Information AboutUranium |
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Uranium ()is a white/black Metal lic Chemical Element in the Actinide series of the Periodic Table that has the Symbol '''U''' and Atomic Number 92. It has 92 Protons and Electrons , 6 of them Valence Electrons . It can have between 141 and 146 Neutrons , with 143 and 146 in its most common isotopes. Uranium has the highest atomic weight of the naturally occurring elements (see Plutonium ). Uranium is approximately 70% more Dense than Lead and is weakly Radioactive . It occurs naturally in low concentrations (a few Parts Per Million ) in soil, rock and water, and is commercially extracted from uranium-bearing Mineral s such as Uraninite (see Uranium Mining ). In nature, uranium atoms exist as Uranium-238 (99.275%), Uranium-235 (0.711%), and a very small amount of Uranium-234 (0.0058%). Uranium decays slowly by emitting an Alpha Particle . The Half-life of uranium-238 is about 4.47 Billion years and that of uranium-235 is 704 Million years,1 making them useful in dating the Age Of The Earth (see Uranium-thorium Dating , Uranium-lead Dating and Uranium-uranium Dating ). Along with Thorium and Plutonium , uranium is one of the three Fissile elements, meaning it can easily break apart to become lighter elements. While uranium-238 has a small probability to fission spontaneously or when bombarded with fast neutrons, the much higher probability of uranium-235 and to a lesser degree Uranium-233 to fission when bombarded with slow neutrons generates the heat in Nuclear Reactor s used as a source of power, and provides the fissile material for Nuclear Weapon s. Both uses rely on the ability of uranium to produce a sustained Nuclear Chain Reaction . Depleted Uranium (uranium-238) is used in Kinetic Energy Penetrator s and Armor Plating .Emsley, ''Nature's Building Blocks'' (2001), page 479 Uranium is used as a colorant in Uranium Glass , producing orange-red to lemon yellow hues. 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 , who named the new element after the planet Uranus . Eugène-Melchior Péligot was the first person to isolate the metal, and its radioactive properties were uncovered in 1896 by Antoine Becquerel . Research by Enrico Fermi and others starting in 1934 led to its use as a fuel in the nuclear power industry and in '' Little Boy '', the First Nuclear Weapon Used In War . An ensuing Arms Race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear weapons that used Enriched Uranium and uranium-derived plutonium. The security of those weapons and their fissile material following the Breakup Of The Soviet Union in 1991 along with the legacy of Nuclear Testing and Nuclear Accident s is a concern for public health and safety. CHARACTERISTICS When Refined , uranium is a silvery white, weakly radioactive Metal , which is slightly softer than Steel ,2 strongly Electropositive and a poor Electrical Conductor . It is Malleable , Ductile , and slightly Paramagnetic . Uranium metal has very high Density , being approximately 70% more dense than Lead , but slightly less dense than Gold . Uranium metal reacts with nearly all nonmetallic elements and their Compounds , with reactivity increasing with temperature.3 Hydrochloric and Nitric Acid s dissolve uranium, but nonoxidizing acids attack the element very slowly. When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of uranium oxide. Uranium in ores is extracted chemically and converted into Uranium Dioxide or other chemical forms usable in industry. Uranium was the first element that was found to be Fissile . Upon bombardment with slow Neutron s, its Uranium-235 Isotope becomes a very short-lived uranium-236 isotope, which immediately divides into two smaller Nuclei , releasing nuclear Binding Energy and more neutrons. If these neutrons are absorbed by other uranium-235 nuclei, a Nuclear Chain Reaction occurs and, if there is nothing to absorb some neutrons and slow the reaction, the reaction is explosive. As little as 15 lb (7 kg) of uranium-235 can be used to make an atomic bomb.4 The first atomic bomb worked by this principle (nuclear fission). APPLICATIONS Military is used by various militaries as high-density penetrators.]] The major application of uranium in the military sector is in high-density penetrators. This ammunition consists of Depleted Uranium (DU) alloyed with 1–2% other elements. At high impact speed, the density, hardness, and flammability of the projectile enable destruction of heavily armored targets. Tank armor and the removable armor on combat vehicles are also hardened with depleted uranium (DU) plates. The use of DU became a contentious political-environmental issue after the use of DU munitions by the US, UK and other countries during wars in the Persian Gulf and the Balkans raised questions of uranium compounds left in the soil (see Gulf War Syndrome ). Depleted uranium is also used as a shielding material in some containers used to store and transport radioactive materials. Other uses of DU include counterweights for aircraft control surfaces, as ballast for missile Re-entry Vehicle s and as a shielding material. Due to its high density, this material is found in Inertial Guidance devices and in Gyroscopic Compass es. DU is preferred over similarly dense metals due to its ability to be easily machined and cast as well as its relatively low cost.Emsley, ''Nature's Building Blocks'' (2001), page 480 Counter to popular belief, the main risk of exposure to DU is chemical poisoning by uranium oxide rather than radioactivity (uranium being only a weak Alpha Emitter ). During the later stages of and a more complicated mechanism that uses Uranium-238 -derived Plutonium-239 . Later, a much more complicated and far more powerful fusion bomb that uses a plutonium-based device in a uranium casing to cause a mixture of Tritium and Deuterium to undergo Nuclear Fusion was built.5 Civilian s.]] The main use of uranium in the civilian sector is to fuel commercial Nuclear Power Plant s; by the time it is completely fissioned, one kilogram of uranium can theoretically produce about 20 Trillion Joule s of energy (20 joules); as much Electricity as 1500 Tonne s of Coal . Generally this is in the form of Enriched Uranium , which has been processed to have higher-than-natural levels of uranium-235 and can be used for a variety of purposes relating to nuclear fission. Commercial Nuclear Power plants use fuel that is typically enriched to around 3% uranium-235, though some reactor designs (such as the CANDU Reactor s) can use unenriched uranium fuel. Fuel used for United States Navy reactors is typically highly enriched in uranium-235 (the exact values are Classified ). In a Breeder Reactor , uranium-238 can also be converted into Plutonium through the following reaction: U(n, gamma) -> U -(beta)-> Np -(beta)-> Pu. glowing under UV Light ]] Prior to the discovery of Radiation , uranium was primarily used in small amounts for yellow glass and pottery dyes (such as Uranium Glass and in Fiestaware ). Uranium was also used in Photographic chemicals (esp. Uranium Nitrate as a Toner ), in lamp filaments, to improve the appearance of Dentures , and in the leather and wood industries for stains and dyes. Uranium salts are Mordant s of silk or wool. Uranyl acetate and uranyl formate are used as stains in Transmission Electron Microscopy , to increase the contrast of biological specimens in ultrathin sections and in Negative Staining of Virus es, isolated Cell Organelle s and Macromolecule s. The discovery of the radioactivity of uranium ushered in additional scientific and practical uses of the element. The long Half-life of the isotope uranium-238 (4.51 years) makes it well-suited for use in estimating the age of the earliest Igneous Rock s and for other types of Radiometric Dating (including Uranium-thorium Dating and Uranium-lead Dating ). Uranium metal is used for X-ray targets in the making of high-energy X-rays. HISTORY Pre-discovery use The use of uranium in its natural Oxide form dates back to at least the year 79, when it was used to add a yellow color to Ceramic glazes.6 Yellow glass with 1% uranium oxide was found in a Roman villa on Cape Posillipo in the Bay Of Naples , Italy by R. T. Gunther of the University Of Oxford in 1912.Emsley, ''Nature's Building Blocks'' (2001), page 482 Starting in the late Middle Ages , Pitchblende was extracted from the Habsburg silver mines in Joachimsthal , Bohemia (now Jáchymov in the Czech Republic ) and was used as a coloring agent in the local Glass making industry. In the early 19th century, the world's only known source of uranium ores were these old mines. Discovery discovered the phenomenon of Radioactivity by exposing a Photographic Plate to uranium (1896).]] Calcined uranium yellowcake as produced in many large mills contains a distribution of uranium oxidation species in various forms ranging from most oxidized to least oxidized. Particles with short residence times in a calciner will generally be less oxidized than particles that have long retention times or are recovered in the stack scrubber. While uranium content is referred to for content, to do so is inaccurate and dates to the days of the Manhattan Project when was used as an analytical chemistry reporting standard. Phase Relationship s in the uranium-oxygen system are highly complex. The most important oxidation states of uranium are uranium(IV) and uranium(VI), and their two corresponding Oxide s are, respectively, Uranium Dioxide () and Uranium Trioxide ().Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 779 Other Uranium Oxide s such as uranium monoxide (UO), diuranium pentoxide (), and uranium peroxide () are also known to exist. The most common forms of uranium oxide are Triuranium Octaoxide () and the aforementioned .27 Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octaoxide is (depending on conditions) the most stable compound of uranium and is the form most commonly found in nature. Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel. At ambient temperatures, will gradually convert to . Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal. Hydrides, carbides and nitrides Uranium metal heated to 250 to 300 °C (482 to 572 °F ) reacts with Hydrogen to form Uranium Hydride . Even higher temperatures will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium Carbide , Nitride , and Halide compounds.Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 782 Two crystal modifications of uranium hydride exist: an α form that is obtained at low temperatures and a β form that is created when the formation temperature is above 250 °C. Uranium Carbide s and Uranium Nitride s are both relatively Inert Semimetal lic compounds that are minimally soluble in Acid s, react with water, and can ignite in Air to form . Carbides of uranium include uranium monocarbide (U C ), uranium dicarbide (), and diuranium tricarbide (). Both UC and are formed by adding carbon to molten uranium or by exposing the metal to Carbon Monoxide at high temperatures. Stable below 1800 °C, is prepared by subjecting a heated mixture of UC and to mechanical stress.Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 780 Uranium nitrides obtained by direct exposure of the metal to Nitrogen include uranium mononitride (UN), uranium dinitride (), and diuranium trinitride (). Halides is the feedstock used to separate uranium-235 from natural uranium.]] All uranium fluorides are created using Uranium Tetrafluoride (); itself is prepared by hydrofluorination of uranium dioxide. Reduction of with hydrogen at 1000 °C produces uranium trifluoride (). Under the right conditions of temperature and pressure, the reaction of solid with gaseous Uranium Hexafluoride () can form the intermediate fluorides of , , and . At room temperatures, has a high Vapor Pressure , making it useful in the Gaseous Diffusion process to separate highly valuable uranium-235 from the far more common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process: The resulting white solid is highly Reactive (by fluorination), easily Sublimes (emitting a nearly Perfect Gas vapor), and is the most volatile compound of uranium known to exist. One method of preparing Uranium Tetrachloride () is to directly combine Chlorine with either uranium metal or uranium hydride. The reduction of by hydrogen produces uranium trichloride () while the higher chlorides of uranium are prepared by reaction with additional chlorine. All uranium chlorides react with water and air. s are water-soluble and include , , , and . Stability of the oxyhalides decrease as the Atomic Weight of the component halide increases. ISOTOPES Natural concentrations See Also: Isotopes of uranium Naturally occurring uranium is composed of three major Isotope s, Uranium-238 (99.28% Natural Abundance ), Uranium-235 (0.71%), and Uranium-234 (0.0054%). All three isotopes are Radioactive , creating Radioisotope s, with the most abundant and stable being uranium-238 with a Half-life of 4.51 years (close to the Age Of The Earth ), uranium-235 with a half-life of 7.13 years, and uranium-234 with a half-life of 2.48 years.Seaborg, ''Encyclopedia of the Chemical Elements'' (1968), page 777 Uranium-238 is an α emitter, decaying through the 18-member uranium natural decay series into Lead-206 . The decay series of uranium-235 (also called actino-uranium) has 15 members that ends in lead-207, Protactinium-231 and Actinium-227 . The constant rates of decay in these series makes comparison of the ratios of parent to daughter elements useful in Radiometric Dating . Uranium-233 is made from Thorium-232 by Neutron bombardment. The isotope uranium-235 is important for both Nuclear Reactor s and Nuclear Weapon s because it is the only isotope existing in nature to any appreciable extent that is Fissile , that is, can be broken apart by thermal neutrons. The isotope uranium-238 is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope Plutonium-239 , which also is fissile. Enrichment See Also: Enriched uranium s are used to enrich uranium ore to concentrate its fissionable isotopes.]] Enrichment of uranium ore through Isotope Separation to concentrate the fissionable uranium-235 is needed for use in nuclear power plants and nuclear weapons. A majority of neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the Nuclear Chain Reaction needed for these applications. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass.' To be considered 'enriched', the uranium-235 fraction has to be increased to significantly greater than its concentration in naturally-occurring uranium. Enriched uranium typically has a uranium-235 concentration of between 3 and 5%.28 The process produces huge quantities of uranium that is depleted of uranium-235 and with a correspondingly increased fraction of uranium-238, called Depleted Uranium or 'DU'. To be considered 'depleted', the uranium-235 isotope concentration has to have been decreased to significantly less than its natural concentration. Typically the amount of uranium-235 left in depleted uranium is 0.2% to 0.3%.29 As the price of uranium has risen since 2001, some enrichment tailings containing more than 0.35% uranium-235 are being considered for re-enrichment, driving the price of these depleted uranium hexafluoride stores above $130 per kilogram in July, 2007 from just $5 in 2001.dummytext The Gas Centrifuge process, where gaseous Uranium Hexafluoride () is separated by weight using high-speed Centrifuge s, has become the cheapest and leading enrichment process (lighter concentrates in the center of the centrifuge).Emsley, ''Nature's Building Blocks'' (2001), page 478 The Gaseous Diffusion process was the previous leading method for enrichment and the one used in the Manhattan Project . In this process, uranium hexafluoride is repeatedly Diffused through a Silver - Zinc membrane, and the different isotopes of uranium are separated by diffusion rate (uranium 238 is heavier and thus diffuses slightly slower than uranium-235). The Molecular Laser Isotope Separation method employs a Laser beam of precise energy to sever the bond between uranium-235 and fluorine. This leaves uranium-238 bonded to fluorine and allows uranium-235 metal to precipitate from the solution. Another method is called Liquid Thermal Diffusion . PRECAUTIONS Exposure A person can be exposed to uranium (or its radioactive daughters such as Radon ) by inhaling dust in air or by ingesting contaminated water and food. The amount of uranium in air is usually very small; however, people who work in factories that process Phosphate Fertilizer s, live near government facilities that made or tested nuclear weapons, live or work near a modern battlefield where Depleted Uranium Weapons have been used, or live or work near a Coal -fired power plant, facilities that mine or process uranium ore, or enrich uranium for reactor fuel, may have increased exposure to uranium.3031 Houses or structures that are over uranium deposits (either natural or man-made slag deposits) may have an increased incidence of exposure to radon gas. Almost all uranium that is ingested is excreted during Digestion , but up to 5% is absorbed by the body when the soluble Uranyl ion is ingested while only 0.5% is absorbed when insoluble forms of uranium, such as its oxide, are ingested. However, soluble uranium compounds tend to quickly pass through the body whereas insoluble uranium compounds, especially when ingested via dust into the Lung s, pose a more serious exposure hazard. After entering the bloodstream, the absorbed uranium tends to Bioaccumulate and stay for many years in Bone tissue because of uranium's affinity for phosphates. Uranium does not absorb through the skin, and Alpha Particle s released by uranium cannot penetrate the skin. Effects |
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