Neutron gun...

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Post Reply
Posts: 28
Joined: Mon Feb 26, 2007 8:17 pm
Real name:

Neutron gun...

Post by TheTim » Wed Apr 04, 2007 1:11 am

I understand the basic principles of ion/electron gun function...I'm curious to know if it's possible to create a directional neutron gun. I don't mean making an omni-direction neutron generator and blocking it all the way around except for a small opening...That's not exactly directional...

Obviously neutrons lack charge, so I would assume differentially polarized electric or magnetic fields would do absolutely nothing.

User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 11:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA

Re: Neutron gun...

Post by Carl Willis » Wed Apr 04, 2007 1:57 am

Hi Timothy

Getting highly directional neutrons is possible via kinematic constraint in the reaction used to produce the neutrons. Consider an endothermic reaction like Li-7(p,n)Be-7, whose threshold is about 1.8 MeV. If you carry out this reaction with a beam of protons incident on a piece of lithium right at 1.8 MeV, momentum and energy can only be simultaneously conserved if the neutron is expelled into a very small forward-directed angle. The cost of using this method to make a beam of neutrons is the low efficiency. Almost all of the proton beam energy is wasted heating the target. Any other similar threshold (X,n) reaction could be used in a similar manner.

Carl Willis
TEL: +1-505-412-3277

User avatar
Richard Hull
Posts: 11531
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Neutron gun...

Post by Richard Hull » Wed Apr 04, 2007 5:37 pm

Carl beat me to the Li+P reaction, which is classic for neutrons in the forward direction. There are others as Carl notes.

The cost of such a very inefficent source would be in the $50,000 range with new stuff used. Getting the proton beam up to 1.8 mev + at a sufficient beam current to be effective would be the real cost here.

Got big bucks? You can have a tolerable beam of neutrons all within the confines of a small 8X12 foot room full of gear, complete with leathal x-ray radiation and other sprays of EM radiation.

Looking for a cheap beam? You are back to blocking off a small section of an isotropic source operated at low cost.

Again, all hinges on your desired beam energy or desired flux.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Post Reply