Neutron scattering kernels in pronounced resonances for stochastic doppler effect calculations

The purpose of the present study is to provide data for stochastic calculations of the Doppler effect in nuclear reactor assemblies, which are as far as possible free from approximations. It is then possible to use the Monte Carlo method to study the effect of the fine structure of the neutron flux on resonance absorption rates in the pronounced resonances of U-238, and similar abundant nuclei in reactor fuel, as well as their changes with temperature. The data required for such calculations must provide an accurate description of neutron scattering in such resonances. The material presented here is a sequel to the paper [1] which was published recently in the Annals of Nuclear Energy, and which dealt with the calculations of the moments of the neutron scattering kernel for energy dependent scattering cross sections. It substantiates the conclusions which were reached at the time by means of Monte Carlo calculations made with the MCNP code [2]. In addition a formulation is given for the temperature dependent double differential scattering kernels of neutrons colliding with nuclei, which behave like a Maxwellian Gas, and which have strongly varying scattering cross sections in pronounced resonances, such as the fertile nuclei in the fuel lumps of heterogeneous reactor assemblies. Finally the use of such scattering kernels in Monte Carlo calculations of the Doppler Effect is discussed, and compared with the simpler method used in the MCNP code, in which the velocity of the target nucleus is sampled for this purpose in the low epithermal energy region