Structure of the pygmy dipole resonance in 124Sn

In atomic nuclei, a concentration of electric dipole strength around the particle threshold, commonly denoted as pygmy dipole resonance, may have a significant impact on nuclear structure properties and astrophysical scenarios. A clear identification of these states and the structure of this resonance is still under discussion. Experimental and theoretical study of the isospin character of the pygmy dipole resonance and investigation of a splitting of the electric dipole strength previously observed in experiments on N=82 nuclei. The pygmy dipole resonance has been studied in the semi-magic Z=50 nucleus 124Sn, by means of the coincidence (a,a'g) method at Ea=136MeV using the Big-Bite Spectrometer at the KVI in Groningen, The Netherlands. A splitting of the low-energy part of the electric dipole strength was identified by comparing the differential cross sections measured in (a,a'g) to results stemming from photon-scattering experiments. An experimental signature of the neutron-skin oscillation of the pygmy dipole resonance has been corroborated. The combination of the presented reactions might give a possibility to identify states of this resonance.