Neutrons are born out of fission at a high energy and must be
slowed down to the low energy region, called the “thermal energy”
region, to cause another fission. A material called a “moderator”
is used to slow the neutrons down, or “moderate” them, by elastic
scattering collisions.The average neutron energy coming out of
fission of thermal neutrons is 1.98 MeV in kinetic energy. What is
the number of collisions required to bring its average kinetic
energy to 0.1 eV...