A Nice Open-Source Design!

I've built photodiode-based particle detectors before. So when I saw this nice-looking, open-source design from Oliver Keller at CERN, I thought it would be fun to make a few.

The detector is based around either the BPW34F photodiode (mostly for electrons / gamma rays), or a "metal-can" photodiode with the glass window removed (for alpha particles that are easily obstructed).

The BPW34 diode is cheap, and a few of them together can be used as a radiation detector.

Boards

The boards were really nice. Small, but not cramped! I sent them off without changes to my local PCB manufacturer, and a couple weeks later, 5 units arrived. I had spare op-amps from a previous particle detector (OPA2132), so I used those, as well as the TLE2072 used in the original. Both worked fine.

The board was easy to assemble, even though the components were through-hole.

This one uses the TLE2072 and 4x BPW34, and mainly detects electrons / muons.

Metal Case and First Light

I added the board to a milled aluminium enclosure I had picked up in Akihabara while traveling. The size was perfect, I just used a drill press to make holes in the front for bolts to hold the board securely in place.

I also drilled a wider hole for the BNC connector, which lets me conveniently connect the detector directly to my oscilloscope.

Finally, I cut a window in the enclosure to more easily let particles pass. The window material is kapton, clad with a very thin layer of copper to minimize electrical interference. It's held in place with a little bit of black electrical tape.

Perfect fit, very solid. The radiation window is under the black tape.

The detector worked almost immediately. Leaving it on my desk for a short time, I was able to detect a stray particle, probably either an electron or muon.

This is my old handheld oscilloscope. It's served me well for ages. You'll have to pardon the damaged screen.

Concluding Remarks

The particle detector worked very well. I also built the alpha detector version, and included a weak alpha particle source inside the detector to hopefully detect lots of events. However, it only detected a few -- my alpha source is very weak. Unfortunately and also fortunately, I don't have any stronger radiation sources to check with.

Did you know that bananas emit antimatter though? Bananantimatter, if you will. The potassium in bananas contains an unstable isotope, that very rarely undergoes a decay mode that emits a positron. Sadly, the average banana emits far too little antimatter for me to detect. In fact, placing a bag of KCl on top of the detector will likely result in only a moderate increase in detection events. Still, this was fun to build and some simple experiments are possible with it.

I was hoping to use this detector as the basis for a random number generator, and it would work, but for all radioactive sources I have access to, would be very slow. To make it fast would require a moderately unsafe source, so I won't do that. Instead I use avalanche noise for high-speed random number generation.