  Unlike their lighter counterparts, most odd-odd N=Z nuclei with mass A > 40
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.
