Georges Charpak revolutionized particle detection and received the Nobel Prize in Physics in 1992 for inventing and developing particle detectors, in particular the multiwire proportional chamber. He died on 29 September 2010 in Paris.
Georges was born in Dabrovica, Poland, on 8 March 1924, and in 1932 he and his family moved to Paris. During World War II he took part in the French Resistance and was later imprisoned by the Nazis in the Dachau concentration camp in Germany. He obtained French citizenship after the war, and in 1948 he entered CNRS. He studied under Nobel laureate Frédéric Joliot-Curie at the Collège de France in Paris, where he earned his PhD in nuclear physics in 1954. He received the CNRS silver medal for young researchers in 1960.
After Georges went to work at CERN in Geneva in 1959, he switched his scientific interest to high-energy particle physics. In 1961 his group demonstrated that the muon was only a heavy cousin of the electron and not a separate particle of the nucleus. That was the first successful attempt to precisely measure the magnetic-moment anomaly for muons. Very high precision for that value is of great significance in particle physics; a small deviation from the theoretical value could predict the energy scale of new physics. Georges became a CERN employee in 1963.
During his time at CERN, Georges developed the multiwire proportional chamber, a gas-filled box in which a series of thin wires in parallel rows was suspended between two flat cathodes. With the wires linked to a computer through individual amplifiers, it could achieve a counting rate up to a thousand times higher than existing detectors, such as the bubble chamber. It allowed scientists to record up to 1 million particle tracks per second rather than just a few. The device ushered in a revolution in high-energy physics; researchers began using much higher particle collision rates and analyzing theories that predicted new massive particles and rare events. Even today scientists conducting high-energy physics experiments rely on such detectors.
Among the discoveries made by devices based on Georges’s multiwire chamber were the elementary particles known as W and Z, both found at CERN, and the top quark detected at Fermilab in Chicago.
Collaborating with Fabio Sauli, who joined CERN in 1969, Georges worked to further improve the multiwire detector; its descendant, the drift chamber; and, to achieve better counting rates, the multistep avalanche chamber. They worked on the multistep technology with Amos Breskin, Stan Majewski, Vladimir Peskov, and others. Later enhancements have allowed the device to detect UV light. Georges joined Tom Ypsilantis and his team in enhancing the ring imaging Cherenkov detector for elementary particles.
Georges also was interested in using the multistep device to advance the fields of medicine and biology. It has been applied in radiographic imaging of human and animal tissue injected with beta-emitting radionuclides.
In the mid 1980s, Georges began working closely with one of us (Giomataris) in elaborating new detector ideas, including a wide high-energy gamma telescope with good angular resolution. They collaborated with Leon Lederman in 1990 in developing an optical trigger that in real time chooses particles that carry the fifth (bottom) quark during high-intensity proton collisions. Those particles fly a short length before they decay, which amplifies the Cherenkov light produced by relativistic particles inside a thin crystal cell. The trigger “tags” the particles and enhances the collected sample with “good” events.
An international team built a hadron-blind detector based on a 1991 concept by Georges and Giomataris of a gaseous parallel-plate device. Georges and Giomataris proposed that such a detector does not see most of the hadrons produced during collisions, but it efficiently re-creates electrons and high-momentum muons and rejects unwanted events, which highly improves the signal-to-background ratio. They demonstrated it in a particle beam at CERN on 13 October 1992—the day before the Royal Swedish Academy of Sciences announced that Georges had been awarded the Nobel Prize in Physics—and during the optimization process they were able to show experimentally the advantage of a narrow amplification gap.
Their experiments on the hadron-blind detector led Georges and Giomataris in 1996 to conceive of an even narrower amplification gap in the form of the micromegas detector. The micromesh gaseous device was built by Giomataris’s group in the laboratory at the Atomic Energy Commission in Saclay, France. Georges used to predict that like his detector, the micromegas and other such innovative devices would open a new era in physics. During his visits to Giomataris’s lab, he would spend a lot of time using an old oscilloscope to watch the detector signals because he did not like digital devices.
Georges’s house in the Corsican village of Cargèse—his weekend and summer holiday home—was a welcome respite for those attending the Cargèse Institute of Scientific Studies, a summer school for theoretical physics. Georges would attend lectures and invite attendees back to his home, just a few steps from the school.
Because of his beliefs regarding human rights and freedom, in 1978 Georges canceled his participation in a congress in Dubna, Soviet Union, to protest the imprisonment of physicist Yuri Orlov.
Georges was a concerned citizen involved in many social and educational activities. He was passionate about popularizing science, and he wrote several books to make physics accessible to the general public. They include Debunked! (Johns Hopkins University Press, 2004), in which he and Henri Broch poke fun at astrology, other superstitions, and pseudoscience; and Megawatts and Megatons: A Turning Point in the Nuclear Age? (Random House, 2001), in which Georges—a proponent of nuclear power—and Richard Garwin discuss how nuclear energy can be an economically feasible and environmentally responsible energy source and present strategies to achieve arms control. Recently he and François Vannucci published Le vrai roman des particules élémentaires (The True Story of Elementary Particles; Dunod, 2010), which describes the extraordinary development of particle physics and what we know of the standard model today.
In 1996 Georges started a program that trains primary school teachers in bringing hands-on science to students in France. He followed in the footsteps of his friend Lederman, who first began such an initiative in Chicago in 1990.
We will fondly remember this great humanist who was highly enthusiastic, creative, open minded, and thoughtful.
