How can fast neutrons be slowed down easily?

The Correct answer is Passing them through water.

Key Points

• Fast neutrons can be slowed down or moderated by passing them through a substance that contains light nuclei.
• Water is an effective moderator because it contains hydrogen atoms, which have a mass similar to that of neutrons.
• When fast neutrons collide with the hydrogen nuclei in water, they lose energy through a process called elastic scattering.
• This reduction in energy slows down the fast neutrons, turning them into slow or thermal neutrons.
• Slow or thermal neutrons are more likely to induce fission in certain nuclear materials, such as Uranium-235.
• Water is commonly used in nuclear reactors as both a coolant and a moderator.

 Additional Information

• Lead shielding
  • Lead is primarily used for its ability to absorb gamma rays and X-rays, not for moderating neutrons.
  • It is not effective in slowing down fast neutrons.
• Elastic collisions with heavy nuclei
  • Heavy nuclei are less effective in slowing down neutrons compared to light nuclei like hydrogen.
  • Neutrons lose more energy per collision when they collide with light nuclei.
• Applying a strong electric field
  • Neutrons are neutral particles and are not affected by electric fields.
  • This method would not be effective in slowing down fast neutrons.