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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.

Bismuth-209,  209Bi
Name, symbolBismuth-209,209Bi
Nuclide data
Natural abundance100%
Half-life1.9×1019 years
Parent isotopes209Pb (β)
209Po (β+)
213At (α)
Decay products205Tl
Isotope mass208.9803987 u
Excess energy−18 258.461± 2.4 keV
Binding energy7847.987± 1.7 keV
Decay modes
Decay modeDecay energy (MeV)
Alpha emission3.1373
Complete table of nuclides


Decay propertiesEdit

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 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:

+ 4

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).[4]

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 204keV, which was estimated to be 1.66×1021 years.[5] 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 [6] (double beta decay would produce energy lines only in neutrinoless transitions, which has not been observed yet).


210Po can be manufactured by bombarding 209Bi with neutrons in a nuclear reactor. Only some 100 grams of 210Po are produced each year.[7]


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.[8]

See alsoEdit


Bismuth-209 is an
isotope of bismuth
Decay product of:
astatine-213 (α)
polonium-209 (β+)
lead-209 (β)
Decay chain
of bismuth-209
Decays to:
thallium-206 (α)


  1. ^ Dumé, Belle (2003-04-23). "Bismuth breaks half-life record for alpha decay". Physicsweb.
  2. ^ Marcillac, Pierre de; Noël Coron; Gérard Dambier; Jacques Leblanc; Jean-Pierre Moalic (April 2003). "Experimental detection of α-particles from the radioactive decay of natural bismuth". Nature. 422 (6934): 876–878. Bibcode:2003Natur.422..876D. doi:10.1038/nature01541. PMID 12712201.
  3. ^
  4. ^ "Archived copy". Archived from the original on 2011-09-28. Retrieved 2013-01-10.CS1 maint: Archived copy as title (link) Tellurium-128 information and half-life. Accessed July 14, 2009.
  5. ^ J.W. Beeman; et al. (2012). "First Measurement of the Partial Widths of 209Bi Decay to the Ground and to the First Excited States". Phys. Rev. Letters 108(6) 062501.
  6. ^ "Particle lifetimes from the uncertainty principle".
  7. ^ "Swiss study: Polonium found in Arafat's bones". Al Jazeera. Retrieved 2013-11-07.
  8. ^ Chaisson, Eric, and Steve McMillan. Astronomy Today. 6th ed. San Francisco: Pearson Education, 2008.