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 2.GQ Geiger Muller Counter
 high CPM on only one tube

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damien-mattei Posted - 06/06/2022 : 10:06:17
i just bought a GMC-500+ to measure watch radioactivities,
on a soviet era stursmankie watch i can get 1000 to 2000 CPM approaching the "black tube" (bottom of case) to the watch's dial and when approaching the "glass tube" i get 50 to 100 CPM. Approaching means sometimes the GQ GMC 500 plastic case touch the plexiglass glass of the watch.

Any explain because this is a bit scary!!! ???


19   L A T E S T    R E P L I E S    (Newest First)
damien-mattei Posted - 07/15/2022 : 01:28:04
thank you EmfDev ,it works.
EmfDev Posted - 07/14/2022 : 14:34:35
Hi damien-mattei,
you can turn on CPM1(tube1) and CPM2(tube2) by going to Main Menu -> Init Setup -> Tube Settings -> Tube1,2 CPM display. Then you can see the readings on Large Font Mode.
damien-mattei Posted - 07/14/2022 : 13:33:32
i made a test and video with my radioactive watch and got 758 hexa on CPMLow and 05 hexa on CPMHigh but the decimal display is only those of CPMLow ,on 4 byte we can go to 65536 so what it does with the 5 of CPMHigh ??? in normal condition CPMHigh is at 0
damien-mattei Posted - 07/14/2022 : 12:58:49
hello, finally configured my GMC-500+ on gcmap,
does any one know if there is a way to display both CPM tube on LCD display at least?
i can manually send GETCPML and GETCPMH command to get the low and high tube values in hexadecimal on 4 bytes each but i want to have it displayed on the LCD in decimal when in stand alone mode without Mac or PC...
i see it seems possible but perheaps with a special firmware :
damien-mattei Posted - 06/14/2022 : 01:15:43
"I looked at details of the nuclear excitation levels of Ra226, and found that there are (at least) 117 levels, which result in gamma emission."
whoow i will make a video and will put this watch in a set of metal box definitely....
damien-mattei Posted - 06/14/2022 : 01:12:17
i did not said the opposite,X ray is out of scope here, again Gamma has intra-nuclear origin, X ray outside nuclear. Bremsstrahlung effect information i read in a paper biophysic book of medecine is said to have a continuum spectrum.(i suppose this is due to the speed slow down creating a continous energy value as speed has no discrete values but continues ones)
Fun to see Radium takes his name from radioactivity because radioactivity was discovered by Marie Curie and Henry Becquerel with this element.
ullix Posted - 06/13/2022 : 01:05:37
One thing to note is that Bremsstrahlung is ALWAYS a gamma CONTINUUM, reaching from energy zero to max of electron energy. It thus cannot result in a single line, like 186 keV!

I looked at details of the nuclear excitation levels of Ra226, and found that there are (at least) 117 levels, which result in gamma emission.

Unfortunately, there is no absolute intensity given. The 3% could have been a measure of the relative intensity of gamma lines, but this also is not supported by the data, as the 186keV line is only 73% of the 253keV line, so then the latter one would be more intense.

I think the authors of this article may have used very unfortunate wording or not understood the situation.

Anyway, there is quite a bit of gamma, of this isotope alone, and the many daughter nuclei may add to that.

damien-mattei Posted - 06/12/2022 : 13:56:57
yes i apologize, Ra 226 is a pure alpha emitter (no beta at this step).It desintegrate first in Radon (gaz) emitting an alpha particle, it is at this step too that the Gamma emission is done by de-excitation of nuclear.Gamma are photons emitted intra-nuclear,instead X ray are emmited extra-nuclear (Bremsstrahlung effect and de-excitation of electrons moving from one orbit to a lower one but this is perheaps out of scope here).The descendant Rn,Po,Pb,Bi also emit various radiations (Alpha,Beta- associated with Gamma) all ionizing and be able to be detected by a Geiger counter.
Damien68 Posted - 06/12/2022 : 06:28:35
the article says that for 100 decays all (94%+6%) will emit an alpha and 3% will emit a gama in addition to the emitted alpha. the gamma emission (pure energy) must be due to a rearrangement of the nucleus or something else. if some know?...
damien-mattei Posted - 06/12/2022 : 03:00:14
Dear Ullix, i'm not author of scientific articles and responsible of their content ,if the percentage seems wrong it has an explaination.
the french page with this information is :
and it cite an english language article : ICRP, 1983 - Browne et Firestone 1986 that is not accessible without paying for it.
My opinion is that as you early mention it the Radium desintegrate in descendants that can emit other type of radiation than alpha, i mean beta too that perheaps can emit neutrino (undetectable except with special geiger counter: ) but anyway it exists a gamma radiation with Radium:
so my supposition is that the 3% Gamma are the result of Bremsstrahlung effect that you also have mention it, this radiation effect is well know in medicine because the slowing of a charged particle is emmiting energy in the form of X ray (Gamma of special energy)
I think the way thei count that is 94% (alpha) + 6% (beta) = 100% but in the same times those charged particles emit some 3% of gamma by Bremsstrahlung effect that the authors does not count in the initials desintegrations but add them in some way.But i admit i do not understand how they count that without having access to the original article, i think this a not good presentation of the results.
ullix Posted - 06/11/2022 : 23:15:09
The type of plastic does not matter much as long as it is composed of chemical elements of low atomic number (carbon, oxygen, ...). That is why wood, often known as "copy-paper", is also ok! Just compensate thickness for the lower density.

The aim of a plastic-metal sandwich is to reduce Bremsstrahlung, see "Appendix Range of Electrons in Matter and some History" in Potty Training article.

N.B.: 94% + 6% + 3% = 103%. Really? it is a heck of a radiator!
damien-mattei Posted - 06/10/2022 : 23:03:00
yes i think it is Radium , not only Alpha but Gamma too, from documentation about Radium:
for 100 desintegrations:
Emission Alpha;
E = 4784 keV (94%)
E = 4602 keV (6%)
Emission Gamma;
E = 186 keV (3%)
but descendant of Radium 226 also emit Beta:
as you mention it.
Half life of Radium is 1600 years, so do not expect it to decrease naturally during a human life...It is not like Tritium watch with half life of 13 years or some rare Prometheum watch display which half life is 2.6234 year.
When i have time i will try to make a video and tests, i already know there is few radiation from metal back cover watch, glass watch is in fact plexiglass as plastic was more "modern" and valuable for quality watches in the '50 and '60 than true glass.If i add a 2mm plastic (Polyurethane?) on it it blocks more the radioactivity but not all, i will test with metal boxes.
Also i need to connect the Geiger counter to a windows system to configure it with wifi and show counts from both glass tubes (the darkened one and the other)
ullix Posted - 06/08/2022 : 00:29:35
nice watch!

I think we have a big misunderstanding, and the situation is far less severe as it seemed yesterday.

The GMC-500+ counter has two tubes built in: Tube #1 and #2. Both are clear glass tubes. The obvious difference on first sight is length: Tube #1 is approx 9 cm long, Tube #2 only 5.5 cm.

Tube #1 is supposed to be a M4011 tube, but GQ is now also using a J305 instead, even when the specs still say otherwise. Tube #2 is a SI3BG tube, and to my knowledge no alternatives were used.

Some of the M4011 tubes have been found to be light sensitive, i.e. plain daylight might create spurious counts. GQ is now trying to mitigate this by wrapping the tube in something that looks like black paper. So, unless you open the counter and look closer, the clear glass tube looks black! This is a bit confusing, because there also exist M4011 tube varieties, which were clear glass tubes coated with some black plastic or paint, which however - surprise - still resulted in light sensitive tubes!

So far I have not seen any report on the paper-wrapped tubes being or not being light sensitive.

The Tube #1 is much more sensitive to radioactivity than Tube #2. Specifically, I determined Tube #2 to be 74 times less sensitive than Tube #1. For details see GeigerLog manual.

GQ then made the odd decision to report as CPM the sum of counts of the two tubes, which is a truly meaningless value. In newer firmware of the 500, one can switch off the Tube #2, and I suggest to do that and keep it this way. The tube is not really helping for anything.

Now to the radioactive source. I found no mentioning of what had been used with these watches, but very likely is was Radium. Ra-226 is a pure alpha emitter. When inhaled or otherwise incorporated, Ra-226 is a serious danger to health. But as long as it is contained inside the intact watch, this is of no concern.

The alpha particle itself cannot pass neither the watch's metal backing, nor the (plexi-)glass cover (are you sure it is plexiglass and not real glass?). And if it could pass, the 500 counter could not detect it.

But Ra-226 decays in a chain, and within this are multiple beta and gamma emitter, and this is what a GMC-500+ can detect. Predicting the energy spectra of beta and gamma and their relative contribution is impossible, as it depends on the original purity of the Ra being used for the watches and the time passed since then. But it is reasonable to assume a strong beta and minor gamma component.

Betas and gammas can both exit on the glass side, but, I assume, betas will not be able to exit on the metal side, while gammas can exit.

Measure count rate on the glass cover side, and on the metal side. You reported CPM=1000+ on the glass side; I expect no more than CPM=100(+) on the metal side?

I don't see this as dangerous.

For further insight play with absorbers, as mentioned before.
damien-mattei Posted - 06/07/2022 : 04:33:25
the watch tested by the geiger counter is the first one on this page:

i will try to create a youtube video to show the effect with the Geiger counter
damien-mattei Posted - 06/07/2022 : 02:46:33
I just bought the GMC 500+ monday on amazon and it is new from GQ england/europe.
on the rear there is 2 grids where i can see a glass tube and a black tube.
the thousands cpm value with the "black" tube is get with detector touching the watch at 10 - 20 cm i got normal or medium CPM values
but did not made more test from yesterdays.
I had put a plastic (2mm) piece between detctor and watch and it slow the CPM rate but do not stop it. I will test with metal boxes too.
i bought the watch on ebay 10 years ago,i wear it some weeks and leave it stocked for many years.The watch date back 1940-1960 i think, it is said that Youri Gagarine used the same model.
the behavior is typical the one described here by another people:
ullix Posted - 06/07/2022 : 00:23:55
Well, if these count rates are not due to a defect of the counter, I do suggest some caution handling it! First measure is to keep distance to it.

It is unclear what you refer to with "black tube" and "glass tube". So far the GMC-500 counters' tubes were all made from glass, and only the long, sensitive tube (Tube#1), mostly a type M4011, has appeared as blackened tube, while the other, shorter, less sensitive one (Tube#2), so far always was type SI3BG. Can you provide a photo?

If the count rates are real, then the high count rate on the insensitive Tube#2, with (almost) no counts on the sensitive Tube#1, point to a count rate which is so high that the load on the tube resulted in its anode voltage collapsing, which resulted in no counts at all or very low counts. This has happened before and gave a lengthy debate here in the forum. You can also read about the issue in the GeigerLog manual, chapter Appendix G Calibration

First, try to establish that the counter is not defect. What are the background count rates? The Tube#1 should give CPM=10 ... 30, while Tube#2 something 74fold lower (so basically nothing on background).

If you want some higher count rates - like CPM=>100 - use Potassium. See article "Potty Training" here:

If this comes out as expected, then your counter seems to be ok.

Now put the counter at a distance to the watch, like 1 meter. What CPM do you get for Tube#1 and #2 respectively? Then get closer to the watch, and observe count rates (50cm, 20cm, 10cm, 5cm, 1cm). Chances are your watch is a strong beta emitter, so the count rates should increase rapidly on approaching.

Now go back in distance to where the Tube#1 shows high but still meaningful CPM values. Put an "absorber" between counter and watch, and measure CPM.

An absorber could be a sandwich of some 3mm plastic plus some 1 ... 3 mm metal (Alu, iron, copper, steel, lead ,...). If no plastic available, a cm of copy paper might do as well. For explanation see Potty Training chapter "Appendix Range of Electrons in Matter and some History".

P.S. if it is indeed a strong beta emitter, then the conversion of CPM to uSv/h is meaningless! I refer you again to chapter Appendix G Calibration in the GeigerLog manual.

Damien68 Posted - 06/06/2022 : 21:01:43
CPM values observed are always subject to interpretation because CPM value observed is dependent on the type of tube used. to interpret the measurement we therefore go through a calibration parameter which is not the same for tube 1 and tube 2. after having applied the calibration parameter we obtain uSv/h which are a physical quantity and the value of tube 1 and tube 2 once converted into uSv/h must be substantially identical.

so to be universal it suffices to consider not the CPM but the display in uSv/h otherwise it is necessary to convert the CPM into uSv/h with the correct coefficient.

These coefficients ares:
- for large black tube (M4011): 1 cpm -> 0.0065 uSv/h
- for small glass tube(SI-3BG): I don't know exactly but around 1 cpm -> 0.2 uSv/h.

damien-mattei Posted - 06/06/2022 : 13:26:06
ok thanks
but what is the true value so ??? the GMC 500+ say it is 'high' , how can i make a difference between a true high source and a simple old watch that should have radium on display?
Damien68 Posted - 06/06/2022 : 10:12:03
the second tube is much less sensitive, it is because of that. second tube is used to take over from the first tube to measure really high radiation levels.

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