It is an instrument used for the detection and identification of the path of subatomic particles.
In Wilson Cloud Chamber, paths of subatomic particles or ionized particles can be photographed.
When a particle is passed through the supersaturated vapours, droplets are formed on the line due
to ionization along the track and particle is detected.
It is consist of a closed cylinderical chamber with the transparent glass top,a movable piston at the bottom. On the sides near the top, the cylinder is provided with a glass window. inside the cylinder
a liquid of low boiling point is placed. The piston can be moved up or down. The whole system is air tight.A strong light source isused to illuminate the chamber while the photograph is taken by the
camera as shown.
Some volatile liquid having low boiling point (methanol CH3OH or ethanol C2H5OH) is poured on the inner surface of the chamber. The piston first is moved slowly up so that the air inside the chamber is cleaned and then it is then moved down, so that the internal pressure is dropped and the air get vapours of the liquid and becomes supersaturated and a fog is observed in the chamber.
At the right moment particles are allowed to enter into the chamber and a powerful and intense beam of light is used to illuminate the track of the particles
and photos are taken by the sensitive camera.
If a strong electric or magnetic field is applied to the particles (charged) then their path is altered.
By the study of path`s length, thickness, continuity or discontuinity and the influence of magnetic
field (curve) .i.e. geometry the e/m ratio can be calculated and hence the particle is detected.