Proton-skins in momentum space and neutron-skins in coordinate space in   heavy nuclei
  Neutron-skins in coordinate space and proton-skins in momentum space are predicted to coexist in heavy nuclei and their correlation is governed by Liouville's theorem and Heisenberg's uncertainty principle. An analysis of their correlation within a further extended Thomas-Fermi (ETF$^+$) approximation incorporating effects of nucleon short-range correlations reveals generally that protons move faster than neutrons in neutron-skins of heavy nuclei. 
Bao-Jun Cai, Bao-An Li and Lie-Wen Chen
nucl-th astro-ph.SR nucl-ex