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         V. = average neutron velocity in group i
         1

         ij = neutron energy transfer coefficient from
              group i to group j


The GAM-l (32) and SOPHIST-I (33) codes are used to calculate the transfer coefficients. Using the effective hydrogen scattering cross section with fuel and reflector cross sections computed in the usual manner, a one dimensional multigroup diffusion theory was used to make a parametric study based on various hydrogen temperatures and pressures, fuel nuclei, reflector materials, and fuel distributions. The details of these calculations and the assumptions involved are presented in the original article and will not be discussed here. However, it is worthwhile to discuss the results of this study, which are significant for two reasons. First, the group-averaged cross sections include the spectral hardening effects of high temperature hydrogen and second, the fact that high temperature hydrogen strongly influences the critical mass through a complex interaction of multiple processes is clearly demonstrated. Within the framework of multigroup diffusion theory, the technique of using an effective hydrogen scattering cross section is a practical approach to the treatment of thermal neutron scattering by high temperature hydrogen. Before adopting this technique as a standard method of calculating