Have you ever seen a Wilson cloud chamber — a science experiment that lets you visualize ionizing radiation? How hard would it be to build one? If you follow [stoppi’s] example, not hard at all (German, Google Translate link). A plastic bottle. some tape, a flashlight, some water, hot glue, and — the only exotic part — a bit of americium 241. You can see the design in the video below and the page also has some more sophisticated designs including one that uses a CPU cooler. Even if you don’t speak German, the video will be very helpful.
You need to temper your expectations if you build the simple version, but it appears to work. The plastic bottle is a must because you have to squeeze it to get a pressure change in the vessel.
If you are wondering where to get americium-241, check out a junked smoke detector. The second video, below, has details about how to harvest it from that common source. You need something that fits in the bottle cap.
It is hard to see on the video, but different types of ionizing radiation leave telltale tracks in the chamber. Alpha particles tend to leave thick straight tracks whereas beta particles tend to be more delicate and curvy. Although in modern times these are more or less science curiosities, there was a time they were real lab equipment and they participated in the discovery of the positron, the muon, and the kaon.