I just posted in the files section my small paper on GM tube "boosting" that I promised in image du jour a month ago.
viewtopic.php?f=19&t=7980#p57384
Please post any comments here in this forum as it will keep discussion in this radiation and detection forum.
Richard Hull
Article on GM tube boositng.
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Richard Hull
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Article on GM tube boositng.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
-
Jon Rosenstiel
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Re: Article on GM tube boositng.
Well done and very interesting, thanks Richard. I just happen to have a CK-1026 (bought it new in 1955). I’ll have to see if I can duplicate your experiment.
Jon Rosenstiel
Jon Rosenstiel
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Richard Hull
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Re: Article on GM tube boositng.
Glad you enjoyed the paper Jon. I have used beta recoil to herd betas for years, but never thought of using it for boosting until the poor response of this tube disappointed me.
Richard Hull
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
-
Carl Willis
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- Real name: Carl Willis
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Re: Article on GM tube boositng.
Hi Richard,
This was a very interesting piece of work and I appreciate the post.
A standard Geiger tube has almost no energy-transfer cross-section for gamma photons, which would include photoelectric, Compton, and pair-producing effects. After all, it is composed of low-Z materials at low densities (usually a neon-chlorine fill, thin mica window, glass wall). It is an excellent charged-particle detector however. The trick to detecting high-energy photons in a Geiger tube is to increase the charged-particle energy deposited in the tube by surrounding it with just enough of some certain material that charged-particle equilibrium will be reached in the tube, yet not enough of that material that self-shielding of the photon flux negates the buildup gains.
The design issue of how thick to make the "buildup cap" such that the maximum absorbed dose is delivered to into the center of the GM tube ,and what material to use is not straightforward, and does depend on the intended energy range of use. As a general rule, the thickness shouldn't be thicker than the maximum range of a photoelectron in the material. The material should be chosen to be a strong photoelectric absorber at the energy of interest. In some of the old Detectron prospecting Geiger counters, as many as 20 or more 1B85 GM tubes with special bismuth cathodes were lined up in parallel in the bottom of the unit. They were said to be as good at radium gamma detection as a small and much more expensive NaI(Tl) unit. The normal 1B85 has an aluminum wall and is a great beta detector but has awful gamma efficiency.
-Carl
This was a very interesting piece of work and I appreciate the post.
A standard Geiger tube has almost no energy-transfer cross-section for gamma photons, which would include photoelectric, Compton, and pair-producing effects. After all, it is composed of low-Z materials at low densities (usually a neon-chlorine fill, thin mica window, glass wall). It is an excellent charged-particle detector however. The trick to detecting high-energy photons in a Geiger tube is to increase the charged-particle energy deposited in the tube by surrounding it with just enough of some certain material that charged-particle equilibrium will be reached in the tube, yet not enough of that material that self-shielding of the photon flux negates the buildup gains.
The design issue of how thick to make the "buildup cap" such that the maximum absorbed dose is delivered to into the center of the GM tube ,and what material to use is not straightforward, and does depend on the intended energy range of use. As a general rule, the thickness shouldn't be thicker than the maximum range of a photoelectron in the material. The material should be chosen to be a strong photoelectric absorber at the energy of interest. In some of the old Detectron prospecting Geiger counters, as many as 20 or more 1B85 GM tubes with special bismuth cathodes were lined up in parallel in the bottom of the unit. They were said to be as good at radium gamma detection as a small and much more expensive NaI(Tl) unit. The normal 1B85 has an aluminum wall and is a great beta detector but has awful gamma efficiency.
-Carl
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Richard Hull
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Re: Article on GM tube boositng.
The reason the large 2" pancakes do as good as they do on gamma is due to photons popping out of the steel backing and walls back into the sensitive volume of the tube.
The little glass tube in my tests might be the most horrid GM tube I have ever seen or used. It had almost everything going against it.
1. walls too thick to pass alpha or extremely weak beta
2. walls too thin to interact with almost any gamma save for very weak stuff.
3. really low sensitive volume of small dimensions so that only a few lucky, mid range betas might be detected.
Still this is the very first GM tube that I ever had as a child. It was cheap and used in a million electronics articles on roll your own counters like Scientific American, Electronics Illustrated, Poular Electronics and Radio-TV Electronics magazines.
I think Jon told me it was his first GM experimenter detector, as well.
More nostalgia than functionality and at a price a kid could afford in the 50's.
Richard Hull
The little glass tube in my tests might be the most horrid GM tube I have ever seen or used. It had almost everything going against it.
1. walls too thick to pass alpha or extremely weak beta
2. walls too thin to interact with almost any gamma save for very weak stuff.
3. really low sensitive volume of small dimensions so that only a few lucky, mid range betas might be detected.
Still this is the very first GM tube that I ever had as a child. It was cheap and used in a million electronics articles on roll your own counters like Scientific American, Electronics Illustrated, Poular Electronics and Radio-TV Electronics magazines.
I think Jon told me it was his first GM experimenter detector, as well.
More nostalgia than functionality and at a price a kid could afford in the 50's.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment