The neutron-proton interaction energy of the valence nucleons

Summary

For a great number of nuclei, it is now possible to calculate the value of the neutron-proton interaction energy of the valence nucleons using experimental mass data. The total n-p interaction energyE _np of the valence shells of,e.g., an odd-odd nucleus can be calculated from partial interaction energies {su\fk}{inn-p}, {su\fk}{inn-2p}{ini}, {su\fk}{inp-2n}{inj},{su\fk}{in2p}{ini}-{in2n}{inJ} which are the interaction energy of the last couple of nucleons or nucleon pairs in this nucleus and in its various underlying nuclei. {su\fk}{inn-p}, defined asE _np divided byN _p N _n, the product of the valence proton and neutron numbers, is only a mean value of the n-p interaction energy per n-p couple in a given nucleus. Tables ofE _np and {su\fk}{inn-p} values, and of,{su\fk}{inn-p} , {su\fk}{inn-2p} , {su\fk}{inp-2n} and {su\fk}{in2p-2n} values, are given for the 1d_5/2, 2s _1/2 and 1d _3/2 valence shells of the doubly magic¹⁶O nucleus. Nucleon pairing is found to play an eminent role. The n-p interaction energy is almost unchanged if every neutron is converted into a proton and vice versa, and is extremely dependent on the rank of the nucleons in their shell, being maximum if they have the same rank. The n-p interaction energy is strongly enhanced at each subshell closure.