Bismuth-209

Bismuth-209 is the "virtually stable" isotope of bismuth with the longest half-life of any radioisotope 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 β⁻product of lead-209.

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 (1.9×10¹⁹ 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 can undergo alpha decay and is produced as part of the decay of Americium-241 (²⁴¹Am):

209
82Pb → 209
83Bi + e−

Bismuth-209 will eventually form ²⁰⁵Tl:

209
83Bi → 205
81Tl + 4
2He^[3]

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]

Hypothetical decay

According to the United States Geological Survey, the 2010 world mining output of Bismuth was 8,900 metric 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]}

Uses

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

Formation

In the red giant stars of the asymptotic giant branch, the s-process (slow process) is ongoing to produce bismuth-209 and polonium-210 by neutron capture as the heaviest elements to be formed, and the latter quickly decays. All elements heavier than it are formed in the r-process, or rapid process, which occurs during the first fifteen minutes of supernovae.^[7]

See also

• Isotopes of bismuth

Notes

References