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

Nuclear level densities and γ-ray strength functions of ^56,57Fe have been extracted from proton-γ coincidences. A low-energy enhancement in the γ-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 ⁵⁶Fe. The high statistics and the excellent energy resolution of the large-volume LaBr₃(Ce) detectors allowed for a thorough analysis of γ 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 γ-ray strength function, in support of the generalized Brink–Axel hypothesis. [ABSTRACT FROM AUTHOR]