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Nuclear weapons tests are experiments carried out to determine the effectiveness, yield, and explosive capability of nuclear weapons. Throughout the 20th century, most nations that developed nuclear weapons tested them. Testing nuclear weapons can yield information about how the weapons work, as well as how the weapons behave under various conditions and how personnel, structures, and equipment behave when subjected to nuclear explosions. Nuclear testing has often been used as an indicator of scientific and military strength, and many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status by means of a nuclear test. The first nuclear weapon was detonated as a test by the United States at the Trinity site on July 16, 1945, with a yield approximately equivalent to 20 kilotons of TNT. The first thermonuclear weapon, codenamed "Mike", was tested at the Enewetak atoll in the Marshall Islands on November 1, 1952 (local date), also by the United States. The largest nuclear weapon ever tested was the "Tsar Bomba" of the Soviet Union at Novaya Zemlya on October 30, 1961, with the largest yield ever seen (), an estimated 50–58 megatons. In 1963, three (UK, US, Soviet Union) of the four nuclear states and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. The treaty permitted underground nuclear testing. France continued atmospheric testing until 1974, and China continued until 1980. Neither has signed the treaty.〔"The Treaty has not been signed by France or by the Peoples Republic of China." U.S. Department of State, (Limited Test Ban Treaty ).〕 Underground tests in the United States continued until 1992 (its last nuclear test), the Soviet Union until 1990, the United Kingdom until 1991, and both China and France until 1996. In signing the Comprehensive Test Ban Treaty in 1996, these states have pledged to discontinue all nuclear testing. However, , the treaty has not yet entered into force because of failure to be signed/ratified by eight specific countries. Non-signatories India and Pakistan last tested nuclear weapons in 1998. The most recent nuclear test in February 2013 in North Korea. In January 2013, North Korea had announced that it planned to conduct further tests involving rockets that can carry satellites as well as nuclear warheads "to strike and attack the United States". ==Types== Nuclear weapons tests have historically been divided into four categories reflecting the medium or location of the test. *Atmospheric testing designates explosions that take place in the atmosphere. Generally these have occurred as devices detonated on towers, balloons, barges, islands, or dropped from airplanes, and also those which are only buried far enough to intentionally create a surface-breaking crater. Nuclear explosions that are close enough to the ground to draw dirt and debris into their mushroom cloud can generate large amounts of nuclear fallout due to irradiation of the debris. This definition of atmospheric is used in the Limited Test Ban Treaty, which banned this class of testing along with exoatmospheric and underwater. *Underground testing refers to nuclear tests conducted under the surface of the earth, at varying depths. Underground nuclear testing made up the majority of nuclear tests by the United States and the Soviet Union during the Cold War; other forms of nuclear testing were banned by the Limited Test Ban Treaty in 1963. True underground tests are intended to be fully contained and emit a negligible amount of fallout. Unfortunately these nuclear tests do occasionally "vent" to the surface, producing from nearly none to considerable amounts of radioactive debris as a consequence. Underground testing almost by definition result in seismic activity which magnitude depends on the yield of the nuclear device and the composition of the medium it is detonated in, and generally result in the creation of subsidence craters.〔For an overview of the preparations and considerations used in underground nuclear testing, see (【引用サイトリンク】title="Underground Nuclear Weapons Testing" (Globalsecurity.org) ) For a longer and more technical discussion, see 〕 In 1976, the United States and the USSR agreed to limit the maximum yield of underground tests to 150 kt with the Threshold Test Ban Treaty. Underground testing also falls into two physical categories: tunnel tests which happen in generally horizontal tunnel "drifts", and shaft tests in vertically drilled holes. *Exoatmospheric testing refers to nuclear tests conducted above the atmosphere. The test devices are lifted on rockets. These high altitude nuclear explosions can generate a nuclear electromagnetic pulse (NEMP) when they occur in the ionosphere, and charged particles resulting from the blast can cross hemispheres following geomagnetic lines of force to create an auroral display. *Underwater testing results from nuclear devices being detonated underwater, usually moored to a ship or a barge (which is subsequently destroyed by the explosion). Tests of this nature have usually been conducted to evaluate the effects of nuclear weapons against naval vessels (such as in Operation Crossroads), or to evaluate potential sea-based nuclear weapons (such as nuclear torpedoes or depth-charges). Underwater tests close to the surface can disperse large amounts of radioactive particles in water and steam, contaminating nearby ships or structures, though they generally do not create fallout other than very local to the explosion. 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「Nuclear weapons testing」の詳細全文を読む スポンサード リンク
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