The differential scattering cross section o(E ,ε, po .po) of a material for neutrons tells the probability that a scattering event involving a neutron of energy E will cause an energy change ε and a change in direction from po to po. Calculations of neutron energy distributions mean free paths, etc., in a material require a knowledge of σ(E o, ε, p • p).nWhen Eo is near kT and less than the energy for breaking chemical bonds in the material the theory for calculating σ is complicated. Few data are available in this region and for this reason a recent approximate method devised by Krieger and Nelkin to simplify the calculation of σ for gases is attractive as a start toward developing feasible computational methods.nThis report evaluates the accuracy of the K. N. approximation by using it to calculate a values for methane and comparing these with results from a more rigorous, but much more time consuming, calculation which avoids most of the K. N. simplifications.
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