Barium-137m

Main isotopes of barium

Iso­tope Decay abun­dance half-life mode energy (MeV) pro­duct 130Ba 0.11% (0.5–2.7)×1021 y εε 2.620 130Xe 132Ba 0.10% is stable with 76 neutrons 133Ba syn 10.51 y ε 0.517 133Cs 134Ba 2.42% is stable with 78 neutrons 135Ba 6.59% is stable with 79 neutrons 136Ba 7.85% is stable with 80 neutrons 137Ba 11.23% is stable with 81 neutrons 138Ba 71.70% is stable with 82 neutrons
Standard atomic weight (Ar)	137.327(7)

Naturally occurring barium (₅₆Ba) is a mix of six stable isotopes and one very long-lived radioactive primordial isotope, barium-130, recently identified as being unstable by geochemical means (from analysis of the presence of its daughter xenon-130 in rocks). This nuclide decays by double-electron capture (absorbing two electrons and emitting two neutrons;) with a half-life of (0.5–2.7)×10²¹ years (about 10¹¹ times the age of the universe).

There are a total of thirty-three known radioisotopes in addition to ¹³⁰Ba, but most of these are highly radioactive with half-lives in the several millisecond to several minute range. The only notable exceptions are ¹³³Ba, which has a half-life of 10.51 years, ¹³¹Ba (11.5 days), and ^137mBa (2.55 minutes), which is the decay product of ¹³⁷Cs (30.17 years, and a common fission product).

Barium-114 is predicted to undergo cluster decay, emitting a nucleus of stable ¹²C to produce ¹⁰²Sn. However this decay is not yet observed; the upper limit on the branching ratio of such decay is 0.0034%.

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