Moderator
Key Stage 4
Meaning
A moderator is a substance used in nuclear fission reactors to slow fast moving neutrons to become thermal neutrons.
About Moderators
- Moderators absorb some of the energy of fast moving neutrons which slows them down to a speed where they are called thermal neutrons which are able to be captured by fissionable isotopes.
- Without a moderator in a nuclear reactor the neutrons released from each fission event would be moving too fast to cause a second fission event so a chain reaction would not be possible.
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As a fast moving neutron passes through a moderator it collides with atoms in the moderator passing on some of their energy and slowing down. After several collisions a neutron becomes slow enough to be captured by a fissionable isotope. At this point it is called a thermal neutron. |