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 2.GQ Geiger Muller Counter
 GMC 600+ Accuracy and repeatability question		  New Topic  Reply to Topic
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Bobakman

USA
97 Posts
Posted - 11/25/2022 :  11:44:25  Show Profile  Reply with Quote
Hi folks I am new to the forum and a soon to be GMC 600+ user, just ordered one yesterday.
A little background on myself I started out my career in 1983 as a radiological De-conner at my utilities first Nuclear Power plant. I currently work as an Electrical and Mechanical technician and operator at one of our Combined Cycle natural Gas plants.
I am an avid Vaseline glass antique collector and the GMC 600+ will be a great addition to the UV light.
I know I will have no issue with the general CPM detection for collecting what I would like to know is how accurate is the 600+ compared to the more expensive Thermo Scientific Rad Eye models?
Secondary use for the 600+ will be for safety survey use if/when needed and this is why I ask.
I do have a 10 Micro Curie CS137 check source purchased new back in 1985 so it is well past its half life.
Thanks for any help information that you can provide.

Bob
“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
Nikola Tesla
Reply #1

ullix

Germany
1171 Posts
Posted - 11/26/2022 :  00:53:25  Show Profile  Reply with Quote
Accuracy does not depend on the price of a counter, but on the accumulated counts in a measurement. Thus it depends on the sensitivity of a tube and the duration of the measurement.

The radioactive decay is of a Poisson nature. From this it follows that the Standard Deviation is given as square-root(counts). From there Std.Error follows by regular statistics-

How well this translates into a health relevant dose rate in e.g. µSv/h is a different matter. Here it depends on the existence of a proper calibration. For the LND7317 tube in the GMC-600 counter the tube manufacturer has published a value for its Gamma sensitivity. https://www.lndinc.com/products/geiger-mueller-tubes/7317/

While this gives you an idea of the sensitivity of the tube in comparison to other tubes, keep in mind that this specific values is valid ONLY for their Cs-137 setup!

For more insight I suggest my "Potty Training" intro https://sourceforge.net/projects/geigerlog/files/Articles/ as well as the chapter "Appendix G – Calibration" in the GeigerLog manual https://sourceforge.net/projects/geigerlog/files/
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Reply #2

Bobakman

USA
97 Posts
Posted - 11/26/2022 :  11:25:48  Show Profile  Reply with Quote
Thank you Sir. I will review this information.
Bob
quote:
Originally posted by ullix

Accuracy does not depend on the price of a counter, but on the accumulated counts in a measurement. Thus it depends on the sensitivity of a tube and the duration of the measurement.

The radioactive decay is of a Poisson nature. From this it follows that the Standard Deviation is given as square-root(counts). From there Std.Error follows by regular statistics-

How well this translates into a health relevant dose rate in e.g. µSv/h is a different matter. Here it depends on the existence of a proper calibration. For the LND7317 tube in the GMC-600 counter the tube manufacturer has published a value for its Gamma sensitivity. https://www.lndinc.com/products/geiger-mueller-tubes/7317/

While this gives you an idea of the sensitivity of the tube in comparison to other tubes, keep in mind that this specific values is valid ONLY for their Cs-137 setup!

For more insight I suggest my "Potty Training" intro https://sourceforge.net/projects/geigerlog/files/Articles/ as well as the chapter "Appendix G – Calibration" in the GeigerLog manual https://sourceforge.net/projects/geigerlog/files/
“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
Nikola Tesla
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