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          S(r) = fission source distribution

          (VEf)i = average number of neutron produced by
                 fission in the i-th group times the
                 fission cross section in the i-th group

             X = criticality eigenvalue


The effects of nuclear motion of absorbing nuclei and scattering nuclei will be treated separately. The absorption cross section, Za*, will include the effects of the motion of uranium nuclei in the treatment of the Doppler broadening of the uranium absorption resonances. The scattering cross section, E si--j, will include the effects of the motion of hydrogen nuclei. Effect of Thermal Motion of Absorbing Nuclei on Epithermal Neutrons

        The macroscopic absorption cross section for the i-th group is the flux weighted average cross section which is defined as


                fEui Ea (E)r    dE

                ELi

           a.      E
           I       Eui J (E4,E)dE

                     L.                            (2.5)


where Eui and EL. are the upper and lower boundaries, respectively, of the i-th group. In the epithermal energy