Tin (50Sn) is the element with the greatest number of naturally abundant isotopes, 10. Seven, 114-120Sn, are theoretically stable, while the remaining three, 112Sn, 122Sn, and 124Sn, are potentially radioactive (to double beta decay, but have not been observed to decay (observationally stable). This is generally attributed to the fact that 50 is a "magic number" of protons. In addition, 32 unstable tin isotopes are known, including tin-100 (100Sn) and tin-132 (132Sn), which are both "doubly magic". The longest-lived of these is tin-126 (126Sn), with a half-life about 230,000 years; with all others less than a year and the majority under 20 minutes.
The number of known metastable states is very large, including a long series of low-lying states in odd isotopes from 117 on, which gives two nuclides with a longer life than any ground-state radioisotope other than 126: 121mSn, half-life 43.9 years, and 119mSn, half-life 293.1 days.
↑ ()– Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
↑ #– Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
1 2 3 #– Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
↑ Decay energy is split among β, neutrino, and γ if any.
↑ Per 65 thermal neutron fissions of 235U and 35 of 239Pu.
1 2 3 Neutron poison; in thermal reactors most is destroyed by further neutron capture.
↑ Less than 1/4 of mass-85 fission products as most bypass ground state: Br-85 -> Kr-85m -> Rb-85.
↑ Has decay energy 546 keV; its decay product Y-90 has decay energy 2.28 MeV with weak gamma branching.
Tin-121m (121mSn) is a nuclear isomer of tin with a half-life of 43.9 years, making it technically a medium-lived fission product.
In a normal thermal reactor, it has a very low fission product yield; thus, this isotope is not a significant contributor to nuclear waste. Fast fission or fission of some heavier actinides will produce it at higher yields. For example, its yield from uranium-235 is 0.0007% per thermal fission and 0.002% per fast fission.[9]
Tin-126 is a radioisotope of tin and one of the only seven long-lived fission products. While tin-126's half-life of 230,000 years means a relatively low specific activity, its short-lived decay products, two isomers of antimony-126, emit a cascade of hard gamma radiation - at least 3 photons above 400 keV per decay - before reaching stable tellurium-126, making it a possible external exposure hazard, which the other long-lived fission products are not by comparison.
Tin-126 is in the middle of the mass range for fission products, so its yield is fairly low (but still dominates that for the element tin). Fission of the common fuels such as 235U and 239Pu into unequal halves is preferred, especially with thermal neutrons, as used in almost all current nuclear power plants.
↑ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3) 030003. doi:10.1088/1674-1137/abddaf.
1 2 M. B. Chadwick et al, "Evaluated Nuclear Data File (ENDF): ENDF/B-VII.1: Nuclear Data for Science and Technology: Cross Sections, Covariances, Fission Product Yields, and Decay Data", Nucl. Data Sheets 112(2011)2887. (accessed at https://www-nds.iaea.org/exfor/endf.htm)
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