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Bismuth-209 is the "virtually stable" isotope of bismuth with the longest half-life of any radioisotope to that undergoes α-decay (alpha decay). It has 83 protons and 126 neutrons, and an atomic mass of 208.9803987 amu (atomic mass units). All primordial bismuth is of this isotope. It is a decay product from lead-209 decaying by β−-decay. ==Stability== Bismuth-209 was long thought to have the heaviest stable nucleus of any element, but in 2003, Noël Coron and his colleagues at the Institut d’Astrophysique Spatiale in Orsay, France, discovered that 209Bi undergoes alpha decay with a half-life of approximately 600 yottaseconds (1.9 years), over a billion times longer than the current estimated age of the universe. Theory had previously predicted a half-life of 4.6 years. The decay event produces a 3.14 MeV alpha particle and converts the atom to thallium-205. Bismuth-209 can undergo alpha decay and is produced as part of the decay of Americium-241 (241Am): : → + Bismuth-209 will eventually form 205Tl: : → + 〔http://periodictable.com/Isotopes/095.241/index.full.html〕 Due to its extraordinarily long half-life, for nearly all applications 209Bi can still be treated as if it were non-radioactive. Although 209Bi holds the half-life record for alpha decay, bismuth does not have the longest half-life of any radionuclide to be found experimentally—this distinction belongs to Tellurium-128 (128Te) with a half-life estimated at 7.7 x 1024 years by double β-decay (beta decay).〔http://presolar.wustl.edu/work/noblegas.html Tellurium-128 information and half-life. Accessed July 14, 2009.〕 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「Bismuth-209」の詳細全文を読む スポンサード リンク
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