  Pseudo-spin symmetry in nuclei is investigated considering the Dirac equation
with a Lorentz structured Woods-Saxon potential. The isospin correlation of the
energy splittings of pseudo-spin partners with the nuclear potential parameters
is studied. We show that in an isotopic chain, the pseudo-spin symmetry is
better realized for neutrons than for protons. This behavior comes from balance
effects amongst the central nuclear potential parameters. In general, we found
an isospin asymmetry of the nuclear pseudo-spin interaction, opposed to the
nuclear spin-orbit interaction which is quasi isospin symmetric.

Nuclear Theory