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Discopotato
Australia
3 Posts |
 Posted - 05/05/2025 : 02:54:49
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Hi everyone
I recently just bought a GMC-600 but when I trst against a uranium glass bowl I have the responds very well to black light the max reading im getting is 36cpm
I don't know, I no expert at all but shouldn't I be seeing atleast 500cpm on something like this? |
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| Reply #1
ullix
Germany
1197 Posts |
Posted - 05/05/2025 : 04:06:33
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36 CPM is barely background, and could well be just electronic noise with a broken Geiger tube.
Can you try some other stuff as readio-source? Potassium, e.g. If you are unfamiliar, I suggest my article "Potty-Training" as a primer.
https://sourceforge.net/projects/geigerlog/files/Articles/
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| Reply #2
Discopotato
Australia
3 Posts |
Posted - 05/07/2025 : 13:31:09
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So in the mean time i pulled the back cover of the gieger counter and put in a plastic snap lock bag and the readings came up to roughly 80-90cpm but the ticks are not a consistent tone. Is that normal?
I did have a quick read of the article you directed me too
Also what is the best setting to use for fast estimate, dynamic? |
Edited by - Discopotato on 05/07/2025 13:37:22 |
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| Reply #3
ullix
Germany
1197 Posts |
Posted - 05/09/2025 : 02:50:53
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What radioactive source did you use? How was the counter place in your room? CPM80-90 would be a lot for just background.
The sequence of clicks is a random distribution. To be more prceise: a Poisson distribution. Google for it, and/or use GeigerLog to see it yourself.
The "Fast Estimate" is the worst feature of the GMC counters I can think of. I urge erveryone to switch it OFF by setting it to 60 sec.
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| Reply #4
ihab17
Italy
220 Posts |
Posted - 05/09/2025 : 12:02:10
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| Either you do not have a real Uranium sample, or your device is broken (in case you were using it the right way). Can you post a short video somewhere to see what and how are you using it? |
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| Reply #5
Discopotato
Australia
3 Posts |
Posted - 05/10/2025 : 03:24:21
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The uranium source i used was a glass bowl i bought, advertised as uranium glass.
The counter back plate was removed and placed in a snap lock sandwich bag and than placed inside the bowl on my loungeroom table
For reference the background here is around 24cpm and 80-90 in the bowl
If i have the back plate on i get around 36cpm for memory. |
Edited by - Discopotato on 05/10/2025 03:25:26 |
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| Reply #6
ullix
Germany
1197 Posts |
Posted - 05/11/2025 : 00:41:03
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Not all "Uranium glass" does exhibit high activity. I also have some such stuff, which basically is not showing any activity :-(.
Your 3 reported count rates do seem reasonable, so it looks like your counter is ok. CPM=24 as background is quite low. Are you living in a wooden house?
For me the one reliable reference sourse is Potassium to which everybody has access; look into my Potty Training article.
I am realizing that my recommendation to remove the backplate is not really relevant for a GMC-600 counter. Here you do have a quasi open back already, and it is only the protective mesh across the pancake tube, which is taking away some counts. The situation is quite different for those other counters with glass Geiger tubes. So, sorry for this advice, but from now on don't bother with removing the backplate!
There is one more thing I'd suggest to do: Erase the counter's memory, place the counter into your Uranium glass bowl, and let it record for at least overnight. Then download the memory and post the bin file e.g. here: https://sourceforge.net/p/geigerlog/discussion/easyuploads/
Reason: all GMC-600 counters that I have seen so far do have a problem which becomes visible when the Poisson check is made. (If you have GeigerLog running already, you can do this yourself, directly in GL).
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New GMC-600
