Spectroscopy of neutron-rich Te and Xe isotopes within a new shell model context

Abstract

Te and Xe isotopes above the $N=82$ shell closure are investigated within a large-scale shell model approach based on an iterative matrix diagonalization algorithm. The spectra and transition strengths, computed using a realistic Hamiltonian, are in overall agreement with the available experimental data. The calculation predicts an increasing neutron weight in the lowest collective ${2}_{1}^{+}$ state of the isotopes as they depart from the doubly magic ${}^{132}$Sn and move toward the neutron drip line. Such a neutron dominance is predicted to cause a breaking of the neutron-proton exchange symmetry and a dramatic drop of the strengths of the $E2$ and $M1$ transitions among the excited ${2}^{+}$ states. This drop establishes a strong asymmetry between Te and Xe isotopes above and below the $N=82$ shell closure.