COLLECTIVE DIPOLE EXCITATIONS IN NEUTRON-RICH NUCLEI FROM 132Sn MASS REGION, THE NUCLEAR SYMMETRY ENERGY AND NEUTRON SKINS.

Dipole strength distributions measured in unstable neutron-rich nuclei in the 132Sn mass region by utilizing relativistic Coulomb excitation of radioactive beams reveal a sizable fraction of "pygmy" strength below the giant dipole resonance. On the grounds of the RQRPA model, a strong linear correlation between the pygmy strength, parameters of the nuclear symmetry energy and the neutron skin thickness has been found. From the experimentally observed low-lying strength, the symmetry energy pressure p0 = 2.3 ± 0.8 MeV/fm³ and neutron skin thicknesses of 0.23 ± 0.04 fm in 130Sn and 0.24 ± 0.04 fm in 132Sn have been extracted. [ABSTRACT FROM AUTHOR]