Fast neutron

Fast Neutron

A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (Mega electron Volts), hence a speed of 14,000 km/s, or higher. They are named fast neutrons to distinguish them from lower-energy thermal neutrons, and high-energy neutrons produced in cosmic showers or accelerators.

Production

Fast neutrons are produced by nuclear processes such as nuclear fission or nuclear fusion. They are also found in cosmic rays. Fast neutrons can be made into thermal neutrons via a process called moderation. This is done in a nuclear reactor using a neutron moderator.

Interaction with matter

Fast neutrons are most effectively absorbed by hydrogen nuclei, so they can be slowed down or "moderated" by substances containing hydrogen, like water or polyethylene. They can also be absorbed by a neutron absorber that reduces their kinetic energy, or they can be scattered out of the system.

Uses

Fast neutrons can be used in nuclear reactors, and they are essential to the basic operation of most nuclear reactors. Fast neutron reactors, specifically, are a type of nuclear fission reactor in which the fission chain reaction is sustained by fast neutrons. Such a reactor needs no neutron moderator, but requires fuel that is relatively rich in fissile material when compared to that required by a thermal reactor.

Health hazards

Fast neutrons are high radiation hazards. They have a high quality factor for radiation protection purposes, and their presence requires protective shielding.

See also

• Neutron radiation
• Neutron source
• Neutron moderator
• Neutron temperature

References

Fast neutron Resources
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