2 pi gas glow proportional counter

[GigaBecquerel]

Hello!

I wanted to share todays afternoon project.
It's a simple proportional detector for alphas, runs on regular propane / butane and is sensitive to alphas only, with almost 2 pi efficiency!
The materials are just a stainless steel hemisphere, two gas connectors and a BNC connector, the readout is done by my ludlum model 12.
I cheated a bit with the anode wire, as I originally wanted to do it with 65 µm Corona Wire, since it' cheap and easily available, but it didn't work well at 2.5 kV, so I took the 20 (or was it 25 µm) wire from a dead counter I have here.
Below is a small text about this counter, taken from Radiation Detection and Measurement by Knoll, my personal bible to live by :D

https://www.youtube.com/watch?v=EDBo59W6Ruc
Here's a video of it, with one of those thorium "Anti Radiation" stickers as test source.

Lukas

[Sesselmann]

Hey, this looks like a nice project, well done...

The super thin wire is hardly visible in the photo, but I can just make it out as a time loop.

Pretty sure we have some stainless steel bowls like that in the kitchen, maybe my wife won't notice if one is missing :)

Steven

[GigaBecquerel]

Thanks!
The wire in the picture was the thick variant, I am having troubles to see the thin one with my own eyes.
It all works surprisingly well, and I ordered some Ar/CO2 welding mix to try that as counting gas.
Not as cheap as butane, but it doesn't burn, and doesn't have thiol additives.
Also it should perform better, if I am not mistaken.

Give it a try with your salad bowls! It's an easy build, and should be very easy to get going if you're not limited to the 2.5 kV of a ludlum model 12.

Lukas

[Sesselmann]

Lukas,

I have an Argon cylinder in my workshop, but Argon is heavy, maybe the salad bowl needs to be upside down?

Steven

[GigaBecquerel]

Argon alone isn't ideal, but should work for low activity stuff.
Butane is denser than air, just like argon, but the constant flow prevents the chamber from backfilling with air.
You can operate the counter in any orientation, but you might risk dropping your sample or dust from it in the detector if you operate it upside down...

[GigaBecquerel]

Oh wow, I just got my bottle of 80/20 Ar/CO2 and it works so well!
With it the Th sticker goes from 100 cpm to 2k cpm, indicating that I'm also seeing betas, and perhaps even gammas.

[GigaBecquerel]

Well, I did some more tests, and Ar/CO2 definitely works better.
The gain is way higher, so I can lower the voltage to about 1/2 to count alphas only. The higher gain also allows me to go back to the 65µm anode wire, which is a huge advantage due to cost and availability.
The difference is so big, that it cannot be explained by the different gas alone, so my main guess is, that the thiol additives quench the signals, and pure butane would work a lot better.

https://www.youtube.com/watch?v=Wpvgp-UbHcQ

[James Luck]

Well, I did some more tests, and Ar/CO2 definitely works better.
The gain is way higher, so I can lower the voltage to about 1/2 to count alphas only. The higher gain also allows me to go back to the 65µm anode wire, which is a huge advantage due to cost and availability.
The difference is so big, that it cannot be explained by the different gas alone, so my main guess is, that the thiol additives quench the signals, and pure butane would work a lot better.

https://www.youtube.com/watch?v=Wpvgp-UbHcQ

Thats pretty cool, i was gonna try my hand at producing a few proportional counting chambers for contamination, i planned on using P10, but i will also try Ar/CO2.
Ill share my work and experiences once i start the project.

-James

[GigaBecquerel]

Thanks, it would be great to get a direct comparasion between P10 and Ar/CO2!
Will you document your build here?

[James Luck]

Thanks, it would be great to get a direct comparasion between P10 and Ar/CO2!
Will you document your build here?

When i find the time to sit down and actually experiment on the build i will be sure to document all if not a majority here.
There are a few builds and experiments i would like to do, and i feel this is a good place to document it. Hopefully these experiments posted here will interest or at least help someone on there way to experimenting.

-James