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: 198
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
Physicists unlock nature of high-temperature superconductivity
Serial time-encoded amplified microscopy for ultrafast imaging based on multi-wavelength laser
Measuring the smallest magnets: Physicists measured magnetic interactions between single electrons
SteamKing
#2
Sep24-13, 07:46 AM
Emeritus
Sci Advisor
HW Helper
Thanks
PF Gold
P: 6,314
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: 16,171
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: 11,589
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: 381
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: 198
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: 16,171
Helium-3 is a gas.

Spectral lines are irrelevant. It works by ionization.
mfb
#8
Sep24-13, 11:51 AM
Mentor
P: 11,589
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: 16,171
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: 198
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