross section for fissile nuclei such as uranium-235 or plutonium-239, the combination of these effects allows light water reactors to use low-enriched uranium
9.
Neutron temperature
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The neutron detection temperature, also called the neutron energy, indicates a free neutrons kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature, the neutron energy distribution is then adopted to the Maxwellian distribution known for thermal motion. Qualitatively, the higher the temperature, the higher the energy of the free neutrons. Kinetic energy, speed and wavelength of the neutron are related through the De Broglie relation, but different ranges with different names are observed in other sources. After a number of collisions with nuclei in a medium at this temperature, neutrons arrive at about this energy level, Neutrons of energy greater than thermal Greater than 0.2 eV Neutrons which are strongly absorbed by cadmium Less than 0.4 eV. Neutrons which are not strongly absorbed by cadmium Greater than 0.6 eV, Neutrons of energy slightly greater than epicadmium neutrons. Refers to neutrons which are strongly susceptible non-fission capture by U-238,1 eV to 300 eV Neutrons that are between slow and fast Few hundred eV to 0.5 MeV. A fast neutron is a neutron with a kinetic energy level close to 1 MeV, hence a speed of 14,000 km/s. They are named fast neutrons to distinguish them from lower-energy thermal neutrons, fast neutrons are produced by nuclear processes, nuclear fission produces neutrons with a mean energy of 2 MeV, which qualifies as fast. Spontaneous fission is a type of decay that some heavy elements undergo. Nuclear fusion, deuterium–tritium fusion produces neutrons of 14.1 MeV that can easily fission uranium-238, neutron emission occurs in very rare situations in which a nucleus contains extra neutrons. Unstable nuclei of this sort will often decay rapidly, with half-lives of a fraction of a second, fast neutrons are usually undesirable in a steady-state nuclear reactor because most fissile fuel has a higher reaction rate with thermal neutrons. Fast neutrons can be changed into thermal neutrons via a process called moderation. This is done through numerous collisions with slower-moving and thus lower-temperature particles like atomic nuclei and these collisions will generally speed up the other particle and slow down the neutron and scatter it. Ideally, a room temperature neutron moderator is used for this process, in reactors heavy water, light water, or graphite are typically used to moderate neutrons. Relativistic Greater than 20 MeV Pile Neutrons of all present in nuclear reactors 0.001 eV to 15 MeV. Ultracold neutrons are free neutrons which can be stored in traps made from certain materials, most fission reactors are thermal reactors that use a neutron moderator to slow down the neutrons produced by nuclear fission. Moderation substantially increases the fission cross section for fissile nuclei such as uranium-235 or plutonium-239, the combination of these effects allows light water reactors to use low-enriched uranium
10.
Fast-neutron reactor
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A fast neutron reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons. Such a reactor needs no moderator, but must use fuel that is relatively rich in fissile material when compared to that required for a thermal reactor. In order to sustain a chain reaction, the neutrons released in fission events have to react with other atoms in the fuel. The chance of this depends on the energy of the neutron, most atoms will only undergo induced fission with high energy neutrons. Natural uranium consists mostly of three isotopes, U-238, U-235, and trace quantities of U-234, a product of U-238. U-238 accounts for roughly 99. 3% of natural uranium and undergoes fission only by neutrons with energies of 5 MeV or greater, about 0. 7% of natural uranium is U-235, which undergoes fission by neutrons of any energy, but particularly by lower energy neutrons. When either of these isotopes undergoes fission they release neutrons around 1 to 2 MeV, too low to cause fission in U-238, and too high to do so easily in U-235. The common solution to this problem is to slow the neutron from these fast speeds using a moderator, any substance which interacts with the neutrons. The most common moderator is normal water, which slows the neutrons through elastic scattering until the neutrons reach thermal equilibrium with the water. Although U-238 will not undergo fission by the released in fission. Pu-239 has a cross section very similar to that of U-235. In most reactors this accounts for as much as ⅓ of the energy being generated, not all of the Pu-239 is burned up during normal operation, and the leftover, along with leftover U-238, can be separated out to be used in new fuel during nuclear reprocessing. Water is a moderator for practical reasons, but has its disadvantages. From a nuclear standpoint, the problem is that water can absorb a neutron. The most common solution to this problem is to concentrate the amount of U-235 in the fuel to produce enriched uranium. Other designs use different moderators, like water, that are much less likely to absorb neutrons. In either case, the neutron economy is based on thermal neutrons. Although U-235 and Pu-239 are less sensitive to higher energy neutrons and this means that if you enrich the fuel you will eventually reach a threshold where there are enough fissile atoms in the fuel that a chain reaction can be maintained even with fast neutrons
11.
Nuclear explosive
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A nuclear explosive is an explosive device that derives its energy from nuclear reactions. Almost all nuclear explosive devices that have designed and produced are nuclear weapons intended for warfare. Other, non-warfare, applications for nuclear explosives have occasionally been proposed, for example, nuclear pulse propulsion is a form of spacecraft propulsion that would use nuclear explosives to provide impulse to a spacecraft. A similar application is the proposal to use explosives for asteroid deflection. From 1958 to 1965 the United States government ran a project to design a nuclear explosive powered nuclear pulse rocket called Project Orion, never built, this vessel would use repeated nuclear explosions to propel itself and was considered surprisingly practical. It is thought to be a design for interstellar travel. Nuclear explosives were once considered for use in large-scale excavation, a nuclear explosion could be used to create a harbor, or a mountain pass, or possibly large underground cavities for use as storage space. It was thought that detonating an explosive in oil-rich rock could make it possible to extract more from the deposit. S government exploded 28 nuclear test-shots in a called the Operation Plowshare. The purpose of the operation was to use nuclear explosions for moving and lifting enormous amounts of earth. The Soviet Union conducted a more vigorous program of 122 nuclear tests, some with multiple devices. 7-Nuclear Explosions for the National Economy, the 1970s PACER project investigated fusion detonation as a power source
12.
Chemical element
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A chemical element or element is a species of atoms having the same number of protons in their atomic nuclei. There are 118 elements that have identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radioactive isotopes, iron is the most abundant element making up Earth, while oxygen is the most common element in the Earths crust. Chemical elements constitute all of the matter of the universe. The two lightest elements, hydrogen and helium, were formed in the Big Bang and are the most common elements in the universe. The next three elements were formed mostly by cosmic ray spallation, and are rarer than those that follow. Formation of elements with from 6 to 26 protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis, the high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. The term element is used for atoms with a number of protons as well as for a pure chemical substance consisting of a single element. A single element can form multiple substances differing in their structure, when different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals, among the more common of such native elements are copper, silver, gold, carbon, and sulfur. All but a few of the most inert elements, such as gases and noble metals, are usually found on Earth in chemically combined form. While about 32 of the elements occur on Earth in native uncombined forms. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, the history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal, alchemists and chemists subsequently identified many more, almost all of the naturally occurring elements were known by 1900. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, almost all other elements found in nature were made by various natural methods of nucleosynthesis. On Earth, small amounts of new atoms are produced in nucleogenic reactions, or in cosmogenic processes. Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope, Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected, the very heaviest elements undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized
13.
Thorium
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Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only two significantly radioactive elements that occur naturally in large quantities as a primordial element. It was discovered in 1829 by the Norwegian amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jacob Berzelius, who named it after Thor, a thorium atom has 90 protons and therefore 90 electrons, of which four are valence electrons. Thorium metal is silvery and tarnishes black when exposed to air, Thorium is weakly radioactive, all of its known isotopes are unstable. Thorium-232, which has 142 neutrons, is the most stable isotope of thorium and accounts for all natural thorium. Thorium is estimated to be three to four times more abundant than uranium in the Earths crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals. Thorium was once used as the light source in gas mantles and as an alloying material. Thorium is still used as an alloying element in TIG welding electrodes. Thorium is predicted to be able to replace uranium as fuel in nuclear reactors. Thorium is a soft, paramagnetic, bright silvery radioactive actinide metal, in the periodic table, it is located to the right of the actinide actinium, to the left of the actinide protactinium, and below the lanthanide cerium. Pure thorium is very ductile and, as normal for metals, can be cold-rolled, swaged, at room temperature, thorium metal has a face-centred cubic crystal structure, additionally, it has two other forms at exotic conditions, one at high temperature and one at high pressure. The properties of thorium vary widely depending on the amount of impurities in the sample, the purest thorium specimens usually contain about a tenth of a percent of the dioxide. These values lie intermediate between those of its neighbours actinium and protactinium, showing the continuity of trends across the early actinides, thoriums melting point of 1750 °C is above both that of actinium and that of protactinium. After thorium, there is a new smooth trend downward in the points of the early actinides from thorium to plutonium where the number of f electrons increases from about 0. Thorium has a modulus of 54 GPa, comparable to those of tin. The hardness of thorium is similar to that of steel, so heated pure thorium can be rolled in sheets. Nevertheless, while thorium is nearly half as dense as uranium and plutonium, Thorium becomes superconductive below 1.4 K. Thorium can also form alloys with many other metals. With chromium and uranium, it forms eutectic mixtures, and thorium is completely miscible in both solid and liquid states with its lighter congener cerium, as such, 232Th still occurs naturally today, four-fifths of the thorium present at Earths formation has survived to the present
14.
Atomic number
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The atomic number or proton number of a chemical element is the number of protons found in the nucleus of an atom of that element. It is identical to the number of the nucleus. The atomic number identifies a chemical element. In an uncharged atom, the number is also equal to the number of electrons. The atomic number Z, should not be confused with the mass number A and this number of neutrons, N, completes the weight, A = Z + N. Atoms with the atomic number Z but different neutron numbers N. Historically, it was these atomic weights of elements that were the quantities measurable by chemists in the 19th century. Only after 1915, with the suggestion and evidence that this Z number was also the nuclear charge, loosely speaking, the existence or construction of a periodic table of elements creates an ordering of the elements, and so they can be numbered in order. Dmitri Mendeleev claimed that he arranged his first periodic tables in order of atomic weight, however, in consideration of the elements observed chemical properties, he changed the order slightly and placed tellurium ahead of iodine. This placement is consistent with the practice of ordering the elements by proton number, Z. A simple numbering based on periodic table position was never entirely satisfactory and this central charge would thus be approximately half the atomic weight. This proved eventually to be the case, the experimental position improved dramatically after research by Henry Moseley in 1913. To do this, Moseley measured the wavelengths of the innermost photon transitions produced by the elements from aluminum to gold used as a series of movable anodic targets inside an x-ray tube. The square root of the frequency of these photons increased from one target to the next in an arithmetic progression and this led to the conclusion that the atomic number does closely correspond to the calculated electric charge of the nucleus, i. e. the element number Z. Among other things, Moseley demonstrated that the series must have 15 members—no fewer. After Moseleys death in 1915, the numbers of all known elements from hydrogen to uranium were examined by his method. There were seven elements which were not found and therefore identified as still undiscovered, from 1918 to 1947, all seven of these missing elements were discovered. By this time the first four transuranium elements had also been discovered, in 1915 the reason for nuclear charge being quantized in units of Z, which were now recognized to be the same as the element number, was not understood
15.
Fermium
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Fermium is a synthetic element with symbol Fm and atomic number 100. It is a member of the actinide series, a total of 19 isotopes are known, with 257Fm being the longest-lived with a half-life of 100.5 days. It was discovered in the debris of the first hydrogen bomb explosion in 1952 and its chemistry is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the amounts of produced fermium and all of its isotopes having relatively short half-lives. Fermium was first discovered in the fallout from the Ivy Mike nuclear test, element 99 was quickly discovered on filter papers which had been flown through the cloud from the explosion. It was then identified in December 1952 by Albert Ghiorso and co-workers at the University of California at Berkeley, about two months after the test, a new component was isolated emitting high-energy α-particles with a half-life of about a day. With such a short half-life, it could only arise from the β− decay of an isotope of einsteinium, and so had to be an isotope of the new element 100, it was quickly identified as 255Fm. The discovery of the new elements, and the new data on neutron capture, was kept secret on the orders of the U. S. military until 1955 due to Cold War tensions. The Ivy Mike studies were declassified and published in 1955, there are 19 isotopes of fermium listed in NUBASE2003, with atomic weights of 242 to 260, of which 257Fm is the longest-lived with a half-life of 100.5 days. 253Fm has a half-life of 3 days, while 251Fm of 5.3 h, 252Fm of 25.4 h, 254Fm of 3.2 h, 255Fm of 20.1 h, and 256Fm of 2.6 hours. All the remaining ones have half-lives ranging from 30 minutes to less than a millisecond, the neutron-capture product of fermium-257, 258Fm, undergoes spontaneous fission with a half-life of just 370 microseconds, 259Fm and 260Fm are also unstable with respect to spontaneous fission. This means that neutron capture cannot be used to create nuclides with a number greater than 257. As 257Fm is an α-emitter, decaying to 253Cf, and no fermium isotopes undergo beta minus decay, fermium is produced by the bombardment of lighter actinides with neutrons in a nuclear reactor. Fermium-257 is the heaviest isotope that is obtained via neutron capture, the major source is the 85 MW High Flux Isotope Reactor at the Oak Ridge National Laboratory in Tennessee, USA, which is dedicated to the production of transcurium elements. Lower mass fermium isotopes are available in quantities, however. However, nanogram quantities of fermium can be prepared for specific experiments, the Hutch experiment produced an estimated total of 250 micrograms of 257Fm. After production, the fermium must be separated from other actinides and this is usually achieved by ion-exchange chromatography, with the standard process using a cation exchanger such as Dowex 50 or TEVA eluted with a solution of ammonium α-hydroxyisobutyrate. Smaller cations form more stable complexes with the anion
16.
Isotope
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Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of an element have the same number of protons in each atom. The number of protons within the nucleus is called atomic number and is equal to the number of electrons in the neutral atom. Each atomic number identifies a specific element, but not the isotope, the number of nucleons in the nucleus is the atoms mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12,13 and 14 respectively. The atomic number of carbon is 6, which means that carbon atom has 6 protons. Nuclide refers to a rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, whereas the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. Because isotope is the term, it is better known than nuclide. An isotope and/or nuclide is specified by the name of the particular element followed by a hyphen, when a chemical symbol is used, e. g. C for carbon, standard notation is to indicate the number with a superscript at the upper left of the chemical symbol. Because the atomic number is given by the element symbol, it is common to only the mass number in the superscript. The letter m is sometimes appended after the number to indicate a nuclear isomer. For example, 14C is a form of carbon, whereas 12C. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, primordial nuclides include 32 nuclides with very long half-lives and 254 that are formally considered as stable nuclides, because they have not been observed to decay. In most cases, for reasons, if an element has stable isotopes. Theory predicts that many apparently stable isotopes/nuclides are radioactive, with extremely long half-lives, of the 254 nuclides never observed to decay, only 90 of these are theoretically stable to all known forms of decay
17.
Neutron number
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The neutron number, symbol N, is the number of neutrons in a nuclide. Atomic number plus neutron number equals mass number, Z+N=A, the difference between the neutron number and the atomic number is known as the neutron excess, D = N - Z = A - 2Z. Neutron number is rarely written explicitly in nuclide symbol notation, in order of increasing explicitness and decreasing frequency of usage, Nuclides that have the same neutron number but a different proton number are called isotones. This word was formed by replacing the p in isotope with n for neutron, Nuclides that have the same mass number are called isobars. Nuclides that have the same neutron excess are called isodiaphers, chemical properties are primarily determined by proton number, which determines which chemical element the nuclide is a member of, neutron number has only a slight influence. Neutron number is primarily of interest for nuclear properties, for example, actinides with odd neutron number are usually fissile while actinides with even neutron number are usually not fissile. Only 57 stable nuclides have an odd number, compared to 200 with an even neutron number. No odd-neutron-number isotope is the most naturally abundant isotope in its element, except for beryllium-9 which is the only stable isotope, nitrogen-14. Only two stable nuclides have fewer neutrons than protons, hydrogen-1 and helium-3
18.
Proton
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A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with masses of one atomic mass unit, are collectively referred to as nucleons. One or more protons are present in the nucleus of every atom, the number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number. Since each element has a number of protons, each element has its own unique atomic number. The word proton is Greek for first, and this name was given to the nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the nucleus could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore a candidate to be a particle, and hence a building block of nitrogen. In the modern Standard Model of particle physics, protons are hadrons, and like neutrons, although protons were originally considered fundamental or elementary particles, they are now known to be composed of three valence quarks, two up quarks and one down quark. The rest masses of quarks contribute only about 1% of a protons mass, the remainder of a protons mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. At sufficiently low temperatures, free protons will bind to electrons, however, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, the result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom. Such free hydrogen atoms tend to react chemically with other types of atoms at sufficiently low energies. When free hydrogen atoms react with other, they form neutral hydrogen molecules. Protons are spin-½ fermions and are composed of three quarks, making them baryons. Protons have an exponentially decaying positive charge distribution with a mean square radius of about 0.8 fm. Protons and neutrons are both nucleons, which may be together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton
19.
Nuclide
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A nuclide is an atomic species characterized by the specific constitution of its nucleus, i. e. by its number of protons Z, its number of neutrons N, and its nuclear energy state. The word nuclide was proposed by Truman P. Kohman in 1947, Kohman originally suggested nuclide as referring to a species of nucleus defined by containing a certain number of neutrons and protons. The word thus was originally intended to focus on the nucleus, nuclide refers to a nucleus rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, while the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. Since isotope is the term, it is better known than nuclide. A set of nuclides with equal number, i. e. of the same chemical element but different neutron numbers, are called isotopes of the element. Particular nuclides are still often loosely called isotopes, but the term nuclide is the one in general. In similar manner, a set of nuclides with equal mass number A, but different atomic number, are called isobars, and isotones are nuclides of equal neutron number but different proton numbers. The name isotone has been derived from the isotope to emphasize that in the first group of nuclides it is the number of neutrons that is constant. See Isotope#Notation for an explanation of the used for different nuclide or isotope types. Nuclear isomers are members of a set of nuclides with equal number and equal mass number. An example is the two states of the single isotope 99 43Tc shown among the decay schemes, each of these two states qualifies as a different nuclide, illustrating one way that nuclides may differ from isotopes. The most long-lived non-ground state nuclear isomer is the nuclide tantalum-180m and this nuclide occurs primordially, and has never been observed to decay to the ground state. There are about 254 nuclides in nature that have never observed to decay. They occur among the 80 different elements that have one or more stable isotopes, see stable isotope and primordial nuclide. Unstable nuclides are radioactive and are called radionuclides and their decay products are called radiogenic nuclides. About 254 stable and about 85 unstable nuclides exist naturally on Earth, natural radionuclides may be conveniently subdivided into three types
20.
Uranium-238
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Uranium-238 is the most common isotope of uranium found in nature, making up over 99% of it. Unlike uranium-235 it is non-fissile, which means it cannot sustain a chain reaction, however, it is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239. 238U cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. Doppler broadening of U-238s neutron absorption resonances, increasing absorption as fuel increases, is also an essential negative feedback mechanism for reactor control. Around 99. 284% of natural uranium is uranium-238, which has a half-life of 1. 41×1017 seconds, depleted uranium has an even higher concentration of the 238U isotope, and even low-enriched uranium, while having a higher proportion of the uranium-235 isotope, is still mostly 238U. In a fission reactor, uranium-238 can be used to generate 239Pu. In a typical nuclear reactor, up to one-third of the power does come from the fission of 239Pu, which is not supplied as a fuel to the reactor. 238U is not usable directly as fuel, though it can produce energy via fast fission. In this process, a neutron that has an energy in excess of 1 MeV can cause the nucleus of 238U to split in two. 238U can be used as a material for creating plutonium-239. Breeder reactors carry out such a process of transmutation to convert the fertile isotope 238U into fissile Pu-239 and it has been estimated that there is anywhere from 10,000 to five billion years worth of 238U for use in these power plants. Breeder technology has been used in experimental nuclear reactors. By December 2005, the breeder reactor producing power was the 600-megawatt BN-600 reactor at the Beloyarsk Nuclear Power Station in Russia. Russia has planned to build another unit, BN-800, at the Beloyarsk nuclear power plant, also, Japans Monju breeder reactor is planned to be started, having been shut down since 1995, and both China and India have announced plans to build nuclear breeder reactors. The breeder reactor as its name implies creates even larger quantities of Pu-239 than the nuclear reactor. This design is still in the stages of development. It is not as effective as ordinary water for stopping fast neutrons, both metallic depleted uranium and depleted uranium dioxide are used for radiation shielding. Uranium is about five times better as a ray shield than lead
21.
Uranium-235
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Uranium-235 is an isotope of uranium making up about 0. 72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i. e. it can sustain a chain reaction. It is the fissile isotope that is a primordial nuclide or found in significant quantity in nature. Uranium-235 has a half-life of 703.8 million years and it was discovered in 1935 by Arthur Jeffrey Dempster. Its nuclear cross section for thermal neutrons is about 584.994 barns. For fast neutrons it is on the order of 1 barn, most but not all neutron absorptions result in fission, a minority result in neutron capture forming uranium-236. This is around 2.5 million times more than the energy released from burning coal, uranium enrichment removes some of the uranium-238 and increases the proportion of uranium-235. Highly enriched uranium, which contains a greater proportion of U-235, is sometimes used in nuclear weapon design. If at least one neutron from U-235 fission strikes another nucleus and causes it to fission, if the reaction will sustain itself, it is said to be critical, and the mass of U-235 required to produce the critical condition is said to be a critical mass. A fission chain reaction produces intermediate mass fragments which are highly radioactive, some of them produce neutrons, called delayed neutrons, which contribute to the fission chain reaction. In nuclear reactors, the reaction is slowed down by the addition of control rods which are made of such as boron, cadmium. In nuclear bombs, the reaction is uncontrolled and the amount of energy released creates a nuclear explosion. The Little Boy gun type atomic bomb dropped on Hiroshima on August 6,1945 was made of enriched uranium with a large tamper. The nominal spherical critical mass for an untampered 235U nuclear weapon is 56 kilograms, the material must be 85% or more of 235U and is known as weapons grade uranium, though for a crude, inefficient weapon 20% is sufficient. Even lower enrichment can be used, but then the critical mass rapidly increases. Most modern nuclear weapon designs use plutonium as the component of the primary stage. Uranium-235 has many such as fuel for nuclear power plants. DOE Fundamentals handbook, Nuclear Physics and Reactor theory Vol.1, Vol.2
22.
Subset
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In mathematics, especially in set theory, a set A is a subset of a set B, or equivalently B is a superset of A, if A is contained inside B, that is, all elements of A are also elements of B. The relationship of one set being a subset of another is called inclusion or sometimes containment, the subset relation defines a partial order on sets. The algebra of subsets forms a Boolean algebra in which the relation is called inclusion. For any set S, the inclusion relation ⊆ is an order on the set P of all subsets of S defined by A ≤ B ⟺ A ⊆ B. We may also partially order P by reverse set inclusion by defining A ≤ B ⟺ B ⊆ A, when quantified, A ⊆ B is represented as, ∀x. So for example, for authors, it is true of every set A that A ⊂ A. Other authors prefer to use the symbols ⊂ and ⊃ to indicate proper subset and superset, respectively and this usage makes ⊆ and ⊂ analogous to the inequality symbols ≤ and <. For example, if x ≤ y then x may or may not equal y, but if x < y, then x definitely does not equal y, and is less than y. Similarly, using the convention that ⊂ is proper subset, if A ⊆ B, then A may or may not equal B, the set A = is a proper subset of B =, thus both expressions A ⊆ B and A ⊊ B are true. The set D = is a subset of E =, thus D ⊆ E is true, any set is a subset of itself, but not a proper subset. The empty set, denoted by ∅, is also a subset of any given set X and it is also always a proper subset of any set except itself. These are two examples in both the subset and the whole set are infinite, and the subset has the same cardinality as the whole. The set of numbers is a proper subset of the set of real numbers. In this example, both sets are infinite but the set has a larger cardinality than the former set. Another example in an Euler diagram, Inclusion is the partial order in the sense that every partially ordered set is isomorphic to some collection of sets ordered by inclusion. The ordinal numbers are a simple example—if each ordinal n is identified with the set of all ordinals less than or equal to n, then a ≤ b if and only if ⊆. For the power set P of a set S, the partial order is the Cartesian product of k = |S| copies of the partial order on for which 0 <1. This can be illustrated by enumerating S = and associating with each subset T ⊆ S the k-tuple from k of which the ith coordinate is 1 if and only if si is a member of T
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Nuclear binding energy
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Nuclear binding energy is the energy that would be required to disassemble the nucleus of an atom into its component parts. These component parts are neutrons and protons, which are called nucleons. The term nuclear binding energy may also refer to the balance in processes in which the nucleus splits into fragments composed of more than one nucleon. If new binding energy is available when light nuclei fuse, or when heavy nuclei split and this energy may be made available as nuclear energy and can be used to produce electricity as in or in a nuclear weapon. When a large nucleus splits into pieces, excess energy is emitted as photons, the nuclear binding energies and forces are on the order of a million times greater than the electron binding energies of light atoms like hydrogen. Nuclear binding energy is explained by the principles involved in nuclear physics. Energy is consumed or liberated because of differences in the binding energy between the incoming and outgoing products of the nuclear transmutation. The best-known classes of nuclear transmutations are fission and fusion. Nuclear energy may be liberated by atomic fission, when atomic nuclei are broken apart into lighter nuclei. The energy from fission is used to generate power in hundreds of locations worldwide. Nuclear energy is released during atomic fusion, when light nuclei like hydrogen are combined to form heavier nuclei such as helium. The Sun and other stars use nuclear fusion to generate thermal energy which is radiated from the surface. In any exothermic nuclear process, nuclear mass might ultimately be converted to thermal energy, in order to quantify the energy released or absorbed in any nuclear transmutation, one must know the nuclear binding energies of the nuclear components involved in the transmutation. Electrons and nuclei are kept together by electrostatic attraction, the force of electric attraction does not hold nuclei together, because all protons carry a positive charge and repel each other. Thus, electric forces do not hold together, because they act in the opposite direction. It has been established that binding neutrons to nuclei clearly requires a non-electrical attraction, therefore, another force, called the nuclear force holds the nucleons of nuclei together. This force is a residuum of the interaction, which binds quarks into nucleons at an even smaller level of distance. The nuclear force must be stronger than the electric repulsion at short distances, unlike gravity or electrical forces, the nuclear force is effective only at very short distances
24.
Kinetic energy
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In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes, the same amount of work is done by the body in decelerating from its current speed to a state of rest. In classical mechanics, the energy of a non-rotating object of mass m traveling at a speed v is 12 m v 2. In relativistic mechanics, this is an approximation only when v is much less than the speed of light. The standard unit of energy is the joule. The adjective kinetic has its roots in the Greek word κίνησις kinesis, the dichotomy between kinetic energy and potential energy can be traced back to Aristotles concepts of actuality and potentiality. The principle in classical mechanics that E ∝ mv2 was first developed by Gottfried Leibniz and Johann Bernoulli, Willem s Gravesande of the Netherlands provided experimental evidence of this relationship. By dropping weights from different heights into a block of clay, Émilie du Châtelet recognized the implications of the experiment and published an explanation. The terms kinetic energy and work in their present scientific meanings date back to the mid-19th century, early understandings of these ideas can be attributed to Gaspard-Gustave Coriolis, who in 1829 published the paper titled Du Calcul de lEffet des Machines outlining the mathematics of kinetic energy. William Thomson, later Lord Kelvin, is given the credit for coining the term kinetic energy c, energy occurs in many forms, including chemical energy, thermal energy, electromagnetic radiation, gravitational energy, electric energy, elastic energy, nuclear energy, and rest energy. These can be categorized in two classes, potential energy and kinetic energy. Kinetic energy is the movement energy of an object, Kinetic energy can be transferred between objects and transformed into other kinds of energy. Kinetic energy may be best understood by examples that demonstrate how it is transformed to, for example, a cyclist uses chemical energy provided by food to accelerate a bicycle to a chosen speed. On a level surface, this speed can be maintained without further work, except to overcome air resistance, the chemical energy has been converted into kinetic energy, the energy of motion, but the process is not completely efficient and produces heat within the cyclist. The kinetic energy in the moving cyclist and the bicycle can be converted to other forms, for example, the cyclist could encounter a hill just high enough to coast up, so that the bicycle comes to a complete halt at the top. The kinetic energy has now largely converted to gravitational potential energy that can be released by freewheeling down the other side of the hill. Since the bicycle lost some of its energy to friction, it never regains all of its speed without additional pedaling, the energy is not destroyed, it has only been converted to another form by friction
25.
Electronvolt
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In physics, the electronvolt is a unit of energy equal to approximately 1. 6×10−19 joules. By definition, it is the amount of energy gained by the charge of an electron moving across an electric potential difference of one volt. Thus it is 1 volt multiplied by the elementary charge, therefore, one electronvolt is equal to 6981160217662079999♠1. 6021766208×10−19 J. The electronvolt is not a SI unit, and its definition is empirical, like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a unit of energy within physics, widely used in solid state, atomic, nuclear. It is commonly used with the metric prefixes milli-, kilo-, in some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts, it is equivalent to the GeV. By mass–energy equivalence, the electronvolt is also a unit of mass and it is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum. It is common to express mass in terms of eV as a unit of mass. The mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅1 V2 =1.783 ×10 −36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, the proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, the unified atomic mass unit,1 gram divided by Avogadros number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula,1 u =931.4941 MeV/c2 =0.9314941 GeV/c2, in high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy and this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of units are LMT−1. The dimensions of units are L2MT−2. Then, dividing the units of energy by a constant that has units of velocity. In the field of particle physics, the fundamental velocity unit is the speed of light in vacuum c. Thus, dividing energy in eV by the speed of light, the fundamental velocity constant c is often dropped from the units of momentum by way of defining units of length such that the value of c is unity
26.
Nuclear weapon yield
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An explosive yield of one terajoule is 0.239 kt of TNT. The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon, the practical maximum yield-to-weight ratio for fusion weapons has been estimated to six megatons of TNT per metric ton of bomb mass. Yields of 5.2 megatons/ton and higher have been reported for large weapons constructed for use in the early 1960s. Most artificial non-nuclear explosions are considerably smaller than even what are considered to be very small nuclear weapons, the yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. According to nuclear-weapons designer Ted Taylor, the practical maximum yield-to-weight ratio for fusion weapons is about 6 megatons of TNT per metric ton. The Taylor limit is not derived from first principles, and weapons with yields as high as 9.5 megatons per metric ton have been designed and built. The 25 Mt yield option reported for the B41 would give it a ratio of 5.1 megatons of TNT per metric ton. This results in the B41 still retaining the record for the highest Yield-to-weight weapon ever designed, in 1963 DOE declassified statements that the U. S. had the technological capability of deploying a 35 Mt warhead on the Titan II, or a 50-60 Mt gravity bomb on B-52s. Neither weapon was pursued, but either would require yield-to-weight ratios superior to a 25 Mt Mk-41, for current smaller US weapons, yield is 600 to 2200 kilotons of TNT per metric ton. By comparison, for the very small devices such as the Davy Crockett it was 0.4 to 40 kilotons of TNT per metric ton. For historical comparison, for Little Boy the yield was only 4 kilotons of TNT per metric ton, and for the largest Tsar Bomba, the yield was 2 megatons of TNT per metric ton. The largest pure-fission bomb ever constructed Ivy King had a 500 kiloton yield, however, there is no known upper yield limit for a fusion bomb. For example, the Mk-36 bomb as built had a ratio of 1.25 megatons of TNT per metric ton. Delivery size limits can be estimated to ascertain limits to delivery of high yield weapons. If the full 250 metric ton payload of the Antonov An-225 aircraft could be used, likewise, the maximum limit of a missile-delivered weapon is determined by the missile gross payload capacity. The large Russian SS-18 ICBM has a capacity of 7,200 kg. A Saturn V-scale missile could deliver over 120 tons, giving a maximum yield of about 700 megatons. The following list is of nuclear explosions
27.
Nuclear fallout
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It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes, but such dust can also originate from a damaged nuclear plant. Fallout may get entrained with the products of a pyrocumulus cloud and this radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron activated by exposure, is a highly dangerous kind of radioactive contamination. An air burst can eventually produce worldwide fallout, a ground burst can produce possibly much more severe, local fallout. These particles may be drawn up into the stratosphere, particularly if the explosive yield exceeds 10 kt. Initially little was known about the dispersion of nuclear fallout on a global scale, the AEC assumed that fallout would be dispersed evenly across the globe by atmospheric winds and gradually settle to the Earths surface after weeks, months, and even years as worldwide fallout. This hazard is less pertinent than local fallout, which is of much greater immediate operational concern, in a land or water surface burst, heat vaporizes large amounts of earth or water, which is drawn up into the radioactive cloud. This material becomes radioactive when it condenses with fission products and other radiocontaminants that have become neutron-activated, the table below summarizes the abilities of common isotopes to form fallout. Some radiation taints large amounts of land and drinking water causing formal mutations throughout animal and human life. The larger particles spill out of the stem and cascade down the outside of the fireball in a downdraft even as the cloud rises, more than half the total bomb debris lands on the ground within about 24 hours as local fallout. Chemical properties of the elements in the control the rate at which they are deposited on the ground. Severe local fallout contamination can extend far beyond the blast and thermal effects, the ground track of fallout from an explosion depends on the weather from the time of detonation onwards. In stronger winds, fallout travels faster but takes the time to descend, so although it covers a larger path. Thus, the width of the pattern for any given dose rate is reduced where the downwind distance is increased by higher winds. The total amount of activity deposited up to any time is the same irrespective of the wind pattern. But thunderstorms can bring down activity as rain more rapidly than dry fallout, particularly if the cloud is low enough to be below, or mixed with. There are two considerations for the location of an explosion, height and surface composition. A nuclear weapon detonated in the air, called an air burst, in case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area. The particles contain mostly sea salts with some water, these can have a cloud seeding effect causing local rainout and areas of high local fallout
28.
Actinide
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The actinide /ˈæktᵻnaɪd/ or actinoid /ˈæktᵻnɔɪd/ series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, the informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell, lawrencium, in comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. They all have very large atomic and ionic radii and exhibit a large range of physical properties. While actinium and the late actinides behave similarly to the lanthanides, all actinides are radioactive and release energy upon radioactive decay, naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth. These are used in nuclear reactors and nuclear weapons, uranium and thorium also have diverse current or historical uses, and americium is used in the ionization chambers of most modern smoke detectors. Of the actinides, primordial thorium and uranium occur naturally in substantial quantities, the radioactive decay of uranium produces transient amounts of actinium and protactinium, and atoms of neptunium and plutonium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements, like the lanthanides, the actinides form a family of elements with similar properties. Within the actinides, there are two overlapping groups, transuranium elements, which follow uranium in the periodic table—and transplutonium elements, compared to the lanthanides, which are found in nature in appreciable quantities, most actinides are rare. The most abundant, or easily synthesized actinides are uranium and thorium, the existence of transuranium elements was suggested by Enrico Fermi based on his experiments in 1934. However, even though four actinides were known by that time, synthesis of transuranics gradually undermined this point of view. By 1944 an observation that curium failed to exhibit oxidation states above 4 prompted Glenn Seaborg to formulate a so-called actinide hypothesis, at present, there are two major methods of producing isotopes of transplutonium elements, irradiation of the lighter elements with either neutrons or accelerated charged particles. The advantage of the method is that elements heavier than plutonium, as well as neutron-deficient isotopes, can be obtained. In 1962–1966, there were attempts in the United States to produce transplutonium isotopes using a series of six underground nuclear explosions and this inobservation was attributed to spontaneous fission owing to the large speed of the products and to other decay channels, such as neutron emission and nuclear fission. Uranium and thorium were the first actinides discovered, uranium was identified in 1789 by the German chemist Martin Heinrich Klaproth in pitchblende ore. He named it after the planet Uranus, which had been discovered eight years earlier. Klaproth was able to precipitate a yellow compound by dissolving pitchblende in nitric acid and he then reduced the obtained yellow powder with charcoal, and extracted a black substance that he mistook for metal. Only 60 years later, the French scientist Eugène-Melchior Péligot identified it with uranium oxide and he also isolated the first sample of uranium metal by heating uranium tetrachloride with potassium
29.
Decay chain
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In nuclear science, the decay chain refers to the radioactive decay of different discrete radioactive decay products as a chained series of transformations. They are also known as radioactive cascades, most radioisotopes do not decay directly to a stable state, but rather undergo a series of decays until eventually a stable isotope is reached. Decay stages are referred to by their relationship to previous or subsequent stages, a parent isotope is one that undergoes decay to form a daughter isotope. One example of this is uranium decaying into thorium, the daughter isotope may be stable or it may decay to form a daughter isotope of its own. The daughter of an isotope is sometimes called a granddaughter isotope. Half-lives have been determined in laboratories for thousands of radioisotopes and these can range from nearly instantaneous to as much as 1019 years or more. The intermediate stages each emit the same amount of radioactivity as the original radioisotope, not only are unstable radium isotopes significant radioactivity emitters, but as the next stage in the decay chain they also generate radon, a heavy, inert, naturally occurring radioactive gas. Rock containing thorium and/or uranium emits radon gas that can accumulate in enclosed places such as basements or underground mines, radon exposure is considered the leading cause of lung cancer in non-smokers.5 billion years ago. All the elements created more than 4.5 billion years ago are termed primordial, at the time when they were created, those that were unstable began decaying immediately. There are only two methods to create isotopes, artificially, inside a man-made reactor, or through decay of a parent isotopic species. Unstable isotopes are in a struggle to become more stable. Stable isotopes have ratios of neutrons to protons in their nucleus that start out at 1 in stable helium-4, the elements heavier than that have to shed weight to achieve stability, most usually as alpha decay. This fact is made inevitable by the two decay methods possible, alpha radiation, which reduces the weight by 4 atomic mass units, and beta, which does not change the weight at all. The four paths are termed 4n, 4n +1, 4n +2, and 4n +3, there are other decay modes, but they invariably occur at a lower probability than alpha or beta decay. Three of those chains have a long-lived isotope near the top, they are bottlenecks in the process through which the chain flows very slowly, the three materials are uranium-238, uranium-235 and thorium-232. The fourth chain has no long lasting bottleneck isotope, so almost all of the isotopes in that chain have long since decayed down to very near the stability at the bottom. Near the end of that chain is bismuth-209, which was thought to be stable. Recently, however, Bi-209 was found to be unstable with a half-life of 19 billion billion years, the four most common modes of radioactive decay are, alpha decay, beta decay, inverse beta decay, and isomeric transition
30.
Half-life
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Half-life is the time required for a quantity to reduce to half its initial value. The term is used in nuclear physics to describe how quickly unstable atoms undergo. The term is used more generally to characterize any type of exponential or non-exponential decay. For example, the medical sciences refer to the biological half-life of drugs, the converse of half-life is doubling time. The original term, half-life period, dating to Ernest Rutherfords discovery of the principle in 1907, was shortened to half-life in the early 1950s. Rutherford applied the principle of a radioactive elements half-life to studies of age determination of rocks by measuring the period of radium to lead-206. Half-life is constant over the lifetime of an exponentially decaying quantity, the accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed. A half-life usually describes the decay of discrete entities, such as radioactive atoms, in that case, it does not work to use the definition that states half-life is the time required for exactly half of the entities to decay. For example, if there are 3 radioactive atoms with a half-life of one second, instead, the half-life is defined in terms of probability, Half-life is the time required for exactly half of the entities to decay on average. In other words, the probability of a radioactive atom decaying within its half-life is 50%, for example, the image on the right is a simulation of many identical atoms undergoing radioactive decay. Note that after one half-life there are not exactly one-half of the remaining, only approximately. Nevertheless, when there are many identical atoms decaying, the law of large numbers suggests that it is a good approximation to say that half of the atoms remain after one half-life. There are various simple exercises that demonstrate probabilistic decay, for example involving flipping coins or running a computer program. The three parameters t1⁄2, τ, and λ are all related in the following way. Amount approaches zero as t approaches infinity as expected, some quantities decay by two exponential-decay processes simultaneously. There is a half-life describing any exponential-decay process, for example, The current flowing through an RC circuit or RL circuit decays with a half-life of RCln or lnL/R, respectively. For this example, the half time might be used instead of half life. In a first-order chemical reaction, the half-life of the reactant is ln/λ, in radioactive decay, the half-life is the length of time after which there is a 50% chance that an atom will have undergone nuclear decay
31.
Year
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A year is the orbital period of the Earth moving in its orbit around the Sun. Due to the Earths axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the globe, four seasons are recognized, spring, summer, autumn. In tropical and subtropical regions several geographical sectors do not present defined seasons, but in the seasonal tropics, a calendar year is an approximation of the number of days of the Earths orbital period as counted in a given calendar. The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a year of 366 days, as do the Julian calendars. For the Gregorian calendar the average length of the year across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a to represent a year of either 365 or 366 days, in English, the abbreviations y and yr are commonly used. In astronomy, the Julian year is a unit of time, it is defined as 365.25 days of exactly 86400 seconds, totalling exactly 31557600 seconds in the Julian astronomical year. The word year is used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year. Similarly, year can mean the period of any planet, for example. The term can also be used in reference to any long period or cycle, west Saxon ġēar, Anglian ġēr continues Proto-Germanic *jǣran. Cognates are German Jahr, Old High German jār, Old Norse ár and Gothic jer, all the descendants of the Proto-Indo-European noun *yeh₁rom year, season. Cognates also descended from the same Proto-Indo-European noun are Avestan yārǝ year, Greek ὥρα year, season, period of time, Old Church Slavonic jarŭ, Latin annus is from a PIE noun *h₂et-no-, which also yielded Gothic aþn year. Both *yeh₁-ro- and *h₂et-no- are based on verbal roots expressing movement, *h₁ey- and *h₂et- respectively, the Greek word for year, ἔτος, is cognate with Latin vetus old, from the PIE word *wetos- year, also preserved in this meaning in Sanskrit vat-sa- yearling and vat-sa-ras year. Derived from Latin annus are a number of English words, such as annual, annuity, anniversary, etc. per annum means each year, anno Domini means in the year of the Lord. No astronomical year has an number of days or lunar months. Financial and scientific calculations often use a 365-day calendar to simplify daily rates, in the Julian calendar, the average length of a year is 365.25 days. In a non-leap year, there are 365 days, in a year there are 366 days
32.
Nuclear fission product
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Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy. The two smaller nuclei are the fission products, about 0. 2% to 0. 4% of fissions are ternary fissions, producing a third light nucleus such as helium-4 or tritium. The fission products themselves are often unstable and radioactive, due to being relatively neutron-rich for their atomic number and this releases additional energy in the form of beta particles, antineutrinos, and gamma rays. Thus, fission events normally result in radiation and antineutrinos. Many of these nuclides have a very short half-life, and therefore are very radioactive, for instance, strontium-90, strontium-89 and strontium-94 are all fission products, they are produced in similar quantities, and each nucleus decays by shooting off one beta particle. But Sr-90 has a 30-year half-life, Sr-89 a 50. 5-day half-life, the same number of atoms of Sr-89 will decay 10,600 times faster than Sr-90, and Sr-94 will do so 915 million times faster. It is these short-half-life nuclides that make spent fuel so dangerous, in addition to generating much heat, immediately after the reactor itself has been shut down. The most radioactive also decay the fastest, after 50 days, Sr-94 has had 58,000 half-lives and is gone, Sr-89 is at half its original quantity. As there are hundreds of different nuclides created, the radioactivity level fades quickly. The sum of the mass of the two atoms produced by the fission of one fissile atom is always less than the atomic mass of the original atom. Since the nuclei that can undergo fission are particularly neutron-rich. The initial fission products therefore may be unstable and typically undergo beta decay to move towards a stable configuration, a few neutron-rich and short-lived initial fission products decay by ordinary beta decay, followed by immediate emission of a neutron by the excited daughter-product. This process is the source of so-called delayed neutrons, which play an important role in control of a nuclear reactor, the first beta decays are rapid and may release high energy beta particles or gamma radiation. However, as the fission products approach stable nuclear conditions, the last one or two decays may have a long half-life and release less energy. Fission products have half-lives of 90 years or less, except for seven long-lived fission products that have lives of 211,100 years. This behavior of pure fission products with actinides removed, contrasts with the decay of fuel that still contains actinides and this fuel is produced in the so-called open nuclear fuel cycle. A number of these actinides have half lives in the range of about 100 to 200,000 years
33.
Fission product yield
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Nuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a product produced per fission. Yield can be broken down by, Individual isotope Chemical element spanning several isotopes of different mass number, nuclei of a given mass number regardless of atomic number. Known as chain yield because it represents a decay chain of beta decay, a few isotopes can be produced directly by fission, but not by beta decay because the would-be precursor with atomic number one greater is stable and does not decay. Chain yields do not account for these isotopes, however. Yield is usually stated as percentage per fission, so that the total yield percentages sum to 200%, less often, it is stated as percentage of all fission products, so that the percentages sum to 100%. Ternary fission, about 0. 2% to 0. 4% of fissions and this is because the fission event causes the nucleus to split in an asymmetric manner, as nuclei closer to magic numbers are more stable. Yield vs. Z - This is a distribution for the fission of uranium. Note that in the used to make this graph the activation of fission products was ignored. In this bar chart results are shown for different cooling times, because of the stability of nuclei with even numbers of protons and/or neutrons the curve of yield against element is not a smooth curve. The curves for the fission of the later actinides tend to even more shallow valleys. In extreme cases such as 259Fm, only one peak is seen, yield is usually expressed relative to number of fissioning nuclei, not the number of fission product nuclei, that is, yields should sum to 200%. The table in the next section gives yields for notable radioactive fission products, and neutron poison fission products, from thermal neutron fission of U-235, computed from
34.
Plutonium-241
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Plutonium-241 is an isotope of plutonium formed when plutonium-240 captures a neutron. Like Pu-239 but unlike 240Pu, 241Pu is fissile, with a neutron cross section about 1/3 greater than 239Pu. In the non-fission case, neutron capture produces plutonium-242, in general, isotopes with an odd number of neutrons are both more likely to absorb a neutron, and more likely to undergo fission on neutron absorption, than isotopes with an even number of neutrons. 241Pu has a half-life of 14 years, corresponding to a decay of about 5% of Pu-241 nuclei over a one-year period, in a thermal reactor, 241Am captures a neutron to become americium-242, which quickly becomes curium-242 via beta decay. In short, Am-241 needs to absorb two neutrons before again becoming a fissile isotope
35.
Plutonium-238
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Plutonium-238 is a radioactive isotope of plutonium that has a half-life of 87.7 years. Plutonium-238 is a very powerful alpha emitter and this makes the plutonium-238 isotope suitable for usage in radioisotope thermoelectric generators and radioisotope heater units. One gram of 238Pu corresponds to 1/238 moles, which is 2. 53×1021 plutonium atoms, considering its half-life t1/2 =87.7 years we can calculate its activity as A = λ N = ln 2 t 1 /2 N =634 GBq. It is the number of 238Pu decays per second, each of the emitted alpha particles has kinetic energy 5.593 MeV or 8. 96×10-13 J which is quickly converted to heat when the particle decelerates in the material. Therefore each gram of 238Pu spontaneously generates 0.568 W of heat, Plutonium-238 was the first isotope of plutonium to be discovered. It was synthesized by Glenn Seaborg and associates in December,1940 by bombarding uranium-238 with deuterons, creating neptunium-238, Plutonium-238 decays to uranium-234 and then further along the radium series to lead-206. Plutonium-238 was produced by irradiating Neptunium-237, which is a by-product of the production of Plutonium-239 weapons-grade material, as produced by Savannah River in their weapons reactor, shut down in 1988, Plutonium-238 was mixed with about 16% Plutonium-239. The first application was its use in a weapons component made at Mound for the Weapons Design Agency Lawrence Livermore Laboratory, Mound was chosen for this work because of its experience in producing the Polonium-210 fueled Urchin initiator and its work with several heavy elements in a Reactor Fuels program. Two Mound scientists spent 1959 at LLL in joint development while the Special Metallurgical Building was constructed at Mound to house the project, meanwhile the first sample of Plutonium-238 came to Mound in 1959. The weapons project was planned for about 1 kg/year of Pu-238 over a 3-year period, but the Pu-238 component could not be produced to the specifications despite a 2 year effort beginning at Mound in mid-1961. A maximum effort was undertaken with 3 shifts a day,6 days a week, a loosening of the specifications resulted in productivity of about 3%, and production finally began in 1964. Capt. R. T. Carpenter had chosen Pu-238 as the fuel for the first RTG to be launched into space as auxiliary power for the Transit IV Navy navigational satellite, June 29,1961. As of January 21,1963, the decision had yet to be made as to what isotope would be used to fuel the large RTGs for NASA programs. Then early in 1964 Mound scientists developed a different method of fabricating the weapon component that resulted in an efficiency of around 98%. When it was recognized that the source would not remain intact through cremation. An addition to the Special Metallurgical building weapon component production facility was completed at the end of 1964 for Pu-238 heat source fuel fabrication, a temporary fuel production facility was also installed in the Research Building in 1969 for Transit fuel fabrication. Pu-238 makes up one or two percent, but it may be responsible for much of the short-term decay heat because of its short half-life relative to other plutonium isotopes. Reactor-grade plutonium is not useful for producing Pu-238 for RTGs because difficult isotopic separation would be needed, in both cases, the targets are subjected to a chemical treatment, including dissolution in nitric acid to extract the plutonium-238
