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hellbet
France
13 Posts |
 Posted - 09/10/2011 : 02:23:36
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Hi there,
Fist off, I received my GMC-200 unit 1 month ago and it works flawlessly out of the box. About 1 week ago, I noticed the background level climbs up like hell at times. I opened up the box and noticed also the GMT02 is pretty sensitive to photon energy and especially to sun rays. I checked carefully the voltage out on the TP's (needs a high class multimeter, I used a 10 MOhm/V Micronta unit) and it was 395 V DC. The unit is online 24/7 so I'm also questioning the GMT02 (like all other Glass tube) lifetime? Do you have some detailed information about that very tube? Is the severe photoelectric effect quite normal on this class of G/M tubes? Might the tube be damaged by direct sun ray exposition, even a short one?
Thanks for any information!
Attached image is an 'ordinary morning' data and BTW none of my others devices (3 of them) were 'smelling' anything unusual even if the GMC200 was clicking like hell at times. BTW I have anything radioactive around the unit LOL
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| Reply #1
hellbet
France
13 Posts |
Posted - 09/10/2011 : 08:44:41
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Some hours later... Funny ride, huh? 'High count' data were 'high luminosity' from the sun. BTW, unit's box is closed and sealed w/ electrical tape. Would you please elaborate around that issue?
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| Reply #2
Odiez1
73 Posts |
Posted - 09/10/2011 : 15:43:07
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Hey there hellbet.
I'm no expert here, but with my general knowledge I believe that photons which makes up the visible light of the electromagnetic spectrum don't react with a Geiger Muller tube.
There are 3 or 4 types of radiation which can be detected by a GM tube, as follows.
..............................Alpha_decay
en.wikipedia.org/wiki/scriptlpha_decay
en.wikipedia.org/wiki/Beta_decay
en.wikipedia.org/wiki/Gamma_ray
en.wikipedia.org/wiki/X_ray
The X Ray can cause ionizing radiation, but it's more similar to light because as you can see from the electromagnetic spectrum chart, is just beyond ultraviolet.. But you won't find sunlight contains much X Rays unless the atmosphere is starting to thin out.. ;-)
At any rate, I don't think sunlight is going to make the GM tube react.
My hunch is either you have some noise creating extra counts in the (-) minus circuit, or the GM tube is bad, or there is a source near that GMC. Maybe Radon?
atomic.dave found that by charging his iPhone while using the Geiger bot connected to the GMC on the wall power charger caused erroneous counts because of ground loops through the 2 "wall wort" chargers...
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-Odie |
Edited by - Odiez1 on 09/10/2011 15:49:16 |
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| Reply #3
ZLM
1261 Posts |
Posted - 09/10/2011 : 18:04:12
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| Try to use battery only to see if it makes difference. |
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| Reply #4
hellbet
France
13 Posts |
Posted - 09/11/2011 : 01:56:51
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Thanks so much for your answers, alas the correlation between sunshine or cloudy weather and high CPM count is flawless... When opening up the box then exposing GMT02 to sun ray CPM count rise to several thousands!
I got exactly the very same issue everything unplugged so to speak, buzzer is clicking like hell.
I guess my GMT02 tube is faulty? I suspect also it hates the direct sunlight so I asked for any technical document about.
This type of glass G/M tube is in fact coated internally with some metallic thin layer to form anode side and maybe this oxide layer has been damaged when hit by direct sun rays? I'll probably test later with another G/M tube like SBM20 or equivalent.
Hereafter is one full day of data, night part and also this morning (cloudy weather) were normal count; yesterday part (variable weather) was a succession of highs and lows count fully correlated with sun occurrences.
Whatever the CPM count looks NOT affected at all by artificial light source like LED or incandescent light against the tube. Very weird issue to say the least. Hlep! I really need more information on the GMT02 tube!
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| Reply #5
hellbet
France
13 Posts |
Posted - 09/11/2011 : 02:06:40
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@odiez: I noticed we're actually in a very strong Sun activity with exceptionally strong CME's hitting earth right now; maybe the tube is very sensitive to Muon activity? I'd like to know about other GMC200 users ;) All "metallic" G/M tubes like SBM20 are shielded and might be less sensitive to Muon activity?
Sorry I mean Cathode and not Anode in my last post that is Cathode is a thin layer of oxide deposited on the glass within the tube.
Kind regards,
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| Reply #6
hellbet
France
13 Posts |
Posted - 09/11/2011 : 03:14:15
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I've done with my homework: "Both of these [G/M] tubes can be considered thin walled beta counters. Since they are photosensitive, they would need to be operated in a light tight enclosure."
www.orau.org/ptp/collection/GMs/TAB1andB3.htm
"Cathode: Inner surface of glass wall coated with silver"
Looks more like gold coating within the GMT02. |
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| Reply #7
ZLM
1261 Posts |
Posted - 09/11/2011 : 15:38:39
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As I know the GMT02 tube is in a high sensitivity tube range. So far this tube is the highest sensitivity tube I ever had. Because it is glass tube, so it also has some capability to detect the alpha ray. Other metal tubes are not able to do this.
To detect the beta and gamma only, the tube should keep in a enclosure.
The tube sensitivity is adjustable by adjusting the tube voltage. If you want to let tube run a lower sensitivity, then you may try to lower down the voltage to 300V or even lower. |
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| Reply #8
Odiez1
73 Posts |
Posted - 09/12/2011 : 00:55:08
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| Nice museum link hellbet! |
-Odie |
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| Reply #9
hellbet
France
13 Posts |
Posted - 09/12/2011 : 09:43:14
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@ZLM:
Nope. Quote from wiki : "GM tubes":
"The glass window type will not detect alpha radiation since it is unable to penetrate the glass, but is usually cheaper and will usually detect beta radiation and X-rays."
Alpha rays are very short range and are not able to enter any glass nor metallic enclosure but only thin mica side or front (pancake) window.
I guess either the GMT02 tube is too much sensitive to X-Rays; X-ray Sun peaks are 10E-5W/cm2 right now, this a high cosmic X-ray rate to say the least : see www.n3kl.org/sun/noaa.html
ZLM, it will be of great help if another GMC200 / GMT02 could possibly be placed directly facing ray sun first off box closed then box open; if your unit will survive then my tube is faulty but if your unit looks as awful as mine after that test we shall definitely deduct some global GMC200 / GMT02 photosensitive issue.
Thanks in advance and 73's,
Jm f5cmq
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| Reply #10
Odiez1
73 Posts |
Posted - 09/12/2011 : 15:08:21
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Would you mind giving a general location where these readings are coming from?
I'm curious because maybe it really is detecting a high background radiation.
Thanks, |
-Odie |
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| Reply #11
hellbet
France
13 Posts |
Posted - 09/13/2011 : 00:52:40
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I don't think so Odiez1, GMC200 unit is registering data but 4 other units are monitoring around including "pancaking" Alpha rays. No other unit is more or less affected at once; of course some "unusual spikes" are detected especially from the pancake tube but such spikes are generally up to 30-35 µR/h that is around 50-60 CPM. GMC200 is at times producing spikes up to 2000 CPM. Ouch...
BTW I'm located in the very South of France near the Spain border.
Have a nice day,
jm
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| Reply #12
Odiez1
73 Posts |
Posted - 09/13/2011 : 10:20:05
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Yes, you are correct. Sounds like some kind of problem..
On the other hand, you have a really sensitive tube there, but it does complicate things that it can't be in sunlight. Maybe you could test a different GM tube in the GMC200 for comparison..
I was also having a problem with noise creating extra counts with the GMC080 when I attached an external RG-58 coax to the GM tube (cbon-6107). The .1uF cap cleared up all the problems I was having, although I don't know if C2 is still the same component on the GMC200. C2 on the GMC080 is the last capacitor before Negative connection to the GM tube, but there must be a capacitor leading to the - Negative connection on the GMC200 as well. It may be worth trying..
Here's the topic. http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=3403
I live in the central valley in California, but I've always loved the South of France. No where else can you get the snow and beaches so close together... :-) |
-Odie |
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| Reply #13
Odiez1
73 Posts |
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| Reply #14
Xanthos
Canada
3 Posts |
Posted - 09/13/2011 : 13:21:28
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Hi Guys,
I have my own issue with my 200 model.
The software just counts up automatically EVEN when the geiger counter is NOT attached. Anyone have this issue?
I just want to get some accurate readings and so far the only thing I can rely on is the flickering of the light.
On a separate note, I must have a fair bit of background radiation because it flicks on every 3-10 seconds. |
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| Reply #15
ZLM
1261 Posts |
Posted - 09/15/2011 : 09:13:24
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| Xanthos, you have to adjust the software sensitivity. |
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| Reply #16
hellbet
France
13 Posts |
Posted - 09/20/2011 : 10:28:37
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Great news: problem solved by replacing glass tube GMT02 by metal tube SBM-20.
Image Insert:
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A pretty flat graph whatever the sun shining or not.
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Thanks,
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| Reply #17
Odiez1
73 Posts |
Posted - 09/20/2011 : 11:22:45
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That's great that you've solved the problem! Can it be a bad tube? or maybe it's just too sensitive for practical uses..
So, that's your GMC200? It looks a whole lot like the GMC080, maybe the ICs are different because the sales section lists the GMC200 for higher count rates than the others..
It looks like your U1 chip isn't scratched off.. I've noticed that on all 3 of the GMC080s I have, the U1 chip's label is obscured. It's probably to maintain the proprietary circuit design. It's just interesting because the maker may have missed one.  |
-Odie |
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| Reply #18
bifferidge
USA
34 Posts |
Posted - 09/21/2011 : 11:14:13
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quote:
Originally posted by Xanthos
Hi Guys,
I have my own issue with my 200 model.
The software just counts up automatically EVEN when the geiger counter is NOT attached. Anyone have this issue?
I just want to get some accurate readings and so far the only thing I can rely on is the flickering of the light.
On a separate note, I must have a fair bit of background radiation because it flicks on every 3-10 seconds.
you need to adjust the sensitity using the calibration procedure.
Clicks every 3-10 seconds does not sound especially abnormal. |
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| Reply #19
ZLM
1261 Posts |
Posted - 09/21/2011 : 20:55:11
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hellbet: Tested my MGC-200 works fine under sun light.
Yes. You can adjust the sensitivity using a small screw driver. Maybe that particular tube need a different voltage.
(Added on: 12-30-2011)
New GMC-200 installed a different tube.
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