NWNC CR39 Project- Summary and Request to Active Fusioneers

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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JakeJHecla
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NWNC CR39 Project- Summary and Request to Active Fusioneers

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Hello All- As Carl Greninger has posted, a team of three students from Northwest Nuclear Consortium has been working on a project involving mapping the neutron output from our onsite fusor. This is in essence an attempt to verify/disprove the idea that the fusor radiates neutrons isotropically, as some (T. Christensen and R. Tubbs) have observed irregularities. I would like to present our findings in this post and also ask for other amateur scientists here to aid us with the verification of our data. If possible, we would greatly appreciate any measurements taken of the neutron flux from other fusors at different points equidistant from the poissor Our findings (see below) indicate that our fusor is not radiating neutrons equally in all directions with reference to the poissor. We believe this may be due to beam-on-target effects where the "star mode" beams impinge on the reactor vessel. We postulate this is creating sources of neutrons away from the poissor and closer to our detectors, distorting the flux to poissor distance relationship that we would normally observe. If other people with functioning fusors and reliable detectors have the time, we would greatly appreciate measurements of the neutron flux at different points around the reactor. These must be taken at the same distance from the poissor, but at different locations (e.g. back, front, left or right of the chamber) ideally, any sources of interference such as moderators should be minimized. Many thanks to anyone who takes the time to undertake this task!

Project Summary: Ray Maung, Rian Chandra and myself designed an experiment employing CR39 SSNTDs to determine the neutron flux distribution around the reactor. This involved building a 50cm side length cube of foam-core board with 230 2cm x 2cm slides affixed to the inside. These were exposed to neutrons, removed, etched, carefully photographed and virtually re-assembled to make a spherical model of the exposure the slides received (corrected for 1/r^2 variations). Should the fusor radiate neutrons solely from the poissor, this sphere should show roughly equal (1/r^2 corrected) values at all points. However, the data we gathered produced a pattern with strong maxima near the front and rear of the reactor, and minima near the sides of the six-way cross. We verified this using BTI Bubble detectors during subsequent runs (image above). At the moment, we have not come to a conclusion as to why we are observing this pattern, and we are in search of more data to clarify our results. Any help is welcome. I have a PDF of the poster we submitted at the Washington State Science Fair, which includes further information not given in the post. Please email me if you would like to look it over if you are so inclined. We always appreciate constructive criticism! (Sadly I cannot upload .pdf files for some reason).


Image

The arrangement of the CR39 slides on the foam core

Image-Rear
Image -Front
Image -Left
Image-Right

The resulting patterns (Note: the slide mapping program results in maps that are a bit crude, the graph below is far more informative)

Image

This graph describes the exposure of the slides (1/r^2 corrected) as a function of the position clockwise in the x-y plane from the front of the reactor. It shows two clear peaks (the far left and right of the graph overlap) that are located near the front and rear.

Image

Two BTI detectors at the same distance but located at different locations 16.5cm from the poissor (one on the front indicating 95+ bubbles, one on the right indicating ~25).


-Jake J. Hecla
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Steven Sesselmann
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by Steven Sesselmann »

Jake,

Well done, great to see some new science coming out of fusion research. many of us have noticed anisotropic neutron flux, but have not been able to prove it. I like the way you have designed the experiment and executed it. Do you think it would be possible to superimpose a diagram of the fusor on the 3D colour coded image?

This would help us see where the hot spots are. Not sure if the thick SS flanges could have an effect on the flux, or if it all happens inside the chamber.

Will be very interesting to see more work in this area.

Steven
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

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I think, in the past, we have always assumed that fusion actually occurs throughout the system and even some beam on target where the walls slowly accumulate a layer of slow neutral D atoms or molecules. This deposition would not necessarily be uniform.

Secondly ,the flanges (thick SS) will certainly tend to scatter even fast neutrons preferentially while the comparitive thin shell would have a vastly reduced scattering section. In general, one might expect at least a 4:1 higher scattering and or absorption where thick flanges are involved over that of the thin shell walls.

Still, your observations are a very good piece of scientific work that proves much of what has only been assumed, heretofore. I doubt if any smallish detector volume will ever give a decent idea of any sort of average flux signature. Very long, (20+ inches), 3He tubes in long moderators placed close enough or far enough away might be the best way to get a general idea of what the true fusion rate might be. The distant ones might provide the best overall data but would demand uniform running for a longer period to grab a decent amount of data.

Certainly a very small remball detector at 6 feet from the device that could be moved about would really map out the neutron story provided stable operation and long run times were possible. (which they usually aren't)

For the most part, any detector is suitable, if left fixed forever, in letting one know if any system mechanical of electrical modifications are positive or negative in ultimate fusion effect.

Your work points out the extreme advantages and disadvantages of the fusor.

Fusors have hot spots which, if located, can aid in activation work by positioning the "neutron oven" in contact with them.
Fusors never produce uniform fluxes over their entire external surface areas. (they are not pure,isotropic neutron sources) However, we know that statistically, the fusion events, themselves, are indeed isotropic emitters.

Again, great work.

Richard Hull
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by Jon Rosenstiel »

Adding to what Richard said...

In my opinion the only way this can be done is to place the neutron detector(s) inside the chamber. Flanges, feedthroughs, vacuum valves, etc. all attenuate and shape the neutron flux external to the chamber to various degrees through elastic and inelastic scattering.

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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by JakeJHecla »

Richard, Jon- I attempted to calculate the number of neutrons that would interact in any way (using Sigma total) with the SS conflats assuming the plates are 2cm thick, 16.5 cm from the poissor and that the SS has a total neutron cross section at 2.5MeV of ~3 barns. I came up with a number that indicated less than .01 % of neutrons would interact. Could someone else run the numbers and verify that I'm not doing something terribly wrong?
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by JakeJHecla »

Looks like I messed up units. The real number should be in the range of 5% interact with the plate. Still far smaller than the observed deviation
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by Jon Rosenstiel »

Jake,

May (or may not) be applicable...

viewtopic.php?f=13&t=5781
viewtopic.php?f=13&t=5803

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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by JakeJHecla »

Jon- Thanks for pointing me to those threads. I had not seen those investigations before! I would like to note that the observations we took seemed to indicate the reverse of what one would expect (and what you saw with the flanges/BTIs). That is, we saw significantly higher neutron counts near the thick SS plates, and lower values near the viewport. At the request of the research team, Carl Greninger ran a shield-up test with the Reuter-Stokes 12" HE-3 tube, and found the CR39/BTI pattern remained consistent. When placed at 16.5cm from the reactor, Carl saw 25-26uSv/hr at the front and rear, while the sides were in the range of 11-14uSv/hr. I'm now really curious as to what is going on here, especially since it seems to not agree with previous measurements by better qualified scientists (never a good sign...).
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

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Hi, I'll throw out a theory as to why. The capacitive coupling to the ground shell causes more charge on those parts of the inner grid, insert wedges of high dialectic constant material between the outer grid and inner would probable increase efficiency. It looks like the fusion is happening were the acceleration is the fastest, before it slows down and enters the electron soup?
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by Carl Willis »

Hi Jake,

This is an impressive and well-executed experiment. Good job to all who participated in the design and analysis.

I'm curious about your uncertainty (or predicted uncertainty) in these experiments. I think enough measurements have been done to suggest that you are seeing real variations, but keeping track of statistical quality would lend a further bit of credibility to your results.

I suspect the explanation for the variability you detect has to do with materials and geometry that aren't being accounted for in the neutronic environment. Materials surrounding the fusor can scatter neutrons away from the detector, moderate and absorb them so that fewer interact with the detector, and reflect them back into the detector. In addition to stainless steel, you have water cooling coils on the fusor, and possibly a large hydrogenous shield surrounding the apparatus. An alternative hypothesis is that fusion is not occurring in a homogenous central volume. Your ion current density in this fusor may not be azimuthally symmetric, leading to hot beams within some arms of the chamber. I think among the least plausible hypotheses is any suggestion that anisotropy in the nuclear reaction itself is responsible. This would implicate some cryptic reaction with major kinematic constraints--not a property of DD fusion.

Good luck in your hunt for answers, and thanks for a good, solid scientific post.

-Carl
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

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" I think among the least plausible hypotheses is any suggestion that anisotropy in the nuclear reaction itself is responsible"
Why not?
Run your fuser with air, and see what the color is with a camera, if purple its magnetic ,electrical based and will follow mhd ,lenz principle with the instabilities.
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

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How are the magnetic fields going to influence neutrons?

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Re: NWNC CR39 Project- Summary and Request to Active Fusione

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"How are the magnetic fields going to influence neutrons?", Positivity charged ions that leave the center head towards the inner grid and fuse with incoming positively charged ions, what is positivity charged and what is not is the area of electrons, which make there own magnetic field by moving. Are you serious?
Yeah, were the source of fusion is happen is what I was meaning, not what happens after it has fused
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by Carl Willis »

Andy, I can't make any sense of what your argument is, nor how it relates to the thread's topic. Sorry.
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

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Andy,

Individual D-D fusions, (the nuclear process), within any volume are statisitcally isotropic emitters. This is a well established fact. Externally measured neutron anisotropy related to this discussion is felt to be related to fusor system construction, operational peculiarities and surrounding structure scattering.

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
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

Post by Andrew Haynes »

Richard Hull , I take it that individual it is isotropic , but due to the grid nature(say fast speed closer to the wire) there will be more fusion reaction per volume in that area, if it all radiates isotropic there will be more in those areas.
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Re: NWNC CR39 Project- Summary and Request to Active Fusione

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My post states that clearly. Any anisotropy would be due to construction, operational issues and unequal scattering. So what is the big issue here. I also state that the fusor is not an isotropic source for all those reasons. D-D Fusion, itself, is always isotropic. Re-read my post.

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
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