A theoretical analysis of the electromagnetic dipole response in odd-A thorium isotopes

Abstract

We here present a theoretical analysis of electric and magnetic dipole (E1 and M1) resonances in the Th229-233 isotopes. In this study, the characteristic features of M1 and E1 excitations were calculated using the rotational invariant (RI-) and the translational Galilean invariant (TGI-) quasiparticle phonon nuclear models (QPNM), respectively.These models have been successfully applied to most rare-earth and actinide nuclei, with them yielding results that are consistent with the available experimental data.This study directly compares the TGI-QPNM results with experimental cross-section data (Oslo type; (gamma,abs.)), and the model was found to reproduce the structural splitting of the E1 strength into two humps in the 8-20 MeV energy region.Furthermore, the study shows that the theoretical spectra of the Th-231,Th-233 isotopes, whose giant dipole resonance (GDR) has not yet been measured, almost overlaps with the experimental GDR spectrum of the neighboring Th-232 nucleus.The predicted GDR parameters, such as peak energy, cross section, and width, are consistent with the experimental results. Our analysis also yields results that are similar to the corresponding parameters reported in the Oslo data for the PDR E1 (omega(pyg) approximate to 7.2MeV; sigma(pyg) approximate to 10 mb) and spin-flip M-1 (omega(M1) approximate to 6.67 MeV; sigma(M1) approximate to 4.36 mb) resonances.