Near-yrast, medium-spin structure of theTc109nucleus

Abstract

Excited levels in the $^{109}\mathrm{Tc}$ nucleus, populated in the spontaneous fission of $^{248}\mathrm{Cm}$, have been studied using the EUROGAM2 array. In $^{109}\mathrm{Tc}$ we have found a new band corresponding to the $\ensuremath{\pi}5$/${2}^{\ensuremath{-}}$[303] configuration and a three-quasiparticle band with ${I}^{\ensuremath{\pi}}=(15/{2}^{\ensuremath{-}})$ band-head level at 1749.5 keV. The structure of the 1749.5-keV level probably involves the ${\ensuremath{\pi}5/{2}^{+}[422]\ensuremath{\nu}(5/{2}^{\ensuremath{-}}[532],5/{2}^{+}[413])}{}_{{15/2}^{\ensuremath{-}}}$ prolate configuration. The quasiparticle-rotor model calculations performed in this work show that the odd-proton configurations observed in $^{107}\mathrm{Tc}$ and $^{109}\mathrm{Tc}$ are consistent with the scheme of proton excitations in a prolate triaxial potential. Significant differences between the degree of triaxiality observed for positive- and negative-parity excitations may be due to blocking of the triaxial shape by the odd proton populating negative-parity orbitals. The properties of the new $494.5\ensuremath{-}$, $1440.7\ensuremath{-}$, and $1748.8$-keV levels found in $^{109}\mathrm{Tc}$ may indicate a change toward an oblate shape in this nucleus.