Low-energy enhancement in the magnetic dipole radiation of actinide nuclei

Abstract

We present the first theoretical results of the magnetic dipole (M1) $γ$-ray strength function ($γ$SF) for actinide nuclei within the shell-model Monte Carlo (SMMC) method. We observe a low-energy enhancement (LEE) in the M1 $γ$SFs of the six nuclei studied here, which serves as the first evidence, theoretical or experimental, that the LEE persists in the actinides. We also identify a scissors mode resonance in all six nuclei, which we compare with recent Oslo-method experiments.

Figures (3)

• Figure 1: The M1 strength functions $S_{M1}$ for the actinides at temperatures near the neutron separation energy. The blue solid lines are the SMMC+MEM results with shaded blue bands representing the uncertainties, and the red dashed lines are the SPA priors.
• Figure 2: The de-excitation strength functions $f_{M1}$ (\ref{['eq:fm1_2']}) of the actinides calculated near the neutron separation energies. The blue solid lines are the SMMC+MEM results with shaded blue bands representing the uncertainties, and the red dashed lines are the SPA priors.
• Figure 3: The slope parameter $\kappa$, obtained by fitting the LEE to Eq. \ref{['eq:LEE_fit']}, as a function of the initial energy for all six nuclei.