Register to reply

How to detect neutrons using Helium 3

by CraigH
Tags: detect, helium 3, neutron
Share this thread:
CraigH
#1
Sep24-13, 06:12 AM
P: 202
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.
Phys.Org News Partner Physics news on Phys.org
Step lightly: All-optical transistor triggered by single photon promises advances in quantum applications
The unifying framework of symmetry reveals properties of a broad range of physical systems
What time is it in the universe?
SteamKing
#2
Sep24-13, 07:46 AM
Emeritus
Sci Advisor
HW Helper
Thanks
PF Gold
P: 6,533
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.
Vanadium 50
#3
Sep24-13, 08:26 AM
Mentor
Vanadium 50's Avatar
P: 16,356
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.

mfb
#4
Sep24-13, 08:27 AM
Mentor
P: 11,903
How to detect neutrons using Helium 3

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.
snorkack
#5
Sep24-13, 08:36 AM
P: 386
Quote Quote by Vanadium 50 View Post
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?)
CraigH
#6
Sep24-13, 10:47 AM
P: 202
Quote Quote by Vanadium 50 View Post
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?
Vanadium 50
#7
Sep24-13, 11:27 AM
Mentor
Vanadium 50's Avatar
P: 16,356
Helium-3 is a gas.

Spectral lines are irrelevant. It works by ionization.
mfb
#8
Sep24-13, 11:51 AM
Mentor
P: 11,903
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.
Vanadium 50
#9
Sep24-13, 12:23 PM
Mentor
Vanadium 50's Avatar
P: 16,356
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.
CraigH
#10
Sep24-13, 12:29 PM
P: 202
Awesome, I get this now. Thanks guys!


Register to reply

Related Discussions
Playing with NEUTRONS. Neutrons thought experiments. General Physics 12
Is liquid helium composed of both ortho and para-helium? Quantum Physics 6
Helium consists of 2 protons, 2 neutrons, and 2 electrons General Physics 5
Fast neutrons vs thermal neutrons High Energy, Nuclear, Particle Physics 1
Accelerating neutrons, production of ultracold neutrons High Energy, Nuclear, Particle Physics 8