Why does Uranium-238 absorb fast moving neutrons

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Discussion Overview

The discussion centers on the behavior of Uranium-238 in relation to neutron absorption, specifically why it absorbs fast-moving neutrons more effectively than slow-moving ones. Participants explore theoretical aspects of neutron interactions with U-238 and U-235, touching on concepts of fission and neutron capture.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions why U-238 absorbs fast-moving neutrons better than slow ones, expressing initial confusion about this behavior.
  • Another participant suggests that U-238 captures slow neutrons as well as fast ones, but highlights that U-235 fissions more easily with slow neutrons, making the fission-to-capture ratio more favorable for slow neutrons.
  • A later reply mentions the pairing force as a factor influencing neutron absorption, referencing an earlier contribution.

Areas of Agreement / Disagreement

Participants express differing views on the absorption characteristics of U-238 and U-235, indicating that the discussion includes multiple competing perspectives and remains unresolved regarding the nuances of neutron interactions.

Contextual Notes

Some assumptions about neutron behavior and the definitions of fast and slow neutrons may not be fully articulated, and the discussion does not resolve the underlying mechanisms influencing neutron absorption.

Ed Aboud
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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.
Thanks.
 
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Hmm, I still don't really get it.
 
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.
 
Oh ok, I get it now. Thanks very much.
 
it has to with the pairing force, the answer vanesh gave you.
 

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