Theoretical description of pygmy and giant dipole resonances in ²³⁷Np

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.

Microscopic calculation of the electromagnetic dipole strength for 239,243Pu isotopes

“…Our previous studies [62,65,[67][68][69] predicted a broadening in the GDR's width at smoothing parameter Δ due to the GDR splitting into two distinct components that correspond to the ΔK=0 and ΔK=1 branches for odd-A deformed nuclei. The photoabsorption cross-section demonstrates a similar trend in the present study in that there is a general splitting of the GDR with strong deformation (see element (a) of figure 1).…”

“…For this study, we applied a quasiparticle phonon nuclear model (QPNM) approach based on rotational invariant (RI-), translational, and Galilean invariant (TGI-) requirements, and this allowed us to analyze the spectral properties of the excited J π =1 − and 1 + states within the same excitation energy region [62][63][64][65][66][67][68][69][70][71]. This extended version of the QPNM [72] formalism considers transitions of the E1 and M1 types.…”

“…This extended version of the QPNM [72] formalism considers transitions of the E1 and M1 types. The literature [65,[67][68][69] has also reported that applying QPNM allows the dipole strength distribution and the related photoabsorption cross sections of the E1 (or M1) transitions to be determined. Furthermore, the sum rules were also confirmed through the determined whole-strength distributions.…”