Decay Scheme ofTb158

Abstract

A study has been made of the decay of $^{158}\mathrm{Tb}$, including measurements of transition intensities, lifetimes of excited states, and angular correlations. The resulting decay scheme is generally in agreement with that proposed in previous studies. Major modifications include a new level at 819 keV in $^{158}\mathrm{Dy}$, and several new $\ensuremath{\gamma}$-ray transitions which were seen in coincidence studies and which may be due to a long-lived isomeric state in $^{158}\mathrm{Tb}$. Also, improvement was attained in the precision of the intensities of several weak $\ensuremath{\gamma}$-ray transitions, and of the $\ensuremath{\beta}$-branching ratio. The lifetimes of the first ${2}^{+}$ states in $^{158}\mathrm{Gd}$ and $^{158}\mathrm{Dy}$ were redetermined for several different cascades through $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ as well as $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence-delay studies; the values measured were, respectively, 2.59\ifmmode\pm\else\textpm\fi{}0.10 and 1.76\ifmmode\pm\else\textpm\fi{}0.10 nsec. The 1188-keV state and the 1107-keV $\ensuremath{\gamma}$-ray transition in the decay to $^{158}\mathrm{Gd}$ were confirmed to be, respectively, a ${2}^{+}$ state and an $E2$ transition through an angular-correlation measurement. These modifications and improvements in the decay scheme are discussed on the basis of the rotational model of deformed nuclei.