Shell-Model Spin-Orbit Force Radius Anomaly

It has recently been shown that the spin-orbit part of the optical-model potential, taken to be a surface-gradient force, is displaced about $0.1{A}^{\frac{1}{3}}$ F inside the central well. For the shell-model potential this feature arises very naturally from the Brueckner many-body theory, the spin-orbit force being strongly density-dependent while the central force saturates at nuclear densities.