Decays of mass-separatedXe138andCs138

Abstract

The $\ensuremath{\beta}$ and subsequent $\ensuremath{\gamma}$ decays of $^{138}\mathrm{Xe}$ and $^{138}\mathrm{Cs}$ were investigated using the on-line isotope separator system TRISTAN at the Ames Laboratory research reactor. Ge(Li) $\ensuremath{\gamma}$-ray singles and Ge(Li)-Ge(Li) $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements were used to construct level schemes for $^{138}\mathrm{Cs}$ and $^{138}\mathrm{Ba}$. For the decay of $^{138}\mathrm{Xe}$, 94 of 99 observed $\ensuremath{\gamma}$-ray transitions have been placed in a level scheme for $^{138}\mathrm{Cs}$ with 27 excited states. For the decay of $^{138}\mathrm{Cs}$, 82 of 86 observed $\ensuremath{\gamma}$ rays are placed in a level scheme for $^{138}\mathrm{Ba}$ with 35 excited states. Ge(Li)-plastic coincidence measurements gave $Q$ values of 2.83 \ifmmode\pm\else\textpm\fi{} 0.08 MeV and 5.29 \ifmmode\pm\else\textpm\fi{} 0.07 MeV for $^{138}\mathrm{Xe}$ and $^{138}\mathrm{Cs}$, respectively. Spin and parity assignments have been deduced using $\ensuremath{\gamma}$-ray transition rates, $\ensuremath{\beta}$-decay $log\mathrm{ft}$ values, and other information existing in the literature. Interpretation of some of the energy levels is made from a shell-model viewpoint.