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Uranium-232 (, , U-232) is an isotope of uranium. It has a half-life of 68.9 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using 233U as the fissile material, because the intense gamma radiation of 232U's decay products makes the 233U contaminated with it more difficult to handle. Production of 233U (through the neutron irradiation of 232Th) invariably produces small amounts of 232U as an impurity, because of parasitic (n,2n) reactions on uranium-233 itself, or on protactinium-233, or on thorium-232: :232Th (n,γ) 233Th (β−) 233Pa (β−) 233U (n,2n) 232U :232Th (n,γ) 233Th (β−) 233Pa (n,2n) 232Pa (β−) 232U :232Th (n,2n) 231Th (β−) 231Pa (n,γ) 232Pa (β−) 232U Another channel involves neutron capture reaction on small amounts of thorium-230, which is a tiny fraction of natural thorium present due to the decay of uranium-238: :230Th (n,γ) 231Th (β−) 231Pa (n,γ) 232Pa (β−) 232U The decay chain of 232U quickly yields strong gamma radiation emitters:〔Griffin, H. C. ''Natural Radioactive Decay Chains'', Chapter 13 of ''Handbook of Nuclear Chemistry'', Second Edition, Springer 2011, ISBN 978-1-4419-0719-6〕 :232U (α, 68.9 years) :228Th (α, 1.9 year) :224Ra (α, 3.6 day, 0.24 MeV) (at this point, the decay chain is identical to that of 232Th) :220Rn (α, 55 s, 0.54 MeV) :216Po (α, 0.15 s) :212Pb (β−, 10.64 h) :212Bi (α, 61 m, 0.78 MeV) :208Tl (β−, 3 m, 2.6 MeV) (35.94% branching ratio) :208Pb (stable) This makes manual handling in a glove box with only light shielding (as commonly done with plutonium) too hazardous, (except possibly in a short period immediately following chemical separation of the uranium from thorium-228, radium-224, radon-220, and polonium) and instead requiring remote manipulation for fuel fabrication. Unusually for an isotope with even mass number, 232U has a significant neutron absorption cross section for fission (thermal neutrons , resonance integral ) as well as for neutron capture (thermal , resonance integral ). ==References== 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「Uranium-232」の詳細全文を読む スポンサード リンク
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