Low-energy enhancement and fluctuations of gamma-ray strength functions in Fe-56,Fe-57: test of the Brink-Axel hypothesis

Nuclear level densities and gamma-ray strength functions of Fe-56,Fe-57 have been extracted from proton-gamma coincidences. A low-energy enhancement in the gamma-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in 57Fe indicate its dipole nature, in agreement with findings for Fe-56. The high statistics and the excellent energy resolution of the large-volume LaBr3(Ce) detectors allowed for a thorough analysis of. strength as function of excitation energy. Taking into account the presence of strong Porter-Thomas fluctuations, there is no indication of any significant excitation energy dependence in the gamma-ray strength function, in support of the generalized Brink-Axel hypothesis.