Effects of the Neutron Spin-Orbit Density on Nuclear Charge Density in   Relativistic Models
  The neutron spin-orbit density contributes to the nuclear charge density as a relativistic effect. The contribution is enhanced by the effective mass stemming from the Lorentz-scalar potential in relativistic models. This enhancement explains well the difference between the cross sections of elastic electron scattering off $^{40}$Ca and $^{48}$Ca which was not reproduced in non-relativistic models. The spin-orbit density will be examined in more detail in electron scattering off unstable nuclei which would be available in the future. 
Haruki Kurasawa (Chiba U.) and Toshio Suzuki (Fukui U.)