Pygmy dipole resonance in the well-deformed even–even ^152–162Gd

The electric dipole E1 strength in the well-deformed even–even ^152–162Gd was calculated using a model based on translational and Galilean invariant quasi-particle random phase approximation (QRPA), where for the first time the highly-fragmented E1 strength has been predicted below the particle threshold energy. The predicted concentration of the electric dipole excitations exhausts less than 2% of the energy weighed sum rules (EWSR) below 20 MeV in rather good agreement with the experimental data for neighbor nuclei. Through cross sections, transition probabilities, and other properties, the electric dipole response was investigated in ^152–162Gd for a wide range of excitation energies from 5 to 20 MeV. The calculation that was performed with the elimination of effects associated with deformation revealed that the effects associated with neutron excess play a more significant role in the formation of the pygmy dipole resonance (PDR) strength when compared to the effects associated with a changing deformation. The calculations indicate the presence of magnetic dipole excitations with summed M1 strengths in the energy region between 5 and 8 MeV was less than 10% of the total dipole strength in the same energy region. We also took into account a recent experimental study of ¹⁵⁶Gd in our discussion and paid particular attention to this isotope. (paper)