Decays of mass-separatedXe139andCs139

Abstract

The $\ensuremath{\beta}$ and subsequent $\ensuremath{\gamma}$ decays of $^{139}\mathrm{Xe}$ and $^{139}\mathrm{Cs}$ have been studied using an on-line isotope separator system. 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 $^{139}\mathrm{Cs}$ and $^{139}\mathrm{Ba}$. For the decay of $^{139}\mathrm{Xe}$, 213 of 230 observed $\ensuremath{\gamma}$-ray transitions have been placed in a level scheme for $^{139}\mathrm{Cs}$ with 55 excited states. For the decay of $^{139}\mathrm{Cs}$, 167 of 179 observed $\ensuremath{\gamma}$-ray transitions are placed in a level scheme for $^{139}\mathrm{Ba}$ with 59 excited states. The $Q$ values for the $\ensuremath{\beta}$ decays of $^{139}\mathrm{Xe}$ and $^{139}\mathrm{Cs}$ were determined from Ge(Li) plastic scintillator coincidence measurements as 5.02\ifmmode\pm\else\textpm\fi{}0.06 and 4.29\ifmmode\pm\else\textpm\fi{}0.07 MeV, respectively. Ground-state $\ensuremath{\beta}$ branches were deduced for the $^{139}\mathrm{Xe}$ and $^{139}\mathrm{Cs}$ decays using relative $\ensuremath{\gamma}$-ray intensities. Spin and parity assignments for levels in $^{139}\mathrm{Cs}$ and $^{139}\mathrm{Ba}$ have been deduced using $\ensuremath{\beta}$-decay $log\mathrm{ft}$ values, $\ensuremath{\gamma}$-ray transition rates, and reaction data in the literature. Interpretation of some of the energy levels is made from a shell-model viewpoint.RADIOACTIVITY $^{139}\mathrm{Xe}$, $^{139}\mathrm{Cs}$ [from $^{235}\mathrm{U}(n,f)$]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin., ${Q}_{\ensuremath{\beta}}$, Ge(Li), and plastic scint. detectors. $^{139}\mathrm{Cs}$, $^{139}\mathrm{Ba}$ deduced levels, $J$, $\ensuremath{\pi}$, $log\mathrm{ft}$. $^{139}\mathrm{Xe}$, $^{139}\mathrm{Cs}$ deduced ground-state $\ensuremath{\beta}$ branches. Mass-separated $^{139}\mathrm{Xe}$ activity.