Competition between high-Kstates and rotational structures in177Ta

Abstract

High-spin states in ${}^{177}\mathrm{Ta}$ have been studied using the ${}^{170}\mathrm{Er}{(}^{11}\mathrm{B},4n)$ reaction. New intrinsic states have been observed corresponding to 3-, 5-, and 7-quasiparticle high-$K$ structures. Rotational bands built on most of the 3- and 5-quasiparticle states and some transitions above the 7-quasiparticle states have been identified. Several isomers have been found, the longest lived being the ${\frac{49}{2}}^{\ensuremath{-}},$ 7-quasiparticle state with a meanlife of 192 $\ensuremath{\mu}\mathrm{s}.$ Configurations for the observed intrinsic states have been assigned on the basis of ${g}_{K}$ values, alignments, and decay properties. While the properties of most of the bands are consistent with their proposed configurations, the behavior of some, including the one built on ${K}^{\ensuremath{\pi}}={\frac{21}{2}}^{\ensuremath{-}}$ 3-quasiparticle isomer, is not well understood. Multiquasiparticle blocking calculations based on the Lipkin-Nogami method, are in good agreement with the excitation energies of the experimentally observed states and all the predicted states close to the yrast line up to spin $\frac{49}{2}$ have been observed experimentally. The calculations predict the existence of a 9-quasiparticle ${\frac{67}{2}}^{\ensuremath{-}}$ yrast trap at $\ensuremath{\sim}8.5 \mathrm{MeV}.$