Cloud Chamber
Cloud Chamber, instrument used to track the paths of charged subatomic particles released by radioactive substances. Physicists learn about a particle’s charge, mass, and energy by observing its path as it moves through a cloud chamber. A cloud chamber is an airtight container, varying in size from a few square centimeters or inches to a room large enough for a person to enter. The container has at least one glass window through which the particle tracks can be observed and photographed. In order to trace the paths of particles, which are invisible to the naked eye, cloud chambers cool a gas saturated with water vapor, methyl alcohol vapor, or ethyl alcohol vapor so the gas becomes supersaturated—so full of vapor that liquid would begin to condense out of the gas under normal conditions. The vapor in the gas will not condense, however, unless there are foreign particles in the gas that the vapor can condense around. As a charged particle passes through the supersaturated gas in the clo...