Variation in Displacement Energies Due to Isospin-Nonconserving Forces

For mirror nuclei with masses $A=42–95$, the effects of isospin-nonconserving nuclear forces are studied with the nuclear shell model using the Coulomb displacement energy and triplet displacement energy as probes. It is shown that the characteristic behavior of the displacement energies can be well reproduced if the isovector and isotensor nuclear interactions with $J=0$ and $T=1$ are introduced into the $f_{7/2}$ shell. These forces, with their strengths being found consistent with the nucleon-nucleon scattering data, tend to modify nuclear binding energies near the $N=Z$ line. At present, no evidence is found that these forces are needed for the upper $fp$ shell. Theoretical one- and two-proton separation energies are predicted accordingly, and locations of the proton drip line are thereby suggested.