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 2.GQ Geiger Muller Counter
 Experiment: High radiation with my 500+
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2 Posts

Posted - 04/16/2020 :  01:45:19  Show Profile  Reply with Quote
Hello everyone!
I want to share a very common experiment but with an NOT expected end.

1- Buy an old watch in a garbage market.

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2- That was the result of my Geiger in his first measurement.

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3- I decide to disassemble the watch, to avoid that separation that the glass provides.

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4- Final result of the Radio measurement without any protection.

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It seems too high to me. What do you think?

Gq GMC-500+
Latitude: 41.221110
Longitude: 1.539394774

Edited by - Marta on 04/16/2020 01:45:53
Reply #1


1438 Posts

Posted - 04/16/2020 :  08:58:41  Show Profile  Reply with Quote
Seems like you got an interesting clock there :D.

How long did you measure the CPM?
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Reply #2


2 Posts

Posted - 04/16/2020 :  23:17:05  Show Profile  Reply with Quote
Hello EmfDev

4-5 minutes.

Gq GMC-500+
Latitude: 41.221110
Longitude: 1.539394774

Edited by - Marta on 04/16/2020 23:17:30
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Reply #3


602 Posts

Posted - 04/17/2020 :  02:03:40  Show Profile  Reply with Quote
I agree that this high-count is highly suspicious.

Is there anywhere something like a manufacturing year on the clock? Very likely the dials are painted with Radium (they do glow in the dark?). Radium 226 is an alpha-emitter, so you could not detect it in an GMC500, but in its decay chain are multiple beta and gamma emitter, which would produce counts.

This link shows a gamma spectrum (despite the labelling - it is from the decay chain compounds, not from Ra226 itself).

But the cover glass of the clock (your first picture) would probably have held back most betas, and yet, 1171 CPM is a pretty good clip, not to mention the 11000 with the glass removed.

I suspect some defect in the counter, perhaps a misadjusted voltage, or an electronic defect. Is that a 500 with a dual-tube?

You probably do not have access to a 2nd counter to compare the readings with?

Then I suggest to verify that your counter gives reasonable readings. The only easily accessible and reproducible source for radioactivity is Potassium salt. I have detailed this in my "Potty Training" article ( ) it includes some advice for what to shop for.

Run a test and post results, please.
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Reply #4


18 Posts

Posted - 01/31/2021 :  04:15:45  Show Profile  Reply with Quote
The decay product of Rad-226 is Radon-222. Remember that even without opening the case, the radiation source (watch, compass) stains your hands when you touch it. Easy tests can be performed, put the watch in the jar and close it, after a few hours the lid will be radioactive. You can see this effect in my video

GC: GMC-300E plus, GMC-500, GMC-500 plus, GMC-600, Exploranium GR-110G, Terra MKS-05 bluetooth, DoseRae 2, RadiaScan 701A, Automess 6150AD6, Soeks Qantum, PRM-9000, Radex Obsidian, Radex RD1008, MKS-03SA

Edited by - Senketsu on 01/31/2021 04:17:27
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Reply #5


48 Posts

Posted - 02/08/2021 :  07:52:19  Show Profile  Reply with Quote
Provided the clock is old enough and from an early time of radium paint when the concentration radium was higher, this is within plausible values. In very early applications of the paint, it would not be unusual to get past one millisievert. Take extra care with the environment you're working this thing in because the paint has flaked into microscopic fine particles that are let out when you fiddle with this stuff.
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Reply #6


80 Posts

Posted - 02/09/2021 :  07:43:02  Show Profile  Reply with Quote
Wow those numbers are pretty high!
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Reply #7


38 Posts

Posted - 03/04/2021 :  06:43:49  Show Profile  Reply with Quote
This reading does not seem very high for a radium clock.
I purchased a Westclox on ebay from the early 40s - my GMC-600+ reads around 28K CPM thru the glass and 77K CPM @ 1cm (centered on both hands) with glass removed.
There was some discoloration on the inside of the glass just above the hands and you can see a very faint "shadow" of each hour dot on the inside of the glass due to radiation damage from the alpha bombardment.

Needless to say, the glass itself was reading over 100 CPM from Radon daughters probably accumulated and /or contaminants shed off from the paint.

Edited by - kotarak on 03/04/2021 06:46:21
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Reply #8


2 Posts

Posted - 08/06/2021 :  15:02:43  Show Profile  Reply with Quote
I also have a 500+ and an old Westclox alarm clock from the 30s and I measured 1100 CPM after a few minutes. Stealth.

Edwin Lebish
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