Vibrational levels in the 86-neutron nucleusGd150

Abstract

The decay of 3.6-h $^{150}\mathrm{Tb}$ to levels in $^{150}\mathrm{Gd}$ has been studied by $\ensuremath{\gamma}$-ray and conversion-electron spectroscopy. A level scheme is proposed which accounts for all but 35 of the 256 $\ensuremath{\gamma}$ rays assigned to this decay. Most of the low-lying levels in $^{150}\mathrm{Gd}$ show a remarkably close correspondence with the predictions of the simple vibrator model. Possible candidates are observed for three-phonon quadrupole states and for the states coupling quadrupole and octupole phonons. The low-lying positive-parity levels can be adequately described by the phenomenological collective model of Gneuss and Greiner. The microscopic boson-expansion model of Kishimoto and Tamura, however, appears to predict $^{150}\mathrm{Gd}$ to be more transitional than the data imply. Systematics of the 86-neutron isotones show increased stability at 64 protons. This can be correlated with the filling of the ${g}_{\frac{7}{2}}$ and ${d}_{\frac{5}{2}}$ spherical proton orbitals.RADIOACTIVITY $^{150}\mathrm{Tb}$ [from $^{151}\mathrm{Eu}(^{3}\mathrm{He},4n)$], measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${E}_{\ensuremath{\beta}+}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{\mathrm{ce}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$, and ${\ensuremath{\beta}}^{+}\ensuremath{-}\ensuremath{\gamma}$ coin; deduced $Q$, $log\mathrm{ft}$. $^{150}\mathrm{Gd}$ deduced levels, ICC, $J$, $\ensuremath{\pi}$. Enriched target, Ge(Li), and Si(Li) detectors.