Q141 / 180 · KCET 2021 · Physics

In a nuclear reactor heavy nuclei is not used as moderators because

  • A
    they will break up
  • Correct answer
    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
    substance with heavy nuclei do not occur in liquid or gaseous state at room temperature

Solution

The moderator used in nuclear reactor, have light nuclei (like proton). When protons undergo perfectly elastic collision with the neutrons emitted, their velocities are exchanged i.e. neutrons. Heavy nuclei will not serve the purpose because elastic collision of neutrons with heavy nuclei will not slow them down.

Hence, the correct answer is option: 'B'.

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