Threshold-Foil Measurements of Reactor Neutron Spectra for Radiation Damage Applications

The accuracy of unfolding neutron spectra with threshold activation foils was investigated by comparing the unfolded spectra with “known” spectra obtained from calculations verified with more accurate spectrometry techniques. Because of the lack of spectral data below 1 MeV (only one useful activation threshold exists between 0.01 and 1 MeV), reliable results are generally obtained only with the a priori constraint of a physically complete trial spectrum. A family of trial spectra useful for reactor spectra [and any nuclear “evaporation” spectra, such as from high-energy (γ, n) reactions] has been formulated. The sensitivity of the solution to the specific unfolding code used, to the threshold-foil cross sections and related nuclear data, and to foil-activation measurement accuracy was also investigated.