Systematic trends of neutron skin thickness versus relative neutron excess

Available experimental neutron skin thicknesses of even-even stable Ca, Ni, Sn, Pb, and Cd isotopes are evaluated, and separate trends of neutron skin thickness versus relative neutron excess $\ensuremath{\delta}=(N\ensuremath{-}Z)/A$ are observed for different isotopic chains. This phenomenon is quantitatively reproduced by the deformed Skyrme Hartree-Fock $+$ Bardeen-Cooper-Schrieffer model with SLy4 force.