Question

In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used have light nuclei. Heavy nuclei will not serve the purpose because
A. they will break up
B. elastic collision of neutrons with heavy nuclei will not slow them down
C. the net weight of the reactor would be unbearably high
D. substances with heavy nuclei do not occur in liquid or gaseous state at room temperature .

Answer 1

Correct Answer - b
During an elastic collision between two particles, the maximum kinetic energy is transferred from one particle to the other when they have the same mass. Therefore , heavy nuclei will not serve the purpose because elastic collision of neutrons with heavy nuclei will not show them down.