How to detect neutrons using Helium 3

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    Helium Neutrons
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Discussion Overview

The discussion centers on the detection of neutrons using helium-3, particularly focusing on the reaction between thermal neutrons and helium-3 that produces tritium and hydrogen. Participants explore the mechanisms of detection, including ionization and the behavior of reaction products.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • Some participants explain that the reaction n + 3He → 3H + 1H + 0.764 MeV occurs, leading to ionization in the gas, which can be detected similarly to charged particle detectors.
  • Others mention that tritium is radioactive and decays back into helium-3, emitting beta particles and potentially producing detectable light.
  • One participant suggests that the high kinetic energies of the produced tritium and hydrogen nuclei allow them to ionize gas atoms by knocking electrons from their shells.
  • There is a discussion about the types of excitations produced by fast hydrogen nuclei in helium-3 and the relevance of spectral lines, with some arguing that spectral lines are irrelevant to the detection mechanism.
  • Participants express uncertainty about the specifics of ionization processes and the conditions under which they occur, particularly regarding the presence of strong magnetic fields or ionizing radiation.

Areas of Agreement / Disagreement

Participants generally agree on the basic detection mechanism involving ionization but express differing views on the relevance of certain details, such as the role of spectral lines and the specifics of the reaction products. The discussion remains unresolved on some technical aspects.

Contextual Notes

There are limitations regarding the assumptions made about the detection environment, such as the presence of gas and the conditions under which ionization occurs. Some participants question the completeness of the explanations provided.

Who May Find This Useful

This discussion may be useful for individuals interested in nuclear physics, radiation detection methods, and the properties of helium-3 in experimental settings.

CraigH
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I understand that helium 3 has a very high probability of fusing with thermal neutrons, and the reaction produces tritium and hydrogen:
n + 3He → 3H + 1H + 0.764 MeV

however I do not understand how this reaction is detected.

Can someone please explain?

Thanks.
 
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Tritium (hydrogen-3) is radioactive, with a half-life of about 12.3 years. It decays back into helium-3 by emitting beta particles. It also glows in the dark.
 
What SteamKing wrote is true. It's also irrelevant.

You have ionization in the gas when this reaction takes place. The ionization is detected just as it is in a charged particle detector.
 
As a more short-term detection method, you produce two high-energetic hydrogen nuclei, maybe together with a photon. They can be detected with conventional particle detectors (scintillators, for example).

Edit: Vanadium was a bit faster.
 
Vanadium 50 said:
What SteamKing wrote is true. It's also irrelevant.

You have ionization in the gas when this reaction takes place. The ionization is detected just as it is in a charged particle detector.

If it IS gas, naturally.

What kinds of excitations do fast hydrogen nuclei produce in helium 3? And which spectral lines do these emit?

(Helium is a notoriously poor solvent. Basically anything will precipitate... In helium 3, would solid diprotium float as it does in helium 4?)
 
Vanadium 50 said:
You have ionization in the gas when this reaction takes place.

Why is this? There are no strong magnetic fields or ionizing radiation present to cause the gas in the detector (e.g geiger tube) to ionise. Is it because the tritium and hydrogen have high kinetic energies (0.764 MeV) so they can "bump" into electrons of the atoms in the gas and knock them from their shell?
 
Helium-3 is a gas.

Spectral lines are irrelevant. It works by ionization.
 
Is it because the tritium and hydrogen have high kinetic energies (0.764 MeV) so they can "bump" into electrons of the atoms in the gas and knock them from their shell?
Right. The fast reaction products are the ionizing radiation.
 
Think of it this way: you have a gas tube, just like a proportional or Geiger tube, but instead of the ionizing particle coming from outside, it's produced in the gas.
 
  • #10
Awesome, I get this now. Thanks guys!
 

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