Electromagnetic properties of neutron-rich nuclei adjacent to the Z=50 shell closure

Low-lying high-spin yrast states in the exotic odd–odd isotopes 124–128Sb (Z=51) and 118–128In (Z=49), studied for the first time, show a striking difference in their observed γ-ray decay. With a single valence proton particle/hole occupying the g7/2/g9/2 spin-orbit partners, dominant electric quadrupole transitions occur in Sb as opposed to magnetic dipole transitions in In. The observed properties are explained on the basis of general principles of symmetry and with large-scale shell-model calculations, and reveal novel aspects of the competition between the neutron–proton interaction and the like-nucleon pairing interaction.