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 Tube upgrade for my GMC 500+ :)		  New Topic  Reply to Topic
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DVE

Netherlands
7 Posts
Posted - 07/18/2025 :  11:39:57  Show Profile  Reply with Quote
Just got a new soviet (made in 1988) SI-22G GM tube by post.

It does not fit a bit into the case, however



A first test with my DIY board shows ~85CPM for a background.

The plan is to put the tube outdoors using a 0.5-meter wire.

What settings are recommended to set?
Edited by - DVE on 07/18/2025 11:44:55
Reply #1

DVE

Netherlands
7 Posts
Posted - 07/20/2025 :  02:56:58  Show Profile  Reply with Quote
I did some tests with the tube (for now, without GMC yet).

Its sensitivity is good - it detects a small uranium drinking glass from 10cm.

Test #1: Background fluctuation (~15 min)



Test #2: I placed 2 radioactive objects of different intensity at ~10cm from the tube (CPM values have some delay because of the sliding 60s window calculation). Even from such a distance, it's detectable.



It works well, but I'm still not sure if it makes sense to connect a SI-22G tube to GMC, or just keep the tube for separate experiments.
Edited by - DVE on 07/20/2025 03:05:21
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Reply #2

EmfDev

2352 Posts
Posted - 07/21/2025 :  12:33:11  Show Profile  Reply with Quote
it is too long. what is the voltage requirements on that tube?
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Reply #3

DVE

Netherlands
7 Posts
Posted - 07/22/2025 :  11:21:03  Show Profile  Reply with Quote
The voltage is 390V, looks standard. A conversion rate is 792 to 1uSv/h (for M4011 it is 151) so it's about 5x more sensitive than a "standard" M4011.

I decided to use it with a Raspberry Pi, and upload the data to gmcmap with a software correction - no need to confuse people with a "red" point with high cpm values on a map :)

It's a weird decision that gmcmap uses CPM values as a default marker; uSv/h would be more universal.
Edited by - DVE on 07/22/2025 11:22:12
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