Is this neutron counter dead?

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Richard Hull
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Re: Is this neutron counter dead?

Post by Richard Hull »

More than hot enough! If the nearness of this source does not increase the tube count and you are still getting a natural one count per second, the tube might indeed be old or have leaked out a bit of the normal 3He fill gas. It still may count neutrons, but just at a higher than normal background that will need to be subtracted. You will need to moderate it and get a neutron source to be sure now.

I have seen some few ancient GM tubes where the normal Geiger plateau length has shrunk from 100 volts to 10 volts! This requires a critically held GM operating voltage if you wish to squeeze the last bit of life out of the GM tube. (should be thrown away - End of life) This was far more normal in the old organic quench tubes. (10e9 counts before death)

Assuming no leaking of original fill, most halogen quenched GM tubes have an effectively infinite life span.

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
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Michael Kaufmann
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Re: Is this neutron counter dead?

Post by Michael Kaufmann »

@Cai Arcos

no physical damage, not even single scratch.

ZY5yKubqrFg.jpg
Yj4b0Hds0Gk.jpg

there is a little dot-like mark on the bottom cap tho - like there was capacitive discharge to the tube body. but i can't find a second one anywhere.
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Michael Kaufmann
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Re: Is this neutron counter dead?

Post by Michael Kaufmann »

Richard - that's why i was asking in the first post of this topic - "so how exactly do they die? what happens at the end of their life?".
tho now i don't think the tube is EOL - more like defective or something.

there is something written on it with a pencil, but I cannot make out what exactly - something like "big", and the second word is not readable.
maybe it's a "big own background"?
i will continue to experiment with it - next step is a LDPE moderator (don't have HDPE), and then something like very small Pu-Be source.
Cai Arcos
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Re: Is this neutron counter dead?

Post by Cai Arcos »

Might be the discharge happened from inside the tube? That might reinforce the idea of internal damage causing spontaneous discharges.

In any case, I wish you the best of luck!
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Richard Hull
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Re: Is this neutron counter dead?

Post by Richard Hull »

I echo what Cai noted, best of luck.

Internal arcing in any gas detector is deleterious, damaging and possibly the end game.

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
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Michael Kaufmann
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Re: Is this neutron counter dead?

Post by Michael Kaufmann »

guys - I found an article that describes 3 different ways to determine the helium pressure inside the counter!

I have the pdf of the original in Russian, but I also found an English version, however, I do not have access to the text to compare it with the original.
the English version is here - https://doi.org/10.1134/S0020441220010236
original - https://sciencejournals.ru/view-article ... silev#text
https://sciencejournals.ru/cgi/getPDF.p ... asilev.pdf

p.s.
since i really love x-rays, i decided to image this counter at 50 and 100 kev - will post the pictures here : )
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Dennis P Brown
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Re: Is this neutron counter dead?

Post by Dennis P Brown »

Thanks for the post on the detector parameters.

Just remember, X-rays don't love you! Proper shielding and detectors to determine exposure is critical for one's long term health - safety matters.
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Michael Kaufmann
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Re: Is this neutron counter dead?

Post by Michael Kaufmann »

heh - nothing really fancy there:

1P1010005.JPG
1P1010006.JPG

and i don't see anode wire - probably coz it's just too tiny. or coz the focus of the x-ray tube is too large.
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Michael Kaufmann
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Re: Is this neutron counter dead?

Post by Michael Kaufmann »

it's there : )

121P1010029.JPG
Matt_Gibson
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Re: Is this neutron counter dead?

Post by Matt_Gibson »

Well that is some next level investigation right there…
Peter Schmelcher
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Re: Is this neutron counter dead?

Post by Peter Schmelcher »

Your operating voltage seems high to me. I tested a CH19N and determined it was working by ramping the voltage up in steps and measuring the resulting pulse heights (Geiger plateau curve). Pulse height is the gain of the detection process and increases with voltage.
From my memory I believe the best signal to noise was around 1200 +-75V for proportional operation. The manufacturer recommended voltage was 1875V to 2100V for Geiger operation but honestly it was unusable at that voltage.
At higher tube operating voltages the circuit you are using becomes an avalanche oscillator.
Cheers -Peter
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