Isotopic dependence of charge radii and pairing energies

In this paper an effective three-body force provides a coupling of the pairing properties (of the neutrons) to the single particle potential (of the protons) (and vice versa), which is shown to be the essential effect causing the structure observed in the dependence of nuclear charge radii on neutron number. Similarly, paring energies show trends which can easily be explained if such a force is assumed