Clifford Charles Butler 1922-1999

Clifford Charles Butler, who was the co-discoverer with George Rochester in 1946-1947 of "V-particles", died on 30 June. Their discovery can be seen as the first step towards the understanding of the quark nature of matter.

Butler spent the war years at the University of Reading. His first research contributions were in electron diffraction, but by 1947, Rochester and Butler had become members of Patrick Blackett's group at Manchester. Under Blackett's guidance they used a cloud chamber with a magnetic field to study the products of the interactions of high-energy cosmic rays in a block of lead. On 15 October 1946 they found an unusual forked track looking like an inverted "V". This was subsequently interpreted as the decay of a neutral particle (now known as a K-meson), which had to be extremely long-lived on the nuclear timescale. In May 1947 they found a second such long-lived particle. This time it was electrically charged.

To increase the cosmic-ray exposure, the Manchester magnet and chamber were transported to the Pic du Midi in the French Pyrenees, and it became clear that the "V-particles" fell into two separate classes, now known as hyperons and K-mesons.

Their long life was only explained in 1952 by Pais, who suggested that the particles were created in pairs. They could be created in fast nuclear reactions, but once separated from their partner they were no longer able to interact rapidly. Gell-Mann and Nishijima clarified this picture by identifying a new quantum number, called "strangeness".

In 1953, Butler moved with Blackett to Imperial College in London, where Butler became a full professor in 1957, heading the High-Energy Nuclear Physics group. He quickly recognized the importance of Glaser's 1952 invention of the bubble chamber, and the first West European hydrogen bubble chamber was built by his group. This led to the 1.5 m UK National Hydrogen Bubble Chamber, used at the Rutherford Laboratory and at CERN. In 1964, Butler succeeded Bernard Gregory as chairman of CERN's Track Chamber Experiments Committee.

Becoming deeply involved in science administration, Butler then became head of the Imperial College Physics Department, which was one of the largest multigroup research departments in Europe, while still leading the High Energy Nuclear Physics group. Between 1966 and 1969 he also served as dean of the Royal College of Science. Butler was a good, kind man who cared about the best interests of his staff, and he led a department that was proud of the standards and achievements in both its teaching and its research.

Butler left Imperial College to become director of the Nuffield Foundation from 1970 to 1975, and from 1975 to 1985 he served as vice-chancellor of Loughborough University of Technology. He never lost his interest in physics, playing vital roles in IUPAP ­ secretary-general (1963-1972), vice-president (1972-1975) and president (1975-1978). IUPAP generally, and Butler in particular, helped to maintain relations between physicists on both sides of the Iron Curtain during the depths of the Cold War.
Ian Butterworth

Efim Fradkin 1924-1999

After 50 years of creative activity at the forefront of theoretical physics, Efim Fradkin died in Moscow on 25 May. His research extended from pioneering the functional method in quantum field theory and discovering, simultaneously with Schwinger, its Euclidean formulation, to basic work in string theory.

He was born in a Jewish neighbourhood near Minsk. At 16 he the university there for a year. The famous mathematician I M Gel'fand, who occasionally lectured there, recognized Fradkin's outstanding abilities and, to support him, gave him 100 roubles. However, the war intervened and Fradkin's family were killed. He joined the army and was wounded in the Battle of Stalingrad.

Fradkin appeared in Moscow in 1948 and was adopted by I E Tamm and V L Ginzburg at the Theoretical Department of the Lebedev Physics Institute, which became his home for the remaining 50 years of his scientific life.

"In the theatre of operations known as theoretical physics, Efim's attacks have been launched along the whole front," wrote Bryce DeWitt in Fradkin's festschrift. Fradkin pioneered conformal field theory and contributed to the theory of turbulent mixing. He developed the Batalin­Fradkin­Vilkovisky method for quantizing general constrained systems, found new ways to solve spin lattice models, tackled the problem of grand unification via exceptional groups and studied transfer processes in plasma.

Fradkin introduced the method of Green's functions in relativistic statistics and discovered, alongside Landau and Pomeranchuk, the zero-charge behaviour of QED (better known in the West as the Landau pole). He discovered open algebras and invented the first example of gauge supergravity. His relativistic eikonal approximation and the Efimov­Fradkin non-perturbative calculus gave birth to whole new trends of research.

Fradkin was awarded the Stalin state prize in 1953, the I E Tamm prize in 1980 and the Dirac medal in 1989 and was the first recipient of the Sakharov medal in 1996. He was a foreign member of Accademia Pontaniana in Naples and a full member of the Academy of Sciences of Russia. He was a member of CERN's Theory Division, as guest professor of the director-general,in 1996/7.

Fradkin acted as a magnet for young theorists. When his coffin was exposed at the Lebedev Institute, two generations of disciples kept guard. For them ­ and for the whole community of theoretical physics­his passing was a tremendous loss.

Peter Kalmus of London's Queen Mary and Westfield College recently toured the UK for the Institute of Physics Schools and Colleges lecture "Particles and the universe". The lecture was given in about 40 venues to a total audience of nearly 10 000 school students. The realization that the great diversity of the universe stems from a limited number of elementary particles interacting through a few fundamental forces is one of the major achievements of 20th-century physics. (M Kalmus.)

Werner Ruckstuhl 1952-1999

The sudden death of our colleague Werner Ruckstuhl has deeply shocked our scientific community, particularly at NIKHEF, where he worked for the last 10 years.

Werner, Swiss born and ETH-Zürich educated, did his PhD on muonic atoms, for which he was awarded the ETH medal. Via Caltech, where he studied lepton universality at the PEP ring at SLAC, and Geneva University as a member of the L3 team at CERN's LEP, he first came to NIKHEF in 1990 to set up the physics analysis for the Dutch DELPHI group at LEP. His interests soon returned to B-physics ­ having pushed for a B-factory at the Swiss PSI lab. Via the GAJET proposal he led NIKHEF into the LHCb experiment at CERN's LHC collider and became the Dutch team leader.

Werner was an excellent, all-round experimental physicist. His catching enthusiasm, in combination with his great sense of humour, stimulated many young physicists. He also made categorical choices ­ he came to NIKHEF, moved with his family to the Netherlands and became a Dutch citizen.

His absence is strongly felt not only at NIKHEF, but also at CERN and DESY.
Ger van Middelkoop

D M (Mike) Sendall 1939-1999

D M (Mike) Sendall of CERN died on 15 July in London after a decade of illness. He would have been 60 in October.

Sendall obtained his PhD in the Cavendish Laboratory in Cambridge under Otto Frisch. He then came to CERN in 1968 to work in Lucien Montanet's group on bubble chamber studies of kaon decays.

In 1972 he became a staff member in the Data Handling Group in CERN's Nuclear Physics Division. Then in 1976 he moved to the Data Handling Division to take charge of the group, looking after data acquisition systems based on PDP-11 computers. He made important contributions in this field for many years, and was leader of the On-line Computing Group from 1985 to 1990.

In addition, Sendall was an unsung hero of international computer networking. He understood the vast potential of open systems when others were limited to supplier-specific approaches. Between 1980 and 1985 he chaired the ECFA-LEP Network Group ­ known to many as Subgroup 5 ­ which established high-energy physics, and in particular CERN, as the focus of academic networking in Europe.

Sendall's leadership style ­ continually pushing, suggesting and encouraging without seeking credit for himself ­ was a natural foil for the exuberance and enthusiasm of young researchers. Future history books are certain to recount how he was an enthusiastic supporter of Tim Berners-Lee in his pioneering work on what would later become the World Wide Web. After reading Berners-Lee's prophetic 1989 proposal, Sendall wrote on the cover: "vague but exciting", adding at the end: "And now?" The door to the Web was not yet open, but Sendall had put a key in the lock. In more recent years he played a major role in defining and implementing CERN's ongoing Web policy.

In 1992 Sendall took on an important responsibility as secretary of CERN's new LHC Committee ­ set up to recommend which experiments should proceed towards a full technical proposal ­ to monitor the development of the proposals and the subsequent progress of the experiments. He brought his customary meticulousness and diligence to this important task.

Mike Sendall was universally admired. Everyone who came into contact with him quickly appreciated his charm and intelligence, his complete devotion to duty and his profound understanding of computing and physics. His modesty masked a much deeper culture. His pronouncements were always incisive and his public talks a model of interest, precision and clarity. With a highly developed sense of humour, he was also a memorable raconteur. Towards the end of his life he faced his future with courage and dignity.