High-spin states of the N=82 isotones Xe136, Cs137 , and Ba138 : Monopole-driven competition of neutron core excitations with two-proton excitations to the h11/2 high- j orbit

Abstract

It is known that the monopole effect in shell-model calculations can influence single-particle states dynamically, resulting in novel shell evolution near the ground state. We show that a monopole-driven competition between different excitation modes can occur in the high-lying, high-spin states in nuclei above $^{132}\mathrm{Sn}$. Stimulated by the recent high-spin data, we extend large-scale shell-model calculations with the effective interaction determined in our previous work [Phys. Rev. C 84, 044324 (2011)] to study the heavier $N=82$ isotones $^{136}\mathrm{Xe}, ^{137}\mathrm{Cs}$, and $^{138}\mathrm{Ba}$. With inclusion of configurations for neutron core excitation across the $N=82$ shell gap, we treat simultaneously two kinds of excitation modes for the high-spin states, namely, those from multiproton coupling within the valence-proton space and from neutron core excitation to the upper orbits above the $N=82$ shell gap. Based on a good reproduction of the experimental data, we discuss the competition mechanism by analyzing the monopole effect in the effective single-particle energies.