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Why does Uranium-238 absorb fast moving neutrons

  1. Jun 13, 2008 #1
    Hi all.
    Why does Uranium-238 absorb fast moving neutrons very well but not slow moving ones?
    My intuition tells me it should be the other way around but its not.
  2. jcsd
  3. Jun 13, 2008 #2


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  4. Jun 13, 2008 #3
    Hmm, I still don't really get it.
  5. Jun 13, 2008 #4


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    U-238 captures slow neutrons as well as fast, and even a bit more slow than fast. However, U-235 fissions MUCH MORE easily with slow neutrons than with fast, and hence the ratio for fission in U-235 over capture in U-238 is more favorable for slow neutrons than for fast.
  6. Jun 13, 2008 #5
    Oh ok, I get it now. Thanks very much.
  7. Jun 13, 2008 #6


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    it has to with the pairing force, the answer vanesh gave you.
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