Pairing and isospin symmetry in proton-rich nuclei

Unlike their lighter counterparts, most odd-odd N = Z nuclei with mass A > 40 have ground states with isospin T = 1, suggesting an increased role for the isovector pairing interaction. A simple SO(5) seniority-like model of this interaction reveals a striking and heretofore unnoticed interplay between like-particle and neutron-proton isovector pairing near N = Z that is reflected in the number of each kind of pair as a function of A and T. Large scale shell-model calculations exhibit the same trends, despite the simultaneous presence of isoscalar pairs, deformation, and other correlations.