Standard counters

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Standard counters

Postby Doug Coulter » Sat Jan 08, 2011 3:58 pm

Bill Fain has kindly arranged to obtain 9 new Russian pancake geiger tubes for us. I am wonder if there is interest among the fusion oriented members in my building some standardized, cross calibrated geiger counters for us, so we can all compare things like silver activation using known sensitivity equipment. Since this is very early stage (they haven't arrived yet) there is some flexibility in the design at this point, and of course a ton of extra features would cost somewhat more to build up. Here is what I am thinking about as a straw man, so anyone interested should reply on this thread with comments -- if you want more or less features, and so on.

Basic idea:
Geiger tube, power supply, microprocessor, LCD display, rs-232, runs off wall wart.
This should give the basic needs. Depending on how easy it is to refactor some code from our fancier multi-geiger project, the code might contain variable measurement intervals, setups that are saved across power downs, and background collection and subtraction. The basic mode I've found most useful here is 10 second counts, normalized to a minute (eg multiplied by 6 for display of cpm), and no background stuff. Our background is so darn variable with cosmics here that subtracting it is kind of a waste of time, since our lab is also very quiet as well. So I never use it myself, I just take an extra count before and after, and kind of visually subtract the average. When counting something like silver or indium, it's kind of obvious if a cosmic ray burst spoiled one count, which is a pretty good reason to do short, 10 second counts, actually. Also, with silver, the decay rate is on the quick side, especially at first (metastable states) and you miss the beauty of that with a longer count interval. On the other side going too short (1 second say) is just too short and might have fenceposting issues when the counter is read and reset in software, so 10 seconds has been the all the time mode here.

Things I could add are battery input -- it won't be too much a pig, but may need 7 volts or so (5 cells) to work correctly, the rs232 converter needs real 5 volts, though the CPU (PIC 18lf2325 doesn't. I find rs-232 very worth it here, as almost any PC has some kind of software that will slurp that into a file for you. Typically, we give a timestamp, the count, interval, and any other data on the interval -- all in human readable form, and easy to parse in other software as well.

Another thing I might be able to add is a couple of a/d channels if I don't run out of pic pins for that. One will be used to sense and regulate the high voltage for the geiger tube via the pic's pwm output, but I might be able to get 4 if the pins are not all used up (the LCD takes 8 for a two line display run in 4 bit mode). When I do that, what I actually do is take data at around 50 samples/second, and sum them all up for reporting once per second -- you get some noise averaging and maybe another bit or two accuracy that way. The basic a/d in this pic is 12 bits, we did this trick with a 10 bit one, and due to the inevitable noises, got 11-13 bit resolution out of it doing it that way. The noise in this case acts like "dithering" for those who speak signal processing. I've been putting that out raw, but I suppose it is possible to input a scaling factor to make it volts. Our basic UI uses a rotary/push knob, so putting in floating point numbers with that is problematic, though it could be accomplished at programming time, or perhaps with rs232 input from a PC.

You tell me. The basic thing I have in mind would have to go for about $225, plus or minus say $30 (US) for me to break even, more if people want a board made by a pro, instead of what I do there (that adds a setup fee from the boardhouse).

Any interest, or did we just get a bunch of nice geiger tubes for ourself alone?
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: Standard counters

Postby johnf » Sat Jan 08, 2011 4:34 pm

Another source for a gieger tube is Jaycar Aus, NZ, GB $179NZ$ 134 US$

article on a counter that ran in Silicon Chip mag 1995
can be found here http://www.jaycar.com.au/products_uploa ... SC1995.pdf
its a mica windowed tube so good for alphas betas gammas

Edit

current catalog number =ZG-6500
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Re: Standard counters

Postby Bill Fain » Sat Jan 08, 2011 4:38 pm

Doug, Hi. If this is made portable, are you going to make provisions for a piezo or led output; maybe even a pager motor output? As longs as it's no bigger than a cigar box (preferably smaller), it would be a great thing to carry into antique stores etc. I have found that I scare the #%$% out of people when my survey meter goes off (even with tape over the speaker). I usually get permission from the owner before I carry one in as well. I know you have a favorite CCFL that you use, but is there one out there that would drive a PMT as well? Maybe you add a jumper to mix and match the voltage from the battery pack. Also there is a limited amount of the Russian "new old stock" tubes and voltages may have to be adjusted up or down to accommodate other tubes. I know the stated purpose for this is to have a standard comparison device, but since you're in the design stage..... If it's not destined to be a portable device, maybe you can add a little section on the board with plated through holes, so the owner can add their own little modifications (place for PMT circuitry etc.). Another thought would be to save back one of these units to travel the country as needed. Kinda like the 4HV forum that has the high voltage parts box that travels around. -bill
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Re: Standard counters

Postby johnf » Sat Jan 08, 2011 4:45 pm

Maybe all we have to do is ship the guts from a smoke detector around inside some Ta oe lead foil to keep the feds away as a calibration standard half life is around 400 years so its real stable
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Re: Standard counters

Postby Doug Coulter » Sat Jan 08, 2011 5:09 pm

Well, I was focusing on a standard for activation here, so the big flat tube is key. This probably won't fit in a pocket (certainly not with batteries) unless I really go all out for miniature, and demand things like CR123 (expensive lithium ones). The LCD display is a little bit large for that, and so is the tube. I get very different results here with different geiger tubes, due to sizes and ratios of sensitivity to different radiations varying. And for hot silver, there's about a 10x variation between a good pancake and a scintillator. That makes comparisons fruitless.

Bill -- I can turn off the beep on henny, that's a jumper in there...but don't you find it useful the scare people out of free samples? I know I would, but then I am learning what's called "social engineering", a little bit. You need to remember to carry that clipboard and look official!

Yes, we could have a standard source, but it's really not the same (not even same type radiation), and there would be calibration issues with a source smaller than the active area of the tube, I believe. What's nice about the 2" tube is it's a nice size to put a standard 2" sq neutron-oven sample over, and count the entire thing -- just in case something isn't activated uniformly (seen that). With these, and I suppose any other tube, the sensitivity varies a little across the face.

Yes, the smoke detector sources are pretty darn hot, and nearly all (but not all) alpha. I haven't measured enough of them to say any two are the same. No two are in our collection, they vary maybe several to one (the stuff Bill has collected) at least. And as a point source, I don't like them as much for calibrating a sensor that has more linear dimensions than the alphas have range (with enough energy left to get through the window)! If we were going to go the standard source approach, it would want to be the same size, the same mix of radiation types, and in the same range count rate or other errors kinda start to creep into things. The main one I can think of would get us in hot water indeed if we shipped them around (U2O3 might do for example).

But maybe I'm thinking wrong here. What I was after with a bulk purchase of all the same type sensor tube was to have something we could use to compare fusion activations with confidence, no second guessing (trying to front-run the inevitable, here), because that's an added feature of having a bunch of things absolutely the same that none of the other options give you. I'd hope we all have counters and survey meters already, this is special purpose in my mind. For example, I have a geiger type survey meter, many many scintillator heads of varying goodness, and Bill has Henny Penny (which still needs a threshold adjustment) which is the most sensitive thing on the block -- to gammas. What having all the same front end gives you is the same ratios of alpha/beta/gamma sensitivity for all owners.

But maybe people just want cheap crappy geiger counters? I get less excited about that because that's less useful to the fusion goals, and I have a ton of them already. You know how it is when you have a long to-do list....things you get excited about actually get done in reasonable time. Of course, if all I have to do is program pic uP's and ship them, that's pretty easy compared to doing all the rest. But I get the feeling that most here wouldn't be doing much with a chip and a tube anytime real soon -- gathering all the parts and packaging is a lot of the battle too.

I'm not real worried about limited stock of these tubes at this point, because we have 2 running fusors total so far, three when TylerC gets off from school, and maybe a couple more on the way (Joe is making one, and Chris is planning something). We'll have them left over for awhile unless there is a groundswell of new fusor builders.
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: Standard counters

Postby Joe Jarski » Sat Jan 08, 2011 8:59 pm

I like the idea, myself. There are so many variables in different detection equipment and methods that getting real, usable data for comparison is darn near impossible without some sort of standardization. This is all new territory to me, so I don't really know what features are good to have. I like the idea of a specified activation material, moderator and cross calibrated (corrected) counters.
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Re: Standard counters

Postby Doug Coulter » Sat Jan 08, 2011 10:05 pm

Right, standardization is the key to cooperation.

This whole issue has led to fights and hassles elsewhere. First you had to buy this expensive thing that one of the "old boys" recommended, or your results wouldn't be acknowledged. Then it was a another expensive and almost un-gettable thing because we all found flaws in the first expensive thing. Then there were fights about whether this or that was being fooled by noise. On and on, and it became kind of a peeing and boasting match (one guy even boasted he'd cornered the market on 3He tubes, but wasn't going to sell any to anyone, while demanding that he wouldn't believe results from anything else) by the few who met all those barriers against all other comers.

I've thought about this one a long time, which is why I've been suggesting something like this. It's far from perfect itself (no real-time feedback, so it's not all you'd want to have). But you just can't count noise with activation of silver or indium -- there's no way to get it seriously wrong, only real neutrons do it. The other radiation and noise sources are turned off when this measurement is taken -- bingo, no issues.

So the only remaining variable is to have a set of counters we can all have one of, that all count the same given the same stimulus. Then we can all use them to compare results with one another, and maybe more importantly, within our own labs -- did I do better or worse this time is the basic question on every experiment, right? If even one person manages to calibrate to absolute numbers, then everyone now has that too, though I think rough numbers that are accurate run-to-run and lab-to-lab are far more important at this time. If anyone's fusion device gets "loud" enough to "boil that cup of tea" we'll be using thermocouples in calorimeters, not neutron detectors! Shaft horsepower from steam engines at that point. Not a worry now (which is too bad, but there it is).

So, having been through that crap-storm elsewhere, buying a bunch of BTI bubble detectors to find out they aren't that reliable and don't live long (and often don't agree with one another), then finally (thanks BillF) finding a 3He tube and having those results rejected because since I was doing well, I must have been counting noise, and finally also getting a b10 tube going -- with the same issues (and it's true, both tubes are prone to count on noise if you're not careful, but I'm pretty ace on that kinda thing, having been an engineer who did everything from signal intelligence gathering to EMP resistance for the government)....I just got fed up with the baloney, and it's part of the reason this place is here, to be honest.

This looked like the net cheapest possible way out of that mess, something that was easy to get right, wasn't prone to the most common issues, and by golly, I'm actually hoping someone can kick my butt at this fusion thing, no kidding, and I won't play those silly games if/when they do -- I'll of course want to know how they did it, so I can return the favor later with my own twist!

But this thing where the old hands continually invent reasons why no one can do it like they do is just anathema to my spirit, and I'm trying to prevent it before I have to figure a way to fix it.

We're talking about something that can last a lifetime for the price of about 2 BTI's, which last about 6 months each if you don't use them much. And perhaps 1/10 the price of a new 3He tube if you can get one at all these days (TSA, DHS have them on allocation and few are available at any price at all, since the only way to get 3He is to make tritium and wait for it to decay, at present, and T is in shortage itself for nuke maintenance).

I think there's room for more than one project here in radiation detection, and probably some software and hardware re-purposing along the way, I know I have a bunch of different detectors for different uses, and they are all nice, and many are also cheap to replicate -- but not to make a bunch precisely the same. And all the other ones have some susceptibility to noise and other variables, this just doesn't have, so that's why I'm proposing this project here and now. Sure with different shape fusors, there will be some easy to calculate sensitivity factor due to neutron oven distance and placement, but the emphasis is on "easy to calculate and correct for" in a way that everyone can agree on.

If you want raw sensitivity, go for a phototube and large area scintillator. But if we try to use that as a standard, there's endless questions about the high variability of phototube gain with voltage (and sometimes age of the scintillator), noise, threshold settings and so on, forever. A geiger tube is an avalanche device, not particularly sensitive to voltage or noise (JoeS for example was getting 100v pulses out of his -- hard for noise to mess that up!). They either count or they don't, and given a particular design, have the same ratio of sensitivity to all forms of radiation as one another -- the standard is kind of "built in" -- all we have to do is make power for them and count output pulses. They are on the numb side, but that doesn't matter if you're not using one for prospecting, and in prospecting, you only need relative numbers at most, not absolutes -- that's done by assay once you find a rock you want to know the quantitative value of. So different tools for different jobs.

Henny (a scintillator, also known as a TSA-470) is for example so sensitive it's almost useless for prospecting! We drove it around here in the truck and found some hot zones for example, but couldn't find the actual sources -- so much radon was coming out of the ground that it saw you couldn't localize anything, and rocks returned from those areas weren't hot anymore by the time they got here! They were just saturated in radon seeping from somewhere else in the about 100 yard square area Henny went nuts in. That's not so useful, it's like trying to use a saturated night vision device in bright sun -- you can't see with it.

So that's why I'm proposing this -- it's not the most sensitive thing on earth, just very very stable and repeatable, and good for things where that is the most important feature.

We can support all manner of other things too -- but the key word is "too".

Sorry about the rant, this is something I feel fairly strongly about. The lack of a standard we can't argue about has been holding the field back for much too long.
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: Standard counters

Postby Joe Jarski » Mon Jan 10, 2011 12:54 am

How critical is the moderator and/or oven design? Does it have a significant effect on the sensitivity of the activation? I'm just wondering if it's something that can be spec'd out by material type and thickness or is it something that should be added to the standard counter "kit" to help keep the results consistent?

As I recall, someone on the other forum was trying to activate a difficult material and needed to find some level of resonance to get it to work. Maybe it's negligible in the overall scope though and any variations would be lost in the noise.
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Re: Standard counters

Postby Doug Coulter » Mon Jan 10, 2011 10:17 am

It's not super critical, but important to get right.
Here is how we built ours.
Since neutron scattering is a random event, and scattering off hydrogen slows them down the best, you use something that has a lot of hydrogen, and a lot of density, because making it thicker on the "input side" makes for more scattering out of the oven entirely. After the sample, you can make it as thick as you like, as at that point, you're hoping to scatter a few back into the sample that missed on the first pass. The link is the standard I recommend, and it's fairly easy to make this. Assuming square law, and that the neutrons are made mostly at grid center, a simple scaling should suffice to compensate for distance, but of course you want to put the thing as close as you can to the source. UMHW HDPE is probably the very best obtainable moderator for this use, in terms of getting the most neutrons into the resonance ranges of either silver or indium in minimum size. It's a little hard to work, but not impossible. I got mine at McMaster, and also use it to moderate for neutron detector tubes that want slow neutrons.

One of the frustrating things about this board is the search really stinks -- I had to go fishing, and that science has enough tie in from one specialty to another that a lot of what is up here could be in more than one place and still be on-topic, so this needed to be linked from here. Maybe I should go edit that post and put in some more keywords to make the search work on it or something.
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: Standard counters

Postby William A Washburn » Tue Jan 11, 2011 3:43 pm

Hi Folks,
Are you using this just for activation thus need the moderator or are you activating various
nuclear samples in order to calibrate your new counter array (congrats). When I did activation
in lab we used neutron sources in our howitzer we can't own nowadays. The moderator we used
was some kind of hard wax (i think) in a 3 ft by 3 ft cylinder. The cylinder had a shaft vertically
down the center with the stuff you can't get anymore in it.
Another thought was that you might be looking at neutrons but wished moderate them to get
the right cross section, activate another nucleus and count that nucleus maybe giving you a better
count rate (of whatever particle the activation produced). Sorry to bug in but I'm trying to learn
and found this thread very interesting.
Thanks
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