What is the process called that slows fast neutrons to thermal energies?

What is the process called that slows fast neutrons to thermal energies?

• A. Absorption
• B. Moderation
• C. Scattering
• D. Fission

Answer: (B)

Slowing fast neutrons to thermal energies is called moderation. This is how fast neutrons, born with high energy from fission, are brought down to the lower, thermal range where they’re most likely to induce fission in many fuels. Moderation happens mainly through elastic scattering off light nuclei such as hydrogen in water or carbon in graphite. Each collision transfers energy from the neutron to the nucleus, and because the target is light, the neutron loses a substantial amount of energy per collision, creating a cascade toward thermal energies (around a few tenths of an eV at room temperature). Absorption removes neutrons from the chain, and scattering refers to the mechanism by which energy is lost, but moderation is the overall process of slowing. Fission is the splitting reaction itself, not the slowing process.

Slowing fast neutrons to thermal energies is called moderation. This is how fast neutrons, born with high energy from fission, are brought down to the lower, thermal range where they’re most likely to induce fission in many fuels. Moderation happens mainly through elastic scattering off light nuclei such as hydrogen in water or carbon in graphite. Each collision transfers energy from the neutron to the nucleus, and because the target is light, the neutron loses a substantial amount of energy per collision, creating a cascade toward thermal energies (around a few tenths of an eV at room temperature). Absorption removes neutrons from the chain, and scattering refers to the mechanism by which energy is lost, but moderation is the overall process of slowing. Fission is the splitting reaction itself, not the slowing process.