Theoretical description of pygmy and giant dipole resonances in 237Np

Abstract

Abstract This study presents the descriptive characteristics of the electric dipole (E1) excitations for the first time in the 237Np nucleus, such as the reduced transition probability, the photo-absorption cross-section, the energy-weighted sum rule, and so on, as calculated by the Translational and Galilean Invariant Quasiparticle Phonon Nuclear Model (TGI-QPNM). To accurately determine the dipole properties of the collective pygmy and giant resonances, it was necessary to eliminate the spurious states mixed into the dipole spectrum because the mean-field Hamiltonian breaks the translational invariance symmetry. We therefore also investigated the effect of spurious states on the PDR and GDR spectra using the TGI-QPNM method. In addition, we consulted the available knowledge for the energy-weighted sum rule to test the TGI-QPNM model, and this resulted in 97% accuracy for E1 dipole excitations. Furthermore, the theoretical results were compared with experimental data for the photo-absorption cross-sections in the 5–20 MeV energy range for the 237Np nucleus, with a satisfactory agreement being found.