Science/Engineering/Technical forums

Well, "it almost worked" and when we get it really going, I have a couple of interesting experiments to try.

The idea went like this - Hornyak detectors see only or mainly fast neutrons. Therefore a moderator with a hole in it in front of one makes it directional...maybe.
To test this idea out, I used 1" thick HDPE between the big fusor (just idling there, enough to see well out of the noise) and...it wasn't that impressive. Either a lot of fast neutrons get through,
or..who knows. Here's the plot - it is fairly obvious where I stuck the hdpe in and took it back out. That declining neutron count after an intial rise at the beginning is characteristic of the fusor no matter what detector is used (we have a few - 3He, B10, another Hornyak). For fun, I also tried sticking a piece of lead sheet in there in the middle of this plot. I even angled it around in case I might see some reflection of neutrons into the detector. Nope. Why did I want to do this anyway?
In part, to help explain why that pattern of neutrons going down (all else controlled the same) with temperture - nothing else seems to matter. Hmmm, what changes with tank temperature - how much D it adsorbed on the walls. So the question becomes - are the neutrons actually being produced locally at the walls? Both Tyler and I've seen data that might mean that before, it'd be nice to do a real cool demo (and make a video of doing it). After all, fusors are so crappy at Q that it could just be that the few rare negatively charged D ions are what's really doing all the fusion in a beam on target mode as they hit the tank walls - the negative ion production rate is terrible, but then, we do see an excess of negative charge, and a terrible fusion rate. That's a hmmmm kind of thing, and it'd be nice to test that idea - true or false, we learn things.

Partner in fusion-crime BillF came out and helped do some basic tests, and he did some camera work. We found out some "interesting" things to say the least, and there are going to be a bunch of youtube videos (I may make them private to us?) showing kind of the smelly underbelly of "real science" - the sort the "real scientists" never show you - they only publish when things match their expectations going in. We're just looking to be correct here - and learn things.

I'll be putting those videos in this post once they get up to you tube - it's going to take a *long time* just to edit things like the floor and other irrelevant stuff out, then upload at 1 megabit. But it'll show, if nothing else, how "regular guys" can in fact get to truth a heck of a lot faster than an experiment that takes months to plan and build (and that's after the major stuff is in place and working reliably) - only to fail and therefore not be written up and published. That's embarrassing to the sensitive grant-seeking academic sorts.

What we did here was use the fusor, running at fairly low settings, to just be a reasonably stable source of neutrons. We then mounted the new hornyak detector around 6" from the edge of the sidearm where we think the neutrons are produced, so we could insert things to see their effect on the neutron count. This was possible due to the fusor being pretty "loud" in neutron output - we ran around 1 million neutrons/second for most of this - and that new Hornyak being pretty sensitive, so we could see plenty of (statistically reliable) neutrons at that distance.

We then inserted various things that are supposed to moderate or stop fast neutrons to see what "contrast ratio" we could get, and got an unpleasant surprise (most moderators let quite the bulk of fast neutrons through till they get really dense and thick, and LiCO3+ wax has no noticeable effect on neutron count when interspersed at 1.5" thick - someone is making a lot of money selling that stuff...and the performance numbers...are horrible (No measurable effect at all!) - but being honest and all, here's that data. We are trying to build a directional neutron "telescope" or at least "pinhole camera" that will let us aim the detector and get some information about where the neutrons are actually being produced. Yes, there is some data out there, kind of, from one source that's not very helpful yet - or replicated - and I have a couple things I want to learn here that this will help with.

Here's a pic of the piece of HDPE that did give us some contrast...not great but it takes at least this much to be "worth it". Our background counts from the standard counter data aq setup - this stuff gets it's own in parallel with the big rig (we can and do compare later on, but the big rig didn't have the spare counter inputs). To wit - one source says most of the fusion is collisions with neutrals, presumably in those nice beams (see eye candy for a nice pic). Could be, the proof is on the weak side for the moment. A theory is that perhaps the neutrons are being largely produced when the rare negative D ion is created - which would be in just the right part of the electrostatic potential well to get full accleration - hits the tank wall at speed, and we get beam-on-target fusion. After all, fusors are so horrible in regards to Q (output over input) that a relatively rare event might account for most or all of the output, and we've also consistently noticed (and it shows here too) - that output goes down as the tank walls heat up. About the only effect that could cause that is less D on the surface of those walls, and the rest is armchair conjecture. BUT! We have the technology, we can build it - we can prove this one way or the other, and do some real science, so here goes.

As usual in this game, I link the site from the video (Assuming I make these public) and I need a post to link to - this is that post, it's far from done yet.
Now for a day or two editing and uploading - Bill took a couple gigs of video (it's a heck of a camera) I need to cut the irrelevant and my cuss words out of, compress and upload.
And I'll apologize in advance for not using the lavalier mic for good audio...we were excited to do some real work and weren't really thinking about production values. Oops, I guess I'm not a real youtuber either.

Video 1 - just the baseline setup. We've got a stable fusor output, a new detector mounted far enough away to try putting things between it and the fusion, and a couple counters to see any effects.
https://youtu.be/w5xmRw0BSpo


The hits just keep on coming (not really, we aren't pro youtubers or videographers by a very long shot).
https://youtu.be/xrwGsJArtsg


One more and I'm done for the day at least:
https://youtu.be/RDCjUMgG8Wg

We tried some LiCO3 we'd cast into wax (which should slow neutrons down to where the Li6 should eat some of them) and it was an utter fail...nice to know. Even without isotopic enrichment from the 7.5% natural abundance of Li6, we'd have been able to see an effect. Nope. Even putting other moderator in front in case the wax wasn't enough (likely) only showed us...no difference at all whether the Li/wax was in the path or not.
Nice to know - we were going to make a lot more as a safety thing. Now we won't waste the time.

Hi Doug
Your recent experiments are very interesting .
In the supposition that the neutron generation occurs at the walls, can we immagine a setup in order to confirm the hypotesis?
May be an internal shutter, covering an important part of the wall, then comparing generation in both conditions.
Also cooling the walls can give some useful info.
Finally, designing a special (and cumbersome) internal surface with more area. Could be a metallic wrapped foil.
What do you think?

Well, right now, I'm working on a couple of things that should illuminate what we want to find out here.
This set of tests showed that with minimal additional effort we can make a sort of directional neutron detector with about 4::1 contrast ratio between where it's pointed and neutrons coming from the sides. So, next is to make a mount that can rotate it around a fusor (there are about to be two here) in operation and see what we see - when pointed at where a beam hits the wall, do we get more?
I'd like to have gotten a better contrast ratio with reasonable size stuff, but we have what we have. Still to finish is the "lens" or in this case "aperture" of our neutron pinhole camera, and the mount, as well as the other fusor (the new system in the upstairs lab) that has a lot more freedom to move such a thing around it's circumference, as it hasn't grown a lot of warts and appendages around where the beams hit. Also, that one is only a 6 way lens, vs an 8 way lens in the big guy (neglecting the beam on the end)

So, if in fact fusion is happening at the walls, it should show as a series of pretty sharp peaks in the detector output as we move around the circumference. If we see really small/wide peaks, it's probably in the beams, if no peaks, in the middle - so we get maybe a little insight, but not the whole story most likely. Baby steps get us there eventually. If I can't find out all I want this way, we may have to make a directional proton scope with energy selection like U of Wisconsin almost finished. I'd really like to have seen that with one more degree of pointing freedom and more data, but evidently each new batch of students changes the direction of their program and there's a strong "not invented here" effect - they were about to do some really good science but dropped it as far as I know.

I'm in the throes of silly things like preparation - if you've done painting, welding, machining or a lot of other things, it's the boring getting ready part that makes the results good. I find that few want to hear about all the little nasties I fight along the way, so...I haven't said much about that - broken ferrules in the cappilary tubing I'm using just aren't that interesting. I have a tiny leak in the upstairs system in the gas inlet setup that will waste some gas by allowing air to get into the gas manifold and destroy its purity. The manifold is perhaps 15 cc and after a few days has leaked halfway up to STP after being taken to vacuum. Doesn't sound like much but if I wanted to fill to say 1/10 of STP and run on that for weeks, not going to work out (and we want to keep that manifold at low pressure so a pulse of the inlet valve won't let in too much gas - it's a harder problem on the smaller system as the same amount of gas let in affect the system pressure more.

Here are some pix of the new system I'm planning to use for this. Right now I'm fighting a bit with what appears to be a really slow leak on the supply manifold side of this little solenoid valve I've modified for this use. I've never seen a faster acting (< 20ms) or smaller wasted volume (about .1 cc) solenoid valve...but it was originally intended to control an air cylinder at high pressure, and let it leak down when commanded - I had to plug the deliberate leak, reverse the direction of flow etc. This setup works fine on the big system; when I found these surplus I bought a bag full of them.
But here, leaks, even a slow one, on the supply side, which wasn't all that well sealed in the original design, is a disaster. I want to put only a few millibars of deuterium into that manifold so one minimal pulse to the valve won't let in too much gas - so air leaking in will destroy purity pretty quickly. This AM I fabricated a teflon washer to back up the evidentlyl inadequate loose O ring it already had between the magnet part and the valve part. I may need to also get a little bit fatter O ring and polish some metal. It's under testing right now.
I used to use that manifold when making glow and gas tubes - you let in X pressure of gas A, B, C while watching the gage, and have a nice supply of mixed gasses (like helium-neon) to fill things from.
Here I just want the one gas, but starting at low pressure because even the "dead" volume in that valve is WAY bigger than desired here, and it's at the point where it's hard to reduce due to tight clearances - I can't really shove in more epoxy or whatever now.