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Bismuth-209
Isotope of bismuth From Wikipedia, the free encyclopedia
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Bismuth-209 (209Bi) is an isotope of bismuth with the longest known half-life of any nuclide that undergoes α-decay (alpha decay); the decay product is thallium-205. It has 83 protons and a magic number[3] of 126 neutrons,[3] and naturally-occurring bismuth consists entirely of this isotope.
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Decay properties
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Perspective
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 now given more precisely as 2.01×1019 years (20.1 quintillion years),[4][5] over 109 times longer than the estimated age of the universe.[6] The heaviest nucleus considered to be stable is now lead-208 and the heaviest stable monoisotopic element is gold (gold-197).
Theory had previously predicted a half-life of 4.6×1019 years. It had been suspected to be radioactive for a long time.[7] The decay produces a 3.14 MeV alpha particle plus thallium-205.[4][5]
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Due to its extremely long half-life, 209Bi can be treated as non-radioactive for nearly all applications. It is much less radioactive than human flesh, so it poses no real radiation hazard. Though 209Bi holds the half-life record for alpha decay, it does not have the longest known half-life of any nuclide; this distinction belongs to tellurium-128 (128Te) with a half-life estimated at 7.7×1024 years by double β-decay (double beta decay).[8][9][10]
The half-life of 209Bi was confirmed in 2012 by an Italian team in Gran Sasso who reported (2.01±0.08)×1019 years. They also reported an even longer partial half-life for alpha decay of 209Bi to the first excited state of 205Tl (at 204 keV), estimated at 1.66×1021 years.[11] Even though this value is shorter than the half-life of 128Te, both alpha decays of 209Bi 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 ≈ 1.3×10−44 eV in application of the uncertainty principle[12] (beta or double beta decay would produce energy lines only in neutrinoless transitions, which have never been observed).
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Applications
Because all primordial bismuth is bismuth-209, bismuth-209 is used for all normal applications of bismuth, such as being used as a replacement for lead,[13][14] in cosmetics,[15][16] in paints,[17] and in several medicines such as Pepto-Bismol.[6][18][19] Alloys containing bismuth-209 such as bismuth bronze have been used for thousands of years.[20]
Synthesis of other elements
210Po can be manufactured by bombarding 209Bi with neutrons in a nuclear reactor[21] and around 100 grams of 210Po are produced each year.[22][21] 209Po and 208Po can be made through the proton bombardment of 209Bi in a cyclotron.[23] Astatine can also be produced by bombarding 209Bi with alpha particles.[24][25][26] Traces of 209Bi have also been used to create gold in nuclear reactors.[27][28]
209Bi has been used as a target for the creation of several isotopes of superheavy elements such as dubnium,[29][30][31][32] bohrium,[29][33] meitnerium,[34][35][36] roentgenium,[37][38][39] and nihonium.[40][41][42]
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Formation
Primordial
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.[43] All elements heavier than it are formed in the r-process, or rapid process, which occurs during the first fifteen minutes of supernovas.[44][43] Bismuth-209 is also created during the r-process.[43]
Radiogenic
Some 209Bi was created radiogenically from the neptunium decay chain.[45] Neptunium-237 is an extinct radionuclide, but it can be found in traces in uranium ores because of neutron capture reactions.[45] This is also ultimately due to the r-process, as every (4n+1) nucleus formed (and not fissioned) ultimately decayed to bismuth.
See also
Notes
- Red horizontal lines with a circle in their right ends represent neutron captures; blue arrows pointing up-left represent beta decays; green arrows pointing down-left represent alpha decays; cyan/light-green arrows pointing down-right represent electron captures.
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References
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