How to detect neutrons using Helium 3

In summary, helium-3 has a high probability of fusing with thermal neutrons, producing tritium and hydrogen. This reaction can be detected through ionization in the gas, as well as through the production of high-energetic hydrogen nuclei. The ionization is caused by the high kinetic energy of the reaction products. Overall, helium-3 is a gas and the spectral lines are not relevant for detection.
  • #1
CraigH
222
1
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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  • #2
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.
 
  • #3
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.
 
  • #4
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.
 
  • #5
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?)
 
  • #6
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?
 
  • #7
Helium-3 is a gas.

Spectral lines are irrelevant. It works by ionization.
 
  • #8
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.
 
  • #9
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!
 

1. How does a Helium 3 detector work to detect neutrons?

The Helium 3 detector works by using the properties of Helium 3 gas to detect the presence of neutrons. When a neutron enters the detector, it collides with the Helium 3 atoms, causing them to release an electron. This electron is then detected, indicating the presence of a neutron.

2. What makes Helium 3 a good material for neutron detection?

Helium 3 has a high cross section for neutron capture, meaning that it is very likely to interact with and capture neutrons. Additionally, Helium 3 gas can be easily contained and purified, making it a reliable and efficient material for neutron detection.

3. Can Helium 3 detectors differentiate between different types of neutrons?

Yes, Helium 3 detectors can differentiate between different types of neutrons based on their energy levels. Fast neutrons, which have higher energy levels, produce a stronger signal in the detector compared to thermal neutrons, which have lower energy levels.

4. Are there any limitations or drawbacks to using Helium 3 detectors?

One limitation of Helium 3 detectors is their sensitivity to environmental factors such as temperature and pressure. Changes in these factors can affect the performance of the detector. Additionally, Helium 3 is a rare isotope, which makes it expensive and difficult to obtain in large quantities.

5. Can Helium 3 detectors be used for other applications besides neutron detection?

Yes, Helium 3 detectors have been used in other fields such as medical imaging and oil exploration. They can also be used to detect other particles such as alpha and beta particles. However, their primary use is for neutron detection due to their high sensitivity and efficiency for this purpose.

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