New Collective Structures in Au179 and Their Implications for the Triaxial Deformation of the Pt178 Core

The extremely neutron-deficient isotope $^{179}\mathrm{Au}$ has been studied by a combination of in-beam $\ensuremath{\gamma}$-ray and isomeric-decay spectroscopy. For in-beam spectroscopy, the recoil-isomer tagging technique was employed, using the known 3/${2}^{\ensuremath{-}}, {T}_{1/2}=328$ ns isomer. A new rotational band, associated with the unfavored signature band of the $1{h}_{9/2}\ensuremath{\bigoplus}2{f}_{7/2}$ proton-intruder configuration, was revealed. A previously unknown, high-spin isomeric state with an excitation energy of 1743(17) keV and ${T}_{1/2}=2.16(8)\phantom{\rule{4pt}{0ex}}\mathrm{\textmu{}s}$ was discovered. Five decay paths were identified, some of them feeding previously unknown non-yrast excited states, associated with the $1{i}_{13/2}$ proton-intruder configuration. Calculations based on the particle-plus-triaxial-rotor model were performed to interpret the data. On the basis of these calculations, the new $1{h}_{9/2}\ensuremath{\bigoplus}2{f}_{7/2}$ rotational band is interpreted as due to triaxial deformation of the underlying configuration with ${\ensuremath{\beta}}_{2}\ensuremath{\approx}0.26$ and $\ensuremath{\gamma}\ensuremath{\approx}{27}^{\ensuremath{\circ}}$. Observed non-yrast states of the positive-parity $1{i}_{13/2}$ intruder configuration are interpreted as due to triaxial deformation with ${\ensuremath{\beta}}_{2}\ensuremath{\approx}0.26$ and $\ensuremath{\gamma}\ensuremath{\approx}{20}^{\ensuremath{\circ}}$.