Cloud chamber

A particle detector in which charged particles leave visible trails of droplets in supersaturated vapor. Its tracks reveal particle paths and interactions.

Supersaturation: A condition in which vapor pressure exceeds the equilibrium pressure for condensation at a given temperature. Cooling creates the supersaturated vapor in which particle tracks become visible.
Charles Thomson Rees Wilson: A Scottish physicist who invented the cloud chamber and shared the 1927 Nobel Prize in Physics. Wilson developed the chamber while studying how clouds form around ions.
Cosmic ray: A high-energy particle, usually a proton or atomic nucleus, arriving at Earth from space. Cloud chambers captured tracks from cosmic rays and their atmospheric secondary particles.
Bubble chamber: A detector in which charged particles form visible trails of bubbles in a superheated liquid. It records tracks through liquid bubbles rather than droplets in supersaturated vapor.
Ionization: The process by which an atom or molecule gains or loses electrons, producing charged particles. A passing particle ionizes vapor molecules, providing sites for droplet formation.
Cloud formation: The process by which water vapor condenses into droplets or ice crystals in the atmosphere. Wilson adapted laboratory studies of cloud formation into a detector for ionizing particles.
Discovery of the positron: The 1932 identification of the positron by Carl Anderson using cosmic-ray track evidence. Anderson used a curved track and its direction through a lead plate to identify positive electrons.
Spark chamber: A particle detector that reveals ionization paths through sparks between electrically charged plates. It produces tracks electronically, avoiding the chamber’s vapor preparation and photographic recording.
Wilson cloud chamber: A cloud chamber that expands moist air to produce supersaturated vapor. This classic design uses rapid expansion to create the sensitive vapor layer.
Nobel Prize in Physics 1927: The 1927 physics Nobel Prize, awarded to Arthur Compton and Charles Wilson for distinct contributions. Wilson’s prize recognized his method for making particle paths visible.

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