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A weapons-grade substance is one that is pure enough to be used to make a nuclear weapon or has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nuclear weapons are the most common examples. (These nuclear materials have other categorizations based on their purity.) Only fissile isotopes of certain elements have the potential for use in nuclear weapons. For such use, the concentration of fissile isotopes uranium-235 and plutonium-239 in the element used must be sufficiently high. Uranium from natural sources is enriched by isotope separation, and plutonium is produced in a suitable nuclear reactor. Experiments have been conducted with uranium-233. Neptunium-237 and some isotopes of americium might be usable, but it is not clear that this has ever been implemented. Substances for chemical and biological warfare may also be described as weapons-grade. ==Countries that have produced weapons-grade nuclear material== Relatively few countries (10) have produced weapons-grade nuclear material: China, France, India, Israel, North Korea, Pakistan, Russia, South Africa, the United Kingdom, and the United States. 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「Weapons-grade」の詳細全文を読む スポンサード リンク
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