Bismuth-209
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Bismuth-209 is the most stable isotope of bismuth. It has 83 protons and 126 neutrons, and an atomic mass of 208.9803987. All naturally occurring bismuth is of this isotope. It is a decay product from Lead-209 decaying by β^--decay.

Bismuth-209 was long thought to have the heaviest stable nucleus of any element, but in 2003 Noël Coron and colleagues at the Institut d’Astrophysique Spatiale in Orsay, France discovered that it underwent alpha decay with a half-life of approximately 19 exayears (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]

Due to its extraordinarily long half-life, for nearly all applications bismuth can still be treated as if it is stable and non-radioactive.

References

See also

• Isotopes of bismuth