Evidence for a high-spinβ-decaying isomer inLu177

Nuclei in the $A\ensuremath{\sim}180$ region have been populated and investigated in a series of multinucleon transfer and deep-inelastic reactions involving an $11.4\phantom{\rule{0.3em}{0ex}}\text{MeV}$ per nucleon $^{136}\mathrm{Xe}$ beam produced by the GSI UNILAC accelerator, impinging on a selection of tantalum and tungsten targets. The reaction products were released from a thermal ion source and subsequently mass selected using the GSI on-line mass separator. The unexpectedly high yield of $\ensuremath{\gamma}$ rays associated with the decay of the well established ${K}^{\ensuremath{\pi}}=37∕{2}^{\ensuremath{-}}$,${t}_{1∕2}=51.4\phantom{\rule{0.3em}{0ex}}\mathrm{min}$ isomer in $_{\phantom{\rule{0.3em}{0ex}}72}^{177}\mathrm{Hf}$ and anomalous half-life characteristics associated with this decay lead to these data being interpreted as the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of a high-$K$ isomer in the mother nucleus, $^{177}\mathrm{Lu}$. By comparing the experimental findings with the predictions obtained from multi-quasiparticle blocked-BCS-Nilsson calculations, the proposed decay is suggested to be from a ${K}^{\ensuremath{\pi}}=39∕{2}^{\ensuremath{-}}$ five-quasiparticle state in $_{\phantom{\rule{0.3em}{0ex}}71}^{177}\mathrm{Lu}$. A half-life of $7\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.3em}{0ex}}\mathrm{min}$ is determined for this $\ensuremath{\beta}$-decay path which is estimated to have an excitation energy of $\ensuremath{\approx}3.9\phantom{\rule{0.3em}{0ex}}\text{MeV}$ above the $^{177}\mathrm{Lu}$ ground state.