Track detectors

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Maciek Szymanski
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Re: Track detectors

Post by Maciek Szymanski »

That are the grat news Jon! Let us stick to the loacations for which you have the best knowlege about the flux. Regarding the exposure: For the limited knowledge we have now the efficiency may be assumed to be 30%. For the reliable counting it is good to have minimum 500 tracks/mm2 and not more than 5000 tracks/mm2. So the exposure sould be between 1500 and 15000 N/mm2. It would be nice to have each set of the detectors exposed at the different level in this range.
As for the x-rays - if you can specify the approximate dose I can do a separate test using the x-ray tube I have at work.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
Jon Rosenstiel
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Re: Track detectors

Post by Jon Rosenstiel »

Maciek,
Recommended exposure at both near and far positions works well at 10 and 20 cm. Calculations show that at those positions both minimum (150000 N/cm^2) and maximum (1500000 N/cm^2) exposures can easily be met. I should be able to knock this out within the next couple of days.

As to my inverse square conundrum…
For longer than I care to admit I’ve been puzzled by unusual and inconsistent inverse square measurements of the cube’s neutrons. Just recently it finally occurred to me that I had not been taking into account the neutrons being emitted from the opposite anode.
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Inverse square model
Inverse square model
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Richard Hull
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Re: Track detectors

Post by Richard Hull »

Just my thoughts gathered from what others have been posting. I once held that the spherical fusor produced the classic perfectly isotropic emission of neutrons. I was disabused of this thought pattern around 2006 with reports from the Washington group doing good experiment. The matter quickly was dropped as we looked for a hot spot to position our moderators, while making them larger using larger detectors so as to seek some moderate, average TIER readings. In only recent years have a lot of tilting as windmills occurred via experiment, spurred on by the total abandonment of the spherical devices in favor of a supposedly BOT approach to favor a more directed neutron beaming.

The beaming seems apparent but is not absolute as fusion at our level is not to be in the true thermal sense, but more in the quantum probabilistic manner where directionality itself seems skewed with some often significant scattering. I feel we must admit to not one semblance of purity of effort in our amateur efforts. We just are not in control of the parameters. No two fusors are alike or are operated alike.

I applaud the bold and great efforts to get a handle on the question, "Where are the neutron most prevalent?" "How much scatter is there?" These are very doable, of course. It is a mere job of multipoint measurement done well over, ideally, a 360 degree sphere about the device at a fixed distance. But the results apply to that one device only and to perhaps any absolute carbon copy device made to the original exact specs and materials.

I am especially interested in the results of the track detection efforts underway expressed in this thread.

The discussion of lab scattered neutrons, cold neutrons, and such meaningless twaddle only figures in on low output devices or to strong devices where measurements are taken at unreasonably long device to detector ranges. It is to be remembered that at the strongest point in the best of fusors, there is little to discuss related to a true laboratory, reactor grade neutron "flux" or "fluence". The same goes for any discussion of scattering affecting results if near zero detector to detector distances are in play.

I fear our old spherical devices were "real" fusors, for they had in their original design, geodesic grids with multiple BOT points within the sphere in pseudo-isotropic emission. The modern BOT fusor devices, (bi-directional) would be better served as being assembled into single point, true beam on target, linear ion accelerators if more of less intense direct neutron beam sources are desired. It is all real D-D fusion, after all.

Again not wet-blanketing all the recent work, it is refreshing and exhilarating to see it being done and well reported on. My skin in this game is neutrons and not fusion at all, it never was. I now fully realize the spherical fusor is the most artistically beautiful expression of the amateur fusion effort with the most beautiful symmetrical imagery. Yet it will forever remain the weakest of all amateur neutron sources when employing small moderators using small detection or activation efforts where the main object of experiment is concentrated neutron output.

Richard
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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Jim Kovalchick
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Re: Track detectors

Post by Jim Kovalchick »

I agree with Richard's discussion. The concept of TIER is a lot more complex than we can understand with our moderated tube detectors hitched up close to our fusors. Calibrating then with fast neutron bubble detectors or CR 39 plastic helps, but unless one maps the fast neutron flux with detail 360 around the fusor, discussing TIER is almost silly. Even after a map is made, Monte Carlo may be needed to tell the tale. It is apparent that point source calculations for TIER are only telling us what the true TIER is less than.

The advent of the cube fusor should be seen as our effective liberation from the futility of comparing each other's fusors by tier. We should really be looking at only the simple concept of flux. Fusors are NOT energy devices. They are neutron flux sources, and getting lots of neutrons as quickly as we can through a cross sectional area we have access to is the name of the game. A big TIER means nothing if by the point you can first put an activation target in the neutrons, the spread is too thin to do anything. We should instead care about flux and fluence. This game should be as much about engineering a useful neutron source as it is about pretending to master the physics of IEC.

It probably looks like I drifted from this thread's topic, but it is my belief that the CR 39 studies will support my point. There is no TIER to be found here, only some good information about flux that we should have been talking about all along.

Jim K
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Richard Hull
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Re: Track detectors

Post by Richard Hull »

Jim supported my thoughts. I have considered a linear accelerator, but the x-ray blast would be significant and one would lose certain aspects of IEC, (kinetic velocity space effects), in such an effort. The track results just might tell us a lot, yet.

It is to be remembered that fusion in velocity space is, by nature isotropic while surmised spherical shell BOT fusion is more directional. All fusion is still ruled by quantum probabilities.

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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Mark Rowley
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Re: Track detectors

Post by Mark Rowley »

Maciek,
I just received the detectors back from Jon (thanks Jon!) and will have them shipped over to you later this week.

Many thanks to Jon R for helping out with the neuts! My system has been totally disassembled due to an upcoming home sale and when I get back in the game it will be beam-on-target from this point forward. Jon's willingness to step in for me is highly appreciated.

Looking forward to the detector results!

Mark Rowley
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Maciek Szymanski
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Re: Track detectors

Post by Maciek Szymanski »

The package with the detectors just arrived back in Warsaw. Seems tha everything is in perfect condition. I am very keen to do de etching and see the results, but unfortunately on Sunday I'm again traveling to Prague for experiment. I will be back on October 20th and will do the etching as soon as I possible.
I would like to thank Mark and Jon for cooperation.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
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