Got a new toy (Geiger)

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Got a new toy (Geiger)

Postby Jerry » Mon May 23, 2011 12:56 pm

My new toy showed up last friday. An old PDR-27P ratemeter. In its box with manual, strap, and headphones. Seems to work. Picked up the alphas from some U glass prepped tungsten electrodes I have. And also picked up betas from some tritium betalights I have, which really surprised me. Of course it would only pick them up with the alpha window open and the tubes as close as possible.
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Re: Got a new toy (Geiger)

Postby Doug Coulter » Mon May 23, 2011 1:09 pm

Nice! -- though I'm also really surprised to see anything from a T tube. I'll have to check my gamma spec (which is busy right this instant with another question) and see if it can see them too on that exit sign -- but that's down in the phototube noise energy level even with a 6" NaI xtal. At a mere 16kv peak from T (and mostly much less), I kinda doubt anything gets through the source, much less the detector window, but...worth a look.

I have seen counts go up when something massy was near a detector, as this increases the cosmic shower count, could be that....
According to the books, the showers go up all the way to 13" or so of iron over the detector -- more chances a primary ray will hit something and cause a high multiplicity shower that makes a lot more counts than the primary alone would.

That beta sensitive detector that can see T I have has a window less than one mil thick, it's insanely fragile....unlike the glass they put the T into.

Do you know the detector type in there? Geiger, or photo tube? Probe looks like it could have something fancy.
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: Got a new toy (Geiger)

Postby Jerry » Mon May 23, 2011 5:23 pm

The geiger uses a JAN 5979 and a JAN 5980 in parallel for high sensitivity modes (.5mR/hr, 5mr/h Full scale) and just the 5980 for low sensitivity (50mR/hr, 500mR/hr). Two tube in front of it read about .05mR/hr and a handful of the tubes reads higher. The tube is a mica end tube and says it .0005" thick in the manual.

Paid $45 for the counter and another $55 for shipping.
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Re: Got a new toy (Geiger)

Postby Doug Coulter » Mon May 23, 2011 5:29 pm

Well, no question at all that was a fantastic score indeed. What's your count rate on the T tube vs background anyway? Is it real obvious, or hard to see? T has a super high rate, but I still doubt much gets past the glass it's in -- it was hard enough to see it (and so far, we're the only guys claiming the ability to see it at all) without the glass in the way. In other words, that would be real interesting -- how did everyone else miss it? I won't say they didn't, understand - the more I do this the more I find out that it's not really as settled or cast in stone as the authorities seem to claim. Some betas or low energy gammas might be sneaking out...somehow and with the high initial decay rate, perhaps detectable enough.
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: Got a new toy (Geiger)

Postby Jerry » Mon May 23, 2011 6:08 pm

Background barely moves the meter. Most I have seen is .01mR/hr.
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Re: Got a new toy (Geiger)

Postby Doug Coulter » Mon May 23, 2011 6:11 pm

Jerry, you're going to like this one.

I hereby retract all my skepticism -- and I refute it thus:
TritNoSht.jpg
Tritium sign, 300 seconds, against a 600 second background. No sht.



Note the leftmost peak is right-shifted as it pushes more other junk above threshold. That means we can't take away much from the supposed energy, just that one heck of a lot of lower energy stuff was there with the X of my exit sign against the detector than not.

You really scored :D
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: Got a new toy (Geiger)

Postby Jerry » Mon May 23, 2011 7:08 pm

Well, I will pretend to know what that means...

Guessing the big peak at the low end is the T?
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Re: Got a new toy (Geiger)

Postby Doug Coulter » Mon May 23, 2011 7:24 pm

Yes, it's the T, no question whatsoever in my mind. While a single pulse from a degraded-energy beta from a T changed into a gamma with attendant further energy loss is below the threshold shown here -- the fact that pileups pushed the usual thresholded-out noise up above threshold on double hits ( and quite a large number of them, evidently) says to me, unequivocally, that yes, outside the glass, T makes a measurable amount of (gamma for sure) radiation, easily (well,,,,I have some great gear here too) detectable.

So much for "you can't do that". Hah. You just did. I check that.

It'd be a lot better and more obvious on an HPGE with cryo, which I don't have and am having trouble craving the rent on but...no question at least as far as I'm concerned, I just checked it myself with stuff I have a lotta reasons to trust. It's way outa background here too -- never thought to check before.

Were I a little more ambitious (maybe this week, more likely next, I have this other telescopic job to do first) I'd put this up on a super good low energy resolver head (have one) and really prove it with an internal spectrum of the various energy "landings" on the decay of T into -- all this stuff. But that insanely higher peak says it all - it's there.
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Re: Got a new toy (Geiger)

Postby Jerry » Mon May 23, 2011 8:18 pm

If it is gamma it is stopped dead by the aluminum protective flap over the sensor.

Ooooo... Telescope.. I like the sounds of that one!
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Re: Got a new toy (Geiger)

Postby Doug Coulter » Mon May 23, 2011 8:38 pm

Yes, tele is on the way as soon as I check it and find out the current condition of the thing so we don't hose each other. Real Soon Now.

Nope, gammas are far harder to stop (re mass-in-the-way) than you'd think. Only neutrons, including their side effects, are harder -- the sides are gamma. It's just that most of them don't plow enough gas to be seen by a normal geiger tube run at normal conditions.

http://www.coultersmithing.com/data/Fus ... elding.gif

Or something like it tells the tale. Stopping some classes of energy input before the detector are tricky -- they only have log attenuation response and shift input energy into a lotta lower energy events along the way, some of which they themselves stop. Tricky. but nope, the Al beta-shield stops nada gamma, just low betas (and of course, all alphas) with a lot higher absorption/reaction coefficient.
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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