We had two opportunities to test the circuit - so the time was tight. However, we managed to capture a muon decay on camera, although we had trouble with the lighting in the cloud chamber. We fixed it somewhat, but still can be improved. Still, a faint, but clear trace of the decay can be seen on the picture below.
Since the track takes time to build up in the cloud chamber the delay in the electronics is actually an advantage; so the trace of the particles have time to form. As a result we can capture the trace on camera.
You can see one picture like this below. The muon is coming in from the left hand side from the bottom then travelling towards the middle of the picture where it decays and an electron is travelling straight up.
The brightness and contrast was adjusted, but the image is original. I put a schematic picture next to the real one to illustrate the process.
When is a track like this formed?
The middle trace is the one that actually leaves a visible track and is captured by the camera.
There is also a chance of getting a false positive detection just by an accidental coincidence from random background radiation. The chance of this is roughly 1 false detection every 4.3 days assuming normal background with this detector. A GM pulse shortening technique is used to achieve this improved coincidence detection. The calculation can be seen on page 33 here.
The odd fixes on the go
Positioning of the GM tubes
However, we tried out a few other arrangements, too. A picture of one can be seen here below. Here we were looking at traces in a very small region. One GM tube is on the top on the right and another is below the chamber.
The prototype we used for this testing consisted of a hand made circuit in a box, two GM tubes and a Raspberry Pi with a camera. Apart from the circuit the scripts to trigger the camera and the data logging scripts are my work, too.
You can read more about this prototype here.