Cloud Chamber
A device that reveals the paths of ionising particles as visible trails of condensed vapour.
Unit
Dimensionless
In depth
Ions left along a particle's path act as nuclei for condensation in a supersaturated vapour, making the track visible. Track thickness and curvature in a magnetic field identify the particle, and the device made the first direct images of radioactive decay possible.
Examples in the real world
Short thick alpha tracks alongside long wispy beta tracks; the positron was discovered in a cloud chamber in 1932.