Nuclear Dipole Resonance in N = 82 Nuclei

In stable and weakly bound neutron-rich nuclei, a resonance-like concentration of dipole states has been observed for excitation energies around the neutron separation energy. This clustering of strong dipole states has been named the pygmy dipole resonance (PDR) in contrast to the giant dipole resonance that dominates the E1 response. High-sensitivity studies of E1 and M1 transitions in N = 82 nuclei using the nearly monoenergetic and 100{\%} linearly-polarized photon beams from TUNL's High-Intensity-Gamma-Ray Source facility will be presented. The nuclear dipole-strength distribution of the PDR has been measured and novel information about the character of this mode of excitation has been obtained. The data will be compared to calculations using statistical and quasiparticle random-phase approximation methods.