Radiative strength function and the pygmy dipole resonance in 208Pb and 70Ni

Abstract

The pygmy-resonance parameters and the E1 strength function are derived for 208Pb using a fully self-consistent microscopic formalism recently developed for magic nuclei, which takes into account quasiparticle phonon interactions (or coupling to phonons) in addition to the random phase approximation. For the radiative strength function of 208Pb at energies above 5 MeV, the experimental data of the Oslo group are adequately described by our predictions, whereby the important role of coupling to phonons is confirmed. By comparing the measurements based on the (3He, 3He′γ) and (γ, γ′) reactions, we discuss the physical properties of the radiative strength function measured for 208Pb. For the neutron-rich 70Ni nucleus, predictions for the radiative strength function and the pygmy resonance are obtained using a partially self-consistent approach, which invokes the Skyrme forces in deriving the mean field, effective nucleon–nucleon interaction, and phonon characteristics.