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B Is this how nuclear fission occurs with neutron bombardment?

  1. Jul 2, 2016 #1
    When neutrons are fired at atoms, if at higher speeds they will behave as waves, wander through and scatter, (which can produce something similar to x-ray diffraction images), but if slowed to the right "thermal energy" speed, they will be captured by (say) U-235, making the U atom unstable, causing it to break up into 2 daughter nuclei + neutrons + gamma radiation

    I'd appreciate further explanation and a correction of any of my statements that are wrong and/or incomplete :)
  2. jcsd
  3. Jul 3, 2016 #2

    Simon Bridge

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    No. The wave behaviour appears at all speeds and is more usefully thought of as part of the statistical behaviour of the particle.
    Neutrons may be captured by a nucleus at any speed - it is just that there is more opportunity to catch a slow neutron than a fast one ... much like it is easier to catch a slow ball than a fast one. It's a bit more complicated for nucleon capture by a nucleus ... you can get graphs of the neutron capture crosssection vs energy online.
  4. Jul 3, 2016 #3
    I see. So what conditions make it so that it can safely wander through the nucleus of an atom and diffract, than otherwise being captured?
    Also, I've seen somewhere that particles are bombarded at nuclei, splitting them apart. Is this the same thing with U-235 capturing a neutron?
  5. Jul 3, 2016 #4


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    Quantum mechanics. There is no classical image that would fit (and waves and particles are classical images).
    No, the direct splitting happens at much higher energies.
  6. Jul 3, 2016 #5

    Simon Bridge

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    In all conditions there is a probability for different interactions to take place. I don't think there is a situation where the n+U capture crossection is zero.
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