The Neutron Spectrum from a Fission Source in Graphite

Time-of-flight measurements of the neutron angular flux spectrum in graphite have been made to provide a standard of comparison for neutron penetration calculations. The spectrum from 0.002 eV to 15 MeV was measured with an accuracy of ±13 to 32% and a resolution of ±2 to 10%, at angles from 0 to 60° and penetrations to 66 cm. Comparisons with Monte Carlo and discrete ordinates calculations using ENDF/B cross sections indicate fairly good agreement except in resonances and near zero degrees for discrete ordinates. Scalar fluxes have also been calculated with the moments method.