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 2.GQ Geiger Muller Counter
 GQ Gmc500+ tube selection		  New Topic  Reply to Topic
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Maharaja

United Kingdom
3 Posts
Posted - 08/15/2021 :  08:03:16  Show Profile  Reply with Quote
Hi folks.Im newbee in Geiger counters world.
I have gmc500+ and I try to check both tubes by selecting only one to work in settings.Its seems like only tube number 1 is registering counting which is up to 30 cpm in my house.Tube 2 is registering zero.Its because there is no high enough radiation? Unfortunately I don't have any source to check sensitivity of tubes.
Two loudest noises
:click when you expect bang,and bang when you expect click.
Reply #1

FBSMatt

Ireland
32 Posts
Posted - 08/15/2021 :  08:10:42  Show Profile  Reply with Quote
Yes. The second tube rarely registers much under normal conditions. If you have a lump of granite in your area, you can try that. Or rip apart an ionizing type smoke detector but even the Americium from that only ever got mine up to 10CPM on T2.
What Signature?
Edited by - FBSMatt on 08/15/2021 08:12:27
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Reply #2

Maharaja

United Kingdom
3 Posts
Posted - 08/15/2021 :  08:13:00  Show Profile  Reply with Quote
Cheers for quick replay!!!
Two loudest noises
:click when you expect bang,and bang when you expect click.
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Reply #3

ullix

Germany
1171 Posts
Posted - 08/15/2021 :  23:47:38  Show Profile  Reply with Quote
The second tube in a 500+ is about 70 times less sensitive than the first one. More precisely, these are the sensitivities as used in GeigerLog:

first:   154    CPM/(µSv/h)
second:    2.08 CPM/(µSv/h)

So, at background of 20 CPM as seen by first, the second delivers 0.3 CPM, which is shown as zero. In 3 min you can expect 1 count.

Whether this tube is even meaningful has been a matter of much discussion in the past in several topics. You'll find one e.g. here:
http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=5369
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Reply #4

Maharaja

United Kingdom
3 Posts
Posted - 08/16/2021 :  02:21:23  Show Profile  Reply with Quote
Thanks ullix!!!
Two loudest noises
:click when you expect bang,and bang when you expect click.
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