Nuclear structure ofLu178

The $^{179}\mathrm{Hf}$(t,\ensuremath{\alpha}${)}^{178}$Lu reaction has been studied using beams of 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. Reaction products were analyzed with a magnetic spectrograph, and the resolution achieved for the alpha spectra was \ensuremath{\sim}20 keV (FWHM). Two-quasiparticle states in $^{178}\mathrm{Lu}$ involving the 9/${2}^{+}$[624] target neutron coupled with the 7/${2}^{+}$[404], 9/${2}^{\mathrm{\ensuremath{-}}}$[514], and 1/${2}^{+}$[411] proton orbitals were identified. The difference in ground-state (t,\ensuremath{\alpha}) Q values for $^{178}\mathrm{Hf}$ and $^{179}\mathrm{Hf}$ components of the target, combined with the known masses of $^{177}\mathrm{Lu}$, $^{178}\mathrm{Hf}$, and $^{179}\mathrm{Hf}$, yields an improved value of -50 351\ifmmode\pm\else\textpm\fi{}5 keV for the mass excess of $^{178}\mathrm{Lu}$. This result, combined with the two-quasiparticle assignments from the present work, has resolved the long-standing puzzle concerning the character and excitation energy of the well-known 23 min high-spin beta-decaying isomer in $^{178}\mathrm{Lu}$.