From a shtetl to Paris
Hersz Georges Charpak was born on August 1, 1924, to Jewish parents, Chana (Szapiro) and Maurice Charpak, in the small town of Dąbrowica in eastern Poland, now Dubrovytsia in Ukraine. When he was seven, in 1932, the family moved to Paris. In 1941 he began studying mathematics in the preparatory classes of the Lycée Saint-Louis, one of the city’s most demanding schools. His younger brother, André, later became an actor and film director.
Resistance and Dachau
France fell in 1940, and Jews in occupied Paris faced roundups and deportation. Charpak, still a teenager, joined the Resistance. In 1943 he was arrested and imprisoned by the Vichy authorities, and in 1944 he was deported to the Nazi concentration camp at Dachau. He remained there until the camp was liberated in 1945. According to his CERN colleague Ioannis Giomataris, he survived because the guards did not realise that their political prisoner was Jewish.
After the war he became a naturalised French citizen in 1946. The experience of imprisonment never left him, and it shaped the campaigner for human rights he would become.
Training with Joliot-Curie
Charpak entered the École des Mines in Paris, one of France’s elite engineering schools, in 1945 and graduated as a mining engineer in 1948. He then joined the laboratory of Frédéric Joliot-Curie at the Collège de France, took a research post with France’s national research agency, the CNRS, and in 1954 received his doctorate in nuclear physics for work on very low-energy radiation from the decay of nuclei. Working with a cylindrical counter in 1948, he had already noticed something important about how gas-filled detectors produce their signals, an insight that would later prove key.
In 1959 he joined CERN, the new European laboratory for particle physics in Geneva. His first work there was on the team that in 1961 made a precise measurement of the magnetic properties of the muon, the beginning of a line of experiments that continues to this day.
The wire chamber
In the 1960s particle physicists recorded collisions mainly with bubble chambers, in which charged particles leave trails of bubbles that are photographed. A bubble chamber could take only about one picture a second, and the photographs had to be measured by hand, a slow and laborious process. Physicists hunting for rare events, sometimes one interesting collision in a billion, needed something much faster.
In 1967 and 1968 Charpak found it. His multiwire proportional chamber was a gas-filled box strung with many fine parallel wires a millimetre or two apart, each connected to its own small electronic amplifier. When a charged particle passed through, it knocked electrons out of the gas atoms; these drifted to the nearest wire and set off a tiny avalanche that produced an electrical signal. Contrary to general belief, Charpak realised that each wire would act as an independent detector, giving the particle’s position to about a millimetre. Crucially, he connected the chamber directly to a computer. The result could record up to a million tracks a second, about a thousand times faster than earlier methods.
Charpak and his colleagues, among them Fabio Sauli, soon developed offshoots: the drift chamber, which measures how long electrons take to reach the wire and so locates tracks even more precisely, and later the multistep avalanche chamber. The drift chamber in turn inspired the time projection chamber. Practically every particle physics experiment since has used a track detector descended from his invention. Wire chambers helped discover the charm quark in 1974 and the W and Z bosons at CERN in 1983, and their descendants are still at work at the Large Hadron Collider.
An inventor to the end
Charpak and his collaborators kept refining the idea. They found that the electrical pulses induced on strips of the chamber’s outer electrodes could give a particle’s position in two dimensions at once, and that by finding the centre of the induced charge they could locate a track to better than a tenth of a millimetre along the wires. This kind of read-out has been used by many experiments and is still in use at the Large Hadron Collider. With Tom Ypsilantis’s group he worked on detectors that identify particles by the faint cone of light they emit, and with Leon Lederman, in 1990, on an optical trigger to pick out rare particles containing the bottom quark.
In 1992, just before the Nobel announcement, his team at CERN demonstrated the Hadron Blind Detector, which ignores most of the debris of a proton collision while catching electrons. While optimising it, they saw the advantage of a very narrow gap for amplifying signals, which led to a new detector, Micromegas, developed by Ioannis Giomataris’s group at Saclay from 1995. Charpak believed this family of micro-pattern gas detectors would transform nuclear and particle physics as his wire chamber had, and Micromegas detectors are now used in many experiments.
Lower doses of X-rays
Charpak always looked for ways to put his detectors to work in medicine and biology. Because a gas detector can register individual X-ray photons efficiently, it can form a good image from far less radiation than photographic film needs. In 1989 he founded a company, Biospace Instruments, to develop his detectors for biomedical uses, including a high-pressure xenon wire chamber for low-dose radiography.
Working with the paediatric orthopaedic surgeon Jean Dubousset and a team of physicists, engineers and radiologists, he helped develop the EOS imaging system, operational from 2003. EOS scans a standing patient from head to toe, from the front and side at the same time. In a study of children with scoliosis, who need repeated spine X-rays as they grow, the French National Academy of Medicine reported that it cut the radiation dose of a standard two-dimensional image by eight to ten times compared with conventional radiography, and allowed three-dimensional reconstructions of the skeleton at doses hundreds of times lower than a CT scan. The system was brought to market by the company that grew out of Biospace, later renamed EOS imaging, so that children and adults needing repeated skeletal X-rays could receive far less radiation.
Hands in the dough
In the mid-1990s Charpak discovered that only about 3 per cent of French primary schools taught science at all. With his fellow academicians Pierre Léna and Yves Quéré, and with the support of the French Academy of Sciences and the Ministry of Education, he organised a study trip to Chicago to see the hands-on science programme for city schools started by his friend, the physicist Leon Lederman. In 1996 they launched La main à la pâte, literally “hands in the dough”, which helps primary teachers teach science through experiment, observation and questioning.
It began with 350 classes and grew to more than a thousand within a year. In 2000 the French government adopted a plan to bring this style of teaching to all schoolchildren, and two years later it was written into the national primary curriculum. The programme, a foundation since 2011, has networks of pilot centres, many in disadvantaged areas, and its approach has spread to many other countries working with partners such as UNESCO, the OECD and the InterAcademy Partnership.
Charpak remained a familiar figure at UNESCO’s scientific conferences, most recently at the launch of the International Year of Physics in 2005.
A humanist and campaigner
The former political prisoner became a tireless defender of persecuted scientists. In 1980 he was a founding member of the Yuri Orlov Committee, formed by physicists at CERN to campaign for the imprisoned Soviet physicist and human rights activist; it soon took up the cases of Anatoly Shcharansky, Andrei Sakharov and others jailed for their beliefs. In 1972 he had launched, with Daniele Amati, a petition against the Vietnam War. With the American physicist Richard Garwin he wrote Megawatts and Megatons, which argued for nuclear energy and for strict arms control to stop the spread of nuclear weapons, and with Henri Broch he wrote a popular book debunking pseudoscience and astrology.
Charpak never wrote much about religion. His Jewish identity was bound up with the experiences of his life: a childhood in an eastern European Jewish town, the persecution of the occupation, survival in Dachau by hiding who he was, and a lifelong commitment to the rights of others.
Family, friends and last years
He married Dominique Vidal in 1953, and they had three children, among them the paediatrician Nathalie Charpak. He loved music and classic songs, invited musicians to his Paris home, and spent summers at his house in Cargèse, Corsica, where he welcomed physicists from the nearby summer school to talk over wine. He retired from CERN in 1991 but kept working, at the École supérieure de physique et de chimie industrielles in Paris, where he had held the Joliot-Curie chair since 1984, and with Giomataris’s group at Saclay on new detectors such as Micromegas.
He was elected to the French Academy of Sciences in 1985 and received the Nobel Prize in Physics in 1992 for his invention and development of particle detectors. He was active to the end, still planning a new radon detector the day before he died. He died in Paris on September 29, 2010, aged 86. UNESCO’s director-general called him a visionary and a staunch supporter of its values.
Sources & further reading
Georges Charpak, Biographical (CV), NobelPrize.org · Press release: The Nobel Prize in Physics 1992, NobelPrize.org · Georges Charpak 1924–2010 (tribute by Ioannis Giomataris), CERN Courier · Une nouvelle imagerie ostéo-articulaire basse dose en position debout: le système EOS, Académie nationale de médecine · History of the Fondation La main à la pâte · UNESCO chief pays tribute to Nobel physics laureate Georges Charpak, UN News · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.