Work, Energy and Power

Slowing down of neutrons:
In a nuclear reactor a neutron of high
speed (typically 107
m s–1) must be slowed
to 103
m s–1 so that it can have a high
probability of interacting with isotope 92
235U
and causing it to fission. Show that a
neutron can lose most of its kinetic energy
in an elastic collision with a light nuclei
like deuterium or carbon which has a mass
of only a few times the neutron mass. The
material making up the light nuclei, usually
heavy water (D2O) or graphite, is called a
moderator.