Calculation of the Neutron Leakage Spectra and Neutron Doses from Bare Critical Systems

Due to the interest in determining the dose received by persons near a criticality accident, a method for calculating the neutron spectra and neutron dose for highly enriched uranium solutions at various hydrogen to U²³⁵ atomic ratios has been developed. This method uses the output from a code for criticality calculations, and determines the average leakage neutron energy, the neutron leakage spectrum, the first collision neutron dose, and the total neutron dose. The results of these calculations show that the average energy of the leakage neutrons and the dose per incident leakage neutron per cm² decrease somewhat with increased hydrogen to U²³⁵ atomic ratio, but it appears that this effect is sufficiently small so that an exact knowledge of the uranium concentration would not be necessary to obtain reasonable dose estimates. The effect of neutron scattering on the neutron spectra and doses is not evaluated. No attempt has been made to describe actual dose determination methods, since these have been adequately described elsewhere.