Decay ofTb146and the lowest2+state inGd146

Abstract

A recent in-beam study indicates that the first-excited state in the $N=82$ nucleus, $^{146}\mathrm{Gd}$, is ${3}^{\ensuremath{-}}$, rather than ${2}^{+}$ as systematics had indicated. A subsequent investigation, which utilized $^{144}\mathrm{Sm}(\ensuremath{\alpha}, 2n\ensuremath{\gamma})$ excitation function measurements, has provided evidence that the lowest ${2}^{+}$ state in $^{146}\mathrm{Gd}$ lies at 1971 keV, about 392 keV above the ${3}^{\ensuremath{-}}$ level. It seems therefore that, as in the case of $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, and $^{208}\mathrm{Pb}$ where the first-excited states are not ${2}^{+}$, $^{146}\mathrm{Gd}$ may have a doubly closed-shell structure. Previously, we investigated levels in $^{146}\mathrm{Gd}$ populated in the decay of 23-s $^{146}\mathrm{Tb}$. Data from these decay studies were reexamined, and a weak 1971.8-keV $\ensuremath{\gamma}$ ray was observed to follow the decay of $^{146}\mathrm{Tb}$. This transition most probably deexcites the ${2}^{+}$ $^{146}\mathrm{Gd}$ level seen in the $^{144}\mathrm{Sm}(\ensuremath{\alpha}, 2n\ensuremath{\gamma})$ reaction. In the light of the newly available information, a modified $^{146}\mathrm{Tb}$ decay scheme is presented and discussed.RADIOACTIVITY $^{146}\mathrm{Tb}$, measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$; $^{146}\mathrm{Gd}$, deduced levels, ${J}^{\ensuremath{\pi}}$.