New Barium and Cesium Isotopes: 12.0d Ba131, 10.2d Cs131, and Long-Lived Ba133

Abstract

A new Ba-Cs chain of probable mass assignment of 131 has been formed by neutron activation of barium. The ${\mathrm{Ba}}^{131}$ isotope decays predominately by orbital electron capture with a half-life of 12.0 days, emitting gamma-radiations of about 0.26 Mev, 0.5 Mev, and roughly 1.2 Mev (the latter in low intensity). Detected also were 31-kev x-rays and 0.42-Mev and 0.24-Mev conversion electrons. The ${\mathrm{Cs}}^{131}$ decays exclusively by $K$-electron capture with a half-life of 10.2 days, emitting no detected gamma-rays. The ${\mathrm{Ba}}^{133}$ has a minimum half-life of 20 years and is very probably the lower state to which the 37.8 hour ${\mathrm{Ba}}^{133}$ decays. The former decays by $K$-capture and emits 31-kev x-rays, 0.36-Mev gamma-rays, 0.34-Mev conversion electrons, and possibly 4.3-kev x-rays.