Uranium is a chemical element; it has symbol U and atomic number 92. It is a silvery-grey 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 radioactively decays, usually by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes, making them useful for dating the age of the Earth. 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 slightly lower than that of gold or tungsten. 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.
Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is varied. The largest variety is used in research. By tonnage, separating natural uranium into enriched uranium and depleted uranium is the largest application. In the following text, mainly uranium enrichment is considered. This process is crucial in the manufacture of uranium fuel for nuclear power plants, and is also required for the creation of uranium-based nuclear weapons. Plutonium-based weapons use plutonium produced in a nuclear reactor, which must be operated in such a way as to produce plutonium already of suitable isotopic mix or grade.
Enriched uranium is a type of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238, uranium-235, and uranium-234. 235U is the only nuclide existing in nature that is fissile with thermal neutrons.
A gas centrifuge is a device that performs isotope separation of gases. A centrifuge relies on the principles of centrifugal force accelerating molecules so that particles of different masses are physically separated in a gradient along the radius of a rotating container. A prominent use of gas centrifuges is for the separation of uranium-235 (235U) from uranium-238 (238U). 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 series, that achieve successively higher concentrations. This process yields higher concentrations of uranium-235 while using significantly less energy compared to the gaseous diffusion process.
Gaseous diffusion is a technology that was used to produce enriched uranium by forcing gaseous uranium hexafluoride (UF6) through microporous membranes. This produces a slight separation (enrichment factor 1.0043) between the molecules containing uranium-235 (235U) and uranium-238 (238U). By use of a large cascade of many stages, high separations can be achieved. It was the first process to be developed that was capable of producing enriched uranium in industrially useful quantities, but is nowadays considered obsolete, having been superseded by the more-efficient gas centrifuge process (enrichment factor 1.05 to 1.2).
A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range.
The Australian Atomic Energy Commission (AAEC) was a statutory body of the Australian Government devoted to nuclear science, engineering and research.
Erich Rudolf Bagge was a German scientist. Bagge, a student of Werner Heisenberg for his doctorate and Habilitation, was engaged in German Atomic Energy research and the German nuclear energy project during the Second World War. He worked as an Assistant at the Kaiser-Wilhelm-Institut für Physik in Berlin. Bagge, who became associated professor at the University of Hamburg in 1948, was in particular involved in the usage of nuclear power for trading vessels, and he was one of the founders of the Society for the Usage of Nuclear Energy in Ship-Building and Seafare.
Uranium-234 is an isotope of uranium. In natural uranium and in uranium ore, 234U occurs as an indirect decay product of uranium-238, but it makes up only 0.0055% of the raw uranium because its half-life of just 245,500 years is only about 1/18,000 as long as that of 238U. Thus the ratio of 234
U to 238
U in a natural sample is equivalent to the ratio of their half-lives. The primary path of production of 234U via nuclear decay is as follows: uranium-238 nuclei emit an alpha particle to become thorium-234. Next, with a short half-life, 234Th nuclei emit a beta particle to become protactinium-234 (234Pa), or more likely a nuclear isomer denoted 234mPa. Finally, 234Pa or 234mPa nuclei emit another beta particle to become 234U nuclei.
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years.
Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors. In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from 214U to 242U. The standard atomic weight of natural uranium is 238.02891(3).
Lead (82Pb) has four observationally stable isotopes: 204Pb, 206Pb, 207Pb, 208Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay chains: the uranium series, the actinium series, and the thorium series, respectively; a fourth decay chain, the neptunium series, terminates with the thallium isotope 205Tl. The three series terminating in lead represent the decay chain products of long-lived primordial 238U, 235U, and 232Th. Each isotope also occurs, to some extent, as primordial isotopes that were made in supernovae, rather than radiogenically as daughter products. The fixed ratio of lead-204 to the primordial amounts of the other lead isotopes may be used as the baseline to estimate the extra amounts of radiogenic lead present in rocks as a result of decay from uranium and thorium.
Molecular laser isotope separation (MLIS) is a method of isotope separation, where specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions of uranium hexafluoride molecules. It is similar to AVLIS. Its main advantage over AVLIS is low energy consumption and use of uranium hexafluoride instead of vaporized uranium.
Laser isotope separation, or laser enrichment, is a technology of isotope separation using selective ionization of atoms or molecules by the means of precisely tuned lasers.
Separation of isotopes by laser excitation (SILEX) is a process under development to enrich uranium on an industrial scale for nuclear reactors. It is strongly suspected that it utilizes laser condensation repression to excite the uranium-235 isotope in uranium hexafluoride (UF6), allowing this lighter molecule to move more rapidly to the outer rim of a gaseous jet and resist condensing compared to the heavier, unexcited 238UF6. This differs greatly from previous methods of laser enrichment explored for their commercial prospects: one using atomic uranium (Atomic Vapor Laser Isotope Separation (AVLIS)) and another molecular method that uses lasers to dissociate a fluorine atom from 235UF6 (Molecular Laser Isotope Separation (MLIS)), allowing the enriched product to precipitate out as a solid.
A copper vapor laser (CVL) uses vapors of copper as the lasing medium in a 4-level laser. It produces green laser light at 510.6 nm and yellow laser light at 578.2 nm. The pulse width is typically from 5 to 60 ns, and peak power from 50 to 5000 kW. Its pulse repetition frequencies can be 2 to 100 kHz. The average power of CVLs can range from 25 W to more than 2 kW.
Francisco Javier "Frank" Duarte is a laser physicist and author/editor of several books on tunable lasers.
Multiple-prism grating laser oscillators, or MPG laser oscillators, use multiple-prism beam expansion to illuminate a diffraction grating mounted either in Littrow configuration or grazing-incidence configuration. Originally, these narrow-linewidth tunable dispersive oscillators were introduced as multiple-prism Littrow (MPL) grating oscillators, or hybrid multiple-prism near-grazing-incidence (HMPGI) grating cavities, in organic dye lasers. However, these designs were quickly adopted for other types of lasers such as gas lasers, diode lasers, and more recently fiber lasers.
A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature (mostly) without forming steam bubbles, exactly as for a pressurized water reactor. While heavy water is very expensive to isolate from ordinary water (often referred to as light water in contrast to heavy water), its low absorption of neutrons greatly increases the neutron economy of the reactor, avoiding the need for enriched fuel. The high cost of the heavy water is offset by the lowered cost of using natural uranium and/or alternative fuel cycles. As of the beginning of 2001, 31 PHWRs were in operation, having a total capacity of 16.5 GW(e), representing roughly 7.76% by number and 4.7% by generating capacity of all current operating reactors.
Depleted uranium hexafluoride (DUHF; also referred to as depleted uranium tails, depleted uranium tailings or DUF6) is a byproduct of the processing of uranium hexafluoride into enriched uranium. It is one of the chemical forms of depleted uranium (up to 73-75%), along with depleted triuranium octoxide (up to 25%) and depleted uranium metal (up to 2%). DUHF is 1.7 times less radioactive than uranium hexafluoride and natural uranium.
