The cloud chamber was invented in 1896 by Charles T.R. Wilson at the Cavendish Laboratory, University of Cambridge, England. He discovered that charged particles travelling through this device would leave "thin, wispy trails".
The modern diffusion cloud chamber uses dry ice and provides for longer viewing than the temporary low pressure invention of Wilson.
When a subatomic particle enters the chamber, they collide with air or alcohol vapor molecules, producing free ions. Vapor in the chamber condenses around these free ions, forming droplets. The droplets are what form the trail. Different types of particles will leave different trails. Alpha particles, which are relatively heavy, will produce straight dense trails. Beta particles are light and leave wispy, irregular trails. When there is no radiation source, cosmic rays may enter the chamber, producing thin misty trails.
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