The ${}^{124}\mathrm{Sn}({}^{37}\mathrm{Cl},6\mathrm{n}\gamma )$ fusion-evaporation reaction at a bombarding energy of 180 MeV has been used to significantly extend the excitation level scheme of ${}_{67}^{155}{\mathrm{Ho}}_{88}$. The collective rotational behavior of this nucleus breaks down above spin $I\sim 30$ and a fully aligned noncollective (band terminating) state has been identified at $I^{\pi }=79/2^{-}$. Comparison with cranked Nilsson–Strutinsky calculations also provides evidence for core-excited noncollective states at $I^{\pi }=87/2^{-}$ and $(89/2^{+})$ involving particle-hole excitations across the $Z=64$ shell gap. A similar core-excited state in ${}_{68}^{156}{\mathrm{Er}}_{88}$ at $I^{\pi }=\left({46}^{+}\right)$ is also presented.

• Received 5 March 2015

DOI:https://doi.org/10.1103/PhysRevC.91.054301