By Sunil Bhardwaj

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Principle: When the particles obtained from ion pairs passes through super saturated water vapour, droplets of water tend to condense along the path of its motion. (Or). If air saturated with water vapour is suddenly allowed to expand then the vapours condenses on particles in the form of fine liquid droplets which can be photographed with dark background.

Construction: It is consist of a vessel, fitted with piston. The Piston encloses dust free air saturated with water vapour. One camera is placed at the appropriate distance to photograph the series of droplets using strong illumination with dark background.

Working: The ionising radiations are allowed to enter the chamber through a window and simultaneously the air in the chamber is suddenly cooled by a adiabatic expansion. The ions produced by the radiations, act as condensation nuclei and fine droplets of water are formed. Cameras placed at the appropriate place photograph the series of droplets using a strong illumination and with dark background. The paths of ionising particles thus photographed are generally called cloud tracks. With the help of Wilson Cloud Chamber we can find out the path in which the ions will travel when, die beX radiations are passed through gas.