Charpak, Georges (1924-2010), a Polish-born French physicist, won the 1992 Nobel Prize in physics for the invention of a device that detects subatomic particles, units of matter smaller than an atom, in particle accelerators, devices that hurl such particles together at extremely high energies. He revolutionized the study of subatomic particles with the multiwire chamber, a detector capable of recording millions of subatomic events per second and feeding precise data straight to computers without the need for human intervention. See Particle accelerator ; Subatomic particle .
The flood of data made possible by the multiwire chamber contributed to important discoveries in particle physics, including the discovery of several new elementary particles. Multiwire chambers are also applied in medical imaging. In computed tomography (CT), X rays are passed through a patient’s body from all directions to build up a three-dimensional image of the internal organs. If multiwire chambers are used to record the X rays, better images can be obtained while exposing the patient to less radiation. See Computed tomography .
Charpak was born on Aug. 1, 1924, in Dabrovica, Poland. He moved with his family to Paris when he was 7 years old. During World War II (1939-1945), he studied at the School of Mines in Paris but, because he worked with the French Resistance, he was taken prisoner in 1943. He was sent to the concentration camp at Dachau in Germany and remained there until the liberation of the camp in 1945 (see Dachau ).
Charpak became a French citizen in 1946. He studied physics in Paris, taking his Ph.D. in 1955. In 1959, he joined CERN, the European Organization for Nuclear Research, near Geneva, Switzerland. At CERN, huge particle-accelerating machines smash streams of subatomic particles into each other—or into atoms in stationary targets. Scientists study the debris flung out of the collisions, including newly created, short-lived particles.
In the early days of CERN, the tracks of particles were made visible in a device called a bubble chamber, in the form of lines of bubbles in liquid hydrogen (see Bubble chamber ). In other devices, the tracks were marked out by electric sparks jumping between electrically charged plates in a stack of such plates, as the particles passed through the stack. There were delays while the detector was reset between one observation and the next, and still more delays scientists analyzed photographs of the tracks. Computers helped with the job of recognizing patterns in the tracks, but the work was still slow.
Charpak made many innovations in detector technology, of which the most important was the invention of the multiwire chamber. Wires kept at a high voltage are mounted in a detection chamber containing pressurized xenon and carbon dioxide. When a burst of particles or high-energy radiation passes through the chamber, the burst creates trails of ions along its path—atoms of the gas that have had electrons knocked off them. The liberated electrons and electrically charged ions are dragged to the wires by the high voltage, causing an avalanche of further ions and electrons as they do so. All these charged particles are drawn into the wires, forming a burst of electric current whose location is precisely known. The signals pass straight to high-speed computers, which can analyze them. The chamber can make many thousands of observations per second, showing millions of tracks, whereas the bubble chamber could show only a few tracks per second. The multiwire chamber and the developments it made possible are now at the heart of major elementary-particle investigations. Charpak died on Sept. 29, 2010.
