How are particles identified in a bubble chamber?

Particles are identified in a bubble chamber by their tracks left in the chamber's liquid.

A bubble chamber is a device used to detect and identify subatomic particles. It consists of a container filled with a superheated liquid, such as liquid hydrogen or helium. When a charged particle passes through the liquid, it ionizes the atoms and molecules in its path, causing them to lose energy and form a trail of bubbles.

The path of the particle can be traced by photographing the bubbles as they form and expand. By analysing the shape, size and curvature of the bubbles, scientists can determine the charge, mass and momentum of the particle that caused them.

Different particles leave different types of tracks in the bubble chamber. For example, an electron will leave a thin, straight track, while a proton will leave a thicker, more curved track. By comparing the tracks left by different particles, scientists can identify the type of particle that caused them.

Bubble chambers were widely used in particle physics experiments until the 1980s, when they were largely replaced by more advanced detectors such as the multiwire proportional chamber and the silicon strip detector. However, they remain an important tool for teaching and outreach, and are still used in some experiments today.