Verification of Neutrons for Student Project

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Tom Bales
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Verification of Neutrons for Student Project

Post by Tom Bales »

It's been a whole year since we have been able to complete the tests Richard asked us to do. Between summers, our students are mostly occupied with school, so it's only been this month that we've been able to get the fusor running again. During the off time we changed our vacuum chamber from the previous one, which was an "ebay special" that had an unfortunate geometry which forced us to have a small (2") anode basket, resulting in a lot of arcing. The new chamber that we call "Mark III" is made from an off-the-shelf six-way 8" conflat cross, so everything is axi-symmetric, so there is room for a 5" anode basket to go with our 1" cathode basket. The larger anode basket, farther from the walls of the chamber and coupled to a grounded guard cage that surrounds the cathode stalk, has pretty much eliminated arcing, so we can keep our Lambda power supply running more than a few seconds at a time. We also improved the cathode high-voltage stalk construction so that there are multiple layers of concentric tubes of aluminum oxide ceramic and quartz tubing. Towards the end of an hour-long session we could see cracking in some of the tubes, but there wasn't enough arcing to shut down the HV power supply.

We added an additional high-vacuum butterfly valve between the chamber and the "Hi-vac" valve on the diffusion pump. We use it as a throttle to minimize the consumption of deuterium gas. The diffusion pump pulls out a lot of gas, so we have to either throttle it or supply a lot of deuterium. With the throttle arrangement, keeping the chamber at 13-15 microns pressure, we consume about half of the gas in our reservoir tank in five to ten minutes. The reservoir tank is a left-over lecture bottle that we refill periodically to 15 psig from the deuterium tank (2 atmospheres, absolute). In rough numbers, then, we're using less than 500 standard cc of D2 every five minutes of run time. A lecture bottle holds 45 liters of D2, so we could get nearly a hundred five-minute runs from a full lecture bottle ($375). At that rate, it doesn't seem so expensive. (Don't ask me what an off-the-shelf 8" conflat six-way cross costs--it way exceeds my hobby budget.)

Last summer we submitted our data and a report for what we thought was a good fusion run with deuterium. Richard wisely asked us to do one more thing: demonstrate that the neutron readings we were getting would greatly diminish when the moderator was removed. It was a good idea, too, because once before we had fallen victim to wishful thinking when our neutron detector wasn't working properly (and, mostly just indicated the presence of electrical noise). So, we set that demonstration as our next goal. However, our old fusor was so unstable that it was impossible to keep it running long enough to actually do the "with-moderator/without-moderator/with-moderator" experiment. Biting the bullet, we decided to completely rebuild the chamber so that we could get arc-free running. Once we got it together last week, we were able to operate more or less consistently for minutes at a time, and the neutron rate was higher than with the old setup. Following is a dropbox link to a video and full report on our run of 21Jul17, in which we removed and replaced the moderator several times while operating (with no other changes being made to the system during that time). Richard was right, of course--once you've seen the neutron rate rise and fall with the presence of the moderator, it makes a believer of you.

All members are welcome to comment and suggest enhancements. We have a few weeks left in the summer, and we plan to do some more runs with more comprehensive videos and better images. (For our previous submission, look in this thread for "Neutrons, finally. Student fusor project successful run" from 02Aug16.)

Our students this summer have been Tomas Panilla, Kat Cochran, Greg Bales, Ines Panilla, and Pedro Pavao. All are in high school, so we limited our celebration to high-fives.

Link to full report and video in dropbox: https://www.dropbox.com/sh/0dhl94o4ii77 ... qFmNa?dl=0
Attachments
Low reading, 8 sec later, without moderator
Low reading, 8 sec later, without moderator
High reading, with moderator
High reading, with moderator
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Richard Hull
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Re: Verification of Neutrons for Student Project

Post by Richard Hull »

I could not get into the drop box. I will not join or become a member.
I sounds like you are doing things right.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
John Futter
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Re: Verification of Neutrons for Student Project

Post by John Futter »

Tom
I agree with Richard
I did have dropbox @ work and a Virus came through my account into the work system (and yes we have a good system but sharing an account with two universities is all that was needed)
please post things direct to this site so your effort does not become a dead thread whenever whatever share site decides you are not a member or has folded for whatever reason.

there are quite a few examples in each forum here already don't add to them
Tom Bales
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Re: Verification of Neutrons for Student Project

Post by Tom Bales »

Here is a compressed version of the report in pdf format. I can't get our video small enough to upload.


Thanks for your consideration,

Tom
Attachments
Fusor run of 21Jul17, Report with MkIII Chamber, compressed.pdf
MkIII Report for 21Jul17
(1.47 MiB) Downloaded 361 times
Tom Bales
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Re: Verification of Neutrons for Student Project

Post by Tom Bales »

Here's the edited video of the MkIII fusor run on 21Jul17:
https://youtu.be/w-zOR6YF4AY
Tom Bales
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Re: Verification of Neutrons for Student Project

Post by Tom Bales »

Rats. I left off a couple of the team members' names. The whole team is: Pedro Pavao, Tomas Pinilla, Kat Cochran, Zeke Andreassen, Gregory Bales.
Attachments
Fusor run of 21Jul17, Report with MkIII Chamber, revA.pdf
MkIII Fusion Report. Corrected team names.
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Richard Hull
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Re: Verification of Neutrons for Student Project

Post by Richard Hull »

Great work! The you tube video was the proof of the pudding. Removal of a moderator and no counting followed by replacement with counting resuming is the tell-tale signature of neutrons being counted.

I have placed the team names in the Neutron club.

The clicking in the background on the video had to be another GM counter or something and not coming from the neutron counter, I am assuming.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Tom Bales
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Re: Verification of Neutrons for Student Project

Post by Tom Bales »

Thanks, Richard! How exciting--a dream come true.

(Would you mind adding my name to our ERGO Fusion team?)
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Scott Moroch
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Re: Verification of Neutrons for Student Project

Post by Scott Moroch »

Excellent job team, congrats on your accomplishment. I am curious however as to what precautions have been taken for limiting exposure to x-rays. With a large glass access door and a 4.5" conflat viewport, I would expect x-rays are pouring out at the voltages required for fusion (even at 25-30kV). Other areas for concern include the glass ion gauge which will be completely transparent to x-rays. Perhaps I missed something in the writeup about shielding. Regardless, I suggest some sheet lead to cover the areas I discussed during operation.

Best of luck in the future.

Scott Moroch
"In the middle of difficulty lies opportunity"
-Albert Einstein
Tom Bales
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Re: Verification of Neutrons for Student Project

Post by Tom Bales »

Scott--thanks for your suggestions. Now that we can run consistently at high voltage, it is time to be more deliberate about shielding, for sure. We have some lead sheet, and I'm arranging to get some Pb-loaded plastic to cover the windows. Also, we are hooking up a gamma spectrometer, so we can see what energies we have to deal with. One thing leads to another--that's where the fun is.

Tom
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Richard Hull
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Re: Verification of Neutrons for Student Project

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Bruce Meagher
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Re: Verification of Neutrons for Student Project

Post by Bruce Meagher »

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 2:58 am, edited 1 time in total.
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Richard Hull
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Re: Verification of Neutrons for Student Project

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
John Futter
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Re: Verification of Neutrons for Student Project

Post by John Futter »

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
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Re: Verification of Neutrons for Student Project

Post by Bruce Meagher »

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 1:49 am, edited 1 time in total.
John Futter
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Re: Verification of Neutrons for Student Project

Post by John Futter »

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
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