  We present an analysis of two-proton shell gaps in Sn isotopes. As the
theoretical tool we use self-consistent mean-field models, namely the
relativistic mean-field model and the Skyrme-Hartree-Fock approach, both with
two different pairing forces, a delta interaction (DI) model and a
density-dependent delta interaction (DDDI). We investigate the influence of
nuclear deformation as well as collective correlations and find that both
effects contribute significantly. Moreover, we find a further significant
dependence on the pairing force used. The inclusion of deformation plus
correlation effects and the use of DDDI pairing provides agreement with the
data.
