Wilson cloud chamber

Scottish physicist Charles Thomson Rees Wilson developed the cloud chamber after studying cloud formation and condensation. In 1911 he constructed a chamber in which traces left by ionising radiation and particles could be made visible and photographed. The Nobel Committee awarded Wilson half of the 1927 Nobel Prize in Physics for his method of making the paths of electrically charged particles visible through vapour condensation. The instrument is also called a Wilson chamber.

A cloud chamber creates a vapour that is close to condensation. When a charged particle moves through the gas, it ionises molecules along its path. In the supersaturated vapour, droplets form preferentially around these ions, outlining the particle's trajectory. The resulting tracks can be photographed and examined. Track appearance depends on the particle and the detector conditions; interpreting it requires care and is not, by itself, a complete identification of every particle.

Cloud chambers made otherwise invisible paths of subatomic particles observable and became a foundational instrument in experimental particle physics. CERN notes that the detector was used in the discoveries of the positron and the muon. Today, cloud chambers are primarily educational demonstrations; modern particle experiments use more advanced detector technologies, although the general idea of registering particle interactions remains central to particle detection.