question_answer

Explain how fast moving neutrons can be quickly slowed down by passing them through water or heavy water.                                                                                                                 Or Hydrogenic materials are used as moderators in nuclear reactors to slow down the neutrons. Why?                

Answer:

                We have studied that when two bodies of same mass undergo an elastic collision, their velocities are interchanged after collision. Water and heavy water are hydrogenic materials containing protons having approximately the same mass as that of a neutron. When fast moving neutrons collide with protons, the neutrons come to rest and protons move with the velocity of neutrons.