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 GQ Geiger Muller Counter
 Counter counts mostly daylight, less radioactivity
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ullix

Germany
49 Posts

Posted - 05/14/2017 :  07:27:22  Show Profile  Reply with Quote
In an attempt to measure more beta activity, I took off the back cover of my GMC300E+ to overcome the damping effect of the plastic case of the counter and with some surprise noticed how strongly the counter is affected by daylight.

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During all measurements the counter laid face-down in an open cardboard box on a shelf in my study behind some light curtains and no radioactive source was around. From the log history (see image 1) you can see the moments of sunrise and sunset, and see how the clouds move in and out. Versus a background of CPM=17.32 (see image 2) measured in the dark at night time, the counts rose more than 10fold and topped out at CPM=207.

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Of course, so far the backside of the counter had been removed. But look at the backside: there are cut-outs, and the material itself is slightly translucent. Putting it back on and measuring again you see that the counter has a pronounced response to the daylight (see image 3)

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From a background value of CPM=17.32 it easily goes up to CPM=50 and tops out at CPM=84.

Just to be sure: there is no radioactive sample near the counter, nor has any sample been moved to and fro the counter, nor has the counter been moved!

Applying the factory default calibration factor to CPM=84 gives you a dose of 84*0.0065 = 0.55 ÁSv/h. The highest background measured in the Swiss mountains is 0.26ÁSv/h, barely half of it!

On top of this you have to consider the contribution of the counter to the count rate due to electronic "noise". The GMC manuals state "Instrument Background: < 0,2 pulses/s" or CPM=<12. Subtract this from the 17.32 and you are left with 5 counts from perhaps radioactivity, and sunshine contributing 10 times as much or more!

My question: when you have a light sensitive system, why is it not built into a lightproof case?

The value of all those background values on the world map seem to be close to nil, as there is no knowledge if and how they are controlled for a sunshine effect.


Reply #1

Distelzombie

Germany
165 Posts

Posted - 05/15/2017 :  08:30:57  Show Profile  Reply with Quote
It is probably reacting to UV light. UV light can be ionizing too. Try a UV filter on the tube.
My SBT11a doesnt react to sunlight at all, even though the window is so thin its capable of measuring alpha. I guess the mica window filters UV. I could test it with my UV lamp and laser, but i think they are not powerful enough or dont have the correct wavelenght.

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

My statements are to be taken as stuff-a-hobbyist-says.
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Reply #2

ZLM

1047 Posts

Posted - 05/16/2017 :  22:47:52  Show Profile  Reply with Quote
The GMC=300E+ is not designed for measuring without case. I believe that the UV light will affect the reading with out cover. Remove the case does not increase the sensitivity except the noise.
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Reply #3

ullix

Germany
49 Posts

Posted - 05/17/2017 :  01:43:09  Show Profile  Reply with Quote
@ZLM:I am afraid you are wrong or misleading on all counts.
quote:
The GMC=300E+ is not designed for measuring without case.
Unfortunately, it is also not designed to measure WITH a case. See the 3rd of my images showing a measurement WITH case. Unless you measure in total darkness you get a faulty measurement.

quote:
I believe that the UV light will affect the reading with out cover.

Let's leave it aside whether the cause is UV light or simply all light, including visible - the cause has not been demonstrated - but that is in fact the point of the post; you do get significantly different readings with and without light, but irrespective of the back cover being in place or not.

quote:
Remove the case does not increase the sensitivity

Wrong. When you provide a beta emitter - like potassium - you get much higher readings WITHOUT a case. The reason is quite simple: even high energy betas (> 1MeV) are absorbed by just a few millimeters of material. The plastic case of the Geiger counter acts an an absorber for a large part of the betas, and therefore they don't even reach the tube and hence give no count. (This is what I tried to quantify when I stumbled over the light-effect; data will come soon.)

While it is correct that the tube itself has the same sensitivity whether the case is on or not, this is not true for the assembled Geiger counter device. Some people on this forum have shown that they did make cutouts in the plastic case to expose larger areas of the naked tube in order to increase sensitivity - the reason for doing this is the same as stated here.
quote:
[but removing the case increases] the noise.
My data tell me otherwise, see e.g. image 2 in my post; you don't get different "noise" with or without the case.

When you measure in the dark and have a source giving beta and/or gamma events, you find a scatter of data with a standard deviation well explained by the properties of a Poisson distribution characteristic for radioactivity data. Noise, defined as scatter of CPM (or CPS) data does NOT change. My GeigerLog program gives easy access to standard deviation - try it out.

For the record: I don't have a problem with instruments having some peculiarities, like light sensitivity, which need to be observed when taking measurements. However, those need to be provided as a data sheet. But GQ, despite selling both the tubes and the instruments has provided no such thing, leaving people in the dark about this brightness issue.

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Reply #4

ullix

Germany
49 Posts

Posted - 05/17/2017 :  02:14:50  Show Profile  Reply with Quote
@Distelzombie: I looked at ionization energies of gases, and it turns out that even the hardest UV light cannot ionize the gases in the tube.

Another problem: I found nowhere a datasheet on the M4011 tube used in GQ's counters, which tells me the gas composition, except that there is "Halogen" inside. Assuming the gas is not too different from the SBM20 tube, I guess it has Ne, Ar, Br.

From this site h**ps://chemglobe.org/general/atomeigenschaften/ionisierung.php I took the ionization energies of several gases:

Ionisierungsenergie [eV];;
1; H;13.59840
2; He;24.58740
6; C;11.26030
7; N;14.53410
8; O;13.61810
9; F;17.42280
10; Ne;21.56450
17; Cl;12.96760
18; Ar;15.75960
35; Br;11.81380
36; Kr;13.99960
53; I;10.45130
54; Xe;12.12990

Whatever the gas filling may be, they are all above 10eV. Extremely hard UV light of 200nm, unlikely to reach the ground, let alone pass through the glass of my window panes, has only 6eV; visible light has even less, only 2-3eV. So, ionization by light is not likely.

What actually might be the cause is the photoelectric effect - a photon hits a surface and kicks out an electron. Seeing the little rainbow shine of the glass tube, it suggests that some metal vapor was deposited on the inside of the tube. I don't know which one(s), but some metals could give off an electron with light of energy as little as 2-3eV, see here

h**p://hydrogen.physik.uni-wuppertal.de/hyperphysics/hyperphysics/hbase/tables/photoelec.html

That electron might then trigger the cascade and result in a count.

Whatever really the cause, you must consider light sensitivity when you take measurements!

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Reply #5

Distelzombie

Germany
165 Posts

Posted - 05/19/2017 :  13:08:36  Show Profile  Reply with Quote
If it is not UV light that causes the false clicks of the tube, then I can not imagine any other part of the spectrum that is under X-rays to cause this. Has to be some weird gas insode there... hm
I know that some ICs can be affected by light. But they usually crash instead and are not potted.

I cant remember that my m4011 tube is affected by light. Its night right now so I'll test this tomorrow.

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

My statements are to be taken as stuff-a-hobbyist-says.
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Reply #6

ullix

Germany
49 Posts

Posted - 05/20/2017 :  03:57:13  Show Profile  Reply with Quote
I had already pointed out the "Photoelectric Effect" as the likely cause. It is a well known effect; Einstein got his Noble Prize for it (and never one for relativity or gravitation!) which in Germany had been commemorated with a postage stamp (pic from wikipedia) showing electrons being kicked out of a surface by light of wavelengths from reddish to blue.
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The early TV cameras were based on this effect, so it surely can be used to measure visible light.

To "bring some light" into the tube issue I tested a red LED, a green Laser (as powerful as legally available, used for presentations in large rooms), a white LED, and a blue-violet LED. The effect of both red and green was zero, the white was significant, but the blue-violet blew it away. This measly thingy, which you sometimes get as a freebie, is intended to test paper bills for fluorescent markers to distinguish from counterfeit money. It is barely able to do it, running on just LR44 batteries. It is pictured in the next graph, which shows that you can get 800CPM from just pointing the light from this little flashlight onto the Geiger tube, no radioactivity needed!
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Since the light is still visible to the human eye, and LEDs tend to have a very narrow range of light emission, there can't be much, if any, UV light in the beam. Blue light, or at least violet light, estimated as well under 4eV per photon, is sufficient to trigger counts in the M4011 tube.
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Reply #7

ZLM

1047 Posts

Posted - 05/20/2017 :  19:40:58  Show Profile  Reply with Quote
Sound like your are right. In this case, to get better result, it needs to insulate the light from M4011. That should not be difficult.

How long your tube has been used? if the tube has problem, it will show similar problem too.

I suggest you to install a new M4011 and see if the problem still exist. The problem is not common.
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Reply #8

ullix

Germany
49 Posts

Posted - 05/21/2017 :  01:42:18  Show Profile  Reply with Quote
I got the device less than 6 months ago; even with the light effect there should have been wayyyy less counts than the specified max for the tube.
Are the tubes new and recently built, or are they from some old production and perhaps were in use before?
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Reply #9

ZLM

1047 Posts

Posted - 05/21/2017 :  07:30:41  Show Profile  Reply with Quote
All tubes should be new. Each tube average life time is about continually running for two years. You can write email to support for your case.
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Reply #10

ullix

Germany
49 Posts

Posted - 05/22/2017 :  02:06:41  Show Profile  Reply with Quote
To top off my problems, the USB connector has fallen off the Geiger board during a logging! The first time ever this happened on any device of mine. This is beyond my soldering abilities to repair.
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I read here ( h**ps://sites.google.com/site/diygeigercounter/gm-tubes-supported ) other reports of light-sensitivity of this tube, which seems to happen, but not always. So, why only sometimes, and how many are sensitive, and what do they have in common? I can't imagine that a device from a single production line sometimes comes out like this and at other times like that?

Maybe the forum users can help with a little experiment:

1) For a clean start, factory reset your counter and set to CPM mode
2) Put device on a bright spot, but avoid direct sunlight (to avoid heating the device)
If you feel ready for it: For best effect take off the backside.
CAUTION: high voltage at the tube! and avoid finger prints or other dirt on the tube
3) Don't move the device for 24h; make sure no major light near it during the night time! (And no radioactive source of any kind)
4) Read out history and post Graph. Can be done nicely with GeigerLog, or send binary data to me.
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Reply #11

the_mike

Switzerland
12 Posts

Posted - 05/23/2017 :  07:45:04  Show Profile  Reply with Quote
Hi Ullix

as recommended, I took a 24h-Testrun with my 320+ and the 500.

I bought the 320+ last December, the 500 is about one month old...

I unmounted the Backplate of the 320+, and put it facedown in the outside; I followed your experiment-guidelines and resetted before measuring; additional Info:
Sundown 05/22/2017: 21:04 (9:04pm)
Sunset 05/23/2017: 05:38 (5:38am)
Weather: 05/22: sunny, 05/23 mostly sunny, in the evening some clouds

Here's the Graph I got with Geigerlog

320Plus:

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As there has been no active source near the counter, I don't have an explanation of the spike. But the CPM are in normal range for my location...

500:

Image Insert:

121982 bytes

Log been taken with Geigerlog, as Ullix and I found out, there's something new to the way the 500 saves data, so i'm not sure on how far this log can be trusted... (E-Mail to support with findings in the work)


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Reply #12

ZLM

1047 Posts

Posted - 05/23/2017 :  07:57:12  Show Profile  Reply with Quote
The USB port you can get it be soldered locally or send it back to GQ for the service.

There are many data available to download from www.gmcmap.com
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Reply #13

the_mike

Switzerland
12 Posts

Posted - 05/23/2017 :  12:44:07  Show Profile  Reply with Quote
Forgot to mention that both Counters use an M4011, both manufactured in 2016 (if the number-coding of the chinese-tubes is similar to the russian-tubes)

ZLM:
question here is: does the M4011 "count" sunlight... It's a reoccuring phenomenon seen all over the internet - some M4011 do, some don't. Question is: why and how to measuer the difference "light or dark"...
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Reply #14

ullix

Germany
49 Posts

Posted - 05/23/2017 :  23:57:04  Show Profile  Reply with Quote
Indeed, the result seems clear: one tube is light-sensitive, and two others are not. Why?
They cannot possibly come from the same production line, so what is the difference, and what is the marker that tells me the tube is or is not sensitive?
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Reply #15

Distelzombie

Germany
165 Posts

Posted - 05/24/2017 :  13:04:50  Show Profile  Reply with Quote
I have a crude VIS-spectrometer. So Im testing with what I have:

- a 405nm 200mW laser
- a 325-330nm probably 5mW laser (Though its really bright and some kind of red shows when looking a the dot. Cant see the red in the spectrometer)
- a Compact fluorescent lamp that peaks at 405, 430, 480, 535, 605nm
- a LED lamp thats pretty much the spectrum of the Sun
- a Halogen lamp thats quite uniform
- a bright blue LED thats around 455nm
and a dim red LED at 630nm

No reaction at all.
Done it at night. So only the specific source was present.

My tube is from 2015. (Its printed on it) The tube also has some kind of coating. It's rainbow colored. Does yours have a coating?

Unfortunately I dropped it while removing and its broken now. :((((((
:((((((( GAAAAAAAARG AAAHG
So I cant test it with sunlight. Again. Since I had it outside many times.

Still got my sbt-11a though. :)

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

My statements are to be taken as stuff-a-hobbyist-says.

Edited by - Distelzombie on 05/24/2017 13:21:22
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Reply #16

ullix

Germany
49 Posts

Posted - 05/25/2017 :  01:53:40  Show Profile  Reply with Quote
quote:
- a 405nm 200mW laser
OMG, 200mW? are you trying to shoot down aircraft?
quote:
- a 325-330nm probably 5mW laser (Though its really bright and some kind of red shows when looking a the dot. Cant see the red in the spectrometer)
330nm in deep in the UV light, not red. Did you mean 725-730nm?

Strange thing is, it keeps the rainbow color despite the cracks. I'd have assumed the rainbow is due to some metal vapor-deposit on the inside, which would oxidize immediately after air contact, and become whitish-powdery?

But thanks for the thorough tests; it is getting odder by the minute. I attach a pic of my tube, still built-in (pic is mirrored to ease reading of the imprint, in case you wonder).

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It does show the rainbow color, and a 2016 date.

So, now we have in terms of light sensitivities and manufacturing year:
2015: 1x not
2016: 1x yes, 2x not

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Reply #17

Distelzombie

Germany
165 Posts

Posted - 05/25/2017 :  11:13:45  Show Profile  Reply with Quote
quote:
Originally posted by ullix

quote:
- a 405nm 200mW laser
OMG, 200mW? are you trying to shoot down aircraft?
quote:
- a 325-330nm probably 5mW laser (Though its really bright and some kind of red shows when looking a the dot. Cant see the red in the spectrometer)
330nm in deep in the UV light, not red. Did you mean 725-730nm?

Strange thing is, it keeps the rainbow color despite the cracks. I'd have assumed the rainbow is due to some metal vapor-deposit on the inside, which would oxidize immediately after air contact, and become whitish-powdery?

But thanks for the thorough tests; it is getting odder by the minute. I attach a pic of my tube, still built-in (pic is mirrored to ease reading of the imprint, in case you wonder).

It does show the rainbow color, and a 2016 date.

So, now we have in terms of light sensitivities and manufacturing year:
2015: 1x not
2016: 1x yes, 2x not


Yes, 200 milliwatt. Its for CNC Wood burning stuff and such things. Its a "UV" laser though it barely touches UV. Probably the same as they use in BlueRay drives.

"- a 325-330nm probably 5mW laser" Uups, no. I made a mistake. Its 525-530nm. A green laser pointer.

"some metal vapor-deposit" Like cesium in Sodium-vapor lamps or old Tubes? I only know of cesium in vaccum tubes. Did they use others? Cesium is for binding oxygen.

"But thanks for the thorough tests" Yeah,... unfortunately they were the last tests I can ever do with it. :(
I would have showed you some graphs, but there was definetely no increase in CPM. I could speculate about a 5 CPM increase but even that is still outside significance.

Ok, so if its not the coating, it has to be the gas. Which gas is sensitive to visile EM fields, while being the insulator of two electron potentials? Does that makes sense?
I'd assume it has to be a very energetic visual bombardement.
Maybe ... its the voltage. Maybe the gas is the same but the voltage differs. If you set the voltage too high it will count many things that are not radioactivity- Maybe even daylight.

Could you test this? I can only assume my voltage since you cant directly measure it with a multimeter. (Which sounds odd to me too)

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

My statements are to be taken as stuff-a-hobbyist-says.
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Reply #18

ZLM

1047 Posts

Posted - 05/25/2017 :  17:43:46  Show Profile  Reply with Quote
The tube should not sun light sensitive. However, it may act strangely if the tube has problems, such as leak gas, end of life, voltage too high or incorrect resistor been used. Indeed, the rainbow color is the metal film for the tube negative charge.
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