Dipole excitations in Tin isotopes within finite range approximation of Skyrme-type interaction

We have calculated the properties of Pygmy resonance for the Tin chain 112Sn-134Sn. The structure of the excited states was calculated using 'quasiparticle random phase approximation'. A Skyrme-type interaction has been used as residual particle-hole interaction. It was shown that the model gives good results for the nuclei radii and GDR energies for nuclei in the Tin region. The low-lying part of dipole excitations reveals the existence of group of slightly collective states and the corresponding E1 transition strength increases with the enlargement of neutron excess. These group of states forms Pygmy resonance. (authors)