Low energy magnetic radiation enhancement in the f$_{7/2}$ shell

Abstract

Studies of the $\gamma$-ray strength functions can reveal useful information concerning underlying nuclear structure. Accumulated experimental data on the strength functions show an enhancement in the low $\gamma$ energy region. We have calculated the M1 strength functions for the $^{49,50}$Cr and $^{48}$V nuclei in the $f_{7/2}$ shell-model basis. We find a low-energy enhancement for gamma decay similar to that obtained for other nuclei in previous studies, but for the first time we are also able to study the complete distribution related to M1 emission and absorption. We find that M1 strength distribution peaks at zero transition energy and falls off exponentially. The height of the peak and the slope of the exponential are approximately independent of the nuclei studied in this model space and the range of initial angular momenta. We show that the slope of the exponential fall off is proportional to the energy of the $T=1$ pairing gap.