The relativistic spin-orbit force near the neutron-drip line

The relativistic spin-orbit force and its dependence on neutron excess are studied using the σ-ω-ϱ model. By working within the schematic model of asymmetric semi-infinite nuclear matter we are able to isolate the spin-orbit potential and to investigate the following aspects: (i) the influence of the spin-orbit force on nuclear surface properties as a function of neutron excess, (ii) the local variation of the spin-orbit strength at various asymmetries, and (iii) the dependence of the spin-orbit force on the nucleonic isospin. Calculations have been performed for the currently used parameter sets NL1 and NL-SH up to the corresponding neutron-drip line. We conclude that with increasing neutron excess the spin-orbit strength drastically decreases while its impact on nuclear surface properties depends only slightly on asymmetry. The isospin dependence of the relativistic spin-orbit force is negligible.