| Summary: | We employ a transport model based on Landau-Vlasov equation to explore the dipolar response of neutron rich systems and its dependence on the symmetry energy. We present evidences for collective features of the Pygmy Dipole Resonance (PDR) and study its dependence with the mass number. We extract a parametrization for the energy centroid position, 41A−1/3, which agrees quite well with the data for Ni, Zr, Sn and Pb. A linear correlation between the Energy Weighted Sum Rule (EWSR) associated to PDR and the neutron skin thickness is evidenced. An increase of 15 MeV fm2 of EWSR to a change of 0.1 fm of neutron skin size is obtained. We conclude that different nuclei having close neutron skin size will exhaust the same EWSR in the pygmy region. Consequently a precise experimental estimate of total EWSR exhausted by PDR allows the determination of the neutron skin size and to constrain the slope parameter of the symmetry energy.
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