Isotopes of tin

Tin (50Sn) is the element with the greatest number of stable isotopes (ten; three of them are potentially radioactive but have not been observed to decay), which is probably related to the fact that 50 is a 'magic number' of protons. Twenty-nine additional unstable isotopes are known, including the 'doubly magic' tin-100 (100Sn) (discovered in 1994) and tin-132 (132Sn). The longest-lived radioisotope is 126Sn, with a half-life of 230,000 years. The other 28 radioisotopes have half-lives less than a year. Tin (50Sn) is the element with the greatest number of stable isotopes (ten; three of them are potentially radioactive but have not been observed to decay), which is probably related to the fact that 50 is a 'magic number' of protons. Twenty-nine additional unstable isotopes are known, including the 'doubly magic' tin-100 (100Sn) (discovered in 1994) and tin-132 (132Sn). The longest-lived radioisotope is 126Sn, with a half-life of 230,000 years. The other 28 radioisotopes have half-lives less than a year. Tin-121m is a radioisotope and nuclear isomer of tin with a half-life of 43.9 years. 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 121mSn at higher yields. For example, its yield from U-235 is 0.0007% per thermal fission and 0.002% per fast fission. Tin-126 is a radioisotope of tin and one of only 7 long-lived fission products. While tin-126's halflife of 230,000 years translates to a low specific activity that limits its radioactive hazard, its short-lived decay products 2 isomers of antimony-126 emit 17 and 40 keV gamma radiation, making external exposure to tin-126 a potential concern. 126Sn is in the middle of the mass range for fission products. Thermal reactors, which make up almost all current nuclear power plants, produce it at a very low yield (0.056% for 235U), since slow neutrons almost always fission 235U or 239Pu into unequal halves. Fast fission in a fast reactor or nuclear weapon, or fission of some heavy minor actinides like californium, will produce it at higher yields.