High-spin structure in the transitional nucleus 131Xe: Competitive neutron and proton alignment in the vicinity of the N=82 shell closure

Abstract

The transitional nucleus 131Xe is investigated after multinucleon transfer in the 136Xe + 208Pb and 136Xe + 238U reactions employing the high-resolution Advanced γ -Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and as an elusive reaction product in the fusion-evaporation reaction 124Sn(11B,p3n) 131Xe employing the High-efficiency Observatory for γ -Ray Unique Spectroscopy (HORUS) γ -ray array coupled to a double-sided silicon strip detector at the University of Cologne, Germany. The level scheme of 131Xe is extended to 5 MeV. A pronounced backbending is observed at hω¯ ≈ 0.4 MeV along the negative-parity one-quasiparticle νh11/2(α = −1/2) band. The results are compared to the high-spin systematics of the Z = 54 isotopes and the N = 77 isotones. Large-scale shell-model calculations employing the PQM130, SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in 129−132Xe provide insight into the changing nuclear structure along the Xe chain towards the N = 82 shell closure. Proton occupancy in the π 0h11/2 orbital is found to be decisive for the description of the observed backbending phenomenon.