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Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium with a lower content of the fissile isotope U-235 than natural uranium.〔: "Depleted uranium possesses only 60% of the radioactivity of natural uranium, having been 'depleted' of much of its most highly radioactive U234 and U235 isotopes."〕 (Natural uranium contains about 0.72% of its fissile isotope U-235, while the DU used by the U.S. Department of Defense contain 0.3% U-235 or less). Uses of DU take advantage of its very high density of 19.1 g/cm3 (68.4% denser than lead). Civilian uses include counterweights in aircraft, radiation shielding in medical radiation therapy and industrial radiography equipment, and containers for transporting radioactive materials. 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. Enrichment processes generate uranium with a higher-than-natural concentration of lower-mass-number uranium isotopes (in particular U-235, which is the uranium isotope supporting the fission chain reaction) with the bulk of the feed ending up as depleted uranium, in some cases with mass fractions of U-235 and U-234 less than a third of those in natural uranium. Since U-238 has a much longer half-life than the lighter isotopes, DU emits less alpha radiation than natural uranium. 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.〔(【引用サイトリンク】title=UN Press Release UNEP/81: Uranium 236 found in depleted uranium penetrators )〕 DU used in US munitions has 60% of the radioactivity of natural uranium.〔("Properties and Characteristics of DU" ) U.S. Office of the Secretary of Defense〕 Trace transuranics (another indicator of the use of reprocessed material) have been reported to be present in some US tank armor.〔 The use of DU in munitions is controversial because of concerns about potential long-term health effects.〔〔.〕 Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by exposure to uranium, a toxic metal.〔 It is only weakly radioactive because of its long radioactive half-life (4.468 billion years for uranium-238, 700 million years for uranium-235; or 1 part per million every and years, respectively). The biological half-life (the average time it takes for the human body to eliminate half the amount in the body) for uranium is about 15 days.〔(【引用サイトリンク】title= Biological Half Lives )〕 The aerosol or spallation frangible of powder produced by impact and combustion of depleted uranium munitions can potentially contaminate wide areas around the impact sites, leading to possible inhalation by human beings.〔Mitsakou C., Eleftheriadis K., Housiadas C., Lazaridis M. (Modeling of the dispersion of depleted uranium aerosol. ) 2003 Apr. Retrieved 15 January 2009.〕 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, and neurological effects from chronic exposure.〔.〕 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."〔 ==History== Enriched uranium was first manufactured in the early 1940s when the United States and Britain began their nuclear weapons programs. Later in the decade, France and the Soviet Union began their nuclear weapons and nuclear power programs. It was at this time that depleted uranium was first stored as an unusable waste product (uranium hexafluoride). There was some hope that the enrichment process would be improved and additional quantities of the fissionable U-235 isotope could, at some future date, be extracted from it. This re-enrichment recovery of the residual uranium-235 contained in the depleted uranium is no longer a matter of the future: it has been practiced for several years.〔 〕 Also, it is possible to design civilian power-generating reactors using unenriched fuel, but only about 10% of those ever built (such as the CANDU reactor) utilize that technology. Both nuclear weapons production and naval reactors require fuel containing concentrated U-235. 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,〔Mughal, Muhammad Aurang Zeb. 2013. "Persian Gulf Desert and Semi-desert." ''Biomes & Ecosystems'', Vol. 3, Robert Warren Howarth (ed.). Ipswich, MA: Salem Press, pp. 1000-1002.〕 the Bosnia war, bombing of Serbia, and the 2003 invasion of Iraq. It is estimated that between 315 and 350 tons of DU were used in the 1991 Gulf War.〔(【引用サイトリンク】url=http://www.energysolutions.com/depleted-uranium/history/ )〕 While clearing a decades-old Hawaii firing range in 2005, workers found depleted uranium fins dating from the 1960s and 1970s that were from training rounds from the formerly classified Davy Crockett recoilless gun tactical battlefield nuclear delivery system. These training rounds had been forgotten because they were used in a highly classified program and had been fired before DU had become of widespread interest, more than 20 years before the Gulf War. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Depleted uranium」の詳細全文を読む スポンサード リンク
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