Pygmy Dipole Resonance in Exotic Nuclei

Abstract The evolution of the PDR strength with the neutron excess is investigated in Sn isotopic and N=82 isotonic chains with regard to its possible connection with the neutron skin thickness. For this purpose a recently proposed method incorporating both HFB and multi-phonon QPM theory is applied. Analysis of the corresponding neutron and proton dipole transition densities is presented. 1 Theoretical approach and results The existence of low-energy dipole excitations located close to the particle emission threshold is observed as a common feature in many isospin asymmetric atomic nuclei. These modes are related to the socalled Pygmy Dipole Resonance (PDR) which has been explained in neutron-rich nuclei as generated by oscillations of weakly bound neutrons in respect of isospin symmetric core [1, 2, 3, 4]. In our approach the nuclear ground states are determined by a procedure based on a fully microscopic HFB description [1, 6].