ON THE NATURE OF THE PYGMY DIPOLE RESONANCE IN 124SN VIA INELASTIC SCATTERING OF 17O

Giant resonances are fundamental modes of excitations at high frequency, corresponding to shape oscillations around the equilibrium of the nuclear system. Their study over the years has provided useful information on nuclear structure and on the effective nucleon–nucleon interaction. In particular, the understanding of the electric-dipole response around the binding energy is presently attracting considerable interest, since the dipole strength distribution in that region affects the reaction rates in astrophysical scenarios. Moreover, it provides information on the neutron skin and thus on the symmetry energy of the equation of state. This concentration of electric dipole strength around the particle threshold is commonly denoted as Pygmy Dipole Resonance (PDR) and it is caused by the oscillation of the neutron skin against the inert proton-neutron core. From the experimental point of view, by comparing results of photon-scattering and a scattering experiments, a clear selectivity in the population of these “pygmy” states has been observed. These findings have called for additional high resolution investigation, by studying the γ-decay with advanced Ge array (such as AGATA), making use of different probes to excite the resonance states, as heavy ions. For this reason, an experiment aimed at the study of the γ-decay from high-lying bound and unbound states in several nuclei (124Sn, 208Pb and 140Ce) has been performed at Legnaro National Laboratories (LNL - INFN). The giant resonance modes have been excited by inelastic scattering of 17O beam at 20 MeV/u. The analysis described in this thesis has been focused on the studies of the Pygmy Dipole Resonance in the 124Sn nucleus.