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2.GQ Geiger Muller Counter

New GMC-600

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T O P I C R E V I E W
Discopotato	Posted - 05/05/2025 : 02:54:49 Hi everyone I recently just bought a GMC-600 but when I trst against a uranium glass bowl I have the responds very well to black light the max reading im getting is 36cpm I don't know, I no expert at all but shouldn't I be seeing atleast 500cpm on something like this?
13 L A T E S T R E P L I E S (Newest First)
ihab17	Posted - 05/16/2025 : 08:57:56 Well what do you know! You always learn something new from Ullix! Thanks mate, I'll try the new software once I have time.
ullix	Posted - 05/16/2025 : 03:17:24 quote: Hey Ullix how are you? Busy with putting Gamma Spectrometer software into GeigerLog. And I am VERY sure YOU do need a RadiaCode Spectrometer! quote: ... is an Alpha emitter that your GMC-800 cannot detect NOT true at all! An alpha emission (almost?) never results in a stable daughter nucleus. Instead it results in a decay chain, in which you find more alpha, beta, and gamma emissions. It can even be more complicated when K_alpha, K_beta, ..., and L_xyz,... X-ray emissions also come into play. This is in fact the situation with Am-241! And while a glass-Geiger-tube can never detect alpha, it can detect beta and gamma. However, here beta may not be an option as long as the Am-241 is left in its smoke-detector-casing - and I urge you to not unpack it! I would not want to have any crumbs of an alpha emitter floating in my house! This leaves gamma. The next pic gives proof that it can easily be detected. Recorded with an RadiaCode-102 spectrometer, and analyzed and presented with GeigerLog's new spectrometer feature: Marked in green is the Gauss-fit to the 59 keV line. To its left is the 26 keV K_alpha X-ray. The 17 keV L_alpha is not visible. Maybe it is below energy detection level of the RadiaCode, but I don't know. The 59 keV for sure, and perhaps the other two lines as well, will make a glass-Geiger-tube counter click. Next pic shows a recording with a FNIRSI GC-01 counter with RadPro firmware. It has a J321 glass tube (also used in GMC counters). It gives CPM=73 with a single, intact smoke-detector module sitting close to the tube. The Poisson check confirms a good recording. Thus the Am-241 is a good compound to calibrate the spectrometer at very low gamma energies, nicely complemented with K-40 with rather high gamma energy!
ihab17	Posted - 05/15/2025 : 05:06:44 quote: Originally posted by ullix Back to Square-One ... Hey Ullix how are you? Yes, Discopotato, so Americium 241 even though radioactive, it is an Alpha emitter that your GMC-800 cannot detect, and as Ullix mentioned, you have to get another reliable source of radiation. I was wondering because GMC-600 does not have a cap to cover the detector!
Discopotato	Posted - 05/13/2025 : 04:23:29 Thanks ullix I will try and source some known samples and see what happens
ullix	Posted - 05/12/2025 : 23:47:12 Back to Square-One ... All the backplate-removal discussion becomes valid again. You should get some good radio-source now. Get Potassium-Chloride - even the health food stuff from a Bio store. Imagine the fun you could have by holding a counter to their product in the store and have the counter ticking !!! The Am241 mentioned by Ihab17 is another good option. You can get them on AliExpress https://de.aliexpress.com/item/1005005865232110.html
Discopotato	Posted - 05/12/2025 : 08:59:08 My bad guys im sorry for the stupid mistake but the gieger counter is a GMC-800 I don't know how i didn't puck up on it until now
ihab17	Posted - 05/11/2025 : 22:46:50 Do you have a smoke detector that you can use and play around with? If yes, then smoke detectors have a tiny bit of Americium 241 that you can put just in front of your counter and see what happens. Americium 241 is an Alpha emitter and if you carefully open the radioactive source and carefully place it on the counter detector, you should be able to get 60K CPM. Mine for example got 66409 CPM (271.17 uSv/h)
ullix	Posted - 05/11/2025 : 00:41:03 Not all "Uranium glass" does exhibit high activity. I also have some such stuff, which basically is not showing any activity :-(. Your 3 reported count rates do seem reasonable, so it looks like your counter is ok. CPM=24 as background is quite low. Are you living in a wooden house? For me the one reliable reference sourse is Potassium to which everybody has access; look into my Potty Training article. I am realizing that my recommendation to remove the backplate is not really relevant for a GMC-600 counter. Here you do have a quasi open back already, and it is only the protective mesh across the pancake tube, which is taking away some counts. The situation is quite different for those other counters with glass Geiger tubes. So, sorry for this advice, but from now on don't bother with removing the backplate! There is one more thing I'd suggest to do: Erase the counter's memory, place the counter into your Uranium glass bowl, and let it record for at least overnight. Then download the memory and post the bin file e.g. here: https://sourceforge.net/p/geigerlog/discussion/easyuploads/ Reason: all GMC-600 counters that I have seen so far do have a problem which becomes visible when the Poisson check is made. (If you have GeigerLog running already, you can do this yourself, directly in GL).
Discopotato	Posted - 05/10/2025 : 03:24:21 The uranium source i used was a glass bowl i bought, advertised as uranium glass. The counter back plate was removed and placed in a snap lock sandwich bag and than placed inside the bowl on my loungeroom table For reference the background here is around 24cpm and 80-90 in the bowl If i have the back plate on i get around 36cpm for memory.
ihab17	Posted - 05/09/2025 : 12:02:10 Either you do not have a real Uranium sample, or your device is broken (in case you were using it the right way). Can you post a short video somewhere to see what and how are you using it?
ullix	Posted - 05/09/2025 : 02:50:53 What radioactive source did you use? How was the counter place in your room? CPM80-90 would be a lot for just background. The sequence of clicks is a random distribution. To be more prceise: a Poisson distribution. Google for it, and/or use GeigerLog to see it yourself. The "Fast Estimate" is the worst feature of the GMC counters I can think of. I urge erveryone to switch it OFF by setting it to 60 sec.
Discopotato	Posted - 05/07/2025 : 13:31:09 So in the mean time i pulled the back cover of the gieger counter and put in a plastic snap lock bag and the readings came up to roughly 80-90cpm but the ticks are not a consistent tone. Is that normal? I did have a quick read of the article you directed me too Also what is the best setting to use for fast estimate, dynamic?
ullix	Posted - 05/05/2025 : 04:06:33 36 CPM is barely background, and could well be just electronic noise with a broken Geiger tube. Can you try some other stuff as readio-source? Potassium, e.g. If you are unfamiliar, I suggest my article "Potty-Training" as a primer. https://sourceforge.net/projects/geigerlog/files/Articles/

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