Bismuth-209 is the "quasi-stable" isotope of bismuth with the longest known half-life of any radioisotope that undergoes α-decay (alpha decay). It has 83 protons and a magic number of 126 neutrons, and an atomic mass of 208.9803987 amu (atomic mass units). All of the primordial bismuth is of this isotope. It is also the β daughter of lead-209.

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 19 exayears (1.9×1019 which is 19 quintillion years), over a billion times longer than the current estimated age of the universe. Theory had previously predicted a half-life of 4.6×1019 years. The decay event produces a 3.14 MeV alpha particle and converts the atom to thallium-205.[1][2]

Bismuth-209 will eventually form 205Tl:

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).[4]

According to the United States Geological Survey, the 2010 world mining output of bismuth was 8,900 tonnes[5] (of which virtually 100% is 209Bi).

Hypothetically, if the entire 2010 output were to be stored until the doubling of the current age of the universe (~13.8 billion years from now), less than 4.5 grams would have decayed based upon Coron's half-life data (which is less than the weight of a US quarter dollar).[notes 1]

210Po can be manufactured by bombarding 209Bi with neutrons in a nuclear reactor. Only some 100 grams of 210Po are produced each year.[6]

Bismuth-209 is widely used in digestive medicines such as Pepto-Bismol.

This page was last edited on 22 June 2018, at 01:24 (UTC).
Reference: under CC BY-SA license.

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