Low-energy x-rays and GMC 300e Plus Geiger Counter

[Plat]

Hello everybody, this is a bit of an unusual question, so I hope this is an appropriate place to post this.

I am experimenting with cathode rays and high-voltage electrical discharges at low pressure, so I bought the GMC 300e Plus geiger counter to check for x-rays. I know the meter is working from a test source, and have not detected anything from my experiments, but I wonder if this device will register very low-energy x-ray photons that I could be producing. The specs say the instrument will register down to 30kev x-ray photons. The voltages I am using are somewhere(unknown) between 25kv and 35kv, which will similarly produce x-rays with energies from 25kev to 35kev. I guess I am wondering if anyone has used this instrument with x-rays, and how did it perform? It makes sense that if it detects a 30kev photon, then a 20kev photon that enters the geiger tube should set it off just the same. Thanks for any input.

[KE5FX]

The 20 kV photon might not have enough energy to ionize the gas in the tube, and if that's the case, the counter won't trigger.  Remember that it's not the intensity or the quantity of radiation that determines whether ionization occurs, but the energy.

Another problem is that X-ray sources can saturate Geiger tubes.  The gas stays ionized at high radiation levels so the instrument remains silent.  Some counters detect saturation but I don't think they all do.  So it's a good idea to have a secondary detection mechanism handy when playing with this stuff. 

[daqq]

Saturation of the detector generally occurs at high radiation levels. You should be able to check for saturation relatively easily though - just put some attenuation between your source and your detector (or move the detector far away from the source), if you suddenly get a massive reading after that you are not running fast enough from the affected area.

As to the main question, you assume a lot - the output spectrum of a tube is not monochromatic and it does not peak around the excitation voltage - basically, the excitation voltage is the highest energy achievable, but the bulk of the spectrum will be lower than the excitation voltage. See this picture:
http://www.sprawls.org/ppmi2/XRAYPRO/XRAYPRO05.jpg

edit:

It makes sense that if it detects a 30kev photon, then a 20kev photon that enters the geiger tube should set it off just the same.

To the best of my knowledge: Not necessarily, at low energies you get low penetration - as such the bulk of the photons may get absorbed into the tube material itself.

[Plat]

I am sure saturation is not occuring, because if I approach the experiment from a distance, the meter reads nothing above background the whole time. From an attenuation calculator, I know that the majority, 57% of 20kev photons will penetrate 1mm of SiO2, so I should still get plenty of photons into the tube to detect. At lower energies where the photons cannot penetrate the glass geiger tube, I am not concerned, because that means they also cannot escape the much thicker glass walls of my possible source. I guess it really depends on whether the gas inside the tube will be excited and register a count by a 20kev or 25kev photon. Maybe I am being paranoid and over thinking this.

[Fraser]

I use both soft and hard X-Ray generators and have the following comments for you.

1. The GM tube is not the most suitable detection device for X-Ray generators running at much less than 45keV. They will not respond well to the low X-Ray energy levels being emitted from the tube

2. Remember that the excitation voltage applied to the tube produces a far lower keV at the output and so KVp is NOT a direct indicator of keV being emitted. That is to say, if you apply 45kV to an X-Ray tube, it's theoretical maximum output energy is 45keV, but in reality the output is far less.

3. For X-Ray energy levels of 45keV and lower, the most appropriate measuring and detection devices use a scintillation probe, ionisation chamber or semiconductor detector. The GM tube is unlikely to respond and even if it does, it will be hopelessly inaccurate. GM tubes normally have a minimum detection keV specification and the correction factor needed for any meaningful measurement. Below this level of energy, the tube is virtually blind to the energy.

4. I own a Tel-X-ometer 580 that uses a 20 or 30kVp excitation voltage on the X-Ray tube. There is an optional GM tube and rate counter available for the 580 so there are GM tubes that will respond to such low levels of keV. They will likely be on the edge of their detection capability though.

5. If you wish to continue your use of GM tubes in your experiments, you need to find one with a very low keV threshold as anything else will be misleading in its operation.

6. Personal Dosimeters for use with X-Ray need to be accurate and effective at lower keV levels. They often use a scintillator, or more modern versions, a specially doped semiconductor detector. GM tubes are normally found in the units designed for higher levels of Gamma radiation, such as found in the Nuclear industry or high energy X-Ray generation.

If you are interested in X-Ray's and generators, you may wish to search this forum for my posts on the Faxitron MX-20 and Tel-X-ometer 580 machines. I also provide comment on the appropriate personal dosimeters that I use.

Fraser

[daqq]

Fraser:

Could this work for the low energies:

http://www.ebay.com/itm/LYSO-Scintillator-Crystal-for-Gamma-Radiation-Scintillation-Detector-BGO-NaITl-/251986066149?hash=item3aab8a3ae5:g:aA8AAOSwofxUfiW1

?

[Fraser]

NaI(TI) produces approx 45000 photons per MeV
LYSO produces approx 34000 photons per MeV

NaI(TI) is a nightmare to keep dry as it is highly hygroscopic. LYSO is non hydroscopic but produces less light output at a given energy input level

A very sensitive photo multiplier tube is needed when using such scintillators.

Fraser

[Plat]

I use both soft and hard X-Ray generators and have the following comments for you.

1. The GM tube is not the most suitable detection device for X-Ray generators running at much less than 45keV. They will not respond well to the low X-Ray energy levels being emitted from the tube

2. Remember that the excitation voltage applied to the tube produces a far lower keV at the output and so KVp is NOT a direct indicator of keV being emitted. That is to say, if you apply 45kV to an X-Ray tube, it's theoretical maximum output energy is 45keV, but in reality the output is far less.

3. For X-Ray energy levels of 45keV and lower, the most appropriate measuring and detection devices use a scintillation probe, ionisation chamber or semiconductor detector. The GM tube is unlikely to respond and even if it does, it will be hopelessly inaccurate. GM tubes normally have a minimum detection keV specification and the correction factor needed for any meaningful measurement. Below this level of energy, the tube is virtually blind to the energy.

4. I own a Tel-X-ometer 580 that uses a 20 or 30kVp excitation voltage on the X-Ray tube. There is an optional GM tube and rate counter available for the 580 so there are GM tubes that will respond to such low levels of keV. They will likely be on the edge of their detection capability though.

5. If you wish to continue your use of GM tubes in your experiments, you need to find one with a very low keV threshold as anything else will be misleading in its operation.

6. Personal Dosimeters for use with X-Ray need to be accurate and effective at lower keV levels. They often use a scintillator, or more modern versions, a specially doped semiconductor detector. GM tubes are normally found in the units designed for higher levels of Gamma radiation, such as found in the Nuclear industry or high energy X-Ray generation.

If you are interested in X-Ray's and generators, you may wish to search this forum for my posts on the Faxitron MX-20 and Tel-X-ometer 580 machines. I also provide comment on the appropriate personal dosimeters that I use.

Fraser

Thanks for all the information on this. Would you hapoen to know what tube is normally installed in a CDV-700? I have read that these are not very sensitive but know they will produce a good reading from a tube powered by just 20kv. Some hobbyists have demonstrated this.

I did a little experiment, I have a crookes paddlewheel tube, and just connected that to a small tesla coil. With foil shielding covering the geiger counter for emf, I get 100cpm and 0.50 micro-sieverts at one foot from the tube. My background is about 16 cpm. This is a very low voltage tesla coil, it only arcs about 2cm max. Does this demonstrate enough sensitivity to low-energy x-rays? Using a higher voltage in my main experiment, I get no reading above background.

[Fraser]

Some reading for you

http://rfelektronik.se/manuals/Datasheets/Tubes/geiger_tube_theory2.pdf

Page 13 onwards provides you with an insight into GM tubes when used at low energy levels.

I am not familiar with the tube used in the CDV700 so cannot comment on its performance.

I forgot to say, Ionisation Chambers are also good for low energy monitoring and measurement.

Fraser

[Plat]

I have been trying and failing to find information like that, thank you for the link. That text says that photons below 25kev will have a stronger ionizing effect than higher energies. That must mean that tubes that respond weakly to those energies must have too much attenuation in the side of the tube, right?

[Fraser]

Attenuation of the tubes casing and window is an issue at very low keV levels. That is true. If the energy cannot get into the tube interior, it cannot cause an event.

[Plat]

Attenuation of the tubes casing and window is an issue at very low keV levels. That is true. If the energy cannot get into the tube interior, it cannot cause an event.

I have an ionization chamber device, the CDV 715, but it is useless for the small amount of radiation like I may have here. Is it safe to say that if the tube is not significantly attenuating, and the gas inside is ionized by the photons entering, then a qualitative test for the presence of x-rays can be made?

[Fraser]

As you noted, that paper details high sensitivity GM tunes for low energy levels below 25 keV. Such tubes use different gases at higher pressures to achieve more events along the length of the tube.

Basically, if you are working with low energy X-Ray, it is wise to use a detector or tube that is specifically rated for such energies. This is normally in the datasheet.

I also own a GMC 300 and can advise that it is not recommended for use at low energy levels such as you have described. It uses a cheap Russian GM tube that, though very good, is not rated for energies lowers than around 45 keV. Operation with energies below this specification is not predictable or meaningful in terms of any measurements.

The Victoreen 715 Ionisation Chamber meter is designed for nuclear fallout detection. It is designed to be relatively insensitive. Ionisation Chamber detectors can be very sensitive when designed for use at low energy levels. My Eberline ionisation chamber survey meters are very sensitive to Low energy X-Ray's.

Fraser

[Plat]

As you noted, that paper details high sensitivity GM tunes for low energy levels below 25 keV. Such tubes use different gases at higher pressures to achieve more events along the length of the tube.

Basically, if you are working with low energy X-Ray, it is wise to use a detector or tube that is specifically rated for such energies. This is normally in the datasheet.

I also own a GMC 300 and can advise that it is not recommended for use at low energy levels such as you have described. It uses a cheap Russian GM tube that, though very good, is not rated for energies lowers than around 45 keV. Operation with energies below this specification is not predictable or meaningful in terms of any measurements.

The Victoreen 715 Ionisation Chamber meter is designed for nuclear fallout detection. It is designed to be relatively insensitive. Ionisation Chamber detectors can be very sensitive when designed for use at low energy levels. My Eberline ionisation chamber survey meters are very sensitive to Low energy X-Ray's.

Fraser

That was another piece of information I was looking for, the model of tube in the GMC 300e. It's funny that the device is specificied to 30kev if the tube is not designed for that.

I did a couple more tests and I am now sure that my geiger counter is working for my purposes. I ran the paddle wheel tube again with the tesla coil to get a baseline reading, then placed a 1mm glass sheet between the meter and source. This reduced the reading by 80%. Then I placed 4mm of glass between meter and source and got a 100% reduction in the reading to only background. At 20kev, 4mm of SiO2 attenuates 90% of photons, so the energies produced and detected here must be about 20kev or less.

I know the energy is emitted on a spectrum, but to get 100% attenuation, the quantity of photons above 25-30kev must be neglible.

I know the glass walls of the geiger tube are a factor here but they are very thin compared to the attenuation I mentioned above. I just want to test for presence of radiation(don't want any!), not the quantity.

[Fraser]

It uses the M4011 GM tube. There is plenty on the web about this tube on the web.

Check out the OEM web forum for the GMC Geiger counters. I believe there has been previous discussion of using the unit for low energy X-Ray.

http://www.gqelectronicsllc.com/forum/forum.asp?FORUM_ID=14

X-Ray discussion....

http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4202

M4011 discussion

http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=3654

M4011 spec

http://www.ebay.com/itm/New-High-Sensitivity-M4011-Geiger-Counter-Tube-/260835055100?hash=item3cbafb15fc&pt=LH_DefaultDomain_0&nma=true&si=%252FVaJmex8AHUY8eYEI9ZIoeRCIR8%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

Note 0.1Mev detection threshold for Gamma. X-Ray will be similar.

Also be careful if using static generators to create high voltages....... If the GM tube gets too close you get false readings due to static charge and not X-Ray energy.

Fraser

[Fraser]

And finally, here is someone asking about the true low energy capabilities of the GMC 3xx series........

http://www.gqelectronicsllc.com/forum/topic.asp?TOPIC_ID=4040

Geiger counter specs can be a bit of a mine field. Detection does not always mean useful data is produced!

Fraser

[Plat]

Thanks for those links. The owner's manual definately says it is sensitive to 30kev x-rays. It's unfortunate if that is a typo. Again, just looking to determine the presence or absence of x-rays. I first tried to determine if my experiment could theoretically produce x-rays by asking on various physics forums. Nobody could tell one way or another. My vacuum pump is capable to evacuating down to 5 pascals of pressure. If that is low enough to allow the production of x-rays, I don't think so, but that is the question.

Perhaps I could record and link a video of the GMC 300 detecting radiation from the paddlewhele tube, with and without attenuation, just to get your opinion on it's behavior?

[Fraser]

I am feeling helpful so tomorrow I will dig out my GMC300E and place in in my Tel-X-Ometer. It can produce X-Rays using either 20 or 30kvp. I shall try both.

The test does not prove that your unit will work the same, but at least we can see if mine registers the low energy X-Ray beam. This is why I love the Tel-X-Ometer 580. Great for experiments, and safe.

If you get a chance, take a look at my Tel-X-Ometer and Faxitron threads on this forum. Lots of Faxitron X-Ray images in my X-Ray pictures thread as well.

Fraser

[Plat]

I am feeling helpful so tomorrow I will dig out my GMC300E and place in in my Tel-X-Ometer. It can produce X-Rays using either 20 or 30kvp. I shall try both.

The test does not prove that your unit will work the same, but at least we can see if mine registers the low energy X-Ray beam. This is why I love the Tel-X-Ometer 580. Great for experiments, and safe.

If you get a chance, take a look at my Tel-X-Ometer and Faxitron threads on this forum. Lots of Faxitron X-Ray images in my X-Ray pictures thread as well.

Fraser

That would be fantastic, thank you! That sounds like an awesome piece of equipment!

[KE5FX]

I am feeling helpful so tomorrow I will dig out my GMC300E and place in in my Tel-X-Ometer. It can produce X-Rays using either 20 or 30kvp. I shall try both.

The test does not prove that your unit will work the same, but at least we can see if mine registers the low energy X-Ray beam. This is why I love the Tel-X-Ometer 580. Great for experiments, and safe.

If you get a chance, take a look at my Tel-X-Ometer and Faxitron threads on this forum. Lots of Faxitron X-Ray images in my X-Ray pictures thread as well.

Fraser

Just as one data point, a Radalert 100 counter with the LND712 tube makes a lot of noise if you put it in an MX20 cabinet.  10 kVp causes a fast buzzing sound, which turns into a continuous tone by 30 kVp.  So that particular tube can definitely be used to detect soft X rays.

[Plat]

I am feeling helpful so tomorrow I will dig out my GMC300E and place in in my Tel-X-Ometer. It can produce X-Rays using either 20 or 30kvp. I shall try both.

The test does not prove that your unit will work the same, but at least we can see if mine registers the low energy X-Ray beam. This is why I love the Tel-X-Ometer 580. Great for experiments, and safe.

If you get a chance, take a look at my Tel-X-Ometer and Faxitron threads on this forum. Lots of Faxitron X-Ray images in my X-Ray pictures thread as well.

Fraser

Just as one data point, a Radalert 100 counter with the LND712 tube makes a lot of noise if you put it in an MX20 cabinet.  10 kVp causes a fast buzzing sound, which turns into a continuous tone by 30 kVp.  So that particular tube can definitely be used to detect soft X rays.

I wonder of the mica window was facing the tube during that test? The reading would probably be greatly aftected.

[KE5FX]

I wonder if the mica window was facing the tube during that test? The reading would probably be greatly aftected.

No, the counter was just sitting on the floor of the cabinet, a few centimeters away from the image sensor.  It will respond to scattered radiation inside the cabinet regardless of orientation.

[Fraser]

I have just completed the quick tests using my Tel-X-Ometer as the X-Ray source.

The results are shown in the attached pictures

I tested the GMC-300E, The SOEKS-01M and my reference Mini Monitor 900 with Type D probe.

Note that the Mini Monitor type D probe uses a Geiger Muller tube designed for use with low energy sources, specified down to 30kvp. It is calibrated and its readings are more trustworthy than either the GMC or SOEKS products. There is a Mini Monitor Geiger Muller tube based probe that is specifically designed for use with low energy X-Rays down to 10kvp but it is for relative indication only and provides a CPS reading. The tubes low efficiency at such energy levels prevents calibrated measurements.

The GMC-300E uses a M4011 Geiger Muller tube that is made in China.
The SOEKS-01M uses a SBM-20 Geiger Muller tube that is made in Russia.
The Mini Monitor 900 Type D probe uses either the Centronics ZP1490 or its equivalent LND-7231 Geiger Muller tube

Readings produced:

GMC-300E
20kvp =   211 uSieverts/hour
30kvp =   271 uSieverts/hour

SOEKS-01M
20kvp =   320 uSieverts/hour (Over-Range)
30kvp =   320 uSieverts/hour (Over-Range)

MM900D
20kvp = Over-Range >1000 uSieverts/hour
30kvp = Over-Range >1000 uSieverts/hour

The GMC-300E provided a reading but it is very low when compared to the reference MM900D. The SOEKS unit officially has a range of 0.03 to 100 uSieverts per hour and so Over-Ranged with a reading of 320 uSieverts per hour.

This is why I warned about the issues of using GM tube based units to monitor or measure low levels of X-Ray energy. Results vary greatly depending upon the exact GM tube used and whether such has been designed for working with low keV sources.

The GMC-300E also behaved strangely when operating inside the Tel-X-Ometer. The Geiger Click mode was enabled yet when the unit was illuminated with X-Rays, the Geiger click was silent. as soon as the X-Ray source was switched off, the unit went into a wild Geiger clicking tantrum and continued until the reading on it had decreased to background. The unit took quite some time to settle back to background from a reading of 200+ uSieverts/Hour.

Such behaviour does not inspire confidence in the unit in this application.

Both the GMC-300E and SOEKS-01M are designed for background radiation monitoring rather than survey work. The MM900D is designed for monitoring and survey work and is a far more effective tool when checking equipment for X-Ray leakage.

Hope this helps a little.

Fraser

[Fraser]

Some data on the Mini Monitor 900 and the Type D probe used in the test.

The Datasheet is attached.

The Type D probe contains a partially compensated Centrtonics ZP1490 (LND-7321) Geiger Muller Tube. LND datasheet attached.

Fraser

[Plat]

I can't thank you enough for testing that out, it's really interesting to compare the different meters. Perhaps the 30kev spec of the GMC is wrong, since I would expect much higher reading going from 20-30kvp. Do you know what tha actual outlut of the x-ray tube in the Tel-x-ometer is? I wonder how close they were?