Some Monte Carlo and Analytical Results for Resonance Capture in Lattices

Detailed Monte Carlo studies of the resonance capture in the lowest U²³⁸ resonances have been made for uranium-water lattices and a uranium-graphite lattice. Direct comparison with calculated values is a good test of the validity of the assumptions made in obtaining the theoretical estimates. Good agreement is obtained for the over-all capture in a single resonance and for the energy distribution of absorptions. Monte Carlo tests have also shown that the asymptotic flux is fairly well re-established between the two strongest U²³⁸ resonances, and that the number of neutrons captured in this energy region is only slightly affected by Doppler broadening and interference between resonance and potential scattering. Finally the calculated resonance escape probability in a uranium-water lattice for 26 resolved resonances is compared with the Monte Carlo value. There is quite close agreement.