Cube fusor build

For posts specifically relating to fusor design, construction, and operation.
Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel » Tue May 04, 2021 8:47 pm

Frank, too bad we couldn’t get together, hopefully you’ll have a little more time next time you're out here.

Best fit was with an exponential trendline. I have to wonder if the shape of the curve is affected by the geometry of the Hornyak button vs. the angle in which the neutrons interact with the button. For example, with the button centered on the endcap neutrons are most likely interacting fully with the button’s 8mm diameter and 5/8” depth, but as the button is moved towards the cube’s edge the neutrons are more and more interacting with the button from the side. (Hope this makes sense)

Mark,
For these runs with the A/C blowing through the radiator the chamber temp was around 28~29 C, lowest I’ve ever run. One of these days I need to try adding ice to the cooling H2O, try and get a handle on the "how low can you go" point.

Jon Rosenstiel
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Frank Sanns
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Re: Cube fusor build

Post by Frank Sanns » Wed May 05, 2021 4:28 am

If there is a beam line of anisotropy, then why is it following the inverse square law? Pulling out of a beam (using the term loosely) should give a quick drop when starting to remove the detector. Once out of the beam, the drop would then fall off quickly.

I know most of you are convinced that there is more out of the ends but I still am not convinced it is due to neutron direction from fusion itself. I still think it is a geometric artifact on where the fusion is occurring. I know that ALL of the evidence does not exactly support that but some of it does like this most recent experiment. Still pondering.

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Jim Kovalchick
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Re: Cube fusor build

Post by Jim Kovalchick » Wed May 05, 2021 10:42 am

Frank,
I am with you on this one. This is why I have been harping on geometry of detection. You can't put detectors right up against shells when we have said there is a lot of fusion happening on the walls. All this variance proves is that the fusion isn't happening on the walls uniformly. Why would we assume otherwise when Jon's fusor has a single center line beam?

To understand if there is direction to the neutrons, we need to back out our detectors. I don't believe we are making directional neutron beams.

Jim K

JoeBallantyne
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Re: Cube fusor build

Post by JoeBallantyne » Wed May 05, 2021 4:59 pm

Jon, very outstanding work!

One thing you might try if you are worried the angular orientation of the beam relative to your detector might be having an impact, is to simply do a run where you leave the detector centered on the end cap where the total measured neutron flux is the highest, and then rotate your detector 90 degrees in the horizontal plane while maintaining it centered on the beamline. Start with the detector exactly in line with the beam, and end up with the detector at exactly perpendicular to the beam. You could rotate it in both directions (right and left), although I suspect there should not be much difference in the response between the two rotations. You will need to shift the detector slightly in order to keep the beamline centered on the horniak button as you rotate it.

If there is some detector sensitivity to angle, you should see a change in measured output.

You could then use that data to factor out any detector angular sensitivity from your measured neutron output based on side to side displacement of the detector.

Joe.

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Re: Cube fusor build

Post by JoeBallantyne » Wed May 05, 2021 5:22 pm

Another experiment you could do, would be to figure out the exact location on the endcap that the beam is hitting. Make that the center of a circle of sufficient diameter that you can sweep your detector in a quarter circle around that point, always keeping the detector exactly aligned on a line passing through the center of that point, and so when the detector is at 90 degrees to the beamline, it doesn't hit your chamber. ie: make the radius big enough that your detector can sweep continuously around that point without impacting the chamber at any point.

So the front of the detector will be on the circle, and the angle of the body of the detector with the beamline will be zero degrees initially, and will end up at 90 degrees to the beamline. ie: the detector is always exactly aligned with a ray that goes through the center of the beam impact point on the end cap of your chamber.

If a large percentage of fusions are happening in the wall at that point where the beamline hits, and you maintain a constant distance from that point, and those fusions result in isotropic output, then there should be no difference in detected neutron output from that portion of the neutron signal if you move your detector as described.

Since the distance to the point where the fusions are happening is constant, and the horniak button will always be exactly perpendicular to the line that intersects with that point.

If most of the fusions are happening in the end cap point where the beam hits, then the amount of variation you get from this measurement should be significantly less than the one you get from the side to side sweep.

Joe.

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Thu May 06, 2021 12:04 am

I am beginning to see this device as a BOT system fusor! Backing off my position many posts back in this thread. This thing (cube) as long as the ends are kept cool might just implant D in the end caps and at the same time does a good bit of fusion there as all real evidence so well presented here seems to point out. I am also sure fusion is happening in velocity space as well and I'll bet there are good counts to be had from the tube arm walls, just nothing like Jon is getting on the beam line which is obviously where the action is. Of course, in activation work all this beaming will just slow and scatter in the moderator if it does its true job. However, it is nice to concentrate the neutrons at the moderator. That is where beaming comes in real handy. I like it.

Make no mistake, beaming or not, this is still a fusor!....A simple two electrode amateur fusor that is really cookin'! Jon is a master at setting up experiment and relaying great data and results of his efforts. This may be a long thread but a really valuable one that teaches and inspires thoughtful comment and is another way to skin the cat in amateur fusion.

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.

Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel » Fri May 07, 2021 8:59 pm

Frank,
I’ve found that the inverse square law does not hold up well at small source to detector distances. I ran some tests using a 2” x 2” NaI(Tl) detector and a 10 uCi Cs-137 source and found that in order to get good data the source to detector distance should be no less than 4”. What I’m trying to say is, we probably should not put too much faith in close-in measurements.

As to the anisotropy, take a look at pages 18 thru 20 in the attached paper. (Characterization of Neutron Fields Around an Intense Neutron Generator) I believe this applies to our case, but not really sure. (Dammit Frank, I’m a mechanic, not a physicist) Anyway, I would like to hear your thoughts on this.

Joe,
Nice to hear from you! Thanks for the good ideas, I’ll keep them in mind for future reference.

Richard,
I’ve finally come to the same conclusion; the cube is a BOT device.

Pic of a Monte Carlo neutron flux simulation for a BOT device. Looks quite familiar, huh? Link to complete paper below. (Didn’t attach the paper as it’s nearly 18 MB is size)
https://escholarship.org/content/qt6z74 ... ee762b.pdf

Jon Rosenstiel
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Frank Sanns
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Re: Cube fusor build

Post by Frank Sanns » Sat May 08, 2021 9:14 pm

Jon,

Good paper. Nice compilation of lots of information that we have been discussing.

Some conclusions.

1. We agree that close measurements are not good because neither the neutron producing area nor the detector are points. That is why I asked you to throw the top 3 points away on your original curve. I could see they were corrupted because of the near distance. The minimum distance for a good measurement will depend upon the size of the detector. Smaller detectors look more like point detectors at closer distances.

2. Deuterium is a unique beast in that it is such a simple atom, that minor shift between the center of mass of the atom and its charge location (a neutron and a proton), have meaning in the real world. The nucleus is neutral at one end and positively charged at the other. The inverse square at play so and impact from the neutron side is slightly more desirable since there is just a little less repelling charge at that end. By tritium, this effect is much less and the heavier atoms is probably non existent.

3. There is no neutron beam coming out of the ends of fusor. There is a higher probability of of productive collisions when the deuteron is aligned in an electric field that in a random field.

4. The paper also points out that the polarization of the neutrons are also anisotropic. Good luck with that portion of the experiment. Although, it is interesting to think about that as keeping your detector in place and rotating it 90 degrees should also show a difference. Want to handle some cadmium with slots cut in it for the front of your detectors. lol. I AM KIDDING. DON'T EVEN THINK ABOUT IT. Gadolinium is probably not a whole lot better. Maybe Boron Carbide pieces arranged into slats. Just thinking.

5. Your results are most excellent Jon. The effect is not a huge one but you are detecting it. It is important to point out that the confidence in your numbers is in your technique and setup but the repetition of measurements along multiple changes gives the confidence in the numbers. I single reading close and at another distance for a total of two points cannot tell the story. Multiple data points in good agreement gives a good confidence interval to evaluate the data.

Jon Rosenstiel
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Re: Cube fusor build

Post by Jon Rosenstiel » Tue May 25, 2021 9:15 pm

Frank, you were correct in your skepticism, allow me to explain.

The following 0-degree/90-degree fast neutron-rate comparisons are based on the assumption that the neutron formation area (NFA) of the cube fusor is centered on (or very close to) the endcap surface. Detector for this test was a 2” diameter by 0.6” thick Hornyak button coupled to a Thorn/EMI 9258KB03 PMT. NIM electronics consisted of the following: Ortec 4001M minibin, Canberra 3102D hv supply, Ortec 113 preamp, Ortec 572 amp, Ortec 550 SCA, Tennelec 534 counter/timer. Both amp and SCA outputs were monitored on an oscilloscope.

My initial plan was to run a 0/90-degree comparison at 3” and 13” to the NFA. (13” is the maximum my setup would allow) At 3” to the NFA the 0-degree position count-rate was about 22% higher than that at 90 degrees. At 13” I expected to find a smaller difference in count-rate between the 0/90-degree positions, maybe somewhere around 15%. I was quite surprised when the 0/90 difference increased to 37%. Additional data points at 5.5”, 8”, and 10.5” did nothing to change things.

At this point I was somewhat baffled so I made a simple drawing of the cube. First thing I noticed was that at 0-degrees there is 0.375” of aluminum between the NFA and the detector vs. 2” of aluminum at 90-degrees. Seems so simple, but something that I had, up to this point, failed to recognize.

Ok, with the above in mind I placed a block of aluminum 1.625” in thickness between the detector and the endcap at the 0-degree position to mimic the 2” of aluminum at the 90-degree position. (Endcap + Al block = 2.0”)

With the 1.625” Al block in place a rerun of the 0/90-degree comparison at 3” and 13” resulted in the following.
At 3” to NFA: 0-deg measurement was 2.3% higher than at 90-deg.
At 13” to NFA: 90-deg measurement was 2.7% higher than at 0-deg.

So, what this is telling me is that the previously measured anisotropy was nothing more than neutron absorption/moderation/scattering in the cube’s aluminum walls. The following Richard Feynman quote comes to mind: “The first principle is that you must not fool yourself – and you are the easiest person to fool”.

Jon Rosenstiel
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Drawing_1.jpg
Detector at 90-degree position, 3" from NFA. Shaded areas are 6061 aluminum.
Neutron, sca pulses.jpg
Long-tailed pulse from the ZnS(Ag) loaded scintillator & data pulse from the SCA.
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Setup

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Richard Hull
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Re: Cube fusor build

Post by Richard Hull » Tue May 25, 2021 11:58 pm

Great report and observation, Jon. You are giving a lot of good information based on interesting experiment in detection and sorting out anisotropy. Sure, fooling oneself is easy.

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.

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