- 37 --


          NHs nr =   s nVr = 'snVn                 (2.32)


where the effective macroscopic scattering cross section for hydrogen is given by


                           s V r VIn               (2.33)

The symbols are


        V  = average relative velocity between hydrogen
             and neutrons

        Vn = average neutron speed = (8kT n/Tmn) 1/2 VH = average hydrogen speed = (8kTH/TrmH) 1/2

        a  = microscopic scattering cross section of
             hydrogen

        The effective multigroup hydrogen cross sections are calculated by the following relation:


                 N H a %  - Vi
            S.=      1          = N.ij = Es       Zij
            1         Vi              1          j

                                                   (2.34)

where

        VH - Vi = average relative speed between hydrogen at a given temperature and neutrons in group i

            as. = microscopic scattering cross section for
              I   group i