The Student Room Group

Why does uranium fission only happen when neutrons are moving at slow speeds?

Why does fission only happen when neutrons are moving at slow speeds in a nuclear reactor?
Reply 1
Its a rabbit hole but the jist is that U235 is much more likely to capture a slow moving neutron (and then undergo fission) than a fast moving neutron... And for various reasons we like to design reactors that have a low concentration of U235 in their fuel.

You can design reactors that use fast neutrons, but they're still exotic / experimental

So practical powerstation reactors that produce electricity in the real world are all still dependant on moderators to slow neutrons down in order to make the chain reaction go.

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