High-spin terminating states in the N =88 155Ho and 156Er isotones

The ¹²⁴Sn(³⁷Cl ,6 n γ ) fusion-evaporation reaction at a bombarding energy of 180 MeV has been used to significantly extend the excitation level scheme of ₆₇¹⁵⁵Ho₈₈ . The collective rotational behavior of this nucleus breaks down above spin I ∼30 and a fully aligned noncollective (band terminating) state has been identified at I^π=79 /2^- . Comparison with cranked Nilsson-Strutinsky calculations also provides evidence for core-excited noncollective states at I^π=87 /2^- and (89 /2⁺) involving particle-hole excitations across the Z =64 shell gap. A similar core-excited state in ₆₈¹⁵⁶Er₈₈ at I^π=(46⁺) is also presented.