Bismuth-209 is the 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). Primordial bismuth consists entirely of this isotope.
|Parent isotopes||209Pb (β−)|
|Isotope mass||208.9803987 u|
|Excess energy||−18 258.461± 2.4 keV|
|Binding energy||7847.987± 1.7 keV|
|Decay mode||Decay energy (MeV)|
|Isotopes of bismuth |
Complete table of nuclides
Bismuth-209 was long thought to have the heaviest stable nucleus of any element, but in 2003, a research team 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, approximately 19 quintillion years), over a billion times longer than the current estimated age of the universe. The heaviest nucleus considered to be stable is now Lead-208. 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.
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 × 1024 years by double β-decay (beta decay).
The half-life value of bismuth-209 was confirmed in 2012 by an Italian team in Gran Sasso who reported 2.01±0.08 ×1019 years, and an even longer half-life, for bismuth-209 alpha decay to the first excited state of thalium-205 at 204 keV, which was estimated to be 1.66×1021 years. Even if this value is shorter than the measured half-life of tellurium-128, both alpha decays of bismuth-209 hold the record of the thinnest natural line widths of any measurable physical excitation, estimated respectively at ΔΕ~5.5×10−43 eV and ΔΕ~1.3×10−44eV in application of the uncertainty principle of Heisenberg  (double beta decay would produce energy lines only in neutrinoless transitions, which has not been observed yet).
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 supernovas.
|Bismuth-209 is an
isotope of bismuth
|Decay product of:
|Decays to: |
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