Low-energy enhancement and fluctuations of $\gamma$-ray strength   functions in $^{56,57}$Fe: test of the Brink-Axel hypothesis
  Nuclear level densities and $\gamma$-ray strength functions of $^{56,57}$Fe 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 $^{57}$Fe indicate its dipole nature, in agreement with findings for $^{56}$Fe. The high statistics and the excellent energy resolution of the large-volume LaBr$_{3}$(Ce) detectors allowed for a thorough analysis of $\gamma$ 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. 
A. C. Larsen, M. Guttormsen, N. Blasi, A. Bracco, F. Camera, L. Crespo   Campo, T. K. Eriksen, A. G\"orgen, T. W. Hagen, V. ...
nucl-ex