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

Abstract

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. γ -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 γ γ -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 111Xe 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.