Residual proton-neutron interactions and the NpNn scheme

We investigate the correlation between integrated proton-neutron interactions obtained by using the up-to-date experimental data of binding energies and the product NpNn of valence proton number and valence neutron number with respect to the nearest doubly closed nucleus. We make corrections on a previously suggested formula for the integrated proton-neutron interaction. Our results demonstrate a nice, nearly linear, correlation between the integrated p-n interaction and NpNn, which provides us with a firm foundation of the applicability of the NpNn scheme to nuclei far from the stability line.