NEUTRON MODERATIONDOE-HDBK-1019/1-93Reactor Theory (Neutron Characteristics)NP-02Page 28Rev. 0SummaryThe important information in this chapter is summarized below.Neutron Moderation SummaryThermalization is the process of reducing the energy level of a neutron from theenergy level at which it is produced to an energy level in the thermal range. The moderator is the reactor material that is present for the purpose ofthermalizing neutrons.Moderating ratio is the ratio of the macroscopic slowing down power to themacroscopic cross section for absorption.The average logarithmic energy decrement () is the average change in thelogarithm of neutron energy per collision.Macroscopic slowing down power is the product of the average logarithmic energydecrement and the macroscopic cross section for scattering.There are three desirable characteristics of a moderator.1.large scattering cross section2.small absorption cross section3.large energy loss per collisionThe energy loss after a specified number of collisions can be calculated using theequation below.E = E (1 - x)N oN