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 2.GQ Geiger Muller Counter
 What limit is proper?
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svann

USA
2 Posts

Posted - 04/09/2021 :  08:52:18  Show Profile  Reply with Quote
Ive had my GMC-320 for a couple years running 24/7, and just this morning the beeper started going off for the first time. I checked it and the level was up to 0.75uSV/hr. Alarm was set to 0.5uSV/hr. Not sure if I should be concerned.

It seems to me the alarm was set too low but I may be wrong on the federal allowed limit or my conversion.
I looked up the radiation limit and found
https://news.mit.edu/1994/safe-0105
which says occupational safety limit is 5000mRem/yr above the 300mRem natural radiation. I convert 5300mRem/yr to 6.05uSV/hr, which is about 12x what the alarm was set to, and if correct then I still have plenty of headroom.

Should I change the alarm setting or should I go searching for where the radiation might be sourcing from?

edit: a few hours later the measure has dropped back down to 0.19uSV/hr, which I think is what Im used to seeing. No idea what had made it higher - sunspots? My original question still stands though. Is 0.5uSV/hr the correct alarm limit or should it be raised to 6uSV/hr? This is at home.

Edited by - svann on 04/09/2021 10:33:32
Reply #1

EmfDev

1460 Posts

Posted - 04/09/2021 :  11:45:31  Show Profile  Reply with Quote
The svann, the low alarm threshold is to let you know there might be a radiation slightly higher than background. If you are not worried about low radiation you can set it to higher. Low alarm can let you know if you are bringing something new with radiation.

The trigger may have been just a noise and not a real radiation.
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Reply #2

svann

USA
2 Posts

Posted - 04/10/2021 :  20:44:47  Show Profile  Reply with Quote
Thanks for the answer about the default trigger setting.
I still think this was not just noise fluctuation though. Its now pretty much always down about 0.20 or just under that and I think in the past its been about that, but for a few hours it was up around 0.75. Thats quite a difference. I think something was going on in the area that caused a temporary rise in radiation. Not high enough to be bad, but higher than normal for the area.
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Reply #3

Damien68

France
523 Posts

Posted - 04/10/2021 :  23:06:46  Show Profile  Reply with Quote
Hi svann
going from 0.2uSV/h in average to 0.5-0.7 for many hours, it is suspicious, in the counter there is a history of the measurements made, you can trace them using either the dataviewer software from GQ or the geigerlog software from ullix, it will allow you to better see what happened.

Mastery is acquired by studying, with it everything becomes simple
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Reply #4

Breizh

France
46 Posts

Posted - 06/07/2021 :  07:48:30  Show Profile  Reply with Quote
The measurement may not exceed 0.12ÁSv / h otherwise we exceed the calculated dose of 1 mSV / year / inhabitant, which is the French but not legal standard!
Breizh
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