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.