A method to calculate thermal neutron diffusion parameters for hydrogenous mixtures

A comprehensive method is proposed to calculate the thermal neutron diffusion parameters for homogeneous mixtures of any non-multiplying non-crystalline compounds, in particular including hydrogenous substances. The macroscopic absorption, scattering, and transport cross sections of the mixture are defined generally as functions of the incident neutron energy. The energy-averaged neutron parameters can be calculated when the energy dependence and the thermal neutron energy distribution are known. For most substances the scattering cross section can be assumed as being almost constant in the thermal neutron region (which results from the free gas model). However, serious deviations are observed for hydrogen atoms bound in molecular systems. In the paper certain effective scattering cross sections are found in this case on the basis of individual accurate data for a few hydrogenous media. The macroscopic parameters calculated are averaged over the Maxwellian energy distribution for the thermal neutron flux. Results agree well with available data.