Conversion-Coefficient Measurements and Spin-Parity Assignments for Excited Levels inXe133,135,136,Cs135,137,139, andBa138

Abstract

Solid-state detectors have been used to perform on-line measurements of $\ensuremath{\gamma}$-ray and conversion-electron intensities in $^{133,\phantom{\rule{0ex}{0ex}}135,\phantom{\rule{0ex}{0ex}}136}\mathrm{Xe}$, $^{135,\phantom{\rule{0ex}{0ex}}137,\phantom{\rule{0ex}{0ex}}139}\mathrm{Cs}$, and $^{138}\mathrm{Ba}$. Conversion coefficients were determined for 37 transitions. $\mathrm{Log}\mathrm{ft}$ values were calculated on the basis of reported level schemes. The deduced multipolarities and $log\mathrm{ft}$ values were combined with published reaction and angular-correlation results to assign spins and parities to 24 excited levels of the mentioned nuclei. The obtained $J\ensuremath{\pi}$ contributed 13 new experimentally-well-defined $\ensuremath{\beta}$-transition probabilities to the systematics of this magnitude. In $^{136}\mathrm{Xe}$ and $^{138}\mathrm{Ba}$, three levels with known half-lives were determined to be depopulated by pure-$E2$ transitions; the retardation factors as compared to the Weisskopf estimate were calculated. Apart from $J\ensuremath{\pi}$ assignments, some additional minor contributions were made to the knowledge of the level structure in $^{138}\mathrm{Ba}$ and $^{139}\mathrm{Cs}$. The number of possible spins and parities for some of the excited levels in the nuclei studied was reduced by analyzing the systematic trends of measured $J\ensuremath{\pi}$ values in their neighborhood. No modelistic considerations were taken into account for this purpose.