Slowing Down of Neutrons in Graphite Close to Thermal Equilibrium

Elastic and one-phonon inelastic scattering cross sections of neutrons in graphite have been calculated for neutron energy less than 2000 k₀. For the lattice vibrations in graphite, the model proposed by Krumhansl and Brooks has been used. We have also calculated the mean energy loss per collision and the mean logarithmic energy decrement. Assuming that close to equilibrium the neutron distribution remains Maxwellian, the time variation of the temperature of this distribution has been calculated. The slowing down relaxation time near equilibrium comes out to nearly 170 µsec, which compares well with the experimental value of 185 ± 45 µsec.