Shields up!

For Farnsworth type designs.

Shields up!

Postby Doug Coulter » Sun Jun 29, 2014 4:35 pm

Well, in progress anyway. Due to a rather dramatic (est factor 2800) increase in net fusion here, a dose for the operator that used to be around 10x the background (for X rays and other geiger type things) went up, well, about that factor. That's not acceptable. I'm no stranger to danger, but it's because I see it and do things to prevent my own harm, and here's a case of that, a very loud one, in fact.

I've been spending the last week casting cerro-safe bricks, straightening lead (still lots more to do, along with removing the enormous ant colony that tried to live there, evidently, oxidized lead doesn't bother ants so you can notice), and so on. Curtis Faith and I spent a weekend getting borax (from McMaster, the store stuff has fine silica in it that ruins it for this) to dissolve in enough pure ethylene glycol to fill up an 8x8x4" glass block which will go over my tank's viewport, and still be behind the radiology lead glass we've been using all along. All this to be mounted in a 26" by 24" wood sheet, covered with lead both sides, with a hole for the view, and a small cutout so I can still read and operate the pump controls. Tradeoff here - there's only so much I can lift. So we're going to try 2mm lead on both sides of the wood at first (heck, that glass block isn't light when full of saturated solution either). I'm kind of going backwards here - this is the last line of defense for the operator. As much as possible, there will be other shielding nearer the original source(s) of the rads as well, and some of those uber thick cerro-safe blocks below the cart table surface for the family jewel shielding.

Like I said, work in progress. Here's what it looks like as I type this:
OPShield.JPG
Getting started here...block standing in the hole it'd normally be tlat in. It's only sealed by a cork, and I don't want leaks at this point. It's not easy to get 44g of borax to solve in 100ml of EG after all (takes boiling for hours to clarify).


Of course, there will be some capture gammas from neutrons captured in boron in the block no matter what, and at these energies, the amount of lead required to stop them is serious. We're letting the inverse square law do some of the work here - the main action is a couple feet behind all this already. The point is cutting the total dose the operator(s) - mostly me, get in a run. We can only make the runs so short and be sure we're not seeing flukes - as in statistics lie when you don't have enough samples, even if you're honest.

In case anyone forgot, this is what this is going in front of.
Fusor.JPG
The fusor with the radiological glass etc not on it. This will all go behind that glass. And a couple pieces of leaded acrylic for good measure.


More as I make more progess. This is a lot more labor intensive than it looks.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Shields up!

Postby Doug Coulter » Mon Jun 30, 2014 12:23 pm

Here it is in place, more or less done. Yup, not enough, but some. Around 8mm thick of lead at the places where things overlap (there's more on the back). The glass block is 8x8x4" and filled with a saturated solution of borax in ethylene glycol, which dissolves about 10 times as much of it (or boric acid) as water, leaving me with around 5% boron in a moderator 4" or so thick. Again, not really enough, but should be better than the nothing I had. I'll have to do some measuring here.
FrontShield.JPG
In place for testing real soon now. I need to add some stuff lower in the rack, too - for goodies, kneecaps and so on.


And some learning. We all know that say, 70kv X rays make it all the way through you with enough left to sense or blacken film. The energy you *don't* absorb doesn't really matter, right? So, what about neutron capture gammas - from 500KeV and on up to around 2.2 MeV? How much worse are they? How numerous? Is there any point kind of half-stopping those, or cutting down their energy some? Can they "multiply" via various excitations in the shielding to be more, lower energy X rays and actually be worse for you? The literature seems to go out of it's way to separate the sub-specialties with oddball jargon that makes sense in each, separately, but not for this problem, together. Just "stopping" (it's really an exponential vs mass with photons) would take crazy amounts of mass, much more than my floor will hold up.

And then there are neutrons - lots, these days. Even the guys who came up with Sieverts are so vague it's kinda hard to tell. Really, there are only 3 levels vs energy? Curve fitting anyone? And how to really know?
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Re: Shields up!

Postby Doug Coulter » Mon Jun 30, 2014 4:24 pm

Well, a little more progress, and a test. Things are definitely getting better, but I must admit, I had no idea just how well that radiological lead glass was protecting us before. Sadly, I accidentally wiped out that test data, but gheez - without it (I forgot to put it back) it was simply *nuts*, with it, and with the other new stuff, well, it's a lot better now. By co-incidence, it used to be that the geiger counts pretty much tracked the neutrons, now the red trace stays well below the neutron green one - unless I move the geiger out from behind all this (which I did at around 90 secs here, and agin at about 130 seconds). The going back down to our background count was another test where I put some 2mm lead over the geiger window directly, and you can see the count then doesn't change even though I turn off the main power supply (red trace on the left chart). This was all done with a 10 ma current limit, and we exceeded 4m neutrons/second a few times. Remember, the rest of the thing hasn't had the "tighten it up" done yet - and is leaking like a sieve (as we see just moving the geiger counter out of the direct shadow). That stuff scatters badly - so fixing it at the source will be max use of time/materials per result. On the other hand, it's easy to like having a "cone of safety" as well...so we're doing both.
Here's the plots from the short run. (note, we have at least 4x the power we could use...but aren't)
Shield1.png
First (official) shield test.


And here's what it looks like now, with the glass in place - haven't added the leaded plastic to this yet, but I will. All very good stuff. you'd think the 4" of glycol/borax+ a lot of glass (two 3/8" windows plus the 1/4" thick block walls) would have done more, but nope. That's why we test. Note I used a couple of those big bricks of cerro as well near the geiger (the thing sitting in front of the lead brick) just for grins.
Just in case. Here's what it looks like now. I'll also be adding some shielding below the "shelf" area to handle stuff at groin and below levels while operating. I might try thin sheet lead since I have this nice, calibrated, moveable geiger counter to test things like that with now. As part of this, I moved the "air wired kludge" power supply for the main geiger into a nice box so it's safe to move it around while in operation now. If the thin stuff doesn't "get it" then we go to the real thick stuff...which will be a major pain (but less than sitting in the hospital with rad sickness or a fatal cancer, I'd bet).
Shield1.JPG
What it looks like now.


These guys over at the amateur club who say you're safe at 40kv and under and a few feet away....no, you're not, not even close, if I'm reading all this right and the calibration sheets aren't telling lies. Yes, it gets ridiculously hotter at 50kv, both from "shine through" and from capture gammas as you're making lots more neutrons, but even at 40kv, it's pretty nasty here. Hence all this work that isn't moving fusion Q forward, just keeping the experimenter alive, which kinda seems like an important prerequisite if it's oneself.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Shields up!

Postby Doug Coulter » Mon Jun 30, 2014 4:56 pm

Well, I'm runing out of sunshine for today (actually overcast, but I still get enough power for this when it is as long as the sun is "up"), so this is last for today. I cut a sheet of 2mm lead (the thin stuff I have most of) to cover the groin area of the fusor cart, and took some data. It was bad down there - we knew that and had already covered the major leak - which was the bellows for the turbo pump - very litle gets out through the tank itself there - 1.5" thick stainless steel bottom and so forth stops 'em pretty well. But for various reasons (having to allow for motion, scattering from elsewhere and so on) adding just 2 mm of lead full coverage between it and me had some pretty gratifying results. So, thankfully, I don't have to mess with the super thick and super heavy stuff here - at most a couple sheets worth of this stuff. It will be slightly tricky to allow me to still have my main control panel, there's various high power stuff back there, so I can switch things, but nothing like it would have been had I required 1" thick lead...a two man lift per brick (they're much larger than house bricks).

So, we have before:
ShieldGroinBefore.png
Just moving the geiger around the groin area before doing anything else.

And before is like before was up top - bad for the new levels of output we're getting. 10x the (rather quiet here) background is my personal comfort zone - a lot less than flying a plane, but I don't fly anyway.
And remember, this isn't at full snot, not hardly, this is "at idle" for the current fusor implementation....

And now, after. During this I also put the geiger sensor "on the hot side" of the shielding to just see a quick a/b test of it. It should be obvious from the plot. (hint, at around 80 and again at around 180 seconds). At the very end I put a little lead over the geiger in its home position just to see it go right back to background (cosmics? Internal contamination? That's the lowest I ever see that).
ShieldGroinAfter.png
After sticking up 2mm of lead sheet with duct tape, now to put it in there correctly.


Note that all counters are log plotted, and the power supply stuff is all linear...just a reminder. Now I'll go and mount all this stuff up "right", at least by redneck engineer standards, and try some more things next time the sun shines. It's kinda more fun to be able to say I did this all off the sun - and no gasoline or grid power used at all (I can't use grid power, I don't have it wired anywhere on my property).
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Shields up!

Postby Doug Coulter » Wed Jul 02, 2014 12:40 pm

Just a little ditty to go with the youtube movie I just put up.
http://youtu.be/EevzXs_3szY


We're doing some good on the shielding, but there's far more to do if I want to safely run this at higher than idle (which is now, BTW ~3 million neutrons/second, or twice that many DD fusions - about triple the amateur hot-shot average and thousands of times more than "star in a jar" systems).

I'm going about this kind of backwards. Normally one works at the "source" of the "noise" first. And that's where the large gains will be - and we need large ones indeed as we near power producing levels of fusion. But every factor of 10 or more counts no matter what, and this front part was a lot easier to figure out how to do (but more labor - thanks Bill for spending hours with me schlepping lead around and taking stuff that looked like wadded up tinfoil and untangling it prior to cutting it and pounding it flat).

These are mostly interpretable by us, not so much the public, because as we are doing this, we are moving the geiger sensor around to find leaks, see how well we're doing and so forth. But data is data, if not information, so here's a shot of yesterday's test run. To clarify...the neutron detector (green plot) is right at the "action" while the geiger counter (red plot) is where the operator is - mostly. We expect the neutrons to be a larger issue at the op position later, but for now, I'm just getting the gammas, since we know they're bad as is.
Shield3.png
Some tests with the pictured arrangement...

The stuff on the left plot is power supply. Red is volts, topping out here at 50kv. Green is current, topping out here at 10.5 ma. We save the unit conversion for different software, this stuff is mainly so we can ensure we're not clipping or getting some other sort of ridiculous results while running real time - fancy analysis comes later if desired. This is all now saved in log files, but I'm planning a much more ambitious system with 3rd normal form database and a heck of a lot more inputs (see scope, above, and audio, for a couple. We may ADD the arduino data aq, instead of replacing the pic we now have, as well). While a work in progress, the schema for the DB is all important, as it will allow us to have tables that for example, convert A/D counts from something into real units with real labels, and have multiple setups - all selected by what we say we had when we begin a run, to reduce typing and errors later. Eg, mapping what's on the scope probes to real names (and voltages and speeds and, well, whatever the scope can do, which is a lot - it will do FFT's too), stuff like that.

When we started this, by sheer co-incidence, the geiger counts tended to lie right on top of the neutron counts. It's now 2-3 times better at minimum in the worst place behind the shielding. Turns out we had a leak at kneecap level that was a lot worse than thought, but that's gone now. What we mainly see now is backscatter (Compton scattering) of gammas coming out of the completely (not even the usual) unshielded back end of this where "the action is" - that's a lot more complex to shield due to shapes and space limits, but that's next.

And oh, did I say a few X? Look at that peak when I moved the geiger sensor out from behind the shield at around 280 seconds or so (note - it's a log plot). A few further adjustments produced the results starting around 600 seconds, and for reference, you can see this big blank place in the middle where the power supply was turned off - that's our background from the dirt beneath us and the cosmos above, just for a sense of perspective (and to make sure all the gear is working repeatably).

It's actually harder to run in this "idle" mode than full out (the thing wants to go out, or hit current limit, it's intrinsically divergent - see all the wiggles in the current plot line? That's with me trying to keep it constant via the ion source!). But for now...well, I gotta live through this, I'm sure you can appreciate that. We have another very large (>10^e3) factor on tap for show and tuning, real soon now. It stinks I had to stop on that research path to do this, frankly, but you gotta do what you gotta do.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Shields up!

Postby Doug Coulter » Wed Jul 02, 2014 3:12 pm

Good day for pictures vs working hard - it's hot. I could turn on the AC and then have no power left, or do this. I'm doing this.
As suggested by Bill, I'm going to add that nasty looking piece of iron angle (sitting on the bucket) to extend my "shelf" on the front of the fusor.
I may treat it some, but the rusts and pits have some character...
It's going to require moving my main control panel down 1U, which I've yet to drill and tap for, but that's not so bad, sitting down and indoors on a hot day.
Then I can have a lead flap over the panel I can raise to get to the switches and so on, while keeping the rads off the goodies.

A little drilling here, a little tapping there, some lead cutting (pruning shears for this stuff - not hard), then I move to the harder stuff on the back side.
Angle.JPG
Scrap iron is still strong (and gives shade too).
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Re: Shields up!

Postby Doug Coulter » Fri Jul 04, 2014 2:34 pm

The front part of the shielding appears to be done. Great results! Yes, it could be better still - if we get back to our real breakthrough, but this is a fantastic start. Turns out I had overlooked something VERY important here. Bill had our "CerroSafe" tested, and yup, we got the old kind that has 12%+ Cadmium in it. This is fine for a pure X ray situation (what it was intended for) but terrible where there might be some slow neutrons around (and we have tons here...there's always some moderator around, like humidity, transformer oil, me...). When Cd captures a neutron, it gives off a gamma ray so potent it would take literally many inches if not a foot thick lead to stop it - and that's what we were seeing before - it looked like we were going backwards because we did when I put all that CerroSafe near the "action" part of things.

For this run, I'd taken all that (sweat, groan, 100's of lbs of it) out of here, and have added the full frontal stuff, as well as a half-arsed attempt at blocking the major leaks in the back, which appears to have been moderately acceptable except around the neutron counter port - the one we use to plot, as in this picture here:
Shield4.png
Plot of latest test - July 4 2014 - independence from X rays at last!


In this, you can see the neutron count go way up when the fusor happens to be in the right condition to run, but the gamma count hardly go up at all - maybe double background. I used to be happy with 10x background, so this is nice. It may not be nice enough in the long run as the fusor gets better, but it's a relief to be able to run it at all again - now I can chase down that breaktrhough I think I had - found an oscillating mode that seems to do far better "bunching" and "luminosity" than DC drive like everyone else uses...actually, that wasn't an accident, that's why there is that RF transformer in the HV feed now, it just wasn't hooked up for this test.

Of course, this got a movie, and here it is (or will be when it finishes uploading, it's a bad BW day for my ISP, apparently)
http://youtu.be/lNnhG8UTBEs


I wasn't trying real hard for max anything as far as running the fusor - just to get into that 2-3 million neutrons/second range, and as you can see from the plot = the green line on the left one - I started out at our usual testing 10 ma, but then cranked it way up, as we usually get more X rays with more current (ask any radiologist) and I wanted to see how well we did, regardless of fusion, in that case.
We get even more when fusion scales with current of course - the byproducts for example include fast charged particles in the tank at megavolt energies, but fusion only scales with current (for us) when other things are just so, and I just didn't bother this time - we'll get there, but for now, I think it's time for a little bubbly - I can go back to doing what I love and not die from it!

So what you see in the plot and in the movie is just sweeping the parameter space a little to see if there are any bad - or great - spots re operator safety, not a real "try to do the best we can" kind of running at all.
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Re: Shields up!

Postby Doug Coulter » Fri Jul 04, 2014 3:35 pm

I wasn't sure just where to put this, so I put it here, since this data came from the run above. Pausing the youtube vid - does anyone else see a bit of correlation here? The yellow line is a low-going output from one of our neutron detectors - it has very low quantum efficiency, so it misses most of the neutrons (usually good...we're making them at mhz and seeing these at ~100hz tops).
So, a low going spike (always one in the center, it's what the scope is triggering on) is a neutron hit.
A high going spike on the purple line is the EMI in the room near the HV input - it shows the fusor onset of current draw, kind of differentiated (it's just a probe sitting hear the HV input).
The blue line is a faraday probe inside the tank, off all the axes, about 6" from "the action" out in the main tank. It shows a net-negative plasma when the fusor is going, and is DC coupled.

Correlation.png
A frame from the youtube movie above that shows something interesting. FWIW, the scope is actually on the cart on the "hot side" of the shielding, near the signals in question, and running 5ms/div I believe.


There's probably a lot more anayisis to be done here, this is just the first fruits (and after my celebration beer). Obviously, I need that GUI (I'll write one) to set up the scope parameters remotely so I don't have to go to the hot side of the shield to do that. It IS nice to have the scope near the signals...better fidelity. Also on my TODO list of course is direct raw data capture from it - timestamped and into the same database as the other stuff we plot in realtime as shown in the movie (plus anything else I can think of to store in time-alignment and notes about the run in general). Just keep plugging away at all this till it's done...
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Re: Shields up!

Postby johnf » Sat Jul 05, 2014 2:00 am

OK
Is the blue line a measure of spallation products or is it the neut giving up energy hitting D2 atoms and being slowed

The negative going is probably from secondary electrons hitting your measure plate
interesting!!!
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Re: Shields up!

Postby Doug Coulter » Sat Jul 05, 2014 3:48 am

I didn't really give enough info in this for you to analyze well, sorry, John.

The blue line is hooked via a 100x 100meg probe to what was the 2.4 ghz 1/4 wave antenna, poking into the main volume from the back left at about a 45 deg angle - well "out of the action", though there is a line of sight to the main plasma, barely.

Note where the blue triangle is on the left - that's "zero" volts. It appears (this shows up on the other faraday probe, eg wire, too, on the other side of the tank) that during fusion or just light off - we have a net negative plasma, at least after it gets out of the active sidearm. Yes, probably secondary electrons. When it goes out, this line returns to zero, or near, even with 50kv on the main grid and some 5-20 kv on the ion source.

Some people say that's impossible. I agree with you - it's likely secondary electrons - even though I'm using the lowest secondary emitters I can find for the grid that can take the temps - pure tungsten rods and graphite ends.. After all, we're doing our best to pump negative charge into both grids (FWIW, the ion source dinky one is tantalum wire). Of course, it's a bit hard to find data on secondary electron emission from anything when hit by ions vs electrons. The old books/authors didn't think to measure that. I'd expect a bit more from the ions as they have more net energy and hit harder? I'd guess that even so, the low secondary emission materials would still be the lower ones. Too bad I can't get berillium rods for the grids (e= .5 max with electrons, while most other stuff is 1 or more).

I need to show this kind of plot at both faster and slower sweep speeds to show a better overall picture of what's going on. I'll probably do that in "run data" pretty soon. The thing is, if I go fast - you don't see the slow stuff on the faraday probes well - even here you miss a bunch of what's happening, just seeing the blips on top of the big moves negative. If I go slow, you can't see the skinny pulses from the neutron detector well. I may do a 3 input OR type gate to see all 3 detectors so I effectively have more quantum efficiency there for observation, now that I know they're all pretty good. The one that was swamping (the 3He) has been moved around 4 feet further away so it became more useful at these high outputs. We never really needed that level of sensitivity, and it blocks from pulse pileup all too easily if you really slam it with a lot of neutrons.

The reason for this thread is that when Curtis and I hooked up the hartley oscillator transformer (from grid to grid, with a coupling cap and R so we could "squegg") we had a crazy-enourmous amount of fusion - maybe hit 30 or 100 million neuts/second, but don't know because all my counters blanked, and all the computers crashed. I stupidly took quite a dose of rads of all kinds while trying to find out why before I got smart and turned it off. Actually felt a bit sick for a couple weeks after that. So I did all this work on more shielding so I can hook that all back up again - this run was without it, just idling at a 10 ma current limit (yet still in the 3-4 million neuts/second!). Heck, a bunch of random junk lying around the shop got a little warm, and I had to go around cleaning that up.

It appears that along with the boost I got from having it oscillate (and untuned for max at that - what are the chances I hit on the right tuning first try? e-9?), that the new smaller and more accurate grid is a pretty big deal. I thought I'd be scaling it down...for safety. But the new grid actually works far better. It's the same design as ever, just 3/4 scale. I might try another at 1/2 scale, just to see if we find a peak, or a direction we should keep going in. I had no idea...I do know the new one is a good bit more accurate, though still far from optical grade - much less nuclear wavefunction grade. Heck, it's not even shiny.

In this, I'm just doing a run to test shielding, not really pushing the fusor, that's why it's unstable. With too little gas so I don't hit the 10ma current limit I'd set (mostly, I did sweep a part of the range there), it's hard to keep going in any sort of stable mode, it'd rather run more like 20 or 30 ma with a bit more gas, hooked up "straight" as it is.

I'd expect more kickback on the other line - the radiated EMI, since I do still have around 3.5 mh in series with the main grid (and 50k in series with that, as ever). But I'm not seeing that, perhaps the 50k de-Q's things, RF speaking. During the real hot time we had, we had that 50k shorted, as the new feedthrough makes it not required to protect the spellman - no arcs - big breakthrough all its own.
But for this, I just wanted it to make radiation at all so as to test the new shielding, not new record fusion. That's next, with more intelligent data taking...I hope. That's a project all its own.

It was fairly astonishing that simply moving all Cd containing compounds 20 meters out of here reduced the hot gammas so much. They were all too good at making capture gammas with even that 3 m neuts/sec output, no matter where in the room they were. And those take far more lead to stop than my floor will hold. There's still some Cd in the house - upstairs, but not that far away, gotta move that too.

I admit to some surprise that all that boron in the glass block isn't making more fuss about the neutrons. It's around 5% boron total - 44 grams of borax per 100 ml of ethlyene glycol in there (nearly 4 liters total), and it should be making ~half-meg gammas itself. But I'm not seeing much of that, even moving the geiger near it. Not enough moderation to get down to where the boron is good at 1/V? More data required. It's 4" thick, that stuff.

Note to other readers - John has been here and seen this setup, so I don't need to go into each detail separately for him to know what's going on here.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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