Delayed or absent π(h11/2)2 alignment in Xe 111

Excited states have been identified in the very neutron-deficient N=Z+3 nucleus Xe111 for the first time, using the Ni58(Ni58,αn) heavy-ion fusion-evaporation reaction. γ-ray transitions have been unambiguously assigned to Xe111 by correlation with the characteristic Xe111→Te107→Sn103 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 h11/2 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 Xe111 band are constant over the range of observed rotational frequencies, suggesting that the first π(h11/2)2 alignment is either delayed or absent. It is speculated that the alignment of h11/2 protons in the presence of neutrons in near-identical h11/2 orbitals may be affected by neutron-proton interactions or by the onset of octupole correlations.