Why are the fast neutrons produced in fission deliberately slowed in many uranium-235 power reactors?
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Question

Why are the fast neutrons produced in fission deliberately slowed in many uranium-235 power reactors?

G1 Physics · Accepted Answer

U-235 has a large fission cross-section for thermal neutrons. In other words, a slow neutron has a relatively high probability of being captured in a way that leads to fission. The moderator slows the fast neutrons produced by fission so that a larger fraction of them can efficiently sustain further fissions in U-235. Correct option: A.