Delayed or absent π(h_11/2)² alignment in ¹¹¹Xe

Excited states have been identified in the very neutron-deficient N = Z + 3 nucleus ¹¹¹Xe for the first time, using the ⁵⁸Ni(⁵⁸Ni,αn) heavy-ion fusion-evaporation reaction. Gamma-ray transitions have been unambiguously assigned to ¹¹¹Xe by correlation with the characteristic ¹¹¹Xe→¹⁰⁷Te→¹⁰³Sn α-decay chain using the method of recoil-decay tagging. Inspection of  γγ coincidence data has shown that five of the transitions form a rotational-like sequence. Excitation-energy systematics suggest that the sequence could be the favored signature partner of a band built on an h_11/2 neutron. Aligned angular momenta of states in the band have been compared to analogous bands in neighboring xenon isotopes. The aligned angular momenta for the ¹¹¹Xe band are constant over the range of observed rotational frequencies, suggesting that the first π(h_11/2)² alignment is either delayed or absent. It is speculated that the alignment of h_11/2 protons in the presence of neutrons in near-identical h_11/2 orbitals may be affected by neutron-proton interactions, or by the onset of octupole correlations.