Fr.: détecteur de Charpak
An elementary particle detector using a special apparatus capable of operating at high rates. The detector consists of an → array of many closely spaced parallel wires, or → anodes, in an enclosure filled with a carefully chosen gas. The wires, being placed between two → cathode plates, are under high voltage. Each wire acts as an independent → proportional counter. The particle that passes through the chamber will ionize surrounding gaseous atoms. The resulting ions and electrons are accelerated by the electric field around the wire, causing a localized cascade of ionization which brings about an electric current proportional to the energy of the detected particle. Previous detectors, such as the → bubble chamber, could record the tracks left by particles on photographic emulsions at the rate of only one or two per second. In comparison, the multiwire chamber records up to one million tracks per second in three dimensions with an accuracy of a tenth of a millimeter and moreover sends the data directly to a computer for analysis. The speed and precision of the multiwire chamber has revolutionized high-energy physics. For instance it was crucial in finding the predicted → W boson and → Z boson of the → electroweak interaction theory. Charpak's chamber also has applications in medicine, biology, and industry. Also called → multiwire proportional chamber.
In honor of Georges Charpak (1924-2010), a French physicist, who built the first detector of this type in 1968. He received the Nobel Prize for physics in 1992; → detector.