In a thermal nuclear reactor, fast neutrons produced during fission are slowed down by a moderator. Which property is most desirable for an effective moderator?
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Question

In a thermal nuclear reactor, fast neutrons produced during fission are slowed down by a moderator. Which property is most desirable for an effective moderator?

G1 Physics · Accepted Answer

The purpose of a moderator is to reduce the kinetic energy of fast fission neutrons so that they become thermal neutrons. For fuels such as U-235, thermal neutrons have a high probability of inducing fission. A good moderator should therefore slow neutrons effectively through collisions but should not remove too many neutrons by absorption. Examples include light water, heavy water and graphite. Correct option: B.