Neutron detector tubes

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Neutron detector tubes

Postby Doug Coulter » Fri Apr 22, 2011 3:11 pm

Bill strikes again, and here is a link to some nicely inexpensive B10 lined neutron detectors.
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... SS:US:1123

We bought one of these, and also bought out some 3He and a larger B10 tube, some of which we'll be selling most likely -- we have plenty.

My experience with the bigger, older GE tubes is that they are just fine for a starter fusor, and still fine later for monitoring. They don't count as fast as the 3he in the same field, but -- they are much more EMI resistant, and much more gamma resistant (these don't count on 1k roentgen/hour gammas). When I'm getting a khz of counts out of our really big 3He, I'm getting maybe 100hz out of the B10, which is plenty. If you're getting any fusion, these guys should count decently above the cosmic background.

For the price, y'all better jump on these guys before they're gone.
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Re: Neutron detector tubes

Postby Jerry » Fri Apr 22, 2011 3:41 pm

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Re: Neutron detector tubes

Postby Doug Coulter » Fri Apr 22, 2011 3:44 pm

Yes, but we just bought that one, we think. On the other hand, that's more moderator and total size/weight you wind up with. Different strokes.
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Re: Neutron detector tubes

Postby chrismb » Fri Apr 22, 2011 4:22 pm

These aren't regular B10 tubes. They are coronal discharge tubes. I have some, but haven't been able to operate them in a way that makes sense. But I don't have a neutron source, so I am scrabbling around with trying to discriminate background from noise.

So if you figure out a set of instructions of how to rig a circuit and get them working, then let me know, please!
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Re: Neutron detector tubes

Postby Doug Coulter » Fri Apr 22, 2011 4:35 pm

Absolutely. I don't know what sort of neutron source you've got, but we made a couple with staticmaster sources and Be and they can barely get my most sensitive 3He out of the noise at all, and then you're not really sure. Compared to a fusor, those tend to be pretty weak tea (10's of neutrons/second) -- or impossible for normal people to get. The old guys were using ~ a curie of alpha emitter! You'll not find one of those, and you wouldn't want to be around it if you did. Carl's little source that went clickety click on a 2 foot 3he tube was hundreds of smoke detectors worth of alpha source. Industrial ones.

I'm not sure what they're saying about coronal discharge there, no standard detector books I've got mention such a thing for any sort of detector. They seemed to be saying 25 uA leakage max or something like. I also notice he's got a little confusion between slow neutrons and gamma in one of his titles. I mean, it's a tube with gas in it -- there's not a lot of fancy tech involved. Usually these have to run with real high impedance (megs) or they do go into glow discharge and won't count any more (and are ruined). Each count creates a discharge, you measure that, but there has to be low enough DC current available so it can "turn back off" after that else they are just lighting up in there and "turned on".

At any rate, at first I thought having a neutron source would help me calibrate things like this for the fusor, but it worked out the other way around -- now that I know things work in a real loud neutron flux, I can start working closer to the noise on a "passive" neutron source. Tens of neutrons/second won't get most detectors out of background so's you'd notice. If you are getting some per minute of cosmics, the actual quantum efficiency of these is such that 10's per second entering the moderator won't make enough hits to get reliably above the background the QE of these is pretty low as a system. First, most of the neutrons scatter out of the moderator, then only a few of those that get into the tube count it.
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Re: Neutron detector tubes

Postby Joe Jarski » Fri Apr 22, 2011 6:49 pm

Thanks for the post on these. I haven't had anything capable of neutron detection, so I'll give these a try and see what happens.

Seems to me that the way translations go, a regular GM tube could be considered a "corona discharge" tube. So, maybe that description isn't all that significant. The important part is the B10 lining, I would think.
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Re: Neutron detector tubes

Postby Doug Coulter » Fri Apr 22, 2011 8:29 pm

Right, and unless you get really lucky, these prices are a steal -- or we could be slightly unlucky, and they don't work -- reward/risk ratio seems nicely high, though. I was turned down at an HEAS for 1500 cash for a 3He tube, new ones that size are a few $k.. We got lucky on some B10 tubes from Tyler for about $25 (lucky). I dropped one on its head and broke it (not so lucky) We've paid hundreds for BF3 tubes, which I'm still trying to verify if they work. If these work -- it's a pretty good deal. I concur on the "corona" thing, it's probably translation. He spells roentgens as rengens after all. Too bad that with things like this, you just gotta go for it or not. No point buying one to see if it works, then buying the rest -- they'd be gone regardless by the time the slow boat from Ukraine arrived.
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Re: Neutron detector tubes

Postby chrismb » Sat Apr 23, 2011 2:33 am

It's not a translation thing. These run in the upper end of the Townsend discharge and have a continuous current signal against which you have to discriminate signals of 'additional current' due to large ionising particles. They seem to be much less sensitive to gammas than proportional tubes, probably because all the available gammas are already driving that 'overlay' current so they are already discounted as noise before you start the counting/calculation.

As you have the neutron source, Doug, I'd really like you to get one working reliably and show me your circuit/set-up.
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Re: Neutron detector tubes

Postby Joe Jarski » Sat Apr 23, 2011 11:58 am

Chris, thanks for the additional information. After doing some more searching, I started to find a little bit more information on corona counters. In the first go round I didn't come up with too much so I thought it may be a translation thing since almost all of the information is related to Russian tubes. That type of tube operation is something that I haven't seen in any of my books. I'll keep looking while I wait for mine to show up - maybe I can find something useful that doesn't require downloading a slew of $30 documents.
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Re: Neutron detector tubes

Postby Doug Coulter » Sat Apr 23, 2011 12:27 pm

Chris -- count on it ;)

Could that be why the outside seems to be marked with a plus sign in the picture? That'd be really weird for a geiger or proportional tube, but might make sense if what you're saying is right.

Since they are coming anyway, of course I'll be fooling around with them. We got one each type the guy had on sale -- which bought him out of two of the types. I'll post on it when I know something more -- one has to be patient usually for this Ukraine stuff -- it took forever to get those pancake geiger tubes (which I'm still getting around to doing the rest for the standard counter, got the PICs and USB interfaces, now to WW a test board.)

Edit:

Joe, if you found *anything* about this mode, I'd like to have a link to it if I'm going to be the guinea pig. Hopefully, we'll at least get a Russian data sheet, but you never know with this stuff.
.
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