Neutron capture cross section of tritium is zero

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Discussion Overview

The discussion centers on the neutron capture cross section of tritium (3H) and the existence of the hypothetical nucleus 4H (quadrium). Participants explore the implications of these assertions regarding neutron interactions and the stability of 4H.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that the neutron capture cross section of tritium is zero for all neutron energies, suggesting that this implies the non-existence of 4H.
  • Another participant references Wikipedia, claiming that 4H exists as a very short-lived nucleus and can be produced via the reaction 3H+n, although they note that deuterium is a more practical option for experiments.
  • A different participant expresses uncertainty about the implications of 4H's decay process, which involves ejecting a neutron almost immediately, and questions its relevance in behavioral models.
  • Another participant discusses the similarity of (n,total) and (n,elastic) cross-sections for tritium, concluding that the absorption cross-section is negligible, reinforcing the idea that 4H effectively does not exist.

Areas of Agreement / Disagreement

Participants express differing views on the existence of 4H, with some asserting it does not exist in a useful sense while others suggest it can be produced, indicating a lack of consensus on this topic.

Contextual Notes

Participants reference various sources, including the NNDC and Wikipedia, but there are unresolved questions regarding the definitions and implications of neutron capture and the stability of 4H.

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I wish to verify a couple of assertions. From the NNDC and other references, it appears that the neutron capture cross section of 3H (Tritium) is zero to a first approximation. This holds true for all neutron energies, including cold neutrons. These statements are equivalent to asserting that 4H ("quadrium" !?) does not exist. As a result, all questions about the behavior of putative "quadrium" are not legitimate physics questions. Is this correct?
 
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According to the references at Wikipedia, it exists as a very short-living nucleus. It should be possible to produce 4H with 3H+n, but deuterium is easier to accelerate and the single proton is probably a cleaner signature.
 
Huh. Thanks. I'm not quite sure what to make of that, because it decays by ejecting the neutron again, typically in less than a millionth of a femtosecond. This is going to look almost like a peculiar kind of inelastic collision...neutron in, neutron out. I suppose it might be important to include this in some kind of very detailed behavioral model. But the 4H doesn't exist in any useful sense. Thanks again for your response.
 
Looking at (n,total) vs (n,elastic) cross-sections for H-3 down to 1E-5, they are essentially identical, so the absorption cross-section is neglible, i.e., H-4 effectively doesn't exist, i.e., the binding energy is neglible. Elastic scattering is the more likely outcome.
 

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