Is this how nuclear fission occurs with neutron bombardment?

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Discussion Overview

The discussion revolves around the process of nuclear fission, particularly focusing on neutron bombardment of uranium-235 (U-235) and the conditions under which neutrons are captured or cause fission. Participants explore the behavior of neutrons at different speeds and the implications for nuclear reactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that neutrons behave as waves at higher speeds and can be captured by U-235 at thermal speeds, leading to instability and fission.
  • Another participant counters that wave behavior is present at all speeds and emphasizes the statistical nature of neutron capture, noting that slow neutrons have a higher probability of being captured.
  • A participant questions the conditions under which neutrons can wander through a nucleus without being captured, indicating that quantum mechanics plays a role.
  • It is mentioned that direct splitting of nuclei occurs at much higher energies than those involved in neutron capture.
  • Another participant states that there is always a probability for neutron capture interactions to occur, suggesting that the capture cross-section is never zero.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of neutrons and the conditions for their capture or interaction with nuclei. There is no consensus on the initial claims regarding neutron behavior and the specifics of nuclear fission processes.

Contextual Notes

Participants reference concepts such as neutron capture cross-sections and the role of quantum mechanics, but the discussion does not resolve the complexities of these interactions or the conditions under which they occur.

victorhugo
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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 :)
 
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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.
 
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Simon Bridge said:
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.
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?
 
victorhugo said:
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?
Quantum mechanics. There is no classical image that would fit (and waves and particles are classical images).
victorhugo said:
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?
No, the direct splitting happens at much higher energies.
 
So what conditions make it so that it can safely wander through the nucleus of an atom and diffract, than otherwise being captured?
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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