Dipole states in stable and unstable nuclei

A nuclear structure model based on linear response theory (i.e., random phase approximation) and which includes pairing correlations and anharmonicities (coupling with collective vibrations), has been implemented in such a way that it can be applied on the same footing to magic as well as open-shell nuclei. As applications, we have chosen to study the dipole excitations both in well known, stable isotopes like 208Pb and 120Sn as well as in the neutron-rich, unstable 132Sn nucleus, by addressing in the latter case the question about the nature of the low-lying strength. Our results suggest that the model is reliable and predicts in all cases low-lying strength of non collective nature.