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ullix
Germany
1171 Posts |
 Posted - 05/14/2017 : 07:27:22
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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 µSv/h. The highest background measured in the Swiss mountains is 0.26µSv/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.
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| Reply #1
Distelzombie
Germany
202 Posts |
Posted - 05/15/2017 : 08:30:57
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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-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #2
ZLM
1261 Posts |
Posted - 05/16/2017 : 22:47:52
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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
1171 Posts |
Posted - 05/17/2017 : 01:43:09
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@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.
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[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
1171 Posts |
Posted - 05/17/2017 : 02:14:50
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@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
202 Posts |
Posted - 05/19/2017 : 13:08:36
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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.
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GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #6
ullix
Germany
1171 Posts |
Posted - 05/20/2017 : 03:57:13
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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
1261 Posts |
Posted - 05/20/2017 : 19:40:58
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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
1171 Posts |
Posted - 05/21/2017 : 01:42:18
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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
1261 Posts |
Posted - 05/21/2017 : 07:30:41
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| 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
1171 Posts |
Posted - 05/22/2017 : 02:06:41
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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
53 Posts |
Posted - 05/23/2017 : 07:45:04
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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:
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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
1261 Posts |
Posted - 05/23/2017 : 07:57:12
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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
53 Posts |
Posted - 05/23/2017 : 12:44:07
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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
1171 Posts |
Posted - 05/23/2017 : 23:57:04
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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
202 Posts |
Posted - 05/24/2017 : 13:04:50
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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-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
Edited by - Distelzombie on 05/24/2017 13:21:22 |
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| Reply #16
ullix
Germany
1171 Posts |
Posted - 05/25/2017 : 01:53:40
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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
202 Posts |
Posted - 05/25/2017 : 11:13:45
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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-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #18
ZLM
1261 Posts |
Posted - 05/25/2017 : 17:43:46
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| 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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| Reply #19
Distelzombie
Germany
202 Posts |
Posted - 06/10/2017 : 02:02:05
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| Ullix, did you find a filter foil that stops this reaction? You said blue light was causing it so I think amber or yellow filter should help. Maybe a UV filter? |
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #20
ullix
Germany
1171 Posts |
Posted - 06/10/2017 : 23:22:36
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@Distelzombie: your guess may be right, but I wasn't looking for such a filter. Such a filter would put another layer around the tube and be absorbing betas.
This goes against the idea of sneaking out a few more counts from Potassium, as I have proposed in my Potty Training post. http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4558
There will be some more news on the light sensitivity shortly; I am collecting data.
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| Reply #21
ullix
Germany
1171 Posts |
Posted - 06/13/2017 : 01:14:11
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GQ was so kind to send me a replacement tube, and indeed, the new one is NOT light sensitive!
First pic shows results with the counter, backplate removed, laying face down in a bright spot (but no direct sunlight to avoid heating). The first day was a lot sunnier than the second day, which was overcast and rainy, but no hint whatsoever of light sensitivity for the new tube, while the old one reconfirmed its strong light-sensitivity!
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A histogram of the count rates (done with GeigerLog 0.9.04dev) for the full first 24h shows an almost perfect, text-book quality Poisson Distribution (r²=0.998, Avg±StdDev = 18.2±4.3), again showing no hint of any disturbance.
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Of course, this could be due to the new tube not working at all ;-), so I followed my Potty Training http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4558 protocoll with KCl, and alternated between background and KCl measurements (of course all done in a dark box), with the result shown in next pic:
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No numbers needed; both background and sensitivity are incredibly close for the two tubes!
So, what is the difference between the two tubes? Next pic shows the two side-by-side (M4011-2017 is the new one). They look identical to me.
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In summary, there are M4011 tubes which are light sensitive, while others are not. The sensitive one is from 2016, but it has been demonstrated in this thread that there are tubes from 2015, 2016, and 2017 which are NOT light sensitive.
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| Reply #22
Distelzombie
Germany
202 Posts |
Posted - 06/14/2017 : 15:57:53
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Judging by the data it seems like both tubes are totally fine. (Except one is light sensitive for some reason.)
I figured one would be less sensitive. Interesting to see that this is not the case.
However, you only measured low radiation with both tubes. Can you please try both with high radiation? I cannot believe there is no difference.
If I wouldnt be away for a few month, I would gladly give you access to my collection. But it would cost you as much to come here as it would cost you to buy an ore sample. (And its not particular impressive, though I have some rar things) Probably about 10 to 20€. (I figured you dont have one since you asked me once how I achieved such high CPM values and almost all ore samples are similar)
I could give you a connection to a seller if both parties are ok with it. (Yes, its legal and he's in germany too.) |
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #23
ullix
Germany
1171 Posts |
Posted - 06/16/2017 : 01:21:11
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Well, here is another comparison at a 10 fold higher count rate, and the tubes are still the same!
I used a gas mantle (German: Glühstrumpf) which once were produced with radioactive Thorium for improved light emission properties. Shown in the pic with tube M4011 for size reference.
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Thorium decays in a chain mostly by alpha, but also beta, accompanied with some gamma. Alpha cannot be measured here, but the beta and gamma can. Much of the Beta is absorbed in the case, so I had again removed the backplate.
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There is a bit of a challenge to position the gas mantle near the tube reproducibly between measurements. Slight changes, see right half in pic where the arrow points to, result in different count rates. The radioactive emission from the gas mantle is not even over the geometry of the gas mantle. The geometry of the sources used in my Potty Training are better for reproducible measurements.
Even if there were a slight difference between old an new tube, they would be amazingly close. However, I conclude that there is no difference at all between the two tubes.
The remaining oddity is the light sensitivity of the older tube.
A note on the dose: If the calibration of the counter were still applicable - not sure, because backplate is removed and unknown on what the calibration was originally based on - you would receive 20µSv/h at your fingers holding the plastic bag with the gas mantle. Compared to an occupational dose limit of 20mSv per year, you would receive this limit at your fingertips after holding it for 1000 hours straight. I'd say it is not a significant risk.
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| Reply #24
Distelzombie
Germany
202 Posts |
Posted - 06/16/2017 : 11:21:31
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Thats weird. However, 2750CPM is not very much. I had a radiation closer to saturation in mind. Above 65535 cpm, even better above 130000. Can you achieve this somehow?
From how I understand a calibration, it shouldnt make a difference if the case is on or not. If 1000 particles hit the sensor or 10000, Energy of a single particle is always the same. (virtually. Since you only have one value of energy from the calibration source.) Then dose should rise linear with clicks. I think |
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #25
ullix
Germany
1171 Posts |
Posted - 06/17/2017 : 03:34:03
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quote:
Thats weird. However, 2750CPM is not very much. I had a radiation closer to saturation in mind. Above 65535 cpm, even better above 130000. Can you achieve this somehow?
I sure hope you are fully aware of what you are doing? CPM130000 = CPS2200 = 850µSv/h (on the GMC300series), or 20mSv/24h. In other words, if you were getting this dose to your body, you'd be getting the full one year "allowance" of a professional radiation worker within a single day! In whatever institution such might happen, a very serious investigation would follow. And rightly so!
No, I can't do that and I won't attempt to do it. And anyway, what would be the benefit - to know that a weird tube is or isn't fully identical to a less weird tube up to highest count rates?
quote:
From how I understand a calibration, it shouldnt make a difference if the case is on or not. If 1000 particles hit the sensor or 10000, Energy of a single particle is always the same. (virtually. Since you only have one value of energy from the calibration source.) Then dose should rise linear with clicks. I think
This is already contradicted when you get a higher count rate with the case removed. The source doesn't get more dangerous by any changes made to the detector. Therefore you would have to correct the calibration to account for your changes.
Your particle argument is not relevant for the workings of a Geiger counter (GC). A GC is set to operate in a so called "plateau" region, where a little disturbance results basically in an inside flash, which is counted as a pulse. This is intentionally largely independent of the nature of the disturbance; could be a beta particle or a gamma quant (a photon) ranging in energy from 30 keV to 3.5 MeV (specs from GQ). This always on-the-brink-of-collapse being is also largely responsible for occasional counts that have nothing to do with radioactivity and contribute to an apparent background (GQ specs: Instrument Background: <0,2 pulses/s).
Contrary to what you said the energy of beta particles may actually change. But not the energy of gamma quants. K40 (see my Potty Training post http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4558) emits a 1.46MeV gamma, and for this (rather high energy) the case of the counter is basically transparent and the quant indeed never changes its energy until it is absorbed somewhere.
But K40 also emits a beta particle with a similarly high energy of 1.33MeV. However, this is the MAXIMUM energy the beta particle can have, most of them have a lower one (with the remaining energy up to 1.33 MeV taken up by a neutrino) as shown in this figure (for a different atom, but quite similar):
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Now look at the Range discussion in the Appendix in my Potty Training. While the betas with the highest energy may make it through the plastic of the case, most are of lower energy and might be stuck and never reach the counter tube. The betas also do not buzz through the plastic like the gammas, but more like a ball through the pinball machine, being slowed down with each bump, further reducing the chances of a beta to cross the plastic. (And thereby maybe making Bremsstrahlung; another complication, see Potty Training.)
But when you miss most of the electrons with the case on, you are underestimating the radiative strength of the source, and hence your calibration is wrong if it has been made on a gamma source.
Or the other way around: if the counter had been calibrated with the case on for a mixed beta/gamma source, you would overestimate the source when the case is off!
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| Reply #26
Distelzombie
Germany
202 Posts |
Posted - 06/19/2017 : 08:55:59
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Hm, makes sense. Thank you!
quote:
I sure hope you are fully aware of what you are doing? CPM130000 = CPS2200 = 850µSv/h (on the GMC300series), or 20mSv/24h. In other words, if you were getting this dose to your body, you'd be getting the full one year "allowance" of a professional radiation worker within a single day! In whatever institution such might happen, a very serious investigation would follow. And rightly so!
No, I can't do that and I won't attempt to do it. And anyway, what would be the benefit - to know that a weird tube is or isn't fully identical to a less weird tube up to highest count rate.
It's a point source, basically. Only my fingers would get the described dosage. It's not a problem if I don't use it as a pendant. ;) |
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #27
ullix
Germany
1171 Posts |
Posted - 06/19/2017 : 09:51:15
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yeah, and you have 10 fingers anyway ;-)
Remember the 1/r² law - a little distance (from the point source) goes a long way! |
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| Reply #28
Distelzombie
Germany
202 Posts |
Posted - 06/19/2017 : 11:00:49
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| And a lead reinforced safe. ;) |
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional. |
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| Reply #29
hmw
8 Posts |
Posted - 01/21/2018 : 10:31:13
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| I just tried it. Removing the cover plate and maintaining the same distance to the torbernite sample roughly doubles the cpm. I still have to look up the ratio of the emitted beta and gamma radiation though. |
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| Reply #30
ullix
Germany
1171 Posts |
Posted - 01/22/2018 : 02:18:07
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Torbernite contains Uranium. So the decay chains to consider are those from U-238 (>99%) and U-235 (<1%). Each have a bunch of beta decays in the chain; I count a total of 21 ( https://en.wikipedia.org/wiki/Decay_chain )
If you want some more authoritative source than Wikipedia look here: https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html
Basically it is impossible from those data to figure out the relationship of beta to gamma, because it is way too complex. What I would suggest to do is an experiment:
- Take the back cover of the counter off
- put a ~3mm thick aluminum plate between sample and counter and measure
- remove the plate and measure again
- The difference is the beta contribution (not 100% but close)
Let us know the outcome! |
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| Reply #31
hmw
8 Posts |
Posted - 01/22/2018 : 11:15:39
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quote:
Originally posted by ullix
Torbernite contains Uranium. So the decay chains to consider are those from U-238 (>99%) and U-235 (<1%). Each have a bunch of beta decays in the chain; I count a total of 21 ( https://en.wikipedia.org/wiki/Decay_chain )
If you want some more authoritative source than Wikipedia look here: https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html
Basically it is impossible from those data to figure out the relationship of beta to gamma, because it is way too complex.
Yes, it's hard to do. But in principal it should be possible, because after some time there should be an equilibrium: elements decay at a certain rate, daughter elements are produced at a certain rate. I think I saw such data somewhere, but I couldn't find it last weekend.
quote:
Originally posted by ullix
What I would suggest to do is an experiment:
- Take the back cover of the counter off
- put a ~3mm thick aluminum plate between sample and counter and measure
- remove the plate and measure again
- The difference is the beta contribution (not 100% but close)
Let us know the outcome!
I will do that. But it will take a few days, I usually have some play time at weekends only.
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Counter counts mostly day
