Large enhancement of radiative strength for soft transitions in the quasicontinuum

Radiative strength functions (RSFs) for the Fe-56,Fe-57 nuclei below the separation energy are obtained from the Fe-57(He-3,alphagamma)Fe-56 and Fe-57(He-3,He-3'gamma)Fe-57 reactions, respectively. An enhancement of more than a factor of 10 over common theoretical models of the soft (E(gamma)less than or similar to2 MeV) RSF for transitions in the quasicontinuum (several MeV above the yrast line) is observed. Two-step cascade intensities with soft primary transitions from the Fe-56(n,2gamma)Fe-57 reaction confirm the enhancement.