Isotopes of tin
Tin (Sn) 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 (Sn) (discovered in 1994) and tin-132 (Sn). The longest-lived radioisotope is Sn, with a half-life of 230,000 years. The other 28 radioisotopes have half-lives less than a year. Tin-121m. 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 Sn at higher yields. For example, its yield from U-235 is 0.0007% per thermal fission and 0.002% per fast fission. Tin-126. Tin-126 is a radioisotope of tin and one of only seven long-lived fission products. While tin-126's half-life of 230,000 years translates to a low specific activity of gamma radiation, its short-lived decay products, two isomers  of antimony-126, emit 17 and 40 keV gamma radiation and a 3.67 MeV beta particle on their way to stable tellurium-126, making external exposure to tin-126 a potential concern. Sn 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 U), since slow neutrons almost always fission U or Pu into unequal halves. Fast fission in a fast reactor or nuclear weapon, or fission of some heavy minor actinides such as californium, will produce it at higher yields. Isotopes