Spherical proton-neutron structure of isomeric states in Cd128

The γ-ray decay of isomeric states in the even-even nucleus Cd128 has been observed. The nucleus of interest was produced both by the fragmentation of Xe136 and the fission of U238 primary beams. The level scheme was unambiguously constructed based on γγ coincidence relations in conjunction with detailed lifetime analysis employed for the first time on this nucleus. Large-scale shell-model calculations, without consideration of excitations across the N=82 shell closure, were performed and provide a consistent description of the experimental level scheme. The structure of the isomeric states and their decays exhibit coexistence of proton, neutron, and strongly mixed configurations due to πν interaction in overlapping orbitals for both proton and neutron holes.