Surface-enhanced pair transfer in quadrupole states of neutron-rich Sn isotopes

Abstract

We investigate the neutron pair transfer modes associated with the low-lying quadrupole states in neutron-rich Sn isotopes by means of the quasiparticle random phase approximation based on the Skyrme-Hartree-Fock-Bogoliubov mean field model. The transition strength of the quadrupole pair-addition mode feeding the $2_1^+$ state is enhanced in the Sn isotopes with $A \geq 132$. The transition density of the pair-addition mode has a large spatial extension in the exterior of nucleus, reaching far to $r\sim 12-13$ fm. The quadrupole pair-addition mode reflects sensitively a possible increase of the effective pairing interaction strength in the surface and exterior regions of neutron-rich nuclei.Comment: 14 page