Gamma Rays in the Decay of Barium-131

Abstract

Gamma rays accompanying electron capture of 12-day ${\mathrm{Ba}}^{131}$ have been studied with a single-channel scintillation spectrometer. Relative intensities have been determined for the 122 kev (198), 214 kev (148), 372 kev (100), 496 kev plus satellite (360), and 620 kev (33) gamma-rays. Three new gamma-rays have been found at 823\ifmmode\pm\else\textpm\fi{}20 kev (2.0), 917\ifmmode\pm\else\textpm\fi{}15 kev (7.2), and 1032\ifmmode\pm\else\textpm\fi{}15 kev (11.0), and their assignment to ${\mathrm{Ba}}^{131}$ has been established by chemical purification and half-life. Crystal summing studies confirm that the 620-kev transition is the crossover of the 122-kev and 496-kev transitions, and no significant crystal summing is found for the three new gamma rays. A peak corresponding to 83 kev was observed, which appears to be due to two or more unresolved gamma rays, but no gamma ray could be found at 100 kev. The decay of ${\mathrm{Ba}}^{131}$ was followed for 9 half-lives using an end-window beta proportional counter, and the half-life was found to be 11.52\ifmmode\pm\else\textpm\fi{}0.08 days. The ratio of the pile neutron cross section for the activation of ${\mathrm{Ba}}^{131}$ to that of long-lived ${\mathrm{Ba}}^{133}$ has been found to be $\frac{\ensuremath{\sigma}({\mathrm{Ba}}^{130})}{\ensuremath{\sigma}({\mathrm{Ba}}^{132})}=1.2\ifmmode\pm\else\textpm\fi{}0.3$.