Fluctuations in Neutron-Induced Fission Cross Sections

We examine the published experimental data on the ²³⁵U(n,f) reaction with a goal to quantify cross section fluctuations above the fission barrier. For neutron energies in the range 10 keV - 25 keV we find that there are significant fluctuations of the order of 5% measured at 0.25 keV energy resolution. Here we analyze the fluctuations by the auto-correlation function with the following conclusions: 1) The correlation width associated with peak at zero energy offset is smaller than the experimental energy resolution; 2) there are peaks in the autocorrelation function on an energy scale of several keV. Such a multi-peaked structure is incompatible with Ericson’s statistical treatment of compound nucleus fluctuations but may arise in more detailed models of the fission dynamics.