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Cobalt-60, , is a synthetic radioactive isotope of cobalt with a half-life of 5.2714 years. It is produced artificially in nuclear reactors. Deliberate industrial production depends on neutron activation of bulk samples of the monoisotopic and mononuclidic cobalt isotope .〔Malkoske, G. R. (''Cobalt-60 production in CANDU power reactors'' )〕 Measurable quantities are also produced as a by-product of typical nuclear power plant operation and may be detected externally when leaks occur. In the latter case (in the absence of added cobalt) the incidentally produced is largely the result of multiple stages of neutron activation of iron isotopes in the reactor's steel structures〔US EPA [http://www.epa.gov/radiation/radionuclides/cobalt.html#wheredoes Radiation Protection: Cobalt〕 via the creation of precursor. The simplest case of the latter would result from the activation of . decays by beta decay to the stable isotope nickel-60 (). The activated nickel nucleus emits two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall nuclear equation of the reaction is + n → → + e− + + gamma rays. ==Activity== Corresponding to its half-life the radioactive activity of one gram of is 44 TBq (about 1100 curies). The ''absorbed dose constant'' is related to the decay energy and time. For it is equal to 0.35 mSv/(GBq h) at one meter from the source. This allows calculation of the equivalent dose, which depends on distance and activity. Example: a source with an activity of 2.8 GBq, which is equivalent to 60 µg of pure , generates a dose of 1 mSv at one meter distance within one hour. The swallowing of reduces the distance to a few millimeters, and the same dose is achieved within seconds. Test sources, such as those used for school experiments, have an activity of <100 kBq . Devices for nondestructive material testing use sources with activities of 1 TBq and more. The high γ-energies result in a significant mass difference between and of 0.003 u. This amounts to nearly 20 watts per gram, nearly 30 times larger than that of . 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「Cobalt-60」の詳細全文を読む スポンサード リンク
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