Charge Radius Isotope Shift Across the N=126 Shell Gap

We revisit the problem of the kink in the charge radius shift of neutron-rich even isotopes near the N = 126 shell closure. We show that the ability of a Skyrme force to reproduce the isotope shift is determined by the occupation of the neutron 1i(11/2) orbital beyond N = 126 and the corresponding change it causes to deeply-bound protons orbitals with a principal quantum number of 1. Given the observed position of the single- particle energies, one must either ensure occupation is allowed through correlations, or not demand that the single- particle energies agree with experimental values at the mean- field level. DOI: 10.1103/PhysRevLett.110.032503