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 2.GQ Geiger Muller Counter
 Collapsing Anode Volts with increasing Count Rate
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ullix

Germany
1174 Posts

Posted - 12/01/2024 :  06:15:04  Show Profile  Reply with Quote
This had been a hot topic some years(!) ago, but I taught GeigerLog some new tricks, so I tried it out.

GeigerLog can now communicate with a Bluetooth coupled DMM (Digital Multi Meter) so I could very conveniently measure the Anode Voltage (via 1 GOhm) of a Geiger counter, and read it into GeigerLog.

The counter was a GMC-300E+. The DMM an OWON OW18E (very nice AND LowCost!). I had the counter's backplate removed, and put increasing amount of "stuff" onto the naked tube (M4011) and recorded in GL (Note the LOG scale for CPM!):



CPM of some 6k is the best I could do. I know some of you can do more; you are encouraged to test it out!

The collapsing Anode voltage (in green) is already clearly visible.

Every Geiger tube has a certain minimum voltage, below which no counts whatsoever will be created. For the M4011 tube this minimum is 350V. For some deeper insight I plotted Volt vs CPM for the 4 value pairs. Assuming linearity - which seems to be given - the graph shows that this cutoff voltage of 350V is reached at about CPM=13500 or CPS=225:



Is this in agreement with what GQ is saying about their counter's range? In the manual of the GMC-300E+ I see:



With their "calibration factor" of 154 CPM / (µSv/h) this becomes CPM=50510 / CPS=842.

Really? I think this is a faaar cry away from reality!


Edited by - ullix on 12/01/2024 06:29:31
Reply #1

ihab17

Italy
219 Posts

Posted - 12/02/2024 :  23:19:49  Show Profile  Reply with Quote
You're da Man Ullix! Ullix for president!
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Reply #2

EmfDev

2259 Posts

Posted - 12/03/2024 :  18:21:24  Show Profile  Reply with Quote
hmm actually, the calibrated value for the GMC-SE (similar firmware and hardware) can go up to 200mR/h = 2000 uSv/h.

the multimeter is probably drawing current from the power supply.
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Reply #3

ullix

Germany
1174 Posts

Posted - 12/04/2024 :  01:46:11  Show Profile  Reply with Quote
Yeah, with a 1 GigaOhm resistor in between?

And the DMM, which is present for all count rates, is pulling increasing current with increasing count rate? So, effectively, the DMM would be the better Geiger counter for any count rates, uncluding very much higher ones?

The problem is not the collapsing voltage, the problem is your exaggerated claim about max count rate!

Edited by - ullix on 12/04/2024 07:06:17
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Reply #4

ullix

Germany
1174 Posts

Posted - 12/04/2024 :  07:13:16  Show Profile  Reply with Quote
quote:

hmm actually, the calibrated value for the GMC-SE (similar firmware and hardware) can go up to 200mR/h = 2000 uSv/h.

It does not matter what your claim is, when this device is based on the same hard and software, and you claim an even higher max count rate, then your claim is even much farther away from the true value!

Prove it isn't.

Edited by - ullix on 12/04/2024 07:13:34
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