A cloud chamber is a device that can be used to detect the passage of charged particles that result when a radioactive atom decays. The air within the cloud chamber is saturated with alcohol vapor and chilled with dry ice. When a charged particle passes through the chamber, it ionizes the air along its path. The ionized air allows the alcohol vapor to condense, forming clouds that trace the path the particle took.
Would you like to make your own? This video will show you how!