Georges Charpak Nobel Physics Prize 1992
Georges Charpak at CERN just after hearing the Nobel news.
Wednesday 14 October looked like being a day like any other for detec tor specialist Georges Charpak. Ex cept he had an unwelcome appoint ment with the dentist early that afternoon. Late that morning he was able to telephone to cancel the ap pointment. 1 have a small problem...', he explained. The problem was the announce ment that Georges Charpak receives 1992's most prestigious award for physics - 'for his invention and devel opment of particle detectors, in par ticular the multiwire proportional chamber - a breakthrough in the technique for exploring the innermost parts of matter', reads the citation from the Royal Swedish Academy of Sciences. A means of making the invisible be come visible, Charpak's Nobel-win addition to a periodic Nobel physics particles. At CERN, he initially ning contribution has an immediate theme of improved 'position sensitive worked on the first precision meas appeal to the man in the street, who detectors' - measurement tech urements of the anomalous magnetic is often left in the dark about the sig niques for telling physicists where moment of the muon (g-2), an experi nificance of other major science particles have passed. In 1927 the ment which turned out to be a train awards, not that these are any less award went to C.T.R. Wilson for his ing ground for some of the most important for the development of their invention of the cloud chamber; in gifted post-war European physicists. subject. 1948 Patrick Blackett received the After g-2 he returned to his major Physics is all about observation, coveted prize for his further develop preoccupation - particle detectors. and improved measuring techniques ment and discoveries with cloud Any particle physics detection have always been at the forefront of chambers; in 1950, Cecil Powell's scheme uses ionization - the atomic new directions in science. Just as de prize was in recognition of his work havoc of charged particles left in the velopment of the microscope and the with photographic emulsions and its wake of a subatomic projectile. In telescope did in the seventeenth cen physics outcome; in 1960 came 1968 Charpak was looking for ways tury, so the new methods of the 20th Donald Glaser, for the bubble cham of localizing spark signals without century have lifted scientists' hori ber, while Luis Alvarez was recog having to take photographs. To zons. nized in 1968 for his further develop achieve this he realized he had to un Since its invention in 1968, ment of this technique. derstand the details of what happens Charpak's multiwire proportional Georges Charpak has always been when a gas is ionized between two chamber and his subsequent devel concerned about seeing things that high voltage electrodes, to chart the opments heralded the age of fully are visually obscure but nevertheless different ways that electron chain re electronic particle detection. They important. Before joining CERN in actions caused signals to grow into revolutionized detection techniques 1959, at the Joliot-Curie Laboratory sparks, the role of photons, and the and have become the principal tools in Paris he had an introduction to effect of localized high electric field of the particle physicist's trade, ena particle detectors ('most of them gradients on the drift of electrons and bling them to handle high reaction didn't work', he later admitted) and ions and on the way the signal is rates and to preselect special types pioneered new techniques in the then formed. When his work was done, of interaction. traditional method of photographing not only did he understand better Charpak's Nobel is also the latest the sparks left in the wake of charged what happened between high voltage
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CT 06263,2ùâ /m 'Jtsub, i-ax: uii:i-//-4-iu/:i MESBER oriesheim 124 Ciidw mJvMilinHtnmil imtulmr nn murimr Kinrvlço fa/777 O UN Courier, December 1992 The first large multiwire proportional chamber built at CERN. Left to right, Georges Charpak, Fabio Sauli and Jean-Claude Santiard. (Photo CERNX8.8.70) zation in the MWPC - a set of wires of strips in the cathode plane would pick up this induction, providing a powerful means of localizing ioniza tion away from an anode direction. This two-dimensional localization al lowed detection of X-rays and opened up MWPC applications in medicine anc} biology. By adding suitable additional ingre dients to the gas in the chamber, secondary by-products are quickly absorbed so that one avalanche does not trigger another and the ini tial ionization is quickly confined. The technique can be extended to cover large areas, with each wire read out into appropriate electronics. For the first time, high volumes of data be came available on line. A further Charpak development, the 'drift chamber', measures the time it takes for the electrons to get to the electrodes, but the spinoff was virtu impractical to build large detecting anode. This time then gives a fix on ally immediate. surfaces of such modules, and the where the initial ionization took place, Fortunately, a high energy charged irregular time response (up to a mi and requires less closely spaced de particle passing through matter is the crosecond), makes precision meas tection and readout channels. proverbial bull in a china shop, scat urements difficult. Describing those early days, tering and breaking whatever atomic Charpak's brilliant idea was to use a Charpak says his first attempts at material is in its path. However this plane of anode wires a few millime building proportional tube were so trail of subatomic destruction needs tres apart stretched between two clumsy that when the time came to some method of amplification to cathode planes. This improved ge prototype the MWPC, his team took make it visible, when and where it ometry and higher field of the such care that it worked first time! happens. multiwire proportional chamber Charpak also pays tribute to the fa Some techniques already existed - (MWPC) make the ionization elec cilities at CERN and the team spirit. ion chambers; proportional tubes; trons move faster and more uni 'If you ask someone to do something and the famous Geiger counter - but formly, so that the time resolution im difficult, you're sure to get good re they all had limitations. The classic proves to, say, 25 nanoseconds. sponse,' he says. An ideas man, he proportional tube uses a thin anode At first it was feared that the large stands aside and lets others get on wire along the axis of a cylindrical mutual capacitance between neigh with mass-production and nitty-gritty cathode filled with a suitable gas. As bouring wires would spread the sig applications problems, again an area a charged particle passes through, nal throughout the mesh, frustrating where CERN excels. liberated electrons are pulled towards any attempt to localize tracks. How In more recent years his interest the wire anode, producing more elec ever Nature lent a hand in the form of has turned to applications of physics trons in their wake. An electron 'ava an opposite and almost equal signal instrumentation in other areas, par lanche' is formed. induced by positive ions in the ava ticularly biology and medicine. Here The resultant signal shows that a lanche in all wires but the one directly the improved accuracy and response charged particle has passed through, concerned. Understanding this help of modern electronic detectors prom but with a tube of radius one centi ful signal, Charpak realized it could ise faster scanning and lower radia metre, no real precision is given. It is be exploited to greatly improve locali tion doses. CERN Courier, December 1992 3 Eight year series - three physics Nobels enjoy the CERN Charpak party entertainment. Left to right CERN Director General Carlo Rubbia (1984), Sam Ting (1976) and Georges Charpak (1992). (Photo CERN H184.10.92) Using a wire chamber viewed by an image-intensified CCD camera, a CERN/Geneva Cantonal Hospital team obtained a radiograph of a rat kidney a hundred times faster than conventional methods. This rat kid ney changed my life,' says Charpak. For the future, the quest for 'Dark Matter' - the missing material that makes up most of the Universe - will continue to challenge detector build ers. The detector research and de velopment work being done for the LHC will also provide valuable spinoffs,' claims Charpak. 'When people ask "what use is this work", these are the things to point to'. Charpak admits to having been sur prised by the Nobel news. 'But CERN wasn't surprised,' retorted CERN Di rector General Carlo Rubbia. 'It un derlines that physics instrumentation is just as important as accelerators. position in the forefront of particle has worked with three skilled and The prize is also a great honour for physics.' dedicated specialists - Roger CERN, and underlines its preeminent Born in Poland in 1924, Georges Bouclier, Gilbert Million and Jean- Charpak was educated in France, the Claude Santiard - for practically the country whose nationality he now whole of his CERN career. At CERN, holds. After an introduction to re he was soon joined by Fabio Sauli, This wire chamber radiograph of a rat kidney was obtained about a hundred times faster search at the Collège de France, who has continually shared in a long than using conventional means. 'This rat Paris, he joined CERN in 1959. He series of new developments, and kidney was a turning point in my life, ' says passed a formal 65th birthday career who now formally heads the unit at Georges Charpak. milestone in 1989, but is still very ac CERN. At Charpak's 65th birthday tive with his driving ambition to apply celebrations at CERN, Sauli declared frontier detection ideas. that the name 'Charpak Group' will While ideas in physics are quickly continue to be used. incorporated into ongoing research, Another aspect of Charpak's per convincing the medical community of sonality is his continual concern for the value of new techniques needs a less privileged colleagues. He was a special effort, he says. Charpak has driving force in the late 70s and early made a considerable personal invest 80s in the action by physicists that ment in this research and develop eventually led to the release of Yuri ment work, to the extent of making Orlov and Andrei Sakharov. personal sacrifices. 'Now I can buy With his fame previously restricted some new shoes,' he joked after to physics circles, Charpak became a hearing the Nobel news. celebrity overnight after the Nobel Charpak is popular and widely ad announcement. With last year's mired at CERN. On hearing the physics prize won by Frenchman Nobel news on the car radio, a Pierre-Gilles de Gennes, the news CERN acquaintance was moved to had special impact in France. tears. Charpak inspires loyalty - he Charpak's numerous contributions 4 CERN Courier, December 1992 CH BIS 1NHÏ A new member of the VIC family of connections: The TVIC 7214: THE Turbo Channel to VICbus Interface The TVIC 7214 is the latest companion of the workstations to VICbus family interfaces. 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A cast of the central 'Palenque' with short tion. nearly 500 scientists from all CERN's speeches by the CERN Director 18 Member States brought Cinderella General, Commissioner Cassinello, Science out of its dusty laboratory and Spain's Sepretary of State for seclusion, dressed it up, and took it Universities and Research Elias to the ball. Fereres. CERN's permanent exhibition in Then came the awards for "The Expo 92's Pavilion of the Universe, Young Scientist of the Future", a spe including a 27 metre long section of cially-arranged pan-European com LEP 'tunnel', had already attracted petition. (The winners were: Austria - one and a half million people, but for Christoph Simon; Belgium - Stefan the CERN Day a carnival had been Rummens; Czech and Slovak Fed planned months in advance. With eral Republic - Jiri Vanicek; Den 'discovery' the central theme of Expo mark- Morten B. Pedersen; Finland 92, the special CERN event stressed - Ville Voipio; France - Frederick how scientists are the explorers of Jeske; Germany - Robert our age, having embarked on*the Nitzschmann; Greece- Marcallos greatest voyage of all - back to the Rallidis; Italy - Alberto De Fanis; creation of the Universe. Netherlands- Martijn Leisink; Norway The event began conventionally - Joakim Bergli; Poland - Barbara enough with the official greeting of Smalska; Portugal - Orlando the CERN delegation, led by Director Moreira; Spain - Ana Colorado- CERN Director General Carlo Rubbia enjoys the action at 'CERN Day', the culmination on 30 September of CERN's involvement in the Expo 92 World Fair fiesta in Seville. 6 CERN Courier, December 1992