Barium137

Barium-137, denoted as Ba-137, is a radioactive isotope of the element barium (atomic number 56) with mass number 137. In practice, it exists mainly as two related forms: the metastable isomer Ba-137m and the ground-state Ba-137. The ground-state Ba-137 is stable, while Ba-137m is an excited, short‑lived state that decays to Ba-137.

The decay sequence most commonly associated with Ba-137 involves cesium-137 (Cs-137), a major fission product. Cs-137 beta-decays with a half-life of about 30.17 years to Ba-137m. The metastable Ba-137m then decays to the ground-state Ba-137 with a half-life of about 2.55 minutes, emitting a gamma ray of 661.7 keV in the transition to Ba-137. This characteristic gamma emission is widely used in radiation detection and calibration.

Production and presence: Ba-137 is produced primarily as a decay product in nuclear fission and is not present in significant natural abundances. It is encountered in environments with fission products, in research and industry using Cs-137 sources, and in nuclear fallout as particles decay through the Ba-137m to Ba-137 pathway.

Applications and safety: The 661.7 keV gamma line from Ba-137m to Ba-137 makes Cs-137/Ba-137 sources useful for calibrating gamma spectroscopy instruments and for various radiography and industrial applications. Handling of Ba-137m and Cs-137 requires shielding and regulatory controls due to gamma emission.

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