NEUTRON MODERATION
DOE-HDBK-1019/1-93
Reactor Theory (Neutron Characteristics)
NP-02
Page 28
Rev. 0
Summary
The important information in this chapter is summarized below.
Neutron Moderation Summary
Thermalization is the process of reducing the energy level of a neutron from the
energy 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 of
thermalizing neutrons.
Moderating ratio is the ratio of the macroscopic slowing down power to the
macroscopic cross section for absorption.
The average logarithmic energy decrement ( ) is the average change in the
logarithm of neutron energy per collision.
Macroscopic slowing down power is the product of the average logarithmic energy
decrement and the macroscopic cross section for scattering.
There are three desirable characteristics of a moderator.
1.
large scattering cross section
2.
small absorption cross section
3.
large energy loss per collision
The energy loss after a specified number of collisions can be calculated using the
equation below.
E = E (1 - x)
N
o
N
