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Q & A: neutrons starting fission chain reactions

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Most recent answer: 05/06/2012
Q:
What is the source of neutrons to begin reactions in a nuclear reactor? I understand that U-235 undergoes fission readily on absorbing a slow-moving neutron and releases neutrons as part of the process, hence creating the possibility of a chain reaction, but how is the reaction started, that is, what is the source of the neutrons that initialise the reactions?
- Joe (age 24)
Melbourne, Australia
A:
There's some spontaneous decay of the radioactive isotopes. That's enough to trigger the chain reaction. Only bombs, which require a rapid growing chain reaction, require a separate burst of neutrons to get them started quickly. There are several different ways of obtaining those bursts. Perhaps we should not describe them, in case there are any over-enthusiastic do-it-yourself types among our readers.

Mike W.

(published on 05/06/2012)

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