  Pairing interactions with various density dependencies (surface/volume
mixing) are constrained with the two-neutron separation energy in the Tin
isotopic chain. The response associated with pairing vibrations in very
neutron-rich nuclei is sensitive to the density dependence of the pairing
interaction. Using the same pairing interaction in nuclear matter and in Tin
nuclei, the range of densities where the LDA is valid in the pairing channel is
also studied.
