First identification of20+isomeric states in the odd-odd190,192Aunuclei

Excited isomeric states ${I}^{\ensuremath{\pi}}{=20}^{+}$ have been identified for the first time in odd-odd ${}^{190,192}\mathrm{Au}$ nuclei. Two independent measurements of their half-lives were performed, using the recoil shadow anisotropy method with the Eurogam-II data, and using the time distribution of K-electron lines from the Orsay electron-spectrometer data. Half-lives of $7.0\ifmmode\pm\else\textpm\fi{}0.3$ and $5.4\ifmmode\pm\else\textpm\fi{}0.3$ ns were obtained for these isomers in ${}^{190}\mathrm{Au}$ and ${}^{192}\mathrm{Au},$ respectively, by the latter measurements. The $\ensuremath{\pi}{h}_{11/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}2}{h}_{9/2}^{\ensuremath{-}1}$ configuration was assigned to these isomeric states. A shape transition towards highly triaxial deformation with $\ensuremath{\gamma}\ensuremath{\sim}\ensuremath{-}90\ifmmode^\circ\else\textdegree\fi{}$ is suggested by total Routhian surface calculations, which could be the cause for their relatively hindered decay.