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An underwater explosion (also known as an UNDEX) is a chemical or nuclear explosion that occurs under the surface of a body of water. ==Properties of water== Underwater explosions differ from in-air explosions due to a number of properties characteristic of water: * Mass and incompressibility – water has a much higher density than air, which makes water harder to move (higher inertia). It is also relatively hard to compress (increase density) when under pressure in a low range, say up to 100 atmospheres. These two together make water an excellent conductor of shock waves from an explosion. * Low neutron activation – when exposed to neutron radiation during the microsecond of active detonation of a nuclear pit, water doesn't itself "activate", or become radioactive. The two atoms in water, hydrogen and oxygen, can absorb an extra neutron, becoming deuterium and oxygen-17 respectively, both of which are stable isotopes. Even oxygen-18 is stable. Only if a particular hydrogen atom absorbs two neutrons, oxygen-16 will produce short lived nitrogen-16 via a high energy neutron (n,p) reaction, or an oxygen three neutrons, do the atoms become radioactive. In any typical scenario the probability of such multiple capture in significant numbers in the short time of active nuclear reactions around a bomb are very low. They are somewhat less low when the water is continuously radiated, as in the closed loop of a nuclear reactor. Most underwater blast scenarios happen in seawater, not fresh or pure water. Salt, unlike water, readily absorbs neutrons into the normal sodium-23 and chlorine-35 atoms, which change to radioactive isotopes. Sodium-24 has a half life of about 15 hours, while that of chlorine-36 (which has a lower absorption cross-section) is 300,000 years; the sodium is therefore the most dangerous contaminant. These are generally the main radioactive contaminants in an underwater blast; others are the usual blend of irradiated minerals, coral, unused nuclear fuel and bomb case components present in surface blast nuclear fallout, carried in suspension or dissolved in the water. Thus plain distillation or evaporating water (clouds, humidity, and precipitation) purifies it of radiation contamination, including the hot sea salt. 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「underwater explosion」の詳細全文を読む スポンサード リンク
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