As I mentioned above, fast particles leave tracks behind them which is in their case ions and electrons. Wilson's expansional cloudchamber works with gases and vapours within the particle advance. In this supercharged pot vapours precipitate to the ions along the particle's lane. The hazedrops getting bigger and bigger and become visible. You can track the particle by photographing these lanes. Other kinds of particle lane detectors work like these kind the only differance between them is the usage of matter in the chamber. Nowadays instead of haze they use liquids under high pressure which makes bubbles along the particle's lane. This is a much more qualified way to detect particles.