1.
Ampoule
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An ampoule is a small sealed vial which is used to contain and preserve a sample, usually a solid or liquid. Ampoules are commonly made of glass, although plastic ampoules do exist, modern ampoules are most commonly used to contain pharmaceuticals and chemicals that must be protected from air and contaminants. They are hermetically sealed by melting the thin top with an open flame, if properly done, this last operation creates a clean break without any extra glass shards or slivers, but the liquid or solution may be filtered for greater assurance. The space above the chemical may be filled with a gas before sealing. The walls of glass ampoules are usually sufficiently strong to be brought into a glovebox without any difficulty, historically ampoules were used to contain a small sample of a persons blood after death, which was entombed alongside them in many Christian catacombs. It was originally believed that only martyrs were given this burial treatment, an ampoule, allegedly dating back to the year 305 and filled with the blood of Saint Januarius, bishop of Benevento, has been kept for centuries in the Cathedral at Naples. Another well known ampoule is the Holy Ampulla which held the oil for the coronation of the French monarchs. The oil was allegedly passed down from the time of Clovis I, it was kept for a time in the tomb of Saint Remigius and later in the Cathedral of Notre-Dame, Reims. An order of knights named after the ampoule was created for the coronation of kings to have saved and was used in coronation of Charles X. Modern glass ampoules are produced industrially from short lengths of tubing, shaped by heating with gas torches. Computer vision techniques are employed for quality control. The filling and sealing of ampoules may be done by automated machinery on a scale, or by hand in small-scale industries. Blank ampoules can be purchased from scientific supply houses and sealed with a small gas torch. This forms a membrane allowing someone to turn the open ampule upside down without spilling, a Schlenk line may be used for sealing under inert atmospheres. Ampoules are common practice as containers of low frequency RFID tags and these are used mainly for tagging animals, such as dogs for identification. Ampoules often have colored rings of paint or enamel around their necks, color coding of modern ampoules is done during the manufacturing process. A machine paints colored rings on the ampoule shortly after it has been sealed, the rings are made of a substance that is readable by other machines. These color codes identify the substance inside the ampoule so that it does not need to be tested to verify the contents, the machine-readable color codes allow for accurate handling of the substance for the purposes of storage, labeling, and secondary packaging
2.
FLiBe
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FLiBe is a molten salt made from a mixture of lithium fluoride and beryllium fluoride. It is both a nuclear reactor coolant and solvent for fertile or fissile material and it served both purposes in the Molten-Salt Reactor Experiment. The 2,1 mixture forms a compound, Li2BeF4, which has a melting point of 459 °C, a boiling point of 1430 °C. Its volumetric heat capacity is 4540 kJ/m3K, which is similar to that of water, more than four times that of sodium and its appearance is white to transparent, with crystalline grains in a solid state, morphing into a completely clear liquid upon melting. However, soluble fluorides such as UF4 and NiF2, can change the color salt in both solid and liquid state. This mixture was never used in due to the overwhelming increase in viscosity caused by the BeF2 addition in the eutectic mixture. BeF2, which behaves as a glass, is fluid in salt mixtures containing enough molar percent of Lewis base. Lewis bases, such as the fluorides, will donate fluoride ions to the beryllium. In FLiBe, beryllium fluoride is able to sequester two fluoride ions from two lithium fluorides in a state, converting it into the tetrafluorberyllate ion BeF4−2. The chemistry of FLiBe, and other salts, is unique due to the high temperatures at which the reactions occur, the ionic nature of the salt. At the most basic level, FLiBe melts and complexes itself through 2 L i F + B e F2 ⟶2 L i + + B e F4 −2 and this reaction occurs upon initial melting. However, if the components are exposed to air they will absorb moisture, while BeF2 is a very stable chemical compound, the formation of oxides, hydroxides, and hydrogen fluoride reduce the stability and inertness of the salt. Its important to understand that all dissolved species in these two reactions cause the corrosion—not just the hydrogen fluoride and this is because all dissolved components alter the reduction potential or redox potential. The redox potential is an innate and measurable voltage in the salt which is the indicator of the corrosion potential in salt. Usually, the reaction H F + e − ⟶ F − +1 /2 H2. is set at zero volts. This reaction proves convenient in a setting and can be used to set the salt to zero through bubbling a 1,1 mixture of hydrogen fluoride. Occasionally the reaction, N i F2 +2 e − ⟶ N i +2 F −. is used as a reference. Regardless of where the zero is set, all other reactions occur in the salt will occur at predictable
3.
Uranium tetrafluoride
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Uranium tetrafluoride is a green crystalline solid compound of uranium with an insignificant vapor pressure and very slight solubility in water. Uranium in its tetravalent state is important in different technological processes. In the uranium refining industry it is known as green salt, UF4 is generally an intermediate in the conversion of uranium hexafluoride to either uranium oxides or uranium metal. It is formed by the reaction of UF6 with hydrogen gas in a vertical tube-type reactor or by the action of hydrogen fluoride on uranium dioxide. The bulk density of UF4 varies from about 2.0 g/cm3 to about 4.5 g/cm3 depending on the production process, a molten salt reactor design, a type of nuclear reactor where the working fluid is a molten salt, would use UF4 as the core material. Like all uranium salts UF4 is toxic and thus harmful by inhalation, ingestion, booth, H. S. Krasny-Ergen, W. Heath, R. E. Uranium Tetrafluoride. Journal of the American Chemical Society, kern, S. Hayward, J. Roberts, S. Richardson, J. W. Rotella, F. J. Soderholm, L. Cort, B. Tinkle, M. West, M. Hoisington, D. Lander, temperature Variation of the Structural Parameters in Actinide Tetrafluorides
4.
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
5.
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
6.
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
7.
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
8.
Parent isotope
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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
9.
Isotopes of plutonium
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Plutonium is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes and it was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940. Twenty plutonium radioisotopes have been characterized, the most stable are Pu-244, with a half-life of 80.8 million years, Pu-242, with a half-life of 373,300 years, and Pu-239, with a half-life of 24,110 years. All of the radioactive isotopes have half-lives that are less than 7,000 years. This element also has eight meta states, though none are very stable, the isotopes of plutonium range in atomic weight from 228.0387 u to 247.074 u. The primary decay modes before the most stable isotope, Pu-244, are spontaneous fission and alpha emission, the primary decay products before Pu-244 are isotopes of uranium and neptunium, and the primary products after are isotopes of americium. Plutonium-238 has a half-life of 87.74 years and emits alpha particles, plutonium-239 is the most important isotope of plutonium, with a half-life of 24,100 years. Pu-239 and Pu-241 are fissile, meaning that the nuclei of its atoms can break apart by being bombarded by slow moving thermal neutrons, releasing energy, gamma radiation and it can therefore sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. Pu-239 is synthesized by irradiating uranium-238 with neutrons in a nuclear reactor, further neutron capture produces successively heavier isotopes. Plutonium-240 has a rate of spontaneous fission, raising the background neutron radiation of plutonium containing it. Plutonium is graded by proportion of Pu-240, weapons grade, fuel grade, lower grades are less suited for nuclear weapons and thermal reactors but can fuel fast reactors. Plutonium-241 is fissile, but also beta decays with a half-life of 14 years to americium-241, plutonium-242 is not fissile, not very fertile, has a low neutron capture cross section, and a longer half-life than any of the lighter isotopes. Plutonium-244 is the most stable isotope of plutonium, with a half-life of about 80 million years and it is not significantly produced in nuclear reactors because Pu-243 has a short half-life, but some is produced in nuclear explosions. Pu-240, Pu-241, Pu-242 are produced by neutron capture. In plutonium that has used a second time in thermal reactors in MOX fuel. All plutonium isotopes and other actinides, however, are fissionable with fast neutrons, Pu-240 does have a moderate thermal neutron absorption cross section, so that Pu-241 production in a thermal reactor becomes a significant fraction as large as Pu-239 production. Pu-241 has a half-life of 14 years, and has higher thermal neutron cross sections than Pu-239 for both fission and absorption. While nuclear fuel is being used in a reactor, a Pu-241 nucleus is more likely to fission or to capture a neutron than to decay
10.
Alpha decay
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An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. Alpha decay typically occurs in the heaviest nuclides, in practice, this mode of decay has only been observed in nuclides considerably heavier than nickel, with the lightest known alpha emitters being the lightest isotopes of tellurium. Alpha decay is by far the most common form of cluster decay and it is the most common form because of the combined extremely high binding energy and relatively small mass of the alpha particle. Like other cluster decays, alpha decay is fundamentally a quantum tunneling process, unlike beta decay, it is governed by the interplay between both the nuclear force and the electromagnetic force. Alpha particles have a kinetic energy of 5 MeV and have a speed of about 15,000,000 m/s. There is surprisingly small variation around this energy, due to the dependence of the half-life of this process on the energy produced. Approximately 99% of the helium produced on Earth is the result of the decay of underground deposits of minerals containing uranium or thorium. The helium is brought to the surface as a by-product of natural gas production, Alpha particles were first described in the investigations of radioactivity by Ernest Rutherford in 1899, and by 1907 they were identified as He2+ ions. By 1928, George Gamow had solved the theory of alpha decay via tunneling, the alpha particle is trapped in a potential well by the nucleus. The nuclear force holding an atomic nucleus together is very strong, however, the nuclear force is also short range, dropping quickly in strength beyond about 1 femtometre, while the electromagnetic force has unlimited range. A nucleus with 210 or more nucleons is so large that the nuclear force holding it together can just barely counterbalance the electromagnetic repulsion between the protons it contains. Alpha decay occurs in such nuclei as a means of increasing stability by reducing size, one curiosity is why alpha particles, helium nuclei, should be preferentially emitted as opposed to other particles like a single proton or neutron or other atomic nuclei. Single proton emission, or the emission of any particle with an odd number of nucleons would violate this conservation law, the rest of the answer comes from the very high binding energy of the alpha particle. For example, performing the calculation for uranium-232 shows that alpha particle emission would need only 5.4 MeV, while a single proton emission would require 6.1 MeV. Most of this energy becomes the kinetic energy of the alpha particle itself. However, since the numbers of most alpha emitting radioisotopes exceed 210. These disintegration energies however are substantially smaller than the barrier provided by the nuclear force. An alpha particle can be thought of as being inside a potential barrier whose walls are 25 MeV, however, decay alpha particles only have kinetic energies of 4 MeV to about 9 MeV, far less than the energy needed to escape
11.
Isotopes of neptunium
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Neptunium is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes, the first isotope to be synthesized was 239Np in 1940, produced by bombarding 238U with neutrons to produce 239U, which then underwent beta decay to 239Np. Trace quantities are found in nature from neutron capture by uranium atoms, all of the remaining radioactive isotopes have half-lives that are less than 4.5 days, and the majority of these have half-lives that are less than 50 minutes. This element also has 4 meta states, with the most stable being 236mNp, the isotopes of neptunium range in atomic weight from 225.0339 u to 244.068 u. The primary decay mode before the most stable isotope, 237Np, is electron capture, the primary decay products before 237Np are isotopes of uranium and protactinium, and the primary products after are isotopes of plutonium. Neptunium-235 has 142 neutrons and a half-life of 400 days and this isotope of Neptunium either decays by, Emitting an alpha particle, the decay energy is 5.2 MeV and the decay product is Protactinium-231. It can decay by the methods, Electron capture, the decay energy is 0.93 MeV. Beta emission, the energy is 0.48 MeV. Alpha emission, the energy is 5.007 MeV. It is a material with a critical mass of 6.79 kg. 236Np is produced in small quantities via the and capture reactions of 237Np and it is for this reason that, despite its low critical mass and high neutron cross section, it has not been researched as a nuclear fuel in weapons or reactors. 237Np decays via the series, which terminates with thallium-205, which is stable, unlike most other actinides. In 2002, 237Np was shown to be capable of sustaining a chain reaction with fast neutrons, as in a nuclear weapon, however, it has a low probability of fission on bombardment with thermal neutrons, which makes it unsuitable as a fuel for conventional nuclear power plants. Over the long term, 237Np also forms in spent nuclear fuel as the product of americium-241. 237Np was projected to be one of the most mobile nuclides at the Yucca Mountain nuclear waste repository and these applications are economically practical where photovoltaic power sources are weak or inconsistent. Values marked # are not purely derived from data. Spins with weak assignment arguments are enclosed in parentheses, uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, isotope masses from, G. Audi, A. H. Wapstra, C
12.
Positron emission
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Positron emission is mediated by the weak force. The positron is a type of particle, the other beta particle being the electron emitted from the β− decay of a nucleus. Positron decay results in nuclear transmutation, changing an atom of one element into an atom of an element with an atomic number that is less by one unit. Positron emission should not be confused with electron emission or beta decay, which occurs when a neutron turns into a proton and the nucleus emits an electron. This was the first example of β+ decay, the Curies termed the phenomenon artificial radioactivity, since 30 15P is a short-lived nuclide which does not exist in nature. The discovery of radioactivity would be cited when the husband. Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40, nitrogen-13, oxygen-15, aluminium-26, sodium-22, fluorine-18, the two most common types of quarks are up quarks, which have a charge of +2/3, and down quarks, with a −1/3 charge. Quarks arrange themselves in sets of three such that they make protons and neutrons, in a proton, whose charge is +1, there are two up quarks and one down quark. Neutrons, with no charge, have one up quark and two down quarks, via the weak interaction, quarks can change flavor from down to up, resulting in electron emission. Positron emission happens when an up quark changes into a down quark, nuclei which decay by positron emission may also decay by electron capture. For low-energy decays, electron capture is energetically favored by 2mec2 =1.022 MeV, as the energy of the decay goes up, so does the branching ratio towards positron emission. However, if the difference is less than 2mec2, then positron emission cannot occur. Certain isotopes are stable in galactic cosmic rays, because the electrons are stripped away, a positron is ejected from the parent nucleus, and the daughter atom must shed an orbital electron to balance charge. Isotopes which increase in mass under the conversion of a proton to a neutron, or which decrease in mass by less than 2me and these isotopes are used in positron emission tomography, a technique used for medical imaging. Note that the energy emitted depends on the isotope that is decaying, the short-lived positron emitting isotopes 11C, 13N, 15O and 18F used for positron emission tomography are typically produced by proton irradiation of natural or enriched targets. The LIVEChart of Nuclides - IAEA with filter on β+ decay
13.
Beta decay
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In nuclear physics, beta decay is a type of radioactive decay in which a beta ray, and a neutrino are emitted from an atomic nucleus. Neither the beta particle nor its associated neutrino exist within the prior to beta decay. By this process, unstable atoms obtain a more stable ratio of protons to neutrons, the probability of a nuclide decaying due to beta and other forms of decay is determined by its binding energy. The binding energies of all existing nuclides form what is called the valley of stability. Beta decay is a consequence of the force, which is characterized by relatively lengthy decay times. Nucleons are composed of up or down quarks, and the force allows a quark to change type by the exchange of a W boson. For example, a neutron, composed of two quarks and an up quark, decays to a proton composed of a down quark. Decay times for many nuclides that are subject to beta decay can be thousands of years, electron capture is sometimes included as a type of beta decay, because the basic nuclear process, mediated by the weak force, is the same. In electron capture, an atomic electron is captured by a proton in the nucleus, transforming it into a neutron. The two types of decay are known as beta minus and beta plus. β+ decay is known as positron emission. Beta decay conserves a number known as the lepton number, or the number of electrons. These particles have lepton number +1, while their antiparticles have lepton number −1, since a proton or neutron has lepton number zero, β+ decay must be accompanied with an electron neutrino, while β− decay must be accompanied by an electron antineutrino. This new element has a mass number A, but an atomic number Z that is increased by one. As in all nuclear decays, the element is known as the parent nuclide while the resulting element is known as the daughter nuclide. The beta spectrum, or distribution of values for the beta particles, is continuous. The total energy of the process is divided between the electron, the antineutrino, and the recoiling nuclide. In the figure to the right, an example of an electron with 0.40 MeV energy from the decay of 210Bi is shown
14.
Decay product
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In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps, 234Th is the daughter of the parent 238U. 234mPa is the granddaughter of 238U and these might also be referred to as the daughter products of 238U. Decay products are important in understanding radioactive decay and the management of radioactive waste, for elements above lead in atomic number, the decay chain typically ends with an isotope of thallium or lead. In many cases members of the chain are far more radioactive than the original nuclide. Thus, although uranium is not dangerously radioactive when pure, some pieces of naturally occurring pitchblende are quite dangerous owing to their radium content, similarly, thorium gas mantles are very slightly radioactive when new, but become far more radioactive after only a few months of storage. Although it cannot be predicted whether any given atom of a substance will decay at any given time. Because of this, decay products are important to scientists in many fields who need to know the quantity or type of the parent product, such studies are done to measure pollution levels and for other matters
15.
Fissile material
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In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a reaction with neutrons of any energy. The predominant neutron energy may be typified by slow neutrons or fast neutrons. Fissile material can be used to fuel thermal-neutron reactors, fast-neutron reactors, according to the fissile rule, for a heavy element with 90 ≤ Z ≤100, its isotopes with 2 × Z − N =43 ±2, with few exceptions, are fissile. A nuclide capable of undergoing fission after capturing a high energy neutron is referred to as fissionable, a fissionable nuclide that can be induced to fission with low-energy thermal neutrons with a high probability is referred to as fissile. Although the terms were formerly synonymous, fissionable materials include also those that can be fissioned only with high-energy neutrons, as a result, fissile materials are a subset of fissionable materials. By contrast, the energy released by uranium-238 absorbing a thermal neutron is less than the critical energy. Consequently, uranium-238 is a material but not a fissile material. As such, while all fissile isotopes are fissionable, not all fissionable isotopes are fissile and these are materials that sustain an explosive fast nuclear fission chain reaction. Under all definitions above, uranium-238 is fissionable, but because it cannot sustain a chain reaction. Fast fission of 238U in the stage of a nuclear weapon contributes greatly to yield. The fast fission of 238U also makes a significant contribution to the output of some fast-neutron reactors. In general, most actinide isotopes with an odd number are fissile. Most nuclear fuels have an odd atomic number, and an even atomic number Z. This implies an odd number of neutrons, isotopes with an odd number of neutrons gain an extra 1 to 2 MeV of energy from absorbing an extra neutron, from the pairing effect which favors even numbers of both neutrons and protons. This energy is enough to supply the extra energy for fission by slower neutrons. They are more likely to ignore the neutron and let it go on its way, or else to absorb the neutron and these even-even isotopes are also less likely to undergo spontaneous fission, and they also have relatively much longer partial half-lives for alpha or beta decay. Examples of these isotopes are uranium-238 and thorium-232, the physical basis for this phenomenon also comes from the pairing effect in nuclear binding energy, but this time from both proton–proton and neutron–neutron pairing
16.
Thorium fuel cycle
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The thorium fuel cycle is a nuclear fuel cycle that uses the isotope of thorium, 232Th, as the fertile material. In the reactor, 232Th is transmuted into the fissile artificial uranium isotope 233U which is the nuclear fuel, unlike natural uranium, natural thorium contains only trace amounts of fissile material, which are insufficient to initiate a nuclear chain reaction. Additional fissile material or another source are necessary to initiate the fuel cycle. In a thorium-fuelled reactor, 232Th absorbs neutrons eventually to produce 233U and this parallels the process in uranium breeder reactors whereby fertile 238U absorbs neutrons to form fissile 239Pu. Depending on the design of the reactor and fuel cycle, the generated 233U either fissions in situ or is separated from the used nuclear fuel. Concerns about the limits of worldwide uranium resources motivated initial interest in the fuel cycle. It was envisioned that as uranium reserves were depleted, thorium would supplement uranium as a fertile material, however, for most countries uranium was relatively abundant and research in thorium fuel cycles waned. A notable exception was Indias three-stage nuclear power programme, in the twenty-first century thoriums potential for improving proliferation resistance and waste characteristics led to renewed interest in the thorium fuel cycle. Molten salt reactor experiments assessed thoriums feasibility, using thorium fluoride dissolved in a molten salt fluid that eliminated the need to fabricate fuel elements, the MSR program was defunded in 1976 after its patron Alvin Weinberg was fired. Rubbias proposal offered the potential to incinerate high-activity nuclear waste and produce energy from natural thorium and he first researched thorium reactors while working at NASA, while evaluating power plant designs suitable for lunar colonies. In 2006 Sorensen started energyfromthorium. com to promote and make available about this technology. As such they conclude there is chance of thorium cycles replacing conventional uranium cycles in the current nuclear power market. In the thorium cycle, fuel is formed when 232Th captures a neutron to become 233Th and this normally emits an electron and an anti-neutrino by β− decay to become 233Pa. Other studies assume some actinide losses and find that actinide wastes dominate thorium cycle waste radioactivity at some future periods, in a reactor, when a neutron hits a fissile atom, it either splits the nucleus or is captured and transmutes the atom. In the case of 233U, the transmutations tend to produce nuclear fuels rather than transuranic wastes. When 233U absorbs a neutron, it either fissions or becomes 234U, the result is less transuranic waste than in a reactor using the uranium-plutonium fuel cycle. 234U, like most actinides with an number of neutrons, is not fissile. If the fissile isotope fails to fission on capture, it produces 236U, 237Np, 238Pu
17.
Nuclear weapon
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A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from small amounts of matter. The first test of a bomb released the same amount of energy as approximately 20,000 tons of TNT. The first thermonuclear bomb test released the same amount of energy as approximately 10 million tons of TNT, a thermonuclear weapon weighing little more than 2,400 pounds can produce an explosive force comparable to the detonation of more than 1.2 million tons of TNT. A nuclear device no larger than traditional bombs can devastate a city by blast, fire. Nuclear weapons are considered weapons of destruction, and their use. Nuclear weapons have been used twice in nuclear warfare, both times by the United States against Japan near the end of World War II, the bombings resulted in the deaths of approximately 200,000 civilians and military personnel from acute injuries sustained from the explosions. The ethics of the bombings and their role in Japans surrender remain the subject of scholarly, since the atomic bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated on over two thousand occasions for the purposes of testing and demonstration. Only a few nations possess such weapons or are suspected of seeking them, israel is also believed to possess nuclear weapons, though in a policy of deliberate ambiguity, it does not acknowledge having them. Germany, Italy, Turkey, Belgium and the Netherlands are nuclear weapons sharing states, south Africa is the only country to have independently developed and then renounced and dismantled its nuclear weapons. Modernisation of weapons continues to occur, all existing nuclear weapons derive some of their explosive energy from nuclear fission reactions. Weapons whose explosive output is exclusively from fission reactions are commonly referred to as bombs or atom bombs. This has long noted as something of a misnomer, as their energy comes from the nucleus of the atom. The latter approach is considered more sophisticated than the former and only the approach can be used if the fissile material is plutonium. A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range from the equivalent of just under a ton to upwards of 500,000 tons of TNT, all fission reactions necessarily generate fission products, the radioactive remains of the atomic nuclei split by the fission reactions. Many fission products are highly radioactive or moderately radioactive. Fission products are the radioactive component of nuclear fallout
18.
Nuclear fuel
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Nuclear fuel is a substance that is used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission, most nuclear fuels contain heavy fissile elements that are capable of nuclear fission, such as uranium-235 or plutonium-239. When the unstable nuclei of atoms are hit by a slow-moving neutron, they split. These neutrons then go on to split more nuclei and this creates a self-sustaining chain reaction that is controlled in a nuclear reactor, or uncontrolled in a nuclear weapon. The processes involved in mining, refining, purifying, using, Nuclear fuel has the highest energy density of all practical fuel sources. Uranium dioxide is a black semiconducting solid and it can be made by reacting uranyl nitrate with a base to form a solid. It is heated to form U3O8 that can then be converted by heating in an argon / hydrogen mixture to form UO2, the UO2 is then mixed with an organic binder and pressed into pellets, these pellets are then fired at a much higher temperature to sinter the solid. The aim is to form a solid which has few pores. The thermal conductivity of uranium dioxide is low compared with that of zirconium metal. It is important to note that the corrosion of uranium dioxide in an environment is controlled by similar electrochemical processes to the galvanic corrosion of a metal surface. Mixed oxide, or MOX fuel, is a blend of plutonium, MOX fuel is an alternative to low enriched uranium fuel used in the light water reactors which predominate nuclear power generation. Some concern has been expressed that used MOX cores will introduce new disposal challenges, reprocessing of commercial nuclear fuel to make MOX was done in the Sellafield MOX Plant. As of 2015, MOX fuel is made in France, and to an extent in Russia, India. China plans to develop fast breeder reactors and reprocessing, reprocessing of spent commercial-reactor nuclear fuel has not been permitted in the United States due to nonproliferation considerations. It behaves like U-235 and its fission releases a similar amount of energy, the higher the burn-up, the more plutonium in the spent fuel, but the lower the fraction of fissile plutonium. Typically about one percent of the used fuel discharged from a reactor is plutonium, worldwide, some 70 tonnes of plutonium contained in used fuel is removed when refueling reactors each year. Metal fuels have the advantage of a higher heat conductivity than oxide fuels. Metal fuels have a history of use, stretching from the Clementine reactor in 1946 to many test
19.
Nuclear reactor
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This article is a subarticle of Nuclear power. A nuclear reactor, formerly known as a pile, is a device used to initiate. Nuclear reactors are used at power plants for electricity generation. Heat from nuclear fission is passed to a fluid, which runs through steam turbines. These either drive a ships propellers or turn electrical generators, Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, some are run only for research. As of April 2014, the IAEA reports there are 435 nuclear power reactors in operation, when a large fissile atomic nucleus such as uranium-235 or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more nuclei, releasing kinetic energy, gamma radiation, and free neutrons. A portion of neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons. This is known as a chain reaction. To control such a chain reaction, neutron poisons and neutron moderators can change the portion of neutrons that will go on to cause more fission. Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if monitoring detects unsafe conditions, commonly-used moderators include regular water, solid graphite and heavy water. Some experimental types of reactor have used beryllium, and hydrocarbons have been suggested as another possibility, the reactor core generates heat in a number of ways, The kinetic energy of fission products is converted to thermal energy when these nuclei collide with nearby atoms. The reactor absorbs some of the rays produced during fission. Heat is produced by the decay of fission products and materials that have been activated by neutron absorption. This decay heat-source will remain for some even after the reactor is shut down. A kilogram of uranium-235 converted via nuclear processes releases approximately three times more energy than a kilogram of coal burned conventionally. A nuclear reactor coolant — usually water but sometimes a gas or a metal or molten salt — is circulated past the reactor core to absorb the heat that it generates
20.
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
21.
Protactinium
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Protactinium or protoactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which reacts with oxygen, water vapor. It forms various chemical compounds where protactinium is present in the oxidation state +5. The average concentrations of protactinium in the Earths crust is typically on the order of a few parts per trillion, protactinium was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and named brevium because of the short half-life of the specific isotope studied, namely protactinium-234. The new name meant parent of actinium and reflected the fact that actinium is a product of radioactive decay of protactinium. It is noted that John Arnold Cranston is also credited with discovering the most stable isotope in 1915, the longest-lived and most abundant naturally occurring isotope of protactinium, protactinium-231, has a half-life of 32,760 years and is a decay product of uranium-235. Much smaller trace amounts of the nuclear isomer protactinium-234m occur in the decay chain of uranium-238. Protactinium-233 results from the decay of thorium-233 as part of the chain of used to produce uranium-233 by neutron irradiation of thorium-232. It is an intermediate product in thorium-based nuclear reactors and is therefore removed from the active zone of the reactor during the breeding process. In 1871, Dmitri Mendeleev predicted the existence of an element between thorium and uranium, the actinide element group was unknown at the time. Therefore, uranium was positioned below tungsten, and thorium below zirconium, leaving the space below tantalum empty and, until the 1950s, for a long time chemists searched for eka-tantalum as an element with similar chemical properties to tantalum, making a discovery of protactinium nearly impossible. Tantalums heavier analogue was later found to be the element dubnium. In 1900, William Crookes isolated protactinium as a radioactive material from uranium, however, he could not characterize it as a new chemical element. Crookes dissolved uranium nitrate in ether, the aqueous phase contains most of the 234 90Th and 234 91Pa. His method was used in the 1950s to isolate 234 90Th and 234 91Pa from uranium compounds. They named the new element brevium because of its short half-life,6.7 hours for 234 91Pa, thus the name brevium was changed to protoactinium as the new element was part of the decay chain of uranium-235 before the actinium. For ease of pronunciation, the name was shortened to protactinium by the IUPAC in 1949, the discovery of protactinium completed one of the last gaps in the early versions of the periodic table, proposed by Mendeleev in 1869, and it brought to fame the involved scientists. Aristid von Grosse produced 2 milligrams of Pa2O5 in 1927, for many years, this was the worlds only significant supply of protactinium, which was provided to various laboratories for scientific studies
22.
Molten salt reactor
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A molten salt reactor is a class of generation IV nuclear fission reactor in which the primary nuclear reactor coolant, or even the fuel itself, is a molten salt mixture. MSRs can run at higher temperatures than water-cooled reactors for a thermodynamic efficiency. The nuclear fuel may be solid or dissolved in the coolant, in many designs the nuclear fuel dissolved in the coolant is uranium tetrafluoride. The fluid becomes critical in a core that serves as the moderator. Some solid-fuel designs propose ceramic fuel dispersed in a matrix, with the molten salt providing low pressure. The salts are more efficient than compressed helium at removing heat from the core. The concept was established in the 1950s, the increased research into Generation IV reactor designs included a renewed interest in the technology. Extensive research into molten salt reactors started with the U. S. aircraft reactor experiment in support of the U. S, the ARE was a 2.5 MWth nuclear reactor experiment designed to attain a high energy density for use as an engine in a nuclear-powered bomber. The ARE used molten fluoride salt NaF-ZrF4-UF4 as fuel, moderated by beryllium oxide, liquid sodium was a secondary coolant. The experiment had a temperature of 860 °C. It produced 100 MWh over nine days in 1954 and this experiment used Inconel 600 alloy for the metal structure and piping. After ARE, another reactor was operated at the Critical Experiments Facility of the Oak Ridge National Laboratory in 1957 and it was part of the circulating-fuel reactor program of the Pratt & Whitney Aircraft Company. This was called the PWAR-1, the Pratt and Whitney Aircraft Reactor-1, the experiment was run for only a few weeks and at essentially zero nuclear power, but it reached criticality. The operating temperature was constant at approximately 675 °C. The PWAR-1 used NaF-ZrF4-UF4 as the fuel and coolant, making it one of the three critical molten salt reactors ever built. Oak Ridge National Laboratory took the lead in researching the MSR through the 1960s, much of their work culminated with the Molten-Salt Reactor Experiment. The MSRE was a 7.4 MWth test reactor simulating the neutronic kernel of a type of thorium molten salt breeder reactor called the liquid fluoride thorium reactor. The large breeding blanket of thorium salt was omitted in favor of neutron measurements, the MSRE was located at ORNL
23.
Neutron absorption
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Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a more easily than positively charged protons. Neutron capture plays an important role in the nucleosynthesis of heavy elements. In stars it can proceed in two ways, as a rapid or a slow process, nuclei of masses greater than 56 cannot be formed by thermonuclear reactions, but can be formed by neutron capture. At small neutron flux, as in a reactor, a single neutron is captured by a nucleus. For example, when natural gold is irradiated by neutrons, the isotope 198Au is formed in an excited state. In this process, the number increases by one. This is written as a formula in the form 197Au+n → 198Au+γ, if thermal neutrons are used, the process is called thermal capture. The isotope 198Au is a beta emitter that decays into the mercury isotope 198Hg, in this process the atomic number rises by one. The r-process happens inside stars if the flux density is so high that the atomic nucleus has no time to decay via beta emission in between neutron captures. The mass number therefore rises by a large amount while the atomic number stays the same, only afterwards, the highly unstable nuclei decay via many β− decays to stable or unstable nuclei of high atomic number. It is usually measured in barns, absorption cross section is often highly dependent on neutron energy. As a generality, the likelihood of absorption is proportional to the time the neutron is in the vicinity of the nucleus, the time spent in the vicinity of the nucleus is inversely proportional to the relative velocity between the neutron and nucleus. Other more specific issues modify this general principle, the thermal energy of the nucleus also has an effect, as temperatures rise, Doppler broadening increases the chance of catching a resonance peak. In particular, the increase in uranium-238s ability to absorb neutrons at higher temperatures is a feedback mechanism that helps keep nuclear reactors under control. Neutron capture is involved in the formation of isotopes of chemical elements, as a consequence of this fact the energy of neutron capture intervenes in the standard enthalpy of formation of isotopes. Neutron activation analysis can be used to detect the chemical composition of materials. This is because different elements release different characteristic radiation when they absorb neutrons and this makes it useful in many fields related to mineral exploration and security
24.
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
25.
Plutonium-239
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Plutonium-239 is an isotope of plutonium. Plutonium-239 is the fissile isotope used for the production of nuclear weapons. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum reactors, along with uranium-235. Plutonium-239 has a half-life of 24,110 years, plutonium-239 can also absorb neutrons and fission along with the uranium-235 in a reactor. Of all the common nuclear fuels, Pu-239 has the smallest critical mass, a spherical untamped critical mass is about 11 kg,10.2 cm in diameter. Using appropriate triggers, neutron reflectors, implosion geometry and tampers and this optimization usually requires a large nuclear development organization supported by a sovereign nation. The fission of one atom of Pu-239 generates 207.1 MeV =3.318 × 10−11 J, i. e.19.98 TJ/mol =83.61 TJ/kg, or about 2322719 kilowatt hours/kg. Pu-239 is normally created in nuclear reactors by transmutation of atoms of one of the isotopes of uranium present in the fuel rods. Occasionally, when an atom of U-238 is exposed to radiation, its nucleus will capture a neutron. This happens more easily with lower kinetic energy, the U-239 then rapidly undergoes two beta decays, becoming Pu-239.5 m i n β −93239 N p →2. Only if the fuel has been exposed for a few days in the reactor, Pu-239 has a higher probability for fission than U-235 and a larger number of neutrons produced per fission event, so it has a smaller critical mass. In practice, however, reactor-bred plutonium will invariably contain an amount of Pu-240 due to the tendency of Pu-239 to absorb an additional neutron during production. Pu-240 has a rate of spontaneous fission events, making it an undesirable contaminant. It is because of this limitation that plutonium-based weapons must be implosion-type, moreover, Pu-239 and Pu-240 cannot be chemically distinguished, so expensive and difficult isotope separation would be necessary to separate them. Weapons-grade plutonium is defined as containing no more than 7% Pu-240, Pu-240 exposed to alpha particles will incite a nuclear fission. A reactor running on unenriched or moderately enriched uranium contains a great deal of U-238, however, most commercial nuclear power reactor designs require the entire reactor to shut down, often for weeks, in order to change the fuel elements. They therefore produce plutonium in a mix of isotopes that is not well-suited to weapon construction, in practice, their construction and operation is sufficiently difficult that they are generally only used to produce plutonium. Breeder reactors are generally fast reactors, since fast neutrons are more efficient at plutonium production
26.
Molten-Salt Reactor Experiment
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The MSRE was a 7.4 MWth test reactor simulating the neutronic kernel of a type of inherently safer epithermal thorium breeder reactor called the liquid fluoride thorium reactor. It primarily used two fuels, first uranium-235 and later uranium-233, the latter 233UF4 was the result of breeding from thorium in other reactors. Since this was an engineering test, the large, expensive breeding blanket of thorium salt was omitted in favor of neutron measurements, in the MSRE, the heat from the reactor core was shed via a cooling system using air blown over radiators. It is thought similar reactors could power high-efficiency heat engines such as gas turbines. The MSREs piping, core vat and structural components were made from Hastelloy-N, the result promised to be a simple, reliable reactor. For simplicity, it was to be a small, one-fluid reactor operating at 10 MWth or less. The pyrolytic graphite core, grade CGB, also served as the moderator, before the MSRE development began, tests had shown that salt would not permeate graphite in which the pores were on the order of a micrometer. The first fuel was 33% 235U, later a smaller amount of 233UF4 was used, by 1960 a better understanding of fluoride salt based molten-salt reactors had emerged due to earlier molten salt reactor research for the Aircraft Reactor Experiment. Fluoride salts are ionic, and when melted, are stable at high temperatures, low pressures. Low pressure stability permits less robust reactor vessels and increases reliability, the high reactivity of fluorine traps most fission reaction byproducts. It appeared that the salt would permit on-site chemical separation of the fuel. The fuel system was located in sealed cells, laid out for maintenance with long-handled tools through openings in the top shielding, a tank of LiF-BeF2 salt was used to flush the fuel circulating system before and after maintenance. In a cell adjacent to the reactor was a facility for bubbling gas through the fuel or flush salt, H2-hydrogen fluoride to remove oxide. Haubenreich and Engel, Robertson, and Lindauer provide more detailed descriptions of the reactor and processing plant. The bowl of the pump was the surge space for the circulating loop. Removing the most significant neutron poison xenon-135 made the reactor safer and easier to restart, in solid-fuel reactors, on restart the 135Xe in the fuel absorbs neutrons, followed by a sudden jump in reactivity as the 135Xe is burned out. Conventional reactors may have to wait hours until xenon-135 decays after shutting down, also in the pump bowl was a port through which salt samples could be taken or capsules of concentrated fuel-enriching salt could be introduced. At the time, the temperatures were seen almost as a disadvantage
27.
Shippingport Atomic Power Station
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The Shippingport Atomic Power Station was the world’s first full-scale atomic electric power plant devoted exclusively to peacetime uses. It was located near the present-day Beaver Valley Nuclear Generating Station on the Ohio River in Beaver County, Pennsylvania, United States, the reactor reached criticality on December 2,1957, and aside from stoppages for three core changes, it remained in operation until October 1982. The first electrical power was produced on December 18,1957 as engineers synchronized the plant with the grid of Duquesne Light Company. The first Shippingport core reactor turned out capable of an output of 60 MWe one month after its launch, the second core was similarly designed but more powerful, having a larger seed. The highly energetic seed required more refueling cycles than the blanket in these first two cores, the third and final core used at Shippingport was an experimental, light water moderated, thermal breeder reactor. It kept the same design, but the seed was now Uranium-233. Additionally, being a breeder reactor, it had ability to relatively inexpensive Thorium to Uranium-233 as part of its fuel cycle. The breeding ratio attained by Shippingports third core was 1.01, over its 25-year life, the Shippingport power plant operated for about 80,324 hours, producing about 7.4 billion kilowatt-hours of electricity. Owing to the peculiarities, some non-governmental sources label Shippingport a demonstration PWR reactor. Criticism centers on the fact that the Shippingport plant had not been built to commercial specifications, consequently, the construction cost per kilowatt at Shippingport was about ten times those for a conventional power plant. In 1953, US President Dwight D. Eisenhower gave his Atoms for Peace speech to the United Nations, commercial nuclear power generation was cornerstone of his plan. A proposal by Duquesne Light Company was accepted by Admiral Rickover, ground was broken on Labor Day, September 9,1954. President Eisenhower remotely initiated the first scoop of dirt at the ceremony, the reactor achieved first criticality at 4,30 AM on December 2,1957. Sixteen days later, on December 18, the first electrical power was generated and full power was achieved on December 23,1957, Eisenhower opened the Shippingport Atomic Power Station on May 26,1958. The plant was built in 32 months at a cost of $72.5 million, the type of reactor used at Shippingport was a matter of expediency. The Atomic Energy Commission urged the construction of a reactor integrated into the utility grid, the only suitable reactor available at the time was the one that was intended for the nuclear-powered aircraft carrier desired by the Navy, but which Eisenhower had just vetoed. This explains why the Shippingport reactor used 93%-enriched Uranium, quite unlike later commercial power reactors that dont exceed 5% enrichment, other significant differences from commercial reactors include the use of hafnium for its control rods, although these were necessary and used only in the reactors seed. Shippingport was created and operated under the auspices of Admiral Hyman G. Rickover, the Shippingport reactor was designed to accommodate different cores during its lifetime, three were used
28.
THTR-300
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The THTR-300 was a thorium high-temperature nuclear reactor rated at 300 MW electric in Hamm-Uentrop, Germany. It started operating in 1983, synchronized with the grid in 1985, the THTR-300 served as a prototype high-temperature reactor to use the TRISO pebble fuel produced by the AVR, an experimental pebble bed operated by VEW. The THTR-300 cost €2.05 billion and was predicted to cost an additional €425 million through December 2009 in decommissioning, the German state of North Rhine Westphalia, Federal Republic of Germany, and Hochtemperatur-Kernkraftwerk GmbH financed the THTR-300’s construction. The electrical generation part of the THTR-300 was finished due to ever-newer requirements. It was constructed in Hamm-Uentrop from 1970 to 1983 by Hochtemperatur-Kernkraftwerk GmbH, heinz Riesenhuber, Federal Secretary of Research at that time, inaugurated it, and it first went critical on September 13,1983. It started generating electricity on April 9,1985, but did not receive permission from the atomic legal authorizing agency to feed electricity to the grid until November 16,1985 and it operated at full power in February 1987 and was shut down September 1,1989. The pressure vessel that contained the pebbles was prestressed concrete, the THTR-300s power conversion system was similar to the Fort St. Vrain reactor in the USA, in that the reactor coolant transferred the reactor cores heat to water. Because this system used a Rankine cycle, water could occasionally ingress into the helium circuit, the electric conversion system produced 308 megawatts of electricity. The waste heat from the THTR-300 was exhausted using a dry cooling tower and it had to be bailed out by the government with 92 million Marks. THTR-300 was only in service for 423 days. On May 4,1986, just 6 months after it had connected to the power grid. Consequently, some radioactive dust was released to the environment and this happened just a couple of days after the Chernobyl disaster. The operators played down the incident, which caused a loss of confidence in the regulatory authorities, the Westphalia ministry of commerce created a fact finding committee. After a couple of weeks the power plant was switched on again, the reactor kept experiencing technical difficulties, with fuel elements breaking more often than anticipated. The fuel factory in Hanau was decommissioned for security reasons, the fuel supply had already been difficult before this decision, and now it was truly at risk. It was decided to shut down THTR-300,80 incidents were logged in its short lifetime. From 1985 to 1989, the THTR-300 registered 16410 operation hours and generated 2891000 MWh, the remaining facility was safely enclosed. Dismantling is not expected to start before 2027, as with other inactive reactor facilities, costs are still being incurred
29.
United Nations
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The United Nations is an intergovernmental organization to promote international co-operation. A replacement for the ineffective League of Nations, the organization was established on 24 October 1945 after World War II in order to prevent another such conflict, at its founding, the UN had 51 member states, there are now 193. The headquarters of the UN is in Manhattan, New York City, further main offices are situated in Geneva, Nairobi, and Vienna. The organization is financed by assessed and voluntary contributions from its member states, the UNs mission to preserve world peace was complicated in its early decades by the Cold War between the US and Soviet Union and their respective allies. The organization participated in actions in Korea and the Congo. After the end of the Cold War, the UN took on major military, the UN has six principal organs, the General Assembly, the Security Council, the Economic and Social Council, the Secretariat, the International Court of Justice, and the UN Trusteeship Council. UN System agencies include the World Bank Group, the World Health Organization, the World Food Programme, UNESCO, the UNs most prominent officer is the Secretary-General, an office held by Portuguese António Guterres since 2017. Non-governmental organizations may be granted consultative status with ECOSOC and other agencies to participate in the UNs work, the organization won the Nobel Peace Prize in 2001, and a number of its officers and agencies have also been awarded the prize. Other evaluations of the UNs effectiveness have been mixed, some commentators believe the organization to be an important force for peace and human development, while others have called the organization ineffective, corrupt, or biased. Following the catastrophic loss of life in the First World War, the earliest concrete plan for a new world organization began under the aegis of the US State Department in 1939. It incorporated Soviet suggestions, but left no role for France, four Policemen was coined to refer to four major Allied countries, United States, United Kingdom, Soviet Union, and China, which emerged in the Declaration by United Nations. Roosevelt first coined the term United Nations to describe the Allied countries, the term United Nations was first officially used when 26 governments signed this Declaration. One major change from the Atlantic Charter was the addition of a provision for religious freedom, by 1 March 1945,21 additional states had signed. Each Government pledges itself to cooperate with the Governments signatory hereto, the foregoing declaration may be adhered to by other nations which are, or which may be, rendering material assistance and contributions in the struggle for victory over Hitlerism. During the war, the United Nations became the term for the Allies. To join, countries had to sign the Declaration and declare war on the Axis, at the later meetings, Lord Halifax deputized for Mr. Eden, Wellington Koo for T. V. Soong, and Mr Gromyko for Mr. Molotov. The first meetings of the General Assembly, with 51 nations represented, the General Assembly selected New York City as the site for the headquarters of the UN, and the facility was completed in 1952. Its site—like UN headquarters buildings in Geneva, Vienna, and Nairobi—is designated as international territory, the Norwegian Foreign Minister, Trygve Lie, was elected as the first UN Secretary-General
30.
Glenn T. Seaborg
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Glenn Theodore Seaborg was an American chemist whose involvement in the synthesis, discovery and investigation of ten transuranium elements earned him a share of the 1951 Nobel Prize in Chemistry. His work in this also led to his development of the actinide concept. He advised ten US Presidents – from Harry S, throughout his career, Seaborg worked for arms control. He was a signatory to the Franck Report and contributed to the Limited Test Ban Treaty, the Nuclear Non-Proliferation Treaty and he was a well-known advocate of science education and federal funding for pure research. After sharing the 1951 Nobel Prize in Chemistry with Edwin McMillan, he received approximately 50 honorary doctorates and numerous other awards, the list of things named after Seaborg ranges from his atomic element to an asteroid. He was an author, penning numerous books and 500 journal articles. He was once listed in the Guinness Book of World Records as the person with the longest entry in Whos Who in America, Glenn Theodore Seaborg was born in Ishpeming, Michigan, on April 19,1912, the son of Herman Theodore and Selma Olivia Erickson Seaborg. He had one sister, Jeanette, who was two years younger and his family spoke Swedish at home. When Glenn Seaborg was a boy, the moved to Los Angeles County, California, settling in a subdivision called Home Gardens, later annexed to the City of South Gate. About this time he changed the spelling of his first name from Glen to Glenn, Seaborg kept a daily journal from 1927 until he suffered a stroke in 1998. As a youth, Seaborg was both a sports fan and an avid movie buff. His mother encouraged him to become a bookkeeper as she felt his interests were impractical. He did not take an interest in science until his year when he was inspired by Dwight Logan Reid. Seaborg graduated from Jordan in 1929 at the top of his class and received a bachelor of degree in chemistry at the University of California, Los Angeles. He worked his way through school as a stevedore and an assistant at Firestone. Seaborg was a member of the chemistry fraternity Alpha Chi Sigma. As a graduate student in the 1930s Seaborg performed wet chemistry research for his advisor Gilbert Newton Lewis, and published three papers with him on the theory of acids and bases. Seaborg studied the text Applied Radiochemistry by Otto Hahn, of the Kaiser Wilhelm Institute for Chemistry in Berlin, for several years, Seaborg conducted important research in artificial radioactivity using the Lawrence cyclotron at UC Berkeley
31.
Cold War
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The Cold War was a state of geopolitical tension after World War II between powers in the Eastern Bloc and powers in the Western Bloc. Historians do not fully agree on the dates, but a common timeframe is the period between 1947, the year the Truman Doctrine was announced, and 1991, the year the Soviet Union collapsed. The term cold is used there was no large-scale fighting directly between the two sides, although there were major regional wars, known as proxy wars, supported by the two sides. The Cold War split the temporary alliance against Nazi Germany, leaving the Soviet Union. The USSR was a Marxist–Leninist state ruled by its Communist Party and secret police, the Party controlled the press, the military, the economy and all organizations. In opposition stood the West, dominantly democratic and capitalist with a free press, a small neutral bloc arose with the Non-Aligned Movement, it sought good relations with both sides. The two superpowers never engaged directly in full-scale armed combat, but they were armed in preparation for a possible all-out nuclear world war. The first phase of the Cold War began in the first two years after the end of the Second World War in 1945, the Berlin Blockade was the first major crisis of the Cold War. With the victory of the communist side in the Chinese Civil War and the outbreak of the Korean War, the USSR and USA competed for influence in Latin America, and the decolonizing states of Africa and Asia. Meanwhile, the Hungarian Revolution of 1956 was stopped by the Soviets, the expansion and escalation sparked more crises, such as the Suez Crisis, the Berlin Crisis of 1961, and the Cuban Missile Crisis of 1962. The USSR crushed the 1968 Prague Spring liberalization program in Czechoslovakia, détente collapsed at the end of the decade with the beginning of the Soviet–Afghan War in 1979. The early 1980s were another period of elevated tension, with the Soviet downing of Korean Air Lines Flight 007, the United States increased diplomatic, military, and economic pressures on the Soviet Union, at a time when the communist state was already suffering from economic stagnation. In the mid-1980s, the new Soviet leader Mikhail Gorbachev introduced the reforms of perestroika and glasnost. Pressures for national independence grew stronger in Eastern Europe, especially Poland, Gorbachev meanwhile refused to use Soviet troops to bolster the faltering Warsaw Pact regimes as had occurred in the past. The result in 1989 was a wave of revolutions that peacefully overthrew all of the communist regimes of Central, the Communist Party of the Soviet Union itself lost control and was banned following an abortive coup attempt in August 1991. This in turn led to the dissolution of the USSR in December 1991. The United States remained as the only superpower. The Cold War and its events have left a significant legacy and it is often referred to in popular culture, especially in media featuring themes of espionage and the threat of nuclear warfare
32.
Hanford Site
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The Hanford Site is a mostly decommissioned nuclear production complex operated by the United States federal government on the Columbia River in the U. S. state of Washington. The site has been known by names, including, Hanford Project, Hanford Works, Hanford Engineer Works. Established in 1943 as part of the Manhattan Project in Hanford, south-central Washington, the site was home to the B Reactor, the first full-scale plutonium production reactor in the world. Plutonium manufactured at the site was used in the first nuclear bomb, tested at the Trinity site, and in Fat Man, Nuclear technology developed rapidly during this period, and Hanford scientists produced major technological achievements. DOE later found water intruding into at least 14 single-shell tanks, in 2012, DOE discovered a leak also from a double-shell tank caused by construction flaws and corrosion in the bottom, and that 12 double-shell tanks have similar construction flaws. Since then, DOE changed to monitoring single-shell tanks monthly and double-shell tanks every 3 years, in March 2014, DOE announced further delays in the construction of the Waste Treatment Plant, which will affect the schedule for removing waste from the tanks. Intermittent discoveries of undocumented contamination have slowed the pace and raised the cost of cleanup, in 2007, the Hanford site represented two-thirds of the nations high-level radioactive waste by volume. Hanford is currently the most contaminated site in the United States and is the focus of the nations largest environmental cleanup. On November 10,2015, it was designated as part of the Manhattan Project National Historical Park alongside other sites in Oak Ridge, the Hanford Site occupies 586 square miles —roughly equivalent to half of the total area of Rhode Island—within Benton County, Washington. This land is closed to the general public and it is a desert environment receiving under 10 inches of annual precipitation, covered mostly by shrub-steppe vegetation. The Columbia River flows along the site for approximately 50 miles, the original site was 670 square miles and included buffer areas across the river in Grant and Franklin counties. Some of this land has returned to private use and is now covered with orchards. In 2000, large portions of the site were turned over to the Hanford Reach National Monument, the site is divided by function into three main areas. The site is bordered on the southeast by the Tri-Cities, an area composed of Richland, Kennewick, Pasco, and smaller communities. Hanford is an economic base for these cities. The confluence of the Yakima, Snake, and Columbia rivers has been a place for native peoples for centuries. The archaeological record of Native American habitation of this area back over ten thousand years. Tribes and nations including the Yakama, Nez Perce, and Umatilla used the area for hunting, fishing, Native American use of the area continued into the 20th century, even as the tribes were relocated to reservations
33.
Savannah River Site
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The site was built during the 1950s to refine nuclear materials for deployment in nuclear weapons. It covers 310 square miles and employs more than 10,000 people and it is owned by the U. S. Department of Energy. A major focus is cleanup activities related to work done in the past for American nuclear buildup, currently none of the reactors on-site are operating, although two of the reactor buildings are being used to consolidate and store nuclear materials. SRS is also home to the Savannah River National Laboratory and the USAs only operating radiochemical separations facility and its tritium facilities are also the United States only source of tritium, an essential component in nuclear weapons. The USAs only mixed oxide fuel manufacturing plant is being constructed at SRS overseen by the National Nuclear Security Administration, when operational, the MOX facility will convert legacy weapons-grade plutonium into fuel suitable for commercial power reactors. Future plans for the cover a wide range of options, including host to research reactors, a reactor park for power generation. DOE and its partners are watched by a combination of local, regional and national regulatory agencies. In 1950, the government requested DuPont to build and operate a nuclear facility near the Savannah River in South Carolina. The company had expertise in operations, having designed and built the plutonium production complex at the Hanford site for the Manhattan Project during World War II. S. Biologists from the University of Georgia, led by professor Eugene Odom, began studies of local plants and animals in 1951. Production of heavy water for site reactors started in the Heavy Water Rework Facility in 1952, P, L, and K Reactors followed in 1954, and the first irradiated fuel was discharged. F Canyon, the worlds first operational full-scale PUREX separation plant, PUREX extracted plutonium and uranium products from materials irradiated in the reactors. In 1955, C Reactor went critical, the first plutonium shipment left the site. H Canyon, a chemical separation facility, began radioactive operations, permanent tritium facilities became operational and the first shipment of tritium to the Atomic Energy Commission was made. In 1956, construction of the plant was complete. The neutrino was discovered by Fred Reines and Clyde Cowan using the flux from P Reactor, Reines was awarded the 1995 Physics Nobel Prize, Cowan had already died. In 1961, the AEC established a permanent ecology laboratory on the site, the next year, the University of Georgia hired a full-time staff with doctoral degrees to expand the research effort. In 1962, the Heavy Water Components Test Reactor went into operation, in 1963, Receiving Basin for Off-Site Fuels received its first shipment of off-site spent nuclear fuel
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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
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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
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Nuclear fuel cycle
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The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. If spent fuel is not reprocessed, the cycle is referred to as an open fuel cycle, if the spent fuel is reprocessed. Nuclear power relies on fissionable material that can sustain a reaction with neutrons. Examples of such materials include uranium and plutonium, most nuclear reactors use a moderator to lower the kinetic energy of the neutrons and increase the probability that fission will occur. This allows reactors to use material with far lower concentration of fissile isotopes than nuclear weapons, graphite and heavy water are the most effective moderators, because they slow the neutrons through collisions without absorbing them. Reactors using heavy water or graphite as the moderator can operate using natural uranium, another type of MOX fuel involves mixing LEU with thorium, which generates the fissile isotope U-233. Some reactors do not use moderators to slow the neutrons, like nuclear weapons, which also use unmoderated or fast neutrons, these fast-neutron reactors require much higher concentrations of fissile isotopes in order to sustain a chain reaction. They are also capable of breeding fissile isotopes from fertile materials, during the nuclear reaction inside a reactor, the fissile isotopes in nuclear fuel are consumed, producing more and more fission products, most of which are considered radioactive waste. The buildup of fission products and consumption of fissile isotopes eventually stop the nuclear reaction, when 3% enriched LEU fuel is used, the spent fuel typically consists of roughly 1% U-235, 95% U-238, 1% plutonium and 3% fission products. Safe management of these byproducts of nuclear power, including their storage, uranium reserves are the amounts of ore that are estimated to be recoverable at stated costs. Uranium in nature consists primarily of two isotopes, U-238 and U-235, the numbers refer to the atomic mass number for each isotope, or the number of protons and neutrons in the atomic nucleus. Naturally occurring uranium consists of approximately 99. 28% U-238 and 0. 71% U-235, the atomic nucleus of U-235 will nearly always fission when struck by a free neutron, and the isotope is therefore said to be a fissile isotope. The nucleus of a U-238 atom on the hand, rather than undergoing fission when struck by a free neutron, will nearly always absorb the neutron. This isotope then undergoes natural radioactive decay to yield Pu-239, which, the atoms of U-238 are said to be fertile, because, through neutron irradiation in the core, some eventually yield atoms of fissile Pu-239. Uranium ore can be extracted through mining in open pit. In-situ leach mining methods also are used to mine uranium in the United States, in this technology, uranium is leached from the in-place ore through an array of regularly spaced wells and is then recovered from the leach solution at a surface plant. Uranium ores in the United States typically range from about 0.05 to 0. 3% uranium oxide, some uranium deposits developed in other countries are of higher grade and are also larger than deposits mined in the United States. Uranium is also present in very low-grade amounts in some domestic phosphate-bearing deposits of marine origin, mined uranium ores normally are processed by grinding the ore materials to a uniform particle size and then treating the ore to extract the uranium by chemical leaching
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Nuclear power in India
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Nuclear power is the fourth-largest source of electricity in India after thermal, hydroelectric and renewable sources of electricity. There have been protests against the French-backed 9900 MW Jaitapur Nuclear Power Project in Maharashtra. The state government of West Bengal state has refused permission to a proposed 6000 MW facility near the town of Haripur that intended to host six Russian reactors. A Public Interest Litigation has also filed against the government’s civil nuclear programme at the Supreme Court. Despite this opposition, the capacity factor of Indian reactors was at 79% in the year 2011-12 compared to 71% in 2010-11, nine out of twenty Indian reactors recorded an unprecedented 97% capacity factor during 2011-12. With the imported uranium from France, the 220 MW Kakrapar 2 PHWR reactors recorded 99% capacity factor during 2011-12, the Availability factor for the year 2011-12 was at 89%. The country has also recently re-initiated its involvement in the LENR research activities, Indias and Asias first nuclear reactor was the Apsara research reactor. Designed and built in India, with assistance and fuel from the United Kingdom, a further research nuclear reactor and its first nuclear power plant were built with assistance from Canada. The 40 MW research reactor agreement was signed in 1956, and this reactor was supplied to India on the assurance that it would not be used for military purposes, but without effective safeguards against such use. The agreement for Indias first nuclear plant at Rajasthan, RAPP-1, was signed in 1963. These reactors contained rigid safeguards to ensure they would not be used for a military programme, the 200 MWe RAPP-1 reactor was based on the CANDU reactor at Douglas Point and began operation in 1972. Due to technical problems the reactor had to be downrated from 200 MW to 100 MW, the technical and design information were given free of charge by AECL to India. The United States and Canada terminated their assistance after the detonation of Indias first nuclear explosion in 1974, Indias domestic uranium reserves are small and the country is dependent on uranium imports to fuel its nuclear power industry. Since early 1990s, Russia has been a supplier of nuclear fuel to India. Due to dwindling domestic uranium reserves, electricity generation from nuclear power in India declined by 12. 83% from 2006 to 2008. India has also uranium supply agreements with Russia, Mongolia, Kazakhstan, Argentina and Namibia. An Indian private company won a uranium exploration contract in Niger, the Tummalapalle belt uranium reserves promises to be one of the top 20 uranium reserves discovery of the world. So far 44,000 tonnes of uranium has been discovered in the belt. The natural uranium deposits of the Bhima basin has better grade of uranium ore
38.
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
39.
Mole (unit)
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The mole is the unit of measurement in the International System of Units for amount of substance. This number is expressed by the Avogadro constant, which has a value of 6. 022140857×1023 mol−1, the mole is one of the base units of the SI, and has the unit symbol mol. The mole is used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions. For example, the chemical equation 2 H2 + O2 →2 H2O implies that 2 moles of dihydrogen and 1 mole of dioxygen react to form 2 moles of water. The mole may also be used to express the number of atoms, ions, the concentration of a solution is commonly expressed by its molarity, defined as the number of moles of the dissolved substance per litre of solution. For example, the relative molecular mass of natural water is about 18.015, therefore. The term gram-molecule was formerly used for essentially the same concept, the term gram-atom has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadros number of atoms, whether isolated or combined in molecules. Thus, for example,1 mole of MgBr2 is 1 gram-molecule of MgBr2 but 3 gram-atoms of MgBr2, in honor of the unit, some chemists celebrate October 23, which is a reference to the 1023 scale of the Avogadro constant, as Mole Day. Some also do the same for February 6 and June 2, thus, by definition, one mole of pure 12C has a mass of exactly 12 g. It also follows from the definition that X moles of any substance will contain the number of molecules as X moles of any other substance. The mass per mole of a substance is called its molar mass, the number of elementary entities in a sample of a substance is technically called its amount. Therefore, the mole is a convenient unit for that physical quantity, one can determine the chemical amount of a known substance, in moles, by dividing the samples mass by the substances molar mass. Other methods include the use of the volume or the measurement of electric charge. The mass of one mole of a substance depends not only on its molecular formula, since the definition of the gram is not mathematically tied to that of the atomic mass unit, the number NA of molecules in a mole must be determined experimentally. The value adopted by CODATA in 2010 is NA =6. 02214129×1023 ±0. 00000027×1023, in 2011 the measurement was refined to 6. 02214078×1023 ±0. 00000018×1023. The number of moles of a sample is the sample mass divided by the mass of the material. The history of the mole is intertwined with that of mass, atomic mass unit, Avogadros number. The first table of atomic mass was published by John Dalton in 1805
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Critical mass
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A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a material depends upon its nuclear properties, its density, its shape, its enrichment, its purity, its temperature. The concept is important in nuclear weapon design, when k =1, the mass is critical, and the chain reaction is barely self-sustaining. A subcritical mass is a mass of material that does not have the ability to sustain a fission chain reaction. A population of neutrons introduced to an assembly will exponentially decrease. A steady rate of spontaneous fissions causes a steady level of neutron activity. The constant of proportionality increases as k increases, a supercritical mass is one where there is an increasing rate of fission. The material may settle into equilibrium at an elevated temperature/power level or destroy itself, in the case of supercriticality, k >1. The mass where criticality occurs may be changed by modifying certain attributes such as fuel, shape, temperature, density and these attributes have complex interactions and interdependencies. This section explains only the simplest ideal cases, varying the amount of fuel It is possible for a fuel assembly to be critical at near zero power. If the perfect quantity of fuel were added to a subcritical mass to create an exactly critical mass. Changing the shape A mass may be exactly critical without being a homogeneous sphere. More closely refining the shape toward a sphere will make the mass supercritical. Conversely changing the shape to a perfect sphere will decrease its reactivity. Changing the temperature A mass may be critical at a particular temperature. Fission and absorption cross-sections increase as the neutron velocity decreases. As fuel temperature increases, neutrons of a given energy appear faster and this is not unrelated to Doppler broadening of the U238 resonances but is common to all fuels/absorbers/configurations. Neglecting the very important resonances, the neutron cross section of every material exhibits an inverse relationship with relative neutron velocity
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