How are particles detected in a cloud chamber?

Particles are detected in a cloud chamber by leaving a visible trail as they ionize the gas molecules.

A cloud chamber is a device used to detect and track charged particles, such as electrons and alpha particles. The chamber contains a supersaturated vapour of a liquid, such as alcohol or water. When a charged particle passes through the chamber, it ionizes the gas molecules along its path. This ionization causes the gas molecules to condense into tiny droplets, forming a visible trail that can be photographed or observed directly.

The cloud chamber is typically placed in a magnetic field, which causes charged particles to follow a curved path. By measuring the curvature of the particle's path, it is possible to determine its charge and momentum. The chamber can also be used to identify different types of particles based on their characteristic patterns of ionization and curvature.

Cloud chambers were first developed in the early 20th century and were instrumental in the discovery of many subatomic particles, including the positron and the muon. While newer detection methods, such as particle accelerators, have largely replaced cloud chambers in modern physics research, they remain a useful tool for teaching and outreach activities.