cloud chamber

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cloud chamber Instrument used to detect and identify charged particles, invented in the 1880s by C. T. R. Wilson to study atomic radiation. The principle is the same as the bubble chamber, except liquefied gas is replaced by air supersaturated with water or alcohol vapour. This is cooled quickly to create droplets whose tracks form around the ionizing particle. The tracks are deflected by a magnetic field and photographed for analysis. In a diffusion cloud chamber, a large temperature difference is maintained between the top and bottom of the chamber.