  Oscillations of mainly surface character (S=0 modes) give rise, in atomic
nuclei, to an attractive (induced) pairing interaction, while spin (S=1) modes
of mainly volume character generate a repulsive interaction, the net effect
being an attraction which accounts for a sizeable fraction of the experimental
pairing gap. Suppressing the particle-vibration coupling mediated by the proton
degrees of freedom, i.e., mimicking neutron matter, the total surface plus
spin-induced pairing interaction becomes repulsive.
