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

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 132Sn 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