How does a cloud chamber detect subatomic particles?

A cloud chamber detects subatomic particles by tracking their path through a supersaturated vapour.

A cloud chamber is a device used to detect subatomic particles by observing their tracks as they move through a supersaturated vapour. The chamber consists of a sealed container filled with a gas, such as air or hydrogen, that is cooled to a temperature below its dew point. This creates a supersaturated vapour, which means that there is more water vapour in the gas than it can hold at that temperature and pressure.

When a charged particle, such as an electron or a proton, enters the chamber, it ionizes the gas molecules along its path. This creates a trail of ions, which act as nuclei for the supersaturated vapour to condense around. As the vapour condenses, it forms a visible track that can be photographed or observed under a microscope.

The shape and curvature of the track can provide information about the particle's charge, mass, and energy. For example, a positively charged particle will curve in one direction, while a negatively charged particle will curve in the opposite direction. The radius of curvature depends on the particle's momentum, which is related to its mass and velocity.

Cloud chambers have been used for over a century to study subatomic particles, and they continue to be an important tool in modern physics research. They are relatively simple and inexpensive to build, and they can detect a wide range of particles, from cosmic rays to particles produced in particle accelerators.