NEUTRON MODERATION
DOE-HDBK-1019/1-93
Reactor Theory (Neutron Characteristics)
NP-02
Page 26
Rev. 0
(2-9)
where:
E
= initial neutron energy
o
E
= neutron energy after N collisions
N
x
= average fractional energy loss per collision
N
= number of collisions
Example:
If the average fractional energy loss per collision in hydrogen is 0.63, what will be the
energy of a 2 MeV neutron after (a) 5 collisions? (b) 10 collisions?
Solution:
a)
b)
Macroscopic Slowing Down Power
Although the logarithmic energy decrement is a convenient measure of the ability of a material
to slow neutrons, it does not measure all necessary properties of a moderator. A better measure
of the capabilities of a material is the macroscopic slowing down power. The macroscopic
slowing down power (MSDP) is the product of the logarithmic energy decrement and the
macroscopic cross section for scattering in the material. Equation (2-10) illustrates how to
calculate the macroscopic slowing down power.
(2-10)
