Excited states in the neutron-deficient $N=84$ nuclide ${}^{155}\mathrm{Lu}$ have been populated by using the ${}^{102}\mathrm{Pd}({}^{58}\mathrm{Ni},\alpha \mathrm{p})$ reaction. The ${}^{155}\mathrm{Lu}$ nuclei were separated by using the gas-filled recoil ion transport unit (RITU) separator and implanted into the Si detectors of the gamma recoil electron alpha tagging (GREAT) spectrometer. Prompt $\gamma$-ray emissions measured at the target position using the JUROGAM Ge detector array were assigned to ${}^{155}\mathrm{Lu}$ through correlations with $\alpha$ decays measured in GREAT. Structures feeding the $(11/2^{-})$ and $(25/2^{-})\alpha$-decaying states have been revised and extended. Shell-model calculations have been performed and are found to reproduce the excitation energies of several of the low-lying states observed to within an average of 71 keV. In particular, the seniority inversion of the $25/2^{-}$ and $27/2^{-}$ states is reproduced.

• Received 17 August 2016

DOI:https://doi.org/10.1103/PhysRevC.94.064311