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 2.GQ Geiger Muller Counter
 What tubes are in the GMC+500+
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n8xyn

USA
52 Posts

Posted - 04/13/2018 :  10:35:11  Show Profile  Reply with Quote
I just want to research them

Jim Whitaker
Reply #1

Distelzombie

Germany
202 Posts

Posted - 04/14/2018 :  13:32:58  Show Profile  Reply with Quote
Doesn't it say that in the technical description of it from sellers?
It should just be the M4011. Or two. I don't think they used a different one for it. It's a cheapy.

GMC-300E+ V4.20 with sbt-11a alpha tube

My statements are "stuff-a-hobbyist-says" and not in any way professional.
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Reply #2

the_mike

Switzerland
28 Posts

Posted - 04/15/2018 :  05:22:21  Show Profile  Reply with Quote
@Distelzombie
the 500 is using just an M4011,
the 500+ (@n8xyn) is additionally using an SI3BG for higher ratings - it's described in one of the 500-threads, i think the info slipped unintentionally ;)

(unfortunatly, it's not possible to just "retrofit" an SI3BG into a 500 eventough the socket is there - the + is using another firmware)
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Reply #3

n8xyn

USA
52 Posts

Posted - 04/15/2018 :  15:01:33  Show Profile  Reply with Quote
Is there a more sensitive replacement for the M4011 that is a direct fit?

Jim Whitaker
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Reply #4

ullix

Germany
318 Posts

Posted - 04/16/2018 :  05:59:56  Show Profile  Reply with Quote
@Jim: I'd be surprised if there is one. The tube sensitivity is first proportional to their inner volume, and second to their inner surface. For a given volume a more slender tube is more sensitive than a thicker one.

The SBM20 tube is a little bit longer than the M4011 at about the same diameter, and comes with a 40% improvement. It almost fits as a direct replacement, but you'd have to relocate one of the two tube holders. A comparison of the two here: http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4571&SearchTerms=ullix,sbm20 But note the caveat: probably valid only for a beta-source. The effect on gammas is not known.

In fact, the closeness of the calibration factors between the SBM20 and the M4011 (the latter as reported by GQ) suggests that the expectation is that the two tubes basically are the same, see here http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4578

The size relationship to sensitivity is further corroborated with the choice of the tiny (!) tube SI-3BG as the second tube in a 500+ counter. This website with pictures says: https://www.pocketmagic.net/tube-si-3bg-c%D0%B8-3%D0%B1%D0%B3-small-geiger-muller/
quote:

The SI3BG tube is suitable for use with powerful radiation sources or for severe nuclear incidents resulting in high radiation doses. It makes no sense to use it for your DIY experiments, as the background radiation CPM on this tube is close to 0:



This is all the more ridiculous, as the GMC processor and software at least is the 300series is not even capable of handling the counts possible with the M4011 tube. http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4613&SearchTerms=ullix,overflow


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Reply #5

Distelzombie

Germany
202 Posts

Posted - 04/18/2018 :  04:36:39  Show Profile  Reply with Quote
quote:
Originally posted by ullix
"The SI3BG tube is suitable for use with powerful radiation sources or for severe nuclear incidents resulting in high radiation doses."
This is all the more ridiculous, as the GMC processor and software at least is the 300series is not even capable of handling the counts possible with the M4011 tube. http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4613&SearchTerms=ullix,overflow

Why? It makes perfect sense. It not a more sensitive tube. It is less sensitive = less cpm per ySv

GMC-300E+ V4.20 with sbt-11a alpha tube

My statements are "stuff-a-hobbyist-says" and not in any way professional.
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Reply #6

ullix

Germany
318 Posts

Posted - 04/20/2018 :  23:58:29  Show Profile  Reply with Quote
@Distel: You are right. I should have worded it the other way round: instead of creating a new device with a perhaps 2fold lower sensitivity, GQ could just as well have fixed their flawed firmware and gained a factor of 2 just by that!

If you want to reduce sensitivity of your counter, put it into a metal (iron, lead) enclosure.

And lastly, as a user of these products you better make sure never to get into a situation where you'd need the high count rate sensitivity. Run the other way, then.
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