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
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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
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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
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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
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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
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