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

Abstract

This work investigates the electric and magnetic dipole (E1 and M1) responses for 239,243Pu isotopes based on the quasiparticle phonon nuclear model (QPNM) by adding the residual interactions for addressing the violations of rotational, translational, and Galilean symmetries caused by the mean-field approach, for the first time. We focus on the E1 and M1 dipole strengths and photo-absorption cross sections up to 20 MeV, and the results reveal that the giant dipole resonance (GDR) best describes the experimental trend with a ratio of 95%. It appears that most of the E1 strength is found at Ex=8–20 MeV, but the total B(E1)↑ strength for the pygmy dipole resonance (PDR) at Ex=4–8 MeV accounts for some 1.83 e2fm2, which in turn corresponds to 2% of the Thomas–Reiche–Kuhn (TRK) sum rule. Furthermore, the resultant total B(M1)↑ value for the scissors mode strength below 4 MeV is 5.65 , which is lower than that of the Oslo data (10.1(15) ). However, the theoretically predicted scissors resonance structure with two peaks in the 1–3.5 MeV energy range exhibits a similar trend to that found in the Oslo data.