Isotopes of barium
Naturally occurring barium (Ba) is a mix of six stable isotopes and one very long-lived radioactive primordial isotope, barium-130, identified as being unstable by geochemical means (from analysis of the presence of its daughter xenon-130 in rocks) in 2001. This nuclide decays by double electron capture (absorbing two electrons and emitting two neutrinos), with a half-life of (0.5–2.7)×10 years (about 10 times the age of the universe). There are a total of thirty-three known radioisotopes in addition to Ba. The longest-lived of these is Ba, which has a half-life of 10.51 years . All other radioisotopes have half-lives shorter than two weeks. The longest-lived isomer is Ba, which has a half-life of 38.9 hours. The shorter-lived Ba (half-life 2.55 minutes) arises as the decay product of the common fission product caesium-137. Barium-114 is predicted to undergo cluster decay, emitting a nucleus of stable C to produce Sn. However this decay is not yet observed; the upper limit on the branching ratio of such decay is 0.0034%.