Pygmy and giant electric dipole responses of medium-heavy nuclei in a self-consistent Random Phase Approximation approach with finite-range interaction

TL;DR

This paper investigates the pygmy and giant electric dipole resonances in medium-heavy nuclei using a self-consistent Hartree-Fock plus RPA approach with a Gogny interaction, highlighting differences in structure, collectivity, and the influence of residual interactions.

Contribution

It provides a detailed comparison of PDR and GDR structures in nuclei using a self-consistent finite-range interaction approach, emphasizing the role of shell effects and residual interactions.

Findings

PDR involves in-phase proton-neutron vibrations mainly from excess neutrons.

GDR involves out-of-phase proton-neutron vibrations involving all nucleons.

PDR is less collective than GDR, with residual interactions playing a subtle role.

Abstract

The pygmy dipole resonance (PDR) is studied in various medium-heavy nuclei by using a Gogny interaction in a self-consistent Hartree-Fock plus Random Phase Approximation method. We compare the details of the PDR structure with those of the giant dipole resonance (GDR). In the PDR protons and neutrons vibrate in phase, and the main contributions are given by particle-hole excitations involving the neutrons in excess. On the contrary, in the GDR protons and neutrons vibrate out of phase, and all the nucleons are involved in the excitation. The values of the parameters we used to define the collectivity of an excitation indicate that the PDR is less collective than the GDR. We also investigate the role of the residual interaction in the appearance of the PDR and we find a subtle interplay with the shell structure of the nucleus.