Binding Energies and Two-Particle Spectra

The average interaction of particles in a closed shell is consistent with the spectrum of the nucleus with two particles in the shell only if the correlations which are present in the two-particle case but not in the closed-shell case are considered. Realistic forces which induce large correlations give a sizable effect which is observable in the $d_{\frac{5}{2}}$, $d_{\frac{3}{2}}$, and $f_{\frac{7}{2}}$ shells. This may be interpreted as a repulsive effective three-body force.