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 2.GQ Geiger Muller Counter
 GMC 500+ inaccurate Beta readings
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user06

14 Posts

Posted - 09/28/2018 :  11:57:17  Show Profile  Reply with Quote
Hello, new to the forum.

Courier have just delievred my new GQ GMC-500 Plus rev 1.18 and I wanted to test it with some uranium beads I've got at home.

The manual doesn't say anything about the procedure but I'm guessing that the larger tube should handle this. I measured about 0.50-0.60uSv/h. Compared to this my old Terra P is showing over 2uSvh. Terra doesn't have a CPM function but I can also clearly hear the difference in the frequency of ticks registered by both meters.

I also measured this source with Polaron Pripyat and got a result similar to Terra.

Am I doing something wrong here? I would expect some difference but 4 times is a bit too much to explain. Please see the video below:

https://youtu.be/LY5h_PkICwo



Also, is there any cover available for this meter? The components are exposed via the bottom vent holes, I'd be worried to touch anything contaminated with it.

Edited by - user06 on 09/28/2018 12:13:16
Reply #1

EmfDev

311 Posts

Posted - 09/28/2018 :  12:22:56  Show Profile  Reply with Quote
Hi user06,

The difference might be because of the distance of the tube to the source.
If you want the GMC-500+ to read similar uSv to the Terra P, you can change the calibration values from the unit.
For the cover, you can put the 500+ inside a plastic bag when using it somewhere that it can get contaminated.
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Reply #2

user06

14 Posts

Posted - 09/28/2018 :  13:09:55  Show Profile  Reply with Quote
quote:
Originally posted by EmfDev

Hi user06,

The difference might be because of the distance of the tube to the source.
If you want the GMC-500+ to read similar uSv to the Terra P, you can change the calibration values from the unit.
For the cover, you can put the 500+ inside a plastic bag when using it somewhere that it can get contaminated.



That would be likely, I'll have a chance to compare both in strong gamma sources next week so will post the results. :)

I always use zip lock bags for really nasty samples but a pouch with window would be nice for general use, out in a rain etc. Plastic bags are cumbersome and easy to rip.
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Reply #3

ikerrg

United Kingdom
292 Posts

Posted - 09/28/2018 :  13:58:40  Show Profile  Reply with Quote
quote:

I'll have a chance to compare both in strong gamma sources next week so will post the results. :)



That looks interesting! Please, activate the view of the CPM of both tubes in the "Large text" screen and, when in the strong gamma source, take note of the readings (or a picture/video). You should probably update the firmware to 1.23.
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Reply #4

ullix

Germany
346 Posts

Posted - 09/29/2018 :  03:36:39  Show Profile  Reply with Quote
In all likelihood this is due to different shielding with respect to betas. Read about this effect in my Potty Training article, https://sourceforge.net/projects/geigerlog/files/GeigerLog-Potty%20Training%20for%20Your%20Geiger%20Counter-v1.0.pdf/download

The slits in the counter's case are relevant only for betas; the absorbance of the case for gamma is negligible. But if you are after betas, then any additional wrapping or casing of the counter is a problem! Again, read above mentioned articles.

P.S. Don't change any of the "calibration"; you'd mess up your system profoundly! A bit more on the calibration in the GeigerLog manual https://sourceforge.net/projects/geigerlog/ and a whole lot more elsewhere in this forum.

P.S. if you are afraid of loose particles from your radioactive sample, I would fear a little bit for my counter, but a lot more for my own health! Avoid inhaling any dust, if your sample is indeed giving off dust! A simple wrap with kitchen plastic foil would already be helpful.


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