particle detector

One of a number of instruments designed to detect subatomic particles and track their paths; they include the cloud chamber, bubble chamber, spark chamber, and multiwire chamber.

The earliest particle detector to reveal the paths of particles was the cloud chamber, which contains a super-saturated vapour in which particles leave a trail of droplets, in much the same way that a jet aircraft leaves a trail of vapour in the sky. A bubble chamber contains a superheated liquid, such as liquid hydrogen, in which a particle leaves a trail of bubbles. A spark chamber contains a series of closely-packed parallel metal plates, each at a high voltage. As particles pass through the chamber, they leave a visible spark between the plates. A modern multiwire chamber consists of an array of fine, closely-packed wires, each at a high voltage. As a particle passes through the chamber, it produces an electrical signal in the wires. A computer analyses the signal and reconstructs the path of the particles. Multiwire detectors can be used to detect X-rays and gamma rays, and are used as detectors in positron emission tomography (PET).