1.
Isotope
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Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of an element have the same number of protons in each atom. The number of protons within the nucleus is called atomic number and is equal to the number of electrons in the neutral atom. Each atomic number identifies a specific element, but not the isotope, the number of nucleons in the nucleus is the atoms mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12,13 and 14 respectively. The atomic number of carbon is 6, which means that carbon atom has 6 protons. Nuclide refers to a rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, whereas the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. Because isotope is the term, it is better known than nuclide. An isotope and/or nuclide is specified by the name of the particular element followed by a hyphen, when a chemical symbol is used, e. g. C for carbon, standard notation is to indicate the number with a superscript at the upper left of the chemical symbol. Because the atomic number is given by the element symbol, it is common to only the mass number in the superscript. The letter m is sometimes appended after the number to indicate a nuclear isomer. For example, 14C is a form of carbon, whereas 12C. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, primordial nuclides include 32 nuclides with very long half-lives and 254 that are formally considered as stable nuclides, because they have not been observed to decay. In most cases, for reasons, if an element has stable isotopes. Theory predicts that many apparently stable isotopes/nuclides are radioactive, with extremely long half-lives, of the 254 nuclides never observed to decay, only 90 of these are theoretically stable to all known forms of decay
2.
Chemical element
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A chemical element or element is a species of atoms having the same number of protons in their atomic nuclei. There are 118 elements that have identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radioactive isotopes, iron is the most abundant element making up Earth, while oxygen is the most common element in the Earths crust. Chemical elements constitute all of the matter of the universe. The two lightest elements, hydrogen and helium, were formed in the Big Bang and are the most common elements in the universe. The next three elements were formed mostly by cosmic ray spallation, and are rarer than those that follow. Formation of elements with from 6 to 26 protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis, the high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. The term element is used for atoms with a number of protons as well as for a pure chemical substance consisting of a single element. A single element can form multiple substances differing in their structure, when different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals, among the more common of such native elements are copper, silver, gold, carbon, and sulfur. All but a few of the most inert elements, such as gases and noble metals, are usually found on Earth in chemically combined form. While about 32 of the elements occur on Earth in native uncombined forms. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, the history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal, alchemists and chemists subsequently identified many more, almost all of the naturally occurring elements were known by 1900. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, almost all other elements found in nature were made by various natural methods of nucleosynthesis. On Earth, small amounts of new atoms are produced in nucleogenic reactions, or in cosmogenic processes. Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope, Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected, the very heaviest elements undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized
3.
Nuclide
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A nuclide is an atomic species characterized by the specific constitution of its nucleus, i. e. by its number of protons Z, its number of neutrons N, and its nuclear energy state. The word nuclide was proposed by Truman P. Kohman in 1947, Kohman originally suggested nuclide as referring to a species of nucleus defined by containing a certain number of neutrons and protons. The word thus was originally intended to focus on the nucleus, nuclide refers to a nucleus rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, while the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. Since isotope is the term, it is better known than nuclide. A set of nuclides with equal number, i. e. of the same chemical element but different neutron numbers, are called isotopes of the element. Particular nuclides are still often loosely called isotopes, but the term nuclide is the one in general. In similar manner, a set of nuclides with equal mass number A, but different atomic number, are called isobars, and isotones are nuclides of equal neutron number but different proton numbers. The name isotone has been derived from the isotope to emphasize that in the first group of nuclides it is the number of neutrons that is constant. See Isotope#Notation for an explanation of the used for different nuclide or isotope types. Nuclear isomers are members of a set of nuclides with equal number and equal mass number. An example is the two states of the single isotope 99 43Tc shown among the decay schemes, each of these two states qualifies as a different nuclide, illustrating one way that nuclides may differ from isotopes. The most long-lived non-ground state nuclear isomer is the nuclide tantalum-180m and this nuclide occurs primordially, and has never been observed to decay to the ground state. There are about 254 nuclides in nature that have never observed to decay. They occur among the 80 different elements that have one or more stable isotopes, see stable isotope and primordial nuclide. Unstable nuclides are radioactive and are called radionuclides and their decay products are called radiogenic nuclides. About 254 stable and about 85 unstable nuclides exist naturally on Earth, natural radionuclides may be conveniently subdivided into three types
4.
Chemistry
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Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism. An alchemist was called a chemist in popular speech, and later the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian. Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments. Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, though, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
5.
Enriched uranium
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Enriched uranium is a type of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99. 284% 238U isotope, with 235U only constituting about 0. 711% of its weight, 235U is the only nuclide existing in nature that is fissile with thermal neutrons. Enriched uranium is a component for both civil nuclear power generation and military nuclear weapons. During the Manhattan Project enriched uranium was given the codename oralloy, the term oralloy is still occasionally used to refer to enriched uranium. There are about 2,000 tonnes of enriched uranium in the world, produced mostly for nuclear weapons, naval propulsion. At present,95 percent of the stocks of depleted uranium remain in secure storage. Uranium as it is directly from the Earth is not suitable as fuel for most nuclear reactors. Uranium is mined underground or in an open pit depending on the depth in which it is found. After the uranium ore is mined, it must go through a process to extract the uranium from the ore. 1% uranium. Naturally-occurring uranium is made of a mixture of U-235 and U-238, the U-235 is fissile meaning it is easily split with neutrons while the remainder is U-238, but in nature, more than 99% of the extracted ore is U-238. Most nuclear reactors require enriched uranium, which is uranium with higher concentrations of U-235 ranging between 3. 5% and 4. 5%, there are two commercial enrichment processes, gaseous diffusion and gas centrifugation. Both enrichment processes involve the use of uranium hexafluoride and produce enriched uranium oxide, reprocessed uranium is a product of nuclear fuel cycles involving nuclear reprocessing of spent fuel. Low-enriched uranium has a lower than 20% concentration of 235U, for instance, in light water reactors. Fresh LEU used in research reactors is usually enriched 12% to 19. 75% U-235, highly enriched uranium has a 20% or higher concentration of 235U. 4% 235U being required. For criticality experiments, enrichment of uranium to over 97% has been accomplished, the very first uranium bomb, Little Boy dropped by the United States on Hiroshima in 1945, used 64 kilograms of 80% enriched uranium. Wrapping the weapons fissile core in a neutron reflector can dramatically reduce the critical mass, because the core was surrounded by a good neutron reflector, at explosion it comprised almost 2.5 critical masses. The presence of too much of the 238U isotope inhibits the nuclear chain reaction that is responsible for the weapons power. The critical mass for 85% highly enriched uranium is about 50 kilograms, for the secondary of a large nuclear weapon, the higher critical mass of less-enriched uranium can be an advantage as it allows the core at explosion time to contain a larger amount of fuel
6.
Depleted uranium
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Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium. Natural uranium contains about 0. 72% U-235, while the DU used by the U. S. Department of Defense contains 0. 3% U-235 or less, uses of DU take advantage of its very high density of 19.1 g/cm3. In return, the radioactive and non-fissile uranium-238 constitutes the main component of depleted uranium. Civilian uses include counterweights in aircraft, radiation shielding in medical therapy and industrial radiography equipment. Military uses include armor plating and armor-piercing projectiles, most depleted uranium arises as a by-product of the production of enriched uranium for use as fuel in nuclear reactors and in the manufacture of nuclear weapons. Since U-238 has a much longer half-life than the lighter isotopes, DU from nuclear reprocessing has different isotopic ratios from enrichment–by-product DU, from which it can be distinguished by the presence of U-236. DU used in US munitions has 60% of the radioactivity of natural uranium, trace transuranics have been reported to be present in some US tank armor. The use of DU in munitions is controversial because of concerns about potential health effects. Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by exposure to uranium and it is only weakly radioactive because of its long radioactive half-life. The biological half-life for uranium is about 15 days, the actual level of acute and chronic toxicity of DU is also controversial. Several studies using cultured cells and laboratory rodents suggest the possibility of leukemogenic, genetic, reproductive, a 2005 epidemiology review concluded, In aggregate the human epidemiological evidence is consistent with increased risk of birth defects in offspring of persons exposed to DU. Enriched uranium was first manufactured in the early 1940s when the United States, later in the decade, France and the Soviet Union began their nuclear weapons and nuclear power programs. Depleted uranium was originally stored as a waste product in the hope that improved enrichment processes could extract additional quantities of the fissionable U-235 isotope. This re-enrichment recovery of the residual uranium-235 is now in practice in parts of the world. It is possible to design civilian power-generating reactors using unenriched fuel, thus most civilian reactors as well as all naval reactors and nuclear weapons production require fuel containing concentrated U-235 and generate depleted Uranium. In the 1970s, the Pentagon reported that the Soviet military had developed armor plating for Warsaw Pact tanks that NATO ammunition could not penetrate, the Pentagon began searching for material to make denser armor-piercing projectiles. After testing various metals, ordnance researchers settled on depleted uranium, the US and NATO militaries used DU penetrator rounds in the 1991 Gulf War, the Bosnia war, bombing of Serbia, the 2003 invasion of Iraq, and 2015 airstrikes on ISIS in Syria. It is estimated that between 315 and 350 tons of DU were used in the 1991 Gulf War, natural uranium metal contains about 0. 71% U-235,99. 28% U-238, and about 0. 0054% U-234
7.
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
8.
Chemical reaction
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A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Nuclear chemistry is a sub-discipline of chemistry that involves the reactions of unstable. The substance initially involved in a reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, and they yield one or more products. Reactions often consist of a sequence of individual sub-steps, the elementary reactions. Chemical reactions are described with chemical equations, which present the starting materials, end products. Chemical reactions happen at a characteristic reaction rate at a given temperature, typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium, Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product, in biochemistry, a consecutive series of chemical reactions form metabolic pathways. These reactions are catalyzed by protein enzymes. Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity, in the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to lead into gold, for which purpose they used reactions of lead. The process involved heating of sulfate and nitrate minerals such as sulfate, alum. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid, further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of an element called phlogiston, which was contained within combustible bodies. This proved to be false in 1785 by Antoine Lavoisier who found the explanation of the combustion as reaction with oxygen from the air
9.
Deuterium
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Deuterium is one of two stable isotopes of hydrogen. The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common hydrogen isotope, Deuterium has a natural abundance in Earths oceans of about one atom in 6420 of hydrogen. Thus deuterium accounts for approximately 0. 0156% of all the naturally occurring hydrogen in the oceans, the abundance of deuterium changes slightly from one kind of natural water to another. The deuterium isotopes name is formed from the Greek deuteros meaning second, Deuterium was discovered and named in 1931 by Harold Urey. When the neutron was discovered in 1932, this made the structure of deuterium obvious. Soon after deuteriums discovery, Urey and others produced samples of water in which the deuterium content had been highly concentrated. Deuterium is destroyed in the interiors of stars faster than it is produced, other natural processes are thought to produce only an insignificant amount of deuterium. Nearly all deuterium found in nature was produced in the Big Bang 13.8 billion years ago and this is the ratio found in the gas giant planets, such as Jupiter. However, other bodies are found to have different ratios of deuterium to hydrogen-1. This is thought to be as a result of natural isotope separation processes that occur from solar heating of ices in comets, like the water-cycle in Earths weather, such heating processes may enrich deuterium with respect to protium. The analysis of ratios in comets found results very similar to the mean ratio in Earths oceans. This reinforces theories that much of Earths ocean water is of cometary origin, the deuterium/protium ratio of the comet 67P/Churyumov-Gerasimenko, as measured by the Rosetta space probe, is about three times that of earth water. This figure is the highest yet measured in a comet, deuterium/protium ratios thus continue to be an active topic of research in both astronomy and climatology. Deuterium is frequently represented by the chemical symbol D, since it is an isotope of hydrogen with mass number 2, it is also represented by 2H. IUPAC allows both D and 2H, although 2H is preferred, a distinct chemical symbol is used for convenience because of the isotopes common use in various scientific processes. In quantum mechanics the energy levels of electrons in atoms depend on the mass of the system of electron. For hydrogen, this amount is about 1837/1836, or 1.000545, the energies of spectroscopic lines for deuterium and light-hydrogen therefore differ by the ratios of these two numbers, which is 1.000272. The wavelengths of all deuterium spectroscopic lines are shorter than the lines of light hydrogen
10.
Relative atomic mass
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Relative atomic mass is a dimensionless physical quantity. In its modern definition, it is the ratio of the mass of atoms of an element in a given sample to one unified atomic mass unit. The unified atomic mass unit, symbol u, is defined being 1⁄12 of the mass of a carbon-12 atom, the mass of atoms can vary, due to the presence of various isotopes of that element. Since both values in the ratio are expressed in the unit, the resulting value is dimensionless. Within one source, it is a average over the individual atom weights present. Between sources, the weight can vary when the sources origin resulted in different isotopic concentrations. These differences are real and measurable, and can be used to identify a sample to its origin, for example, a sample of elemental carbon from volcanic methane will have a different relative atomic mass than one collected from plant or animal tissues. The well-known standard atomic weight, or atomic weight, is a usage of relative atomic mass, it is the relative atomic mass. For these sources, research reports are used by the CIAAW of the International Union of Pure, the standard atomic weights are reprinted in a wide variety of textbooks, commercial catalogues, and periodic table wall charts. They are what chemists loosely call atomic weights and it is the most published form of the relative atomic mass. Both terms are officially sanctioned by IUPAC, the term relative atomic mass now seems to be gaining as the preferred term over atomic weight, although in the case of standard atomic weight, this shorter term continues to be used. This comparison is the quotient of the two weights, which makes the value dimensionless and this quotient also explains the word relative, the sample mass value is made relative to carbon-12. It is uses as a synonym for atomic weight, in some circumstances may even be synonymous with standard atomic weight. Here the unified atomic mass unit refers to 1⁄12 of the mass of an atom of 12C in its ground state. The IUPAC definition of relative atomic mass is, An atomic weight of an element from a source is the ratio of the average mass per atom of the element to 1/12 of the mass of an atom of 12C. The definition deliberately specifies An atomic weight…, as an element will have different relative atomic masses depending on the source, for example, boron from Turkey has a lower relative atomic mass than boron from California, because of its different isotopic composition. Nevertheless, given the cost and difficulty of isotope analysis, it is usual to use the values of standard atomic weights which are ubiquitous in chemical laboratories. Older historical relative scales used either the relative isotopic mass for reference
11.
Nuclear magnetic resonance
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Nuclear magnetic resonance is a physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation. NMR allows the observation of quantum mechanical magnetic properties of the atomic nucleus. Many scientific techniques exploit NMR phenomena to study physics, crystals. NMR is also used in advanced medical imaging techniques, such as in magnetic resonance imaging. The most commonly studied nuclei are 1H and 13C, although nuclei from isotopes of other elements have been studied by high-field NMR spectroscopy as well. A key feature of NMR is that the frequency of a particular substance is directly proportional to the strength of the applied magnetic field. Since the resolution of the technique depends on the magnitude of magnetic field gradient, many efforts are made to develop increased field strength. The effectiveness of NMR can also be improved using hyperpolarization, and/or using two-dimensional, three-dimensional and higher-dimensional multi-frequency techniques, the principle of NMR usually involves two sequential steps, The alignment of the magnetic nuclear spins in an applied, constant magnetic field B0. The perturbation of this alignment of the nuclear spins by employing an electro-magnetic, the required perturbing frequency is dependent upon the static magnetic field and the nuclei of observation. The two fields are chosen to be perpendicular to each other as this maximizes the NMR signal strength. The resulting response by the magnetization of the nuclear spins is the phenomenon that is exploited in NMR spectroscopy. NMR phenomena are also utilized in low-field NMR, NMR spectroscopy and MRI in the Earths magnetic field, in 1946, Felix Bloch and Edward Mills Purcell expanded the technique for use on liquids and solids, for which they shared the Nobel Prize in Physics in 1952. Yevgeny Zavoisky likely observed nuclear magnetic resonance in 1941, well before Felix Bloch and Edward Mills Purcell, russell H. Varian filed the Method and means for correlating nuclear properties of atoms and magnetic fields, U. S. Patent 2,561,490 on July 24,1951, Varian Associates developed the first NMR unit called NMR HR-30 in 1952. Purcell had worked on the development of radar during World War II at the Massachusetts Institute of Technologys Radiation Laboratory. His work during that project on the production and detection of radio frequency power, when this absorption occurs, the nucleus is described as being in resonance. Different atomic nuclei within a molecule resonate at different frequencies for the magnetic field strength. The observation of magnetic resonance frequencies of the nuclei present in a molecule allows any trained user to discover essential chemical and structural information about the molecule
12.
Hydrogen
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Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
13.
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
14.
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
15.
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
16.
Cascade (chemical engineering)
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In chemical engineering, a cascade is a plant consisting of several similar stages with each processing the output from the previous stage. Cascades are most commonly used in separation, distillation, flotation. Cascade process is any process that takes place in a number of steps, another example of cascade process is that operating in a cascade liquefier. If a still removes 99% of impurities from water, a cascade of three stills will leave 3 =0.000001 =0. 0001% the amount of impurities
17.
Uranium
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Uranium is a chemical element with symbol U and atomic number 92. It is a metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons, Uranium is weakly radioactive because all its isotopes are unstable. The most common isotopes in natural uranium are uranium-238 and uranium-235, Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead, and it occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite. In nature, uranium is found as uranium-238, uranium-235, Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion years, many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 is the naturally occurring fissile isotope, which makes it widely used in nuclear power plants. However, because of the amounts found in nature, uranium needs to undergo enrichment so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor, another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology. In sufficient concentration, these maintain a sustained nuclear chain reaction. This generates the heat in nuclear reactors, and produces the fissile material for nuclear weapons. Depleted uranium is used in kinetic energy penetrators and armor plating, Uranium is used as a colorant in uranium glass, producing lemon yellow to green colors. Uranium glass fluoresces green in ultraviolet light and it was also used for tinting and shading in early photography. The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by Henri Becquerel. An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of weapons that used uranium metal. The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is a concern for public health. When refined, uranium is a white, weakly radioactive metal
18.
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
19.
Heavy water
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The presence of deuterium gives the chemical different nuclear properties, and the increase of mass gives it different physical and chemical properties compared to normal light water. Deuterium is an isotope with a nucleus containing a neutron and a proton. The additional neutron makes a deuterium atom roughly twice as heavy as a protium atom, a molecule of heavy water has two deuterium atoms in place of the two protium atoms of ordinary light water. For instance, the water used in CANDU reactors is 99. 75% enriched by hydrogen atom-fraction—meaning that 99. 75% of the hydrogen atoms are of the heavy type. For comparison, ordinary water contains only about 156 deuterium atoms per million hydrogen atoms, in its pure form, it has a density about 11% greater than water, but is otherwise physically and chemically similar. This difference increases the strength of waters hydrogen-oxygen bonds, and this in turn is enough to cause differences that are important to some biochemical reactions, the human body naturally contains deuterium equivalent to about five grams of heavy water, which is harmless. When a large fraction of water in higher organisms is replaced by heavy water, Heavy water was first produced in 1932, a few months after the discovery of deuterium. With the discovery of fission in late 1938, and the need for a neutron moderator that captured few neutrons. Since then, heavy water has been a component in some types of reactors. These heavy water reactors have the advantage of being able to run on natural uranium without using graphite moderators that pose radiological, most modern reactors use enriched uranium with ordinary water as the moderator. Semiheavy water, HDO, exists whenever there is water with light hydrogen and this is because hydrogen atoms are rapidly exchanged between water molecules. Water containing 50% H and 50% D in its hydrogen contains about 50% HDO and 25% each of H 2O and D 2O. In normal water, about 1 molecule in 3,200 is HDO, thus semiheavy water molecules are far more common than pure heavy water molecules. Water enriched in the oxygen isotopes 17O and 18O is also commercially available. It is heavy water as it is denser than normal water —but is rarely called heavy water, since it not contain the deuterium that gives D2O its unusual nuclear. It is more expensive than D2O due to the more difficult separation of 17O, H218O is also used for production of fluorine-18 for radiopharmaceuticals and radiotracers and for positron emission tomography. Tritiated water contains tritium in place of protium or deuterium, the physical properties of water and heavy water differ in several respects. Heavy water is 10. 6% denser than water, and heavy waters physically different properties can be seen without equipment if a frozen sample is dropped into normal water
20.
Lithium
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Lithium is a chemical element with the symbol Li and atomic number 3. It is a soft, silver-white metal belonging to the metal group of chemical elements. Under standard conditions, it is the lightest metal and the least dense solid element, like all alkali metals, lithium is highly reactive and flammable. For this reason, it is stored in mineral oil. When cut open, it exhibits a metallic luster, but contact with moist air corrodes the surface quickly to a silvery gray. Because of its reactivity, lithium never occurs freely in nature, and instead, appears only in compounds. Lithium occurs in a number of minerals, but due to its solubility as an ion, is present in ocean water and is commonly obtained from brines. On a commercial scale, lithium is isolated electrolytically from a mixture of lithium chloride, the nucleus of the lithium atom verges on instability, since the two stable lithium isotopes found in nature have among the lowest binding energies per nucleon of all stable nuclides. Because of its relative instability, lithium is less common in the solar system than 25 of the first 32 chemical elements even though the nuclei are very light in atomic weight. For related reasons, lithium has important links to nuclear physics, the transmutation of lithium atoms to helium in 1932 was the first fully man-made nuclear reaction, and lithium-6 deuteride serves as a fusion fuel in staged thermonuclear weapons. These uses consume more than three quarters of lithium production, Lithium is found in variable amounts in foods, primary food sources are grains and vegetables, in some areas, the drinking water also provides significant amounts of the element. Human dietary lithium intakes depend on location and the type of foods consumed, traces of lithium were detected in human organs and fetal tissues already in the late 19th century, leading to early suggestions as to possible specific functions in the organism. However, it took another century until evidence for the essentiality of lithium became available, in studies conducted from the 1970s to the 1990s, rats and goats maintained on low-lithium rations were shown to exhibit higher mortalities as well as reproductive and behavioral abnormalities. Lithium appears to play an important role during the early fetal development as evidenced by the high lithium contents of the embryo during the early gestational period. The available experimental evidence now appears to be sufficient to accept lithium as essential, the lithium ion Li+ administered as any of several lithium salts has proven to be useful as a mood-stabilizing drug in the treatment of bipolar disorder in humans. Like the other metals, lithium has a single valence electron that is easily given up to form a cation. Because of this, lithium is a conductor of heat and electricity as well as a highly reactive element. Lithiums low reactivity is due to the proximity of its electron to its nucleus
21.
Silicon
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Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a metallic luster. It is a member of group 14 in the table, along with carbon above it and germanium, tin, lead. It is not very reactive, although more reactive than germanium, Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earths crust. It is most widely distributed in dusts, sands, planetoids, over 90% of the Earths crust is composed of silicate minerals, making silicon the second most abundant element in the Earths crust after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals, such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with sand and gravel to make concrete for walkways, foundations. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass, Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has an impact on the modern world economy. Most free silicon is used in the refining, aluminium-casting. Silicon is the basis of the widely used synthetic polymers called silicones, Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses. Silicon is a solid at room temperature, with a point of 1,414 °C. Like water, it has a density in a liquid state than in a solid state and it expands when it freezes. With a relatively high conductivity of 149 W·m−1·K−1, silicon conducts heat well. In its crystalline form, pure silicon has a gray color, like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a cubic crystal structure with a lattice spacing of 0.5430710 nm. The outer electron orbital of silicon, like that of carbon, has four valence electrons, the 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six
22.
Thermal conductivity
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In physics, thermal conductivity is the property of a material to conduct heat. It is evaluated primarily in terms of Fouriers Law for heat conduction, heat transfer occurs at a lower rate across materials of low thermal conductivity than across materials of high thermal conductivity. Correspondingly, materials of high thermal conductivity are used in heat sink applications. The thermal conductivity of a material may depend on temperature, the reciprocal of thermal conductivity is called thermal resistivity. Thermal conductivity is actually a tensor, which means it is possible to have different values in different directions, in SI units, thermal conductivity is measured in watts per meter-kelvin. The dimension of thermal conductivity is M1L1T−3Θ−1 and these variables are mass, length, time, and temperature. In Imperial units, thermal conductivity is measured in BTU/, other units which are closely related to the thermal conductivity are in common use in the construction and textile industries. The construction industry makes use of such as the R-value. Although related to the conductivity of a material used in an insulation product, R-. Likewise the textile industry has several units including the tog and the clo which express thermal resistance of a material in a way analogous to the R-values used in the construction industry, there are a number of ways to measure thermal conductivity. Each of these is suitable for a range of materials, depending on the thermal properties. There is a distinction between steady-state and transient techniques, in general, steady-state techniques are useful when the temperature of the material does not change with time. This makes the signal analysis straightforward, the disadvantage is that a well-engineered experimental setup is usually needed. The Divided Bar is the most common used for consolidated rock solids. Thermal conductivity is important in science, research, electronics, building insulation and related fields. Several materials are shown in the list of thermal conductivities and these should be considered approximate due to the uncertainties related to material definitions. High energy generation rates within electronics or turbines require the use of materials with high thermal conductivity such as copper, aluminium, the reciprocal of thermal conductivity is thermal resistivity, usually expressed in kelvin-meters per watt. For a given thickness of a material, that particular constructions thermal resistance, unfortunately, there are differing definitions for these terms
23.
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
24.
Pu-241
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Plutonium-241 is an isotope of plutonium formed when plutonium-240 captures a neutron. Like Pu-239 but unlike 240Pu, 241Pu is fissile, with a neutron cross section about 1/3 greater than 239Pu. In the non-fission case, neutron capture produces plutonium-242, in general, isotopes with an odd number of neutrons are both more likely to absorb a neutron, and more likely to undergo fission on neutron absorption, than isotopes with an even number of neutrons. 241Pu has a half-life of 14 years, corresponding to a decay of about 5% of Pu-241 nuclei over a one-year period, in a thermal reactor, 241Am captures a neutron to become americium-242, which quickly becomes curium-242 via beta decay. In short, Am-241 needs to absorb two neutrons before again becoming a fissile isotope
25.
Isotopes of americium
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Americium 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 241Am in 1944, the artificial element decays into alpha particles. Americium has an number of 95. Nineteen radioisotopes of americium have been characterized, with the most stable being 243Am with a half-life of 7,370 years, all of the remaining radioactive isotopes have half-lives that are less than 51 hours, and the majority of these have half-lives that are less than 100 minutes. This element also has 8 meta states, with the most stable being 242mAm, the isotopes of americium range in atomic weight from 231.046 u to 249.078 u. Americium-241 is the most prevalent isotope of americium in nuclear waste. It is the americium used in an americium smoke detector based on an ionization chamber. It is a fuel for long-lifetime radioisotope thermoelectric generators. Possible parent nuclides, beta from 241Pu, electron capture from 241Cm, Americium-241 decays by alpha emission, with a by-product of gamma rays. Its presence in plutonium is determined by the concentration of plutonium-241. Because of the low penetration of radiation, Americium-241 only poses a health risk when ingested or inhaled. Older samples of plutonium containing plutonium-241 contain a buildup of 241Am, a chemical removal of americium from reworked plutonium may be required. Americium-242m has a mass of 242.0595492 g/mol and it is one of the rare cases, like 180mTa, where a higher-energy nuclear isomer is more stable than the lower-energy one, Americium-242. 242mAm is fissile and has a low mass, comparable to that of 239Pu. It has a high cross section for fission, and if in a nuclear reactor is destroyed relatively quickly. Another report claims that 242mAm has a lower critical mass, can sustain a chain reaction even as a thin film. Americium-243 has a mass of 243.06138 g/mol and a half-life of 7,370 years and it is formed in the nuclear fuel cycle by neutron capture on plutonium-242 followed by beta decay. Production increases exponentially with increasing burnup as a total of 5 neutron captures on 238U are required and it decays by either emitting an alpha particle to become 239Np, which then quickly decays to 239Pu, or infrequently, by spontaneous fission
26.
Diffusion
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Diffusion is the net movement of molecules or atoms from a region of high concentration to a region of low concentration. This is also referred to as the movement of a substance down a concentration gradient, a gradient is the change in the value of a quantity with the change in another variable. The word diffusion derives from the Latin word, diffundere, which means to spread out, a distinguishing feature of diffusion is that it results in mixing or mass transport, without requiring bulk motion. Thus, diffusion should not be confused with convection, or advection, an example of a situation in which bulk flow and diffusion can be differentiated is the mechanism by which oxygen enters the body during external respiration. The lungs are located in the cavity, which expands as the first step in external respiration. This expansion leads to an increase in volume of the alveoli in the lungs and this creates a pressure gradient between the air outside the body and the alveoli. The air moves down the gradient through the airways of the lungs and into the alveoli until the pressure of the air. The air arriving in the alveoli has a concentration of oxygen than the “stale” air in the alveoli. The increase in oxygen concentration creates a concentration gradient for oxygen between the air in the alveoli and the blood in the capillaries that surround the alveoli, oxygen then moves by diffusion, down the concentration gradient, into the blood. The other consequence of the air arriving in alveoli is that the concentration of carbon dioxide in the alveoli decreases and this creates a concentration gradient for carbon dioxide to diffuse from the blood into the alveoli. The pumping action of the heart then transports the blood around the body, as the left ventricle of the heart contracts, the volume decreases, which increases the pressure in the ventricle. This creates a gradient between the heart and the capillaries, and blood moves through blood vessels by bulk flow. The concept of diffusion is widely used in, physics, chemistry, biology, sociology, economics, however, in each case, the object that is undergoing diffusion is “spreading out” from a point or location at which there is a higher concentration of that object. In the phenomenological approach, diffusion is the movement of a substance from a region of high concentration to a region of low concentration without bulk motion, according to Ficks laws, the diffusion flux is proportional to the negative gradient of concentrations. It goes from regions of higher concentration to regions of lower concentration, some time later, various generalizations of Ficks laws were developed in the frame of thermodynamics and non-equilibrium thermodynamics. From the atomistic point of view, diffusion is considered as a result of the walk of the diffusing particles. In molecular diffusion, the molecules are self-propelled by thermal energy. Random walk of small particles in suspension in a fluid was discovered in 1827 by Robert Brown, the theory of the Brownian motion and the atomistic backgrounds of diffusion were developed by Albert Einstein
27.
United States
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean, the geography, climate and wildlife of the country are extremely diverse. At 3.8 million square miles and with over 324 million people, the United States is the worlds third- or fourth-largest country by area, third-largest by land area. It is one of the worlds most ethnically diverse and multicultural nations, paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century, the United States emerged from 13 British colonies along the East Coast. Numerous disputes between Great Britain and the following the Seven Years War led to the American Revolution. On July 4,1776, during the course of the American Revolutionary War, the war ended in 1783 with recognition of the independence of the United States by Great Britain, representing the first successful war of independence against a European power. The current constitution was adopted in 1788, after the Articles of Confederation, the first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and designed to guarantee many fundamental civil liberties. During the second half of the 19th century, the American Civil War led to the end of slavery in the country. By the end of century, the United States extended into the Pacific Ocean. The Spanish–American War and World War I confirmed the status as a global military power. The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the sole superpower. The U. S. is a member of the United Nations, World Bank, International Monetary Fund, Organization of American States. The United States is a developed country, with the worlds largest economy by nominal GDP. It ranks highly in several measures of performance, including average wage, human development, per capita GDP. While the U. S. economy is considered post-industrial, characterized by the dominance of services and knowledge economy, the United States is a prominent political and cultural force internationally, and a leader in scientific research and technological innovations. In 1507, the German cartographer Martin Waldseemüller produced a map on which he named the lands of the Western Hemisphere America after the Italian explorer and cartographer Amerigo Vespucci
28.
Oak Ridge National Laboratory
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Oak Ridge National Laboratory is an American multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the largest science and energy national laboratory in the Department of Energy system by surface, ORNL is located in Oak Ridge, Tennessee, near Knoxville. ORNLs scientific programs focus on materials, neutron science, energy, high-performance computing, systems biology, ORNL partners with the state of Tennessee, universities and industries to solve challenges in energy, advanced materials, manufacturing, security and physics. ORNL hosts the Center for Nanophase Materials Sciences, the BioEnergy Science Center, Oak Ridge National Laboratory is managed by UT-Battelle, a limited liability partnership between the University of Tennessee and the Battelle Memorial Institute, formed in 2000 for that purpose. The annual budget is US$1.65 billion, 80% of which is from the Department of Energy, as of 2012 there are 4,400 staff working at ORNL,1,600 of whom are directly conducting research, and an additional 3,000 guest researchers annually. The total area of the reservation 150 square kilometres of which the lab takes up 18 square kilometres, the town of Oak Ridge was established by the Army Corps of Engineers as part of the Clinton Engineer Works in 1942 on isolated farm land as part of the Manhattan Project. During the war, advanced research for the government was managed at the site by the University of Chicago, in 1943, construction of the Clinton Laboratories was completed, later renamed to Oak Ridge National Laboratory. The site was chosen for the X-10 Graphite Reactor, used to show that plutonium can be extracted from enriched uranium, enrico Fermi and his colleagues developed the worlds second self-sustaining nuclear reactor after Fermis previous experiment, the Chicago Pile-1. The X-10 was the first reactor designed for continuous operation, in 1946 the first medical isotopes were produced in the X-10 reactor, by 1950 almost 20,000 samples had been shipped to various hospitals. As the demand for military science had fallen dramatically the future of the lab was uncertain, management of the lab was contracted by the US government to Monsanto, however, they withdrew in 1947. In 1950 the Oak Ridge School of Reactor Technology was established with two courses in operation and safety, almost 1000 students graduated. Another project was the worlds first light water reactor, with its principles of neutron moderation and fuel cooling by ordinary water it is the direct ancestor of most modern nuclear power stations. The US Military funded much of its development, for nuclear-powered submarines, the US Army contracted portable nuclear reactors in 1953 for heat and electricity generation in remote military bases. The reactors were designed at ORNL, produced by American Locomotive Company and used in Greenland, the United States Air Force also contributed funding to three reactors, the labs first computers, and its first particle accelerators. ORNL designed and tested an aircraft in 1954 as a proof-of-concept for a proposed USAF fleet of long-range bombers. The provision of radionuclides by X-10 for medicine grew steadily in the 1950s with more isotopes available, ORNL scientists lowered the immune systems of mice and performed the worlds first successful bone marrow transplant. In the early 1960s there was a push at ORNL to develop nuclear-powered desalination plants where deserts met the sea to provide water. The Health Physics Research Reactor built in 1962 was used for exposure experiments leading to more accurate dosage limits, dosimeters
29.
Manhattan Project
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The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom, from 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U. S. Army Corps of Engineers. Nuclear physicist J. Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs, the Army component of the project was designated the Manhattan District, Manhattan gradually superseded the official codename, Development of Substitute Materials, for the entire project. Along the way, the project absorbed its earlier British counterpart, the Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US $2 billion. Over 90% of the cost was for building factories and to produce material, with less than 10% for development. Research and production took place at more than 30 sites across the United States, the United Kingdom, two types of atomic bombs were developed concurrently during the war, a relatively simple gun-type fission weapon and a more complex implosion-type nuclear weapon. Chemically identical to the most common isotope, uranium-238, and with almost the same mass, three methods were employed for uranium enrichment, electromagnetic, gaseous and thermal. Most of this work was performed at the Clinton Engineer Works at Oak Ridge, in parallel with the work on uranium was an effort to produce plutonium. The plutonium was then separated from the uranium. The Fat Man implosion-type weapon was developed in a concerted design, the project was also charged with gathering intelligence on the German nuclear weapon project. Through Operation Alsos, Manhattan Project personnel served in Europe, sometimes behind enemy lines, where they gathered nuclear materials and documents, despite the Manhattan Projects tight security, Soviet atomic spies still penetrated the program. The first nuclear device ever detonated was a bomb at the Trinity test, conducted at New Mexicos Alamogordo Bombing. Little Boy and Fat Man bombs were used a later in the atomic bombings of Hiroshima and Nagasaki. It maintained control over American atomic weapons research and production until the formation of the United States Atomic Energy Commission in January 1947, there were fears that a German atomic bomb project would develop one first, especially among scientists who were refugees from Nazi Germany and other fascist countries. In August 1939, Hungarian-born physicists Leó Szilárd and Eugene Wigner drafted the Einstein–Szilárd letter and it urged the United States to take steps to acquire stockpiles of uranium ore and accelerate the research of Enrico Fermi and others into nuclear chain reactions. They had it signed by Albert Einstein and delivered to President Franklin D. Roosevelt, Roosevelt called on Lyman Briggs of the National Bureau of Standards to head the Advisory Committee on Uranium to investigate the issues raised by the letter. Briggs held a meeting on 21 October 1939, which was attended by Szilárd, Wigner, the committee reported back to Roosevelt in November that uranium would provide a possible source of bombs with a destructiveness vastly greater than anything now known. The Advisory Committee on Uranium became the National Defense Research Committee Committee on Uranium when that organization was formed on 27 June 1940, Briggs proposed that the spend $167,000 on research into uranium, particularly the uranium-235 isotope, and the recently discovered plutonium
30.
Uranium hexafluoride
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Uranium hexafluoride, referred to as hex in the nuclear industry, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. It forms solid grey crystals at standard temperature and pressure, is highly toxic and it reacts mildly with aluminium, forming a thin surface layer of AlF3 that resists further reaction. Milled uranium ore—U3O8 or yellowcake—is dissolved in acid, yielding a solution of uranyl nitrate UO22. Pure uranyl nitrate is obtained by solvent extraction, then treated with ammonia to produce ammonium diuranate, reduction with hydrogen gives UO2, which is converted with hydrofluoric acid to uranium tetrafluoride, UF4. During nuclear reprocessing, uranium is reacted with chlorine trifluoride to give UF6, U +2 ClF3 → UF6 + Cl2 At atmospheric pressure, the solid state structure was determined by neutron diffraction at 77 K and 293 K. Polymeric uranium fluorides containing organic cations have been isolated and characterised by X-ray diffraction, fluorine has only a single naturally occurring stable isotope, so isotopologues of UF6 differ in their molecular weight based solely on the uranium isotope present. All the other uranium fluorides are nonvolatile solids that are coordination polymers, in addition to its use in enrichment, uranium hexafluoride has been used in an advanced reprocessing method, which was developed in the Czech Republic. In this process, used nuclear fuel is treated with fluorine gas to form a mixture of fluorides. This mixture is distilled to separate the different classes of material. About 95% of the uranium produced to date is stored as uranium hexafluoride, DUF6. Each cylinder contains up to 12.7 tonnes of solid UF6, in the US alone,560,000 tonnes of depleted UF6 had accumulated by 1993. In 2005,686,500 tonnes in 57,122 storage cylinders were located near Portsmouth, Ohio, Oak Ridge, Tennessee, the long-term storage of DUF6 presents environmental, health, and safety risks because of its chemical instability. When UF6 is exposed to moist air, it reacts with the water in the air to produce UO2F2, storage cylinders must be regularly inspected for signs of corrosion and leaks. The estimated lifetime of the cylinders is measured in decades. There have been accidents involving uranium hexafluoride in the US, including a cylinder-filling accident. The U. S. government has been converting DUF6 to solid uranium oxides for disposal, such disposal of the entire DUF6 inventory could cost anywhere from $15 million to $450 million. Gmelins Handbuch der anorganischen Chemie, System Nr,55, Uran, Teil A, p. 121–123. Gmelins Handbuch der anorganischen Chemie, System Nr,55, Uran, Teil C8, p. 71–163
31.
Centrifugal force
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In Newtonian mechanics, the centrifugal force is an inertial force directed away from the axis of rotation that appears to act on all objects when viewed in a rotating reference frame. When they are analyzed in a coordinate system. The term has also been used for the force that is a reaction to a centripetal force. The centrifugal force is an outward force apparent in a reference frame. All measurements of position and velocity must be relative to some frame of reference. An inertial frame of reference is one that is not accelerating, the use of an inertial frame of reference, which will be the case for all elementary calculations, is often not explicitly stated but may generally be assumed unless stated otherwise. In terms of a frame of reference, the centrifugal force does not exist. All calculations can be performed using only Newtons laws of motion, in its current usage the term centrifugal force has no meaning in an inertial frame. In an inertial frame, an object that has no acting on it travels in a straight line. When measurements are made with respect to a reference frame, however. If it is desired to apply Newtons laws in the frame, it is necessary to introduce new, fictitious. Consider a stone being whirled round on a string, in a horizontal plane, the only real force acting on the stone in the horizontal plane is the tension in the string. There are no forces acting on the stone so there is a net force on the stone in the horizontal plane. In an inertial frame of reference, were it not for this net force acting on the stone, in order to keep the stone moving in a circular path, this force, known as the centripetal force, must be continuously applied to the stone. As soon as it is removed the stone moves in a straight line, in this inertial frame, the concept of centrifugal force is not required as all motion can be properly described using only real forces and Newtons laws of motion. In a frame of reference rotating with the stone around the axis as the stone. However, the tension in the string is still acting on the stone, if Newtons laws were applied in their usual form, the stone would accelerate in the direction of the net applied force, towards the axis of rotation, which it does not do. With this new the net force on the stone is zero, with the addition of this extra inertial or fictitious force Newtons laws can be applied in the rotating frame as if it were an inertial frame
32.
Zippe-type centrifuge
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The Zippe-type centrifuge is a gas centrifuge designed to enrich the rare fissile uranium isotope Uranium-235 out of the mixture of isotopes found in naturally occurring uranium compounds. The isotopic separation is based on the difference in mass of the isotopes. The Zippe design was developed in the Soviet Union by a team led by 60 Austrian and German scientists and engineers captured after World War II. If natural uranium is enriched to contain 3% U-235, it can be used as fuel for light water nuclear reactors, if it is enriched to contain 90% Uranium-235, it can be used for nuclear weapons. Enriching uranium is difficult because the isotopes are practically identical in chemistry and very similar in weight, separation efficiency in a centrifuge depends on weight difference. Separation of uranium isotopes requires a centrifuge that can spin at 1,500 revolutions per second, if we assume a rotor diameter of 20 cm, this corresponds to a linear speed of greater than Mach 2. A Zippe-type centrifuge has a hollow, cylindrical rotor filled with uranium in the form of its hexafluoride. A pulsating magnetic field at the bottom of the rotor, similar to that used in a motor, is able to spin it quickly enough that the U-238 is thrown towards the edge. The lighter U-235 collects near the center, the bottom of the gaseous mix is heated, producing convection currents that move the U-238 down. The U-235 moves up, where scoops collect it, each centrifuge has one inlet and two output lines. At the high speed of rotation, the gas is compressed close to the wall of the rotor, the rotor can be several meters in length and a temperature gradient of 300 °C between the top and bottom of the rotor produces a very strong convection current. In addition, the very strong coriolis forces produced add to the separation efficiency, to reduce friction, the rotor spins in a vacuum. A magnetic bearing holds the top of the steady. The three gas lines must be concentric with the axis as the outer rim is spinning very quickly. After the scientists were released from Soviet captivity in 1956, Gernot Zippe was surprised to find that engineers in the West were years behind in their centrifuge technology. He was able to reproduce his design at the University of Virginia in the United States, publishing the results and this improved centrifuge design is used by the commercial company Urenco to produce enriched uranium fuel for nuclear power stations. The exact details of advanced Zippe-type centrifuges are closely guarded secrets, but the efficiency of the centrifuges is improved by making them longer, the Zippe-type centrifuge is difficult to build successfully and requires carefully machined parts. However, compared to other enrichment methods, it is cheaper and more energy-efficient
33.
Gas centrifuge
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A gas centrifuge is a device that performs isotope separation of gases. A prominent use of gas centrifuges is for the separation of uranium-235 from uranium-238, the gas centrifuge was developed to replace the gaseous diffusion method of uranium-235 extraction. High degrees of separation of these isotopes relies on using many individual centrifuges arranged in cascade and this process yields higher concentrations of uranium-235 while using significantly less energy compared to the gaseous diffusion process. The centrifuge relies on the force resulting from centripetal acceleration to separate according to their mass. The dense molecules move towards the wall and the lighter ones remain close to the center, the centrifuge consists of a rigid body rotor rotating at full period at high speed. The gas tube is located in the center of the rotor, in practice, several such centrifuges are connected in series. Each centrifuge receives one input and produces two lines, corresponding to light and heavy fractions. The input of each centrifuge is the output of the previous centrifuge and this produces an almost pure light fraction from the output of the last centrifuge and an almost pure heavy fraction from the output of the first centrifuge. The gas centrifugation process utilizes a design that allows gas to constantly flow in. Unlike most centrifuges which rely on batch processing, the gas centrifuge utilizes continuous processing, allowing cascading, the gas centrifuge consists of a cylindrical rotor, a casing, an electric motor, and three lines for material to travel. The gas centrifuge is designed with a casing that completely encloses the centrifuge, the cylindrical rotor is located inside the casing, which is evacuated of all air to produce a near frictionless rotation when operating. The motor spins the rotor, creating the force on the components as they enter the cylindrical rotor. There are two lines, one located at the top of the centrifuge and the other located at the bottom. The heavier molecules will segregate to the bottom of the centrifuge while the molecules will segregate to the top of the centrifuge. The output lines take these separations to other centrifuges to continue to the centrifugation process, the process began with the rotor is balanced in three stages. Most of the details on gas centrifuges are difficult to obtain because they are shrouded in nuclear secrecy. The early centrifuges used in the UK used a body wrapped in epoxy impregnated glass fibre. Dynamic balancing of the assembly was accomplished by adding small traces of epoxy at the locations indicated by the balancing test unit
34.
Vortex tube
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The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. The air emerging from the hot end can reach temperatures of 200 °C, pressurised gas is injected tangentially into a swirl chamber and accelerated to a high rate of rotation. Due to the nozzle at the end of the tube. The remainder of the gas is forced to return in a vortex of reduced diameter within the outer vortex. It shows that temperature separation in a gas is due only to enthalpy conservation in a moving frame of reference. The total enthalpy, however, is being conserved, 2) The peripheric rotating gas flow moves towards the hot outlet. Here the heat recuperation effect takes place between the quickly rotating peripheric flow and the opposite slowly rotating axial flow, here the heat transfers from axial flow to the peripheric one. 3) The kinetic energy of rotation turns into the energy by the means of the viscous dissipation. The temperature of the gas rises, as the total enthalpy has been increased during the heat recuperation process, this temperature is higher than the incoming gas. 4) Some of the hot gas leaves the hot outlet, carrying away the excess heat, 5) The rest of the gas turns towards the cold outlet. As it passes its way to the outlet, its heat energy is transferred to the peripheric flow. Although the temperature at the axis and at the periphery is about the same everywhere, 6) The low total enthalpy cooled gas from the axial flow leaves the cold outlet. The main physical phenomenon of the tube is the temperature separation between the cold vortex core and the warm vortex periphery. This equation has been published in 2012, it explains the fundamental operating principle of vortex tubes, the search for this explanation began in 1933 when the vortex tube was discovered and continued for more than 80 years. The above equation is valid for an adiabatic turbine passage, it shows that while gas moving towards the center is getting colder the peripheral gas in the passage is getting faster. Therefore, vortex cooling is due to angular propulsion, the more the gas cools by reaching the center, the more rotational energy it delivers to the vortex and thus the vortex rotates even faster. This explanation stems directly from the law of energy conservation, compressed gas at room temperature is expanded in order to gain speed through a nozzle, it then climbs the centrifugal barrier of rotation during which energy is also lost. The lost energy is delivered to the vortex, which speeds its rotation, in a vortex tube, the cylindrical surrounding wall confines the flow at periphery and thus forces conversion of kinetic into internal energy, which produces hot air at the hot exit
35.
South Africa
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South Africa, officially the Republic of South Africa, is the southernmost country in Africa. South Africa is the 25th-largest country in the world by land area and it is the southernmost country on the mainland of the Old World or the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different Bantu languages, the remaining population consists of Africas largest communities of European, Asian, and multiracial ancestry. South Africa is a multiethnic society encompassing a variety of cultures, languages. Its pluralistic makeup is reflected in the recognition of 11 official languages. The country is one of the few in Africa never to have had a coup détat, however, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a role in the countrys recent history. The National Party imposed apartheid in 1948, institutionalising previous racial segregation, since 1994, all ethnic and linguistic groups have held political representation in the countrys democracy, which comprises a parliamentary republic and nine provinces. South Africa is often referred to as the Rainbow Nation to describe the multicultural diversity. The World Bank classifies South Africa as an economy. Its economy is the second-largest in Africa, and the 34th-largest in the world, in terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa. However, poverty and inequality remain widespread, with about a quarter of the population unemployed, nevertheless, South Africa has been identified as a middle power in international affairs, and maintains significant regional influence. The name South Africa is derived from the geographic location at the southern tip of Africa. Upon formation the country was named the Union of South Africa in English, since 1961 the long form name in English has been the Republic of South Africa. In Dutch the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika, since 1994 the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning south, is a name for South Africa. South Africa contains some of the oldest archaeological and human fossil sites in the world, extensive fossil remains have been recovered from a series of caves in Gauteng Province. The area is a UNESCO World Heritage site and has termed the Cradle of Humankind
36.
Calutron
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A calutron is a mass spectrometer originally designed and used for separating the isotopes of uranium. It was developed by Ernest Lawrence during the Manhattan Project and was based on his earlier invention and its name was derived from California University Cyclotron, in tribute to Lawrences institution, the University of California, where it was invented. Calutrons were used in the industrial-scale Y-12 uranium enrichment plant at the Clinton Engineer Works in Oak Ridge, the enriched uranium produced was used in the Little Boy atomic bomb that was detonated over Hiroshima on 6 August 1945. The calutron is a type of mass spectrometer, an instrument in which a sample is ionized and then accelerated by electric fields. The ions ultimately collide with a plate and produce an electric current. The mass of the ions can be calculated according to the strength of the field, Electromagnetic separation for uranium enrichment was abandoned in the post-war period in favor of the more complicated, but more efficient, gaseous diffusion method. Based on his liquid drop model of the nucleus, he theorized that it was the uranium-235 isotope, to verify this Alfred O. C. Nier at the University of Minnesota used a mass spectrometer to create a microscopic amount of enriched uranium-235 in April 1940, John R. Dunning, Aristid von Grosse and Eugene T. Booth were then able to confirm that Bohr was correct, there were fears that a German atomic bomb project would develop one first, especially among scientists who were refugees from Nazi Germany and other fascist countries. Their March 1940 Frisch–Peierls memorandum indicated that the mass of uranium-235 was within an order of magnitude of 10 kg. The British Maud Committee then unanimously recommended pursuing the development of an atomic bomb, britain had offered to give the United States access to its scientific research, so the Tizard Missions John Cockcroft briefed American scientists on British developments. He discovered that the American project was smaller than the British, a disappointed Oliphant flew to the United States to speak to the American scientists. These included Ernest Lawrence at the University of Californias Radiation Laboratory in Berkeley, the two men had met before the war, and were friends. Lawrence was sufficiently impressed to commence his own research into uranium, uranium-235 makes up only about 0. 72% of natural uranium, so the separation factor of any uranium enrichment process needs to be higher than 1250 to produce 90% uranium-235 from natural uranium. The Maud Committee had recommended that this be done by a process of gaseous diffusion and this was the process that Nier had used. The principle of separation is that charged ions are deflected by a magnetic field. The reason for this was the so-called space-charge limitation, positive ions have positive charge, so they tend to repel each other, which causes the beam to scatter. Oliphant inspired Lawrence to convert his old 37-inch cyclotron into a giant mass spectrometer for isotope separation, the 37-inch cyclotron at Berkeley was dismantled on 24 November 1941, and its magnet used to create the first calutron
37.
Mass spectrometry
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Mass spectrometry is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample, mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio, in a typical MS procedure, a sample, which may be solid, liquid, or gas, is ionized, for example by bombarding it with electrons. This may cause some of the molecules to break into charged fragments. The ions are detected by a capable of detecting charged particles. Results are displayed as spectra of the abundance of detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the sample can be identified by correlating known masses to the masses or through a characteristic fragmentation pattern. Goldstein called these positively charged anode rays Kanalstrahlen, the translation of this term into English is canal rays. Wien found that the charge-to-mass ratio depended on the nature of the gas in the discharge tube, thomson later improved on the work of Wien by reducing the pressure to create the mass spectrograph. The word spectrograph had become part of the international scientific vocabulary by 1884, a mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen. A mass spectroscope configuration was used in early instruments when it was desired that the effects of adjustments be quickly observed, once the instrument was properly adjusted, a photographic plate was inserted and exposed. The term mass spectroscope continued to be used though the direct illumination of a phosphor screen was replaced by indirect measurements with an oscilloscope. The use of the mass spectroscopy is now discouraged due to the possibility of confusion with light spectroscopy. Mass spectrometry is often abbreviated as mass-spec or simply as MS, modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F. W. Aston in 1918 and 1919 respectively. Sector mass spectrometers known as calutrons were used for separating the isotopes of uranium developed by Ernest O. Lawrence during the Manhattan Project, calutron mass spectrometers were used for uranium enrichment at the Oak Ridge, Tennessee Y-12 plant established during World War II. In 1989, half of the Nobel Prize in Physics was awarded to Hans Dehmelt, a mass spectrometer consists of three components, an ion source, a mass analyzer, and a detector. The ionizer converts a portion of the sample into ions, there is a wide variety of ionization techniques, depending on the phase of the sample and the efficiency of various ionization mechanisms for the unknown species. An extraction system removes ions from the sample, which are then targeted through the mass analyzer, the differences in masses of the fragments allows the mass analyzer to sort the ions by their mass-to-charge ratio
38.
Magnetic field
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A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any point is specified by both a direction and a magnitude, as such it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter in the SI, B is measured in teslas and newtons per meter per ampere in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges, Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In quantum physics, the field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields are used throughout modern technology, particularly in electrical engineering. The Earth produces its own field, which is important in navigation. Rotating magnetic fields are used in electric motors and generators. Magnetic forces give information about the carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits, noting that the resulting field lines crossed at two points he named those points poles in analogy to Earths poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them, almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilberts work, De Magnete, helped to establish magnetism as a science, in 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated, building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by magnetic poles, three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it, then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction attract one another. Finally, Jean-Baptiste Biot and Félix Savart discovered the Biot–Savart law in 1820, extending these experiments, Ampère published his own successful model of magnetism in 1825. This has the benefit of explaining why magnetic charge can not be isolated. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism, in 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field
39.
Isotopic labeling
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Isotopic labeling is a technique used to track the passage of an isotope through a reaction, metabolic pathway, or cell. The reactant is labeled by replacing specific atoms by their isotope, the reactant is then allowed to undergo the reaction. The position of the isotopes in the products is measured to determine the sequence the isotopic atom followed in the reaction or the metabolic pathway. The nuclides used in isotopic labeling may be stable nuclides or radionuclides, in the latter case, the labeling is called radiolabeling. In isotopic labeling, there are ways to detect the presence of labeling isotopes, through their mass, vibrational mode. Mass spectrometry detects the difference in a mass, while infrared spectroscopy detects the difference in the isotopes vibrational modes. Nuclear magnetic resonance detects atoms with different gyromagnetic ratios, the radioactive decay can be detected through an ionization chamber or autoradiographs of gels. An example of the use of isotopic labeling is the study of phenol in water by replacing common hydrogen with deuterium, only the hydroxyl group was affected, indicating that the other 5 hydrogen atoms did not participate in these exchange reactions. An isotopic tracer, is used in chemistry and biochemistry to help understand chemical reactions and interactions, in this technique, one or more of the atoms of the molecule of interest is substituted for an atom of the same chemical element, but of a different isotope. The difference in the number of neutrons, however, means that it can be detected separately from the atoms of the same element. Nuclear magnetic resonance and mass spectrometry are used to investigate the mechanisms of chemical reactions, NMR and MS detects isotopic differences, which allows information about the position of the labeled atoms in the products structure to be determined. With information on the positioning of the atoms in the products. Radioactive isotopes can be tested using the autoradiographs of gels in gel electrophoresis, the radiation emitted by compounds containing the radioactive isotopes darkens a piece of photographic film, recording the position of the labeled compounds relative to one another in the gel. Isotope tracers are used in the form of isotope ratios. Isotopic tracers are some of the most important tools in geology because they can be used to understand complex mixing processes in earth systems, further discussion of the application of isotopic tracers in geology is covered under the heading of isotope geochemistry. Isotopic tracers are usually subdivided into two categories, stable isotope tracers and radiogenic isotope tracers, stable isotope tracers involve only non-radiogenic isotopes and usually are mass-dependent. In theory, any element with two isotopes can be used as an isotopic tracer. However, the most commonly used stable isotope tracers involve relatively light isotopes, a radiogenic isotope tracer involves an isotope produced by radioactive decay, which is usually in a ratio with a non-radiogenic isotope
40.
Oak Ridge, Tennessee
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Oak Ridge is a city in Anderson and Roane counties in the eastern part of the U. S. state of Tennessee, about 25 miles west of Knoxville. Oak Ridges population was 29,330 at the 2010 census and it is part of the Knoxville Metropolitan Area. Oak Ridges nicknames include the Atomic City, the Secret City, the Ridge, Oak Ridge was established in 1942 as a production site for the Manhattan Project—the massive American, British, and Canadian operation that developed the atomic bomb. As it is still the site of Oak Ridge National Laboratory, scientific development still plays a role in the citys economy. The earliest substantial occupation of the Oak Ridge area occurred during the Woodland period, two Woodland mound sites—the Crawford Farm Mounds and the Freels Farm Mounds—were uncovered in the 1930s as part of the Norris Basin salvage excavations. Both sites were located just southeast of the former Scarboro community, the Bull Bluff site, which was occupied during both the Woodland and Mississippian periods, was uncovered in the 1960s in anticipation of the construction of Melton Hill Dam. Bull Bluff is a cliff located immediately southeast of Haw Ridge, the Oak Ridge area was largely uninhabited by the time Euro-American explorers and settlers arrived in the late 18th century, although the Cherokee claimed the land as part of their hunting grounds. According to local tradition, John Hendrix, a local resident regarded as a mystic. Upset by the death of his daughter and the subsequent departure of his wife and remaining family, he became religious. When he described his visions, people thought he was insane, for this reason, maj. Gen. Leslie Groves, military head of the Manhattan Project, liked the area for several reasons. Finally, the location was established within a 17-mile-long valley. The new District Engineer Kenneth Nichols had to placate him, cooper came to see the project on November 3,1943, and he appreciated the bourbon-laced punch served. CEW and HEW accommodation in houses and dormitories was basic, with rather than oil or electric furnaces. But it was of a higher standard than Groves would have liked, medical care was provided by Army doctors and hospitals, with civilians paying $2.50 per month to the medical insurance fund. The location and low population also helped keep the town a secret, the K-25 uranium-separating facility by itself covered 44 acres and was the largest building in the world at that time. The name Oak Ridge was chosen for the settlement in 1943 from among suggestions submitted by project employees, the name related to the settlements location along Black Oak Ridge, and officials thought the rural-sounding name held outside curiosity to a minimum. The name wasnt formally adopted until 1949, and the site was referred to as the Clinton Engineer Works until then, the town was surrounded by guard towers and a fence with seven gates. Starting in October 1942, the United States Army Corps of Engineers began acquiring more than 60,000 acres in the Oak Ridge area for the United States Manhattan Project, many residents came home to find eviction notices tacked to their doors
41.
University of California, Berkeley
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The University of California, Berkeley, is a public research university located in Berkeley, California. In 1960s, UC Berkeley was particularly noted for the Free Speech Movement as well as the Anti-Vietnam War Movement led by its students. S, Department of Energy, and is home to many world-renowned research institutes and organizations including Mathematical Sciences Research Institute and Space Sciences Laboratory. Faculty member J. R. Oppenheimer, the father of the atomic bomb, Lawrence Livermore Lab also discovered or co-discovered six chemical elements. The Academic Ranking of World Universities also ranks the University of California, Berkeley, third in the world overall, in 1866, the private College of California purchased the land comprising the current Berkeley campus. Ten faculty members and almost 40 students made up the new University of California when it opened in Oakland in 1869, billings was a trustee of the College of California and suggested that the college be named in honor of the Anglo-Irish philosopher George Berkeley. In 1870, Henry Durant, the founder of the College of California, with the completion of North and South Halls in 1873, the university relocated to its Berkeley location with 167 male and 22 female students and held its first classes. In 1905, the University Farm was established near Sacramento, ultimately becoming the University of California, by the 1920s, the number of campus buildings had grown substantially, and included twenty structures designed by architect John Galen Howard. Robert Gordon Sproul served as president from 1930 to 1958, by 1942, the American Council on Education ranked UC Berkeley second only to Harvard University in the number of distinguished departments. During World War II, following Glenn Seaborgs then-secret discovery of plutonium, UC Berkeley physics professor J. Robert Oppenheimer was named scientific head of the Manhattan Project in 1942. Along with the Lawrence Berkeley National Laboratory, Berkeley is now a partner in managing two other labs, Los Alamos National Laboratory and Lawrence Livermore National Laboratory, originally, military training was compulsory for male undergraduates, and Berkeley housed an armory for that purpose. In 1917, Berkeleys ROTC program was established, and its School of Military Aeronautics trained future pilots, including Jimmy Doolittle, both Robert McNamara and Frederick C. Weyand graduated from UC Berkeleys ROTC program, earning B. A. degrees in 1937 and 1938, in 1926, future fleet admiral Chester W. Nimitz established the first Naval Reserve Officers Training Corps unit at Berkeley. The Board of Regents ended compulsory military training at Berkeley in 1962, during the McCarthy era in 1949, the Board of Regents adopted an anti-communist loyalty oath. A number of faculty members objected and were dismissed, ten years passed before they were reinstated with back pay, in 1952, the University of California became an entity separate from the Berkeley campus. Each campus was given autonomy and its own Chancellor. Then-president Sproul assumed presidency of the entire University of California system, Berkeley gained a reputation for student activism in the 1960s with the Free Speech Movement of 1964 and opposition to the Vietnam War. In the highly publicized Peoples Park protest in 1969, students and the school conflicted over use of a plot of land, then governor of California Ronald Reagan called the Berkeley campus a haven for communist sympathizers, protesters, and sex deviants. Modern students at Berkeley are less active, with a greater percentage of moderates and conservatives
42.
Ernest Lawrence
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Ernest Orlando Lawrence was a pioneering American nuclear scientist and winner of the Nobel Prize in Physics in 1939 for his invention of the cyclotron. A graduate of the University of South Dakota and University of Minnesota, in 1928, he was hired as an associate professor of physics at the University of California, becoming the youngest full professor there two years later. In its library one evening, Lawrence was intrigued by a diagram of an accelerator that produced high-energy particles and he contemplated how it could be made compact, and came up with an idea for a circular accelerating chamber between the poles of an electromagnet. The result was the first cyclotron, Lawrence went on to build a series of ever larger and more expensive cyclotrons. His Radiation Laboratory became a department of the University of California in 1936. In addition to the use of the cyclotron for physics, Lawrence also supported its use in research into medical uses of radioisotopes, during World War II, Lawrence developed electromagnetic isotope separation at the Radiation Laboratory. It used devices known as calutrons, a hybrid of the standard laboratory mass spectrometer, a huge electromagnetic separation plant was built at Oak Ridge, Tennessee, which came to be called Y-12. The process was inefficient, but it worked, Lawrence strongly backed Edward Tellers campaign for a second nuclear weapons laboratory, which Lawrence located in Livermore, California. After his death, the Regents of the University of California renamed the Lawrence Livermore National Laboratory, chemical element number 103 was named lawrencium in his honor after its discovery at Berkeley in 1961. Ernest Orlando Lawrence was born in Canton, South Dakota on August 8,1901 and he had a younger brother, John H. Lawrence, who would become a physician, and was a pioneer in the field of nuclear medicine. Growing up, his best friend was Merle Tuve, who would go on to become a highly accomplished nuclear physicist. Lawrence attended the schools of Canton and Pierre, then enrolled at St. Olaf College in Northfield, Minnesota. He completed his bachelors degree in chemistry in 1922, and his Master of Arts degree in physics from the University of Minnesota in 1923 under the supervision of William Francis Gray Swann. For his masters thesis, Lawrence built an apparatus that rotated an ellipsoid through a magnetic field. He was elected a member of Sigma Xi, and, on Swanns recommendation, instead of using it to travel to Europe, as was customary at the time, he remained at Yale University with Swann as a researcher. With Jesse Beams from the University of Virginia, Lawrence continued to research the photoelectric effect and they showed that photoelectrons appeared within 2 x 10−9 seconds of the photons striking the photoelectric surface—close to the limit of measurement at the time. Reducing the emission time by switching the light source on and off rapidly made the spectrum of energy emitted broader, in conformance with Werner Heisenbergs uncertainty principle. In 1926 and 1927, Lawrence received offers of assistant professorships from the University of Washington in Seattle, Yale promptly matched the offer of the assistant professorship, but at a salary of $3,000
43.
Laser
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A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term laser originated as an acronym for light amplification by stimulated emission of radiation, the first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of light in that it emits light coherently, spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances, Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, i. e. they can emit a single color of light. Temporal coherence can be used to produce pulses of light as short as a femtosecond, Lasers are distinguished from other light sources by their coherence. Spatial coherence is typically expressed through the output being a narrow beam, Laser beams can be focused to very tiny spots, achieving a very high irradiance, or they can have very low divergence in order to concentrate their power at a great distance. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated over a great distance along the beam. A beam produced by a thermal or other incoherent light source has an amplitude and phase that vary randomly with respect to time and position. Lasers are characterized according to their wavelength in a vacuum, most single wavelength lasers actually produce radiation in several modes having slightly differing frequencies, often not in a single polarization. Although temporal coherence implies monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously, there are some lasers that are not single spatial mode and consequently have light beams that diverge more than is required by the diffraction limit. However, all devices are classified as lasers based on their method of producing light. Lasers are employed in applications where light of the spatial or temporal coherence could not be produced using simpler technologies. The word laser started as an acronym for light amplification by stimulated emission of radiation, in the early technical literature, especially at Bell Telephone Laboratories, the laser was called an optical maser, this term is now obsolete. A laser that produces light by itself is technically an optical rather than an optical amplifier as suggested by the acronym. It has been noted that the acronym LOSER, for light oscillation by stimulated emission of radiation. With the widespread use of the acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers. The back-formed verb to lase is frequently used in the field, meaning to produce light, especially in reference to the gain medium of a laser. Further use of the laser and maser in an extended sense, not referring to laser technology or devices, can be seen in usages such as astrophysical maser
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Hyperfine structure
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In atomic physics, hyperfine structure is the different effects leading to small shifts and splittings in the energy levels of atoms, molecules and ions. The name is a reference to the structure, which results from the interaction between the magnetic moments associated with electron spin and the electrons orbital angular momentum. The optical hyperfine structure was observed in 1881 by Albert Abraham Michelson and it could, however, only be explained in terms of quantum mechanics when Wolfgang Pauli proposed the existence of a small nuclear magnetic moment in 1924. In 1935, H. Schüler and Theodor Schmidt proposed the existence of a quadrupole moment in order to explain anomalies in the hyperfine structure. The theory of structure comes directly from electromagnetism, consisting of the interaction of the nuclear multipole moments with internally generated fields. The theory is derived first for the case, but can be applied to each nucleus in a molecule. Following this there is a discussion of the additional effects unique to the molecular case, the dominant term in the hyperfine Hamiltonian is typically the magnetic dipole term. Atomic nuclei with a nuclear spin I have a magnetic dipole moment, given by, μ I = g I μ N I. There is an associated with a magnetic dipole moment in the presence of a magnetic field. For a nuclear magnetic moment, μI, placed in a magnetic field, B. Electron orbital angular momentum results from the motion of the electron about some fixed point that we shall take to be the location of the nucleus. Written in terms of the Bohr magneton, this gives, B el l = −2 μ B μ04 π1 r 3 r × m e v ℏ. Recognizing that mev is the momentum, p, and that r×p/ħ is the orbital angular momentum in units of ħ, l, we can write. The electron spin angular momentum is a different property that is intrinsic to the particle. Nonetheless it is angular momentum and any angular momentum associated with a charged particle results in a dipole moment. The magnetic field of a moment, μs, is given by. The first term gives the energy of the dipole in the field due to the electronic orbital angular momentum. The second term gives the energy of the finite distance interaction of the dipole with the field due to the electron spin magnetic moments
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Electric field
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An electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point. Electric fields are created by electric charges and can be induced by time-varying magnetic fields, the electric field combines with the magnetic field to form the electromagnetic field. The electric field, E, at a point is defined as the force, F. A particle of charge q would be subject to a force F = q E and its SI units are newtons per coulomb or, equivalently, volts per metre, which in terms of SI base units are kg⋅m⋅s−3⋅A−1. Electric fields are caused by electric charges or varying magnetic fields, in the special case of a steady state, the Maxwell-Faraday inductive effect disappears. The resulting two equations, taken together, are equivalent to Coulombs law, written as E =14 π ε0 ∫ d r ′ ρ r − r ′ | r − r ′ |3 for a charge density ρ. Notice that ε0, the permittivity of vacuum, must be substituted if charges are considered in non-empty media, the equations of electromagnetism are best described in a continuous description. A charge q located at r 0 can be described mathematically as a charge density ρ = q δ, conversely, a charge distribution can be approximated by many small point charges. Electric fields satisfy the principle, because Maxwells equations are linear. This principle is useful to calculate the field created by point charges. Q n are stationary in space at r 1, r 2, in that case, Coulombs law fully describes the field. If a system is static, such that magnetic fields are not time-varying, then by Faradays law, in this case, one can define an electric potential, that is, a function Φ such that E = − ∇ Φ. This is analogous to the gravitational potential, Coulombs law, which describes the interaction of electric charges, F = q = q E is similar to Newtons law of universal gravitation, F = m = m g. This suggests similarities between the electric field E and the gravitational field g, or their associated potentials, mass is sometimes called gravitational charge because of that similarity. Electrostatic and gravitational forces both are central, conservative and obey an inverse-square law, a uniform field is one in which the electric field is constant at every point. It can be approximated by placing two conducting plates parallel to other and maintaining a voltage between them, it is only an approximation because of boundary effects. Assuming infinite planes, the magnitude of the electric field E is, electrodynamic fields are E-fields which do change with time, for instance when charges are in motion. The electric field cannot be described independently of the field in that case
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Atomic vapor laser isotope separation
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Atomic vapor laser isotope separation is a method by which specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions. In the largest technology transfer in U. S. government history, however, on June 9,1999 after a $100 million investment, USEC cancelled its AVLIS program. The AVLIS process provides energy efficiency comparable with gas centrifuges, high separation factor. AVLIS continues to be developed by countries and it presents some specific challenges to international monitoring. Iran is now known to have had a secret AVLIS program, however, since it was uncovered in 2003, Iran has claimed to have dismantled it. A similar technology, using instead of atoms, is molecular laser isotope separation. The absorption lines of 235U and 238U differ slightly due to structure, for example. AVLIS uses tunable dye lasers, which can be tuned, so that only 235U absorbs the photons and selectively undergoes excitation. The ions are then electrostatically deflected to a collector, while the neutral unwanted uranium-238 passes through, the AVLIS system consists of a vaporizer and a collector, forming the separation system, and the laser system. The vaporizer produces a stream of gaseous uranium. The laser commonly used is a two-stage tunable pulsed dye laser usually pumped by a copper vapor laser, the oscillator is tunable, narrow-linewidth. Its power is increased by a dye laser amplifier acting as optical amplifier. Three frequencies of lasers are used for full ionization of uranium-235, for AVLIS in other elements, such as lithium, tunable narrow-linewidth diode lasers are used. The history of AVLIS, as recorded in the refereed literature, began in the early-mid 1970s in the former Soviet Union. In the US, AVLIS research was carried out at the Lawrence Livermore National Laboratory although some industrial laboratories were early players. Tunable laser development for AVLIS, applicable to uranium, has also reported from several countries including Australia, France, India. Laser isotope separation uranium enrichment Overview of Uranium Atomic Vapor Laser Isotope Separation R. M, Laser Isotope Separation page at LLNL
