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 ____.

Options

• they will break up

• elastic collision of neutrons with heavy nuclei will not slow then down

• the net weight of the reactor would be unbearably high

• substances with heavy nuclei do not occur in liquid or gaseous state at room temperature

Answer 1

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 elastic collision of neutrons with heavy nuclei will not slow then down.

Explanation:

For elastic collision, masses of both must be equal so that they can exchange the velocities. To slow down the speed of neutron substance should be made up of 1 proton for perfectly elastic collision, that is, we need light nuclei not heavy.

For heavy nuclei only direction will change not the speed.