Empirical proton-neutron interaction energies. Linearity and saturation phenomena

A method to extract empirical proton-neutron interaction energies for individual protons and neutrons as well as integrated valence p-n interaction strenghts is discussed. The results give direct experimental support to the N_pN_n scheme, verifying the linearity of the p-n interaction against N_pN_n early in a shell and its subsequent saturation. They also reflect the behavior i of recently calculated quadrupole p-n strengths which account for the empirical saturation in B(E2: 0 ₁⁺ → 2 ₁⁺) values, and point to the importance of the monopole p-n interaction as well.