Verification of Neutrons for Student Project

For posts specifically relating to fusor design, construction, and operation.
User avatar
Richard Hull
Site Admin
Posts: 10727
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Verification of Neutrons for Student Project

Post by Richard Hull » Mon Jul 31, 2017 5:38 am

That big window appears to be part of a load-lock that would allow easy access to parts change and internal experiments. Nice!
The gamma radiation should be non-existant. The X radiation of any significance would be limited to some kev fraction of the maximum applied voltage.
There might be some high energy x-rays from what protons, tritons and 3He atoms that slam into the walls, but you might not see that with most gamma specs due to the low incidence of such radiation and the low stopping power of detectors commonly used by amateurs.

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.

Bruce Meagher
Posts: 99
Joined: Fri May 13, 2011 3:25 am
Real name: Bruce Meagher
Location: San Diego

Re: Verification of Neutrons for Student Project

Post by Bruce Meagher » Tue Aug 01, 2017 1:17 am

Richard,

I agree the x-ray radiation produced by a fusor will be limited to the power supply's max voltage (with the average energy only a fraction of that maximum). However, I believe you’ll find the bremsstrahlung radiation yield for the heavy charged particles (protons, tritons, He3, …) to be essentially zero. Recall the Coulomb-force interactions are not only proportional to the square of the target’s atomic number (Z^2) but are also proportional to the inverse square of the charged particle mass (1/m^2) at a given velocity.

From Attix “…bremsstrahlung generation by charged particles other than electrons is totally insignificant. As a practical consequence, the spectroscopy of x-rays generated by proton beams colliding with matter reveals the presence of only the characteristic x-ray lines resulting from knock-on collisions, with no detectable bremsstrahlung background…”

Bruce
Last edited by Bruce Meagher on Wed Aug 02, 2017 6:58 am, edited 1 time in total.

User avatar
Richard Hull
Site Admin
Posts: 10727
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Verification of Neutrons for Student Project

Post by Richard Hull » Wed Aug 02, 2017 1:38 am

I am sure the bremsstrahlung is there, but the key word is "not detectable" outside the shell. Again, as there is little fusion there is also only a little bremsstrahlung, most being of lower energy and contained and absorbed in the vessel.

There will be little or no gamma spectrum at all to resolve outside the fusor beyond the fact that it is an effective gas filled, theoretically dangerous x-ray tube that only the most penetrating x-rays make it out through the shell, provided enough voltage is applied to allow, even this.

It is good that a working fusor can't be made of glass or other x-ray transmissive material. Aluminum might be an issue, perhaps by an order of magnitude of more!

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.

John Futter
Posts: 1270
Joined: Thu Apr 22, 2004 2:29 am
Real name:
Contact:

Re: Verification of Neutrons for Student Project

Post by John Futter » Wed Aug 02, 2017 3:34 am

Yes the bremsstrahlung is there and is used for depth profiling of elements at or near the surface of materials.
As your ion goes in it losses energy via collision cascades (bremsstrahlung). We do this at work to depth profile elements from hydrogen to uranium and our results give concentration, and depth (especially in the implanted ion arena) in ppm and depth to a few microns

Bruce Meagher
Posts: 99
Joined: Fri May 13, 2011 3:25 am
Real name: Bruce Meagher
Location: San Diego

Re: Verification of Neutrons for Student Project

Post by Bruce Meagher » Tue Aug 08, 2017 6:29 pm

John,

I’ve heard rumors the laws of physics are different in New Zealand ;-)… However, I’m pretty sure your statement above is incorrect. The characteristic X-rays created when the heavy charge particles knock out electrons is not bremsstrahlung radiation. Bremsstrahlung radiation from heavy charged particles is theoretically possible, but the probability is so low it’s not measurable at any energy of interest to fusion. Are you sure it’s bremsstrahlung radiation you’re measuring in your ion depth profiling?

Sorry for hijacking your thread Tom, and congratulations to you and your team on an outstanding achievement!

Bruce
Last edited by Bruce Meagher on Thu Aug 10, 2017 5:49 am, edited 1 time in total.

John Futter
Posts: 1270
Joined: Thu Apr 22, 2004 2:29 am
Real name:
Contact:

Re: Verification of Neutrons for Student Project

Post by John Futter » Wed Aug 09, 2017 9:12 am

Bruce
I never did say anything about x-rays
bremsstrahlung is braking radiation ( cascade energy transfer) and applies to ions too.
RBS (Rutherford Back scatter uses this to identify what atoms are present and at what depth using this info.
As far As I am concerned I can see why x-ray bremsstrahlung is so prevalent due to the mass of the electron conpared to any periodic table ion /atom
so the electron is a pingpong ball and hydrogen ia a bowling ball electron hits hydrogen and momentum and energy are conserved so the electron leaves losing a very small amount of energy equal to the amount the electron has displaced the hydrogen nuclei ie many thousands to one
now take a proton hitting a silicon atom yes the proton loses plenty of energy which is transferred to the silicon nuclei which moves quite abit a bit like a water melon or pumkin being hit by the bowling ball.
This is all very simplistic and there is no hitting per se it is the interaction with the electric and magnetic fields of each atom being interacted with.
so with electrons many many collisions take place with very small amounts of energy transferred each collision which = heaps of bremsstrahlung
but with ion the difference in mass is much less so fewer collisions transfer the energy so the bremsstrahlung tails off exrtemely quickly
see here for more info
http://www.nuclear-power.net/nuclear-po ... rahlung-2/

The big problem is wikipedia hints at ions but doesn't say, as just about all examples talk about electrons and x-rays

Post Reply