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 2.GQ Geiger Muller Counter
 GMC 600+/DP-66M comparison
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Posted - 02/13/2023 :  12:11:09  Show Profile  Reply with Quote
Nothing scientific here just a simple comparison as best I could measuring a broken Fiestaware
piece with my GMC 600+ and a vintage Polish DP-66M given to me as a gift from my Son.
I can't really compare Apples to Apples here obviously with the Software and LND-7317 with the vintage electronics and the low range probe in the Beta window of the DP-66M a STS-5 /(CTC-5).
I added a bit of packing tape over the 600+ window to simulate the plastic over the DP-66M beta window again the STS5 (CTC-5) is a metal encased probe so it is what it is.
I was surprised though to see that the mR/h readings were almost, if not spot on.
The DP-66M read consistently from 3.5-4mR/h where the 600+ was reading 3.6 almost 3.7 mR/h.
The DP-66M actually has two other glass cased GM tubes installed in the wand as well. As I understand it these are primarily for the high range readings?

Data on the STS-5 (CTC-5) Probe
Gamma radiation sensitivity (Cs137): MED – 0.28mkR#8729;s-1
Operating Voltage Range (volts): 360 – 440V
Starting voltage (volts): 280 – 330V
Geiger plateau length: not less than 80 V
Plateau slope: no more than 0.125%/V
Maximum natural background : 27 pulses / min or 0.45/s
Load resistance : 5…10 MOhm
Allowable stray capacitance of input circuits : 10 pF
Transit capacitor : 7…10 pF
Operation temperature range: -40 to +50C
The maximum operating MED 2500 s-1, 30mkR#8729;s-1,k.n.± 20%
The maximum permissible MED dose – at least 50R#8729; h-1
Length: 110 mm
Diameter: 12 mm
Weight: 8g

Info. From Here: [;tc-5-geiger-tube/]


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

Edited by - Bobakman on 02/13/2023 13:04:52
Reply #1


1121 Posts

Posted - 02/14/2023 :  00:49:15  Show Profile  Reply with Quote
Good Lord, which museum did you rob for all those goodies ;-)

Just a strong reminder: when Betas come into play, you can neither use mR (milli-Röntgen) nor µSv (micro Sievert)! Both are valid ONLY for pure gamma radiation (which includes X-ray).

The one instrument even shows this on its display:

Yet as mR is the only reading shown it is really hard to report CPM ;-))

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