Level structure above the 17⁺ isomeric state in ¹⁵²₆₉Tm₈₃

Excited states above the 17⁺ isomeric state in the proton-rich nucleus ¹⁵²Tm were established by employing the recoil-isomer tagging technique. Data were collected using the JUROGAM gamma-ray array and the GREAT spectrometer together with the recoil ion transport unit (RITU) gas-filled recoil separator and analyzed to identify the prompt and delayed γ decays from the levels in ¹⁵²Tm. Shell-model calculations, either in a large valence space or in a reduced model space with five protons in the π0h_11/2 orbital and one neutron in the ν1f_7/2 orbital, agree with the observed energies of the yrast levels up to angular momentum J = 21. The observation of near degeneracies in the energy spectrum can be attributed to specific components of the proton-neutron interaction. The isomeric decay of the 17⁺ level is not reproduced in the shell-model calculations as it arises from a delicate balance between hindrance due to seniority selection rules and enhancement due to configuration mixing.