Wilson cloud chamber
Wilson cloud chamber, instrument that makes radiation visible and measurable. This device is made out of a container, a piston, and water-concentrated gas. It works on the same principle as natural cloud formation—that is, when more than 100% humidity occurs and water cools, water droplets become apparent either in the form of a cloud in the sky or, in the case of the Wilson cloud chamber, as tracks of charged particles. Particles with an electric charge within the chamber join with molecules of the cooled gas to form the visible tracks. Alpha and beta rays emitted from radioactive materials form these visible streaks.
See also: Radiation.