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.

PACS numbers: 24.30.Cz, 25.60.–t, 25.70.De, 27.90.+j