Test Sources

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Test Sources

Postby Bill Fain » Thu Apr 07, 2011 8:58 pm

Hi,
Geo just posted a bunch of these on ebay: TG77 Signalite Tube
.9uciCs1371966

Item # 220765732951

-bill
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Re: Test Sources

Postby Bill Fain » Thu Apr 07, 2011 10:08 pm

Hi, They look similar to this:
tg77.jpeg
tg77.jpeg (4.13 KiB) Viewed 3295 times

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 3D1&_rdc=1
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Re: Test Sources

Postby Joe Jarski » Thu Apr 07, 2011 10:45 pm

Hi Bill, looks like a nice source - do you have any idea what these were originally used for? Not that it really matters as a test source, but I was just curious.
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Re: Test Sources

Postby johnf » Fri Apr 08, 2011 12:01 am

Got a funny feeling that these are used in microwave systems as a TX/RX switch with the tube inserted inside the waveguide. The Cs is there to help with ionisation
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Re: Test Sources

Postby chrismb » Fri Apr 08, 2011 5:11 am

Presumably old enough to have gone through a half-life by now?

I have been on the lookout for a distinct spectral source to test out gamma spectrometry. Is this a good one to pick up, or are there better things to go for?
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Re: Test Sources

Postby Doug Coulter » Fri Apr 08, 2011 9:31 am

Cs-137 is "the" calibration source to have for a gamma spectrometer, most of them require one for setup. It has two lines, conveniently spanning the range, and is very clean otherwise. It's why we were looking for them ourselves. Bill bought an "official" one outright, but at nose-bleed prices, and it has .25 uCurie activity in the "new" state. Geo says these are down to .3 microcurie as yes, they are old. That's still pretty loud, the .25 uC one we have is plenty loud on the standard counter. What's nice about this is that even after time, no new lines from daughters appear.
Anything much hotter than this I wouldn't keep around the house, even in a lead pig. There's probably some line smearing due to the envelope, but I'd bet very little (and you could take one apart anyway if you cared).

One of the lines is 662 kev, and the other is (I think, but I'm checking) about 30-something kev -- so you have nice single lines at both ends of a spectrum for calibration.
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: Test Sources

Postby Joe Jarski » Fri Apr 08, 2011 12:38 pm

Doug, do you think a source such as this would have any significant effect on the low end operation of the uWave ion gun if it was in close proximity to the quartz tube? For instance, with your beam on target stuff would there be a sufficient amount of ionization to let you work at lower pressures without having to differentially pump the ion gun and chamber?
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Re: Test Sources

Postby chrismb » Fri Apr 08, 2011 12:47 pm

Doug Coulter wrote:It has two lines, conveniently spanning the range, and is very clean otherwise.
Yes, I recognise that, and the use of two simple peaks so as to get scaling right on the spectrometry, but the part of it I'm not sure about is that the 30keV is rather soft and will - presumably - only go through tubes/pancakes with mica. I don't think that Russian job of mine is very good at doing 'proportional', and the thin-walled Ar quenched tube I have won't [I don't think] let through 30keV. I was wondering whether I might get 'cobalt 60' as the answer to my question above, but where can you get check sources of that from!?
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Re: Test Sources

Postby Doug Coulter » Fri Apr 08, 2011 12:51 pm

Who knows? I sort of doubt it, but...

Here's why I think that. It's long mean free path at low pressures. With the uWave ion source, you get an extremely long path, due to the cyclotron effect on the electrons whirling around in there till they hit something -- could be miles long paths for them. Whereas with a source (I'd pick an alpha source myself) you've only got the tank-size worth of path, and at low pressures, not many gas molecules to hit. I just don't think you get enough current to run a fusor easily that way. Probably enough for a beam on target device, which uses a lot less. Even for that, I'd pick the uWave source if I could get it integrated. Due to other limitations, right now my next BOT thing will need split supplies, and floating a magnetron 60kv off ground doesn't sound real practical...
But those limits won't obtain later on, we have a nifty new supply on the way supposedly (1 ma, 160kv, zowie). The design in the Phillips chapter I keep linking gets it done with just a penning source at reasonable pressures for a sealed off borehole tube, pretty simple if not completely ideal.

It's probably worth a test, however. I have a bunch of hot alpha sources (alphas plow the gas much better than other things), and I could try it on some fusor once I have one really stable, and see if it lets me stay "lit" to lower pressures. The big system is in fine tune just now, so perhaps as soon as I get some nice baseline data into my database, I can shove those sources in there and compare. Till then, I'm not opening that door!

But even a pretty hot source is very low "current". Even a whole curie is only 107 decays/second, which sounds big until you realize that an amp second of electrons is 1019 or so. Even assuming multiple ionizations per decay....not that nifty. It could be you only need a little to trigger a process that creates more (like a fusor) however, and this would be a lot more reliable than cosmic rays, which is why they do that in the first place. Heck, I've got one Bill found that has Ra in it, and that sucker sets off geiger counters from across the room. Bill says he can get more, and I might just encourage that, as they are also useful as is -- they were main switches in a radar, not T/R, but the switch for main magnetron power, and they trigger at 2kv -- a few in series might be really nice for a marx generator, a tesla coil, or other pulsed things.
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: Test Sources

Postby Doug Coulter » Fri Apr 08, 2011 1:00 pm

Chris -- just forget doing spectrometry with a geiger type tube, it's terrible even in proportional mode. NaI is cheap, plastic is worse, but cheaper. HPGE is of course the best if you can afford it and the cryogenics.

30kv gamma goes right through most things -- it took 1/2" thick lead glass for CRT faceplates to stop the stuff. It's just hard to detect with a gas.
They only use twice that for dental X rays.

It goes roughly as

HPGE
NaI
CsI
BGO
Plastic

In order of decreasing resolution. A proportional tube is well off scale here to the bottom side.

I'd guess you can get Co60 sources the same place we got our "official" Cs-137 one.
CS137source.jpg


But few like that particular one (Co60). It's hot, it has several lines that make comparisons hard, and it has a fairly short useful life.
Dangerous stuff, Co60. You could always use fusion neutrons to make some, we plan to give it a go here at some point.

A proportional tube has too many variables. You can probably tell alpha from beta from gamma, if you know ahead of time the rough energies of each, and the relative gas cross sections of those at those energies. Else, it's a complete waste of time (or so 100% of the literature says).
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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