Random.

I had an old webcam sitting around and got a cheap smoke detector for a couple of bucks to get the small piece of Americium-241 which is used as the ionizing agent.

The Am-241 is mainly an alpha and gamma emitter with alpha particles easily blocked.
So I used the CMOS sensor of the disassembled webcam to check for decay.
Placing the little piece of Am-241 on the CMOS covers pretty much all the active region of the sensor. The glass protective piece will block the alpha particles but the gammas make it through and are shown as bright flashes in the recording (YouTube). Pretty cool!