Geiger Counter and ultraviolet light sources

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Summary:

An assembled Geiger counter (with a clear J305 tube) is exposed to several UV sources and the recorded counts per minute are compared.

Main Question or Discussion Point

I purchased a RadiationD-v1.1(Cajoe) geiger counter off ebay, and attached an arduino nano and a 16x2 display ( I got the instructions off this site https://www.instructables.com/id/Arduino-DIY-Geiger-Counter/). I noticed that the counter was sensitive to UV when I had it out in the sunlight, so I decided to expose it to several UV sources.

Background Radiation - Average 25.4 counts per minute

Background Radiation inside wooden box – Average 20.4 counts per minute

Incandescent Light Bulb (Frosted Soft White 60 Watt Globe 130 Volt BB 0903)
1st minute 39 counts
2nd minute 35 counts
3rd minute 40 counts
4th minute 29 counts

Incandescent Light Bulb (Frosted Phillips Duramax 60W/120V China 1F)
1st minute 317 counts
2nd minute 203 counts
3rd minute 104 counts
4th minute 112 counts
5th minute 48 counts
6th minute 27 counts

COBB Led Head Lamp – Average 61.7 counts per minute

Fluorescent 13W mini twister Phillips – Average 940 counts per minute

405nm Laser Pointer – 106385 counts per minute the laser pointer was aimed at the point where the anode enters the glass envelope (Green and Red laser pointers had no effect)

UV LED flashlight – Average 35753 counts per minute

UV Tube blacklight (battery powered) - Average 67466 counts per minute

UVB Reptile bulb 13W fluorescent – Average 622211 counts per minute

UVC germicidal tube – got one count of 10314 and then the screen scrambled. The Geiger counter had to be restarted. The screen would start garbling, but the counter would still beep. This was done in a closed wooden box to reduce the exposure to UVC.

What could be done to prevent the screen from scrambling when measuring UVC? Would shielding work? Or should I increase the distance between the UVC tube and the counter?

Why would the incandescent bulbs be emitting UV? Could there be some mercury or halide vapor in the bulb?
 

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  • #2
sophiecentaur
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Summary:: An assembled Geiger counter (with a clear J305 tube) is exposed to several UV sources and the recorded counts per minute are compared.

Why would the incandescent bulbs be emitting UV? Could there be some mercury or halide vapor in the bulb?
Interesting experiment; I'm always in favour of home projects and your results are not, on the face of it, what I'd have expected. I think there must be a humdrum explanation for this, bearing in mind the low level of ionisation radiation in the sources you used.

Could the electrons in the tube be photo-electrons, which do not need 'ionising radiation' ? I guess you could try to resolve the problem by filtering the light. Alternatively you could buy or borrow a higher quality tube - or spend a lot longer than I did in searching for other examples of this apparently (to me) anomalous behaviour.
 
  • #3
gleem
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Could you post a picture of your GM counter just as you exposed it to the light sources?
 
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gc02.JPG
gc03.JPG
gc04.JPG
gc05.JPG
gc06.JPG


When the counter display became garbled when it was exposed to the UVC lamp, it might have been due to overheating. The counter had been running for an hour or two with light sources right up against the case.
I was using a cheap battery powered cell phone charger to supply the five volts to power the counter. I will use a USB hub instead
 
  • #5
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You might try covering the electronics to shield it from the light. Cardboard and masking tape would do, I think. Semiconductor junctions are sensitive to photons and components that have clear plastic, like LEDs and some diodes might cause problems. OTOH, if everything looks like its black plastic or metal, this is probably a waste of time.
 
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  • #6
sophiecentaur
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Why not have the GM tube remote from the electronics? The electronics could be in a metal box and left for a while to arrive at a stable temperature.
Your problem puts me in mind of the Sherlock Holmes idea about eliminate the impossible and you are left with the possible.
 
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  • #7
Vanadium 50
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The UV is not ionizing the gas in the tube, presumably argon. The ionization potential for Ar, O2 and N2 are all about the same, way in the VUV. This won't penetrate the glass wall, won't penetrate the air, and would produce noticeable ozone.

Putting UV light on the tube will not scramble the screen. This is almost certainly due to EMI from the tube.

I would separate the data into fluorescent and non-fluorescent sources.
 
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I separated the GM from the rest of the board
gc07.JPG


I exposed the separated GM tube to a incandescent bulb (Phillips Duramax 60W) and the average count was 98.4 beeps per minute. I put a welding glass filter (shade #12) between the GM and the incandescent bulb. The count was similar to background radiation. The welding glass filter cracked after 5 minutes. I didn't realize how much heat those incandescent bulbs emit. So I decided to use a blow drier on the GM tube while the tube was in a wooden box recording background radiation. I measured the temperature using a cheap IR thermometer
Beeps per Minute Temperature (degrees C)
18 28
39 62
68 63
117 46
39 41
27 38
74 38
29 35
30 33




The temperature of the GM tube might have an effect on the counts per minute.
 
  • #9
256bits
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The temperature of the GM tube might have an effect on the counts per minute.
It shouldn't.

What happens is that an ionizing particle, enters the tube and causes an atom of gas to split into an electron and an ion. The electron is attracted to the positive anode wire, becomes more energetic the closer it gets and with more collisions produces more electron-ion pairs.. This continues and an avalanche of electrons is produced. The ions travel to the casing. Your circuitry detects this as a current All this happens in microseconds.There should be a relax phase after each avalanche, so that the gas can return to as before, and detect another ionizing particle. Each avalanche would be a click. An ionizing particle entering during an avalanche is not detected by the tube, even though it can ionize the gas.

If the UV is entering the tube ( quartz glass )( you shone the laser at the anode end ) and ejecting electrons from the metal rod, this, I would tend to think not be recorded as a click.
 
  • #10
Vanadium 50
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What happens is that
That is what should happen. It is almost certainly not what is happening here. Especially the screen scrambling
 
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  • #11
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It shouldn't.
Why are the cathodes of electron tubes heated?? Seems possibly relevant to me, but I am not an expert..
 
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Why are the cathodes of electron tubes heated?? Seems possibly relevant to me, but I am not an expert..
Greater electron emission without damage to the cathode. You want a "cloud" of free electrons around the cathode, ready to be moved by e-fields. Removing electrons from the cathode by electric forces just doesn't work as well as thermal ionization in terms of reliability and tube function. Cathodes are a key reliability issue in high power tubes. The high power ion lasers I used to work on had each tube/laser calibrated individually to set the optimum cathode heating for long life.

OTOH, I have no idea if/how this applies to a Geiger tube, which is operated at low currents and low stress.
 
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  • #13
256bits
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Why are the cathodes of electron tubes heated?? Seems possibly relevant to me, but I am not an expert..
Hot cathode, cold cathode, thermionic emission, Townsend discharge, gas discharge
Townsend discharge is what is to happen in the geiger tube.
See the graph halfway down of typical characteristics voltage/current

Electron tubes operate in a vacuum - no ionization of gas particles.
Thermionic emission to produce an electron cloud around the cathode.
These electrons are or can be accelerated towards the anode as a controlled, if required, current.

cold cathode, hot cathode, gas discharge ( cold cathode means that the cathode is not heated by external means )
Rarefied gas withing the enclosure.
Electrons emitted from the cathode.
Collisions with the gas particles can produce more electrons in a cascade effect known as Townsend discharge.
examples: Hot cathode - fluorescent lamp ( most of them ). cold cathode - Xenon discharge tube, CFL lighting

Probably left something out.


@Vanadium 50
Upon writing that above, would it be possible that the UV ( IS ) entering the geiger tube is kicking electrons off the cathode ( there should be a thin wire visible surrounding the interior anode wire - for the OP to look at ), rendering the tube to act somewhere within the cold cathode regime without discharge, up to the point of the scrambling when complete ionization and plasma occurs to overload the circuitry.
 
  • #14
Vanadium 50
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would it be possible
Lots of things are possible. Lots of things are probably going on. I'm arguing to separate them as much as possible, starting with the electronic noise. That clearly won't help.
 
  • #15
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Vanadium 50 said:
The UV is not ionizing the gas in the tube, presumably argon. The ionization potential for Ar, O2 and N2 are all about the same, way in the VUV.

The fill gas in a geiger tube is usually at a lower pressure than atmospheric to reduce the ionization potential. This is a diagram of some Paschen curves. Would this allow longer wavelength radiation to ionize the fill gas?
Paschen_curves.jpg
 
  • #16
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The ionization of an atom by a photon doesn't have much to do with how many others are nearby in the gas. The curve you showed is more about electrical discharge because of the energy acquired by electrons (and ions) when they are accelerated by the e-field. It's about the mean-free path being larger at lower pressures. This has a lot to do with the resulting current flow after an ion is created, but not so much to do with the photon interaction that starts it.

edit: photon, neutron, alpha particle... its all the same thing. An interaction with a single atom which is amplified by an avalanche effect mediated by the gas and an applied e-filed.
 
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  • #17
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The ionization potential for Ar, O2 and N2 are all about the same, way in the VUV. This won't penetrate the glass wall, won't penetrate the air, and would produce noticeable ozone.
This is correct. The UV-C will not be able to directly ionize the fill gas (it doesn't have the required energy). The UV-C has to interact with the tin oxide cathode and discharge some electrons (photoelectric effect). These electrons will be attracted to the anode and will have enough energy, due to the reduced pressure in the tube, to ionize the fill gas. The transmittance of soda lime glass at 280nm is about 2%
(Gross, A.; Stangl, F.; Hoenes, K.; Sift, M.; Hessling, M. Improved Drinking Water Disinfection with UVC-LEDs for Escherichia Coli and Bacillus Subtilis Utilizing Quartz Tubes as Light Guide. Water 2015, 7, 4605-4621)
 
  • #18
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gc08.JPG
gc09.jpg
gc10.jpg



The J305 Geiger tube was removed from the Geiger counter and placed in its separate holder. A USB ionizer was used to power it. The USB coupling was removed from the ionizer, and 3 AA batteries in series were hooked up as the power source (no counter attached). The USB ionizer consists of an oscillator, a step up transformer, and two diode capacitor voltage doublers. There is about 420 V of potential between the voltage doublers and ground. The normal operating voltage for the tube is 380 to 450 volts. The tube started to get a red glow when a 405nm laser pointer was directed at the anode. A thorium gas mantle produced sporadic red glows. When I try to read the voltage across the tube when it is installed in the geiger counter the counter starts squealing and the display starts to scramble (240V). Has anyone else been able to get a J305 tube (or any other glass Geiger tube) to do this? I couldn’t use a digital multimeter for the measurements because the reading would constantly change.
 
  • #19
Tom.G
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I think what you have proven is that the J305 is photo-sensitive.

Solution?: Block light getting to it

Method: Try some Aquadag coating on the outside of the tube. It is colloidal Graphite so keep it away from the electrical contacts.

If you were around to remember the televisions that used a CRT (Cathode Ray Tube) for display, you may recall the black coating (inside and outside) on the bell of the CRT. That was Aquadag and at the time was available as a liquid to patch a damaged outer-surface coating. I don't know if it's still readily available.

(seems to be available:
https://www.google.com/search?&q=aquadag+colloidal+graphite)

Cheers,
Tom
 

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