The nuclear physicist William Galbraith was best known for making the first experimental measurements of the Cerenkov radiation produced by the interactions of cosmic rays with the Earth’s atmosphere. This research, conducted with John Jelley, was published in the science journal Nature in 1953.
Cosmic rays are energetic charged particles, originating from outer space, which enter the Earth’s atmosphere. They consist of the components of the atoms that normally occur on Earth — electrons, protons and atomic nuclei.
Cerenkov radiation (discovered in 1934 by the Soviet physicist Pavel Alekseyevich Cerenkov) is electromagnetic radiation (usually bluish light) emitted when a charged particle (such as an electron) passes through a transparent medium (such as air or water) at a speed greater than the speed of light in that medium. The characteristic blue glow of the core of a nuclear reactor is due to Cerenkov radiation.
The interactions of cosmic rays with molecules in the air produce showers of particles. Traditionally, air showers had been detected by identifying the surviving particles at ground level.
Galbraith and Jelley speculated that the air showers might be detectable optically by the Cerenekov radiation produced by the cosmic rays as they passed through the air. They made a number of simple but very elegant experiments to show that this actually happened.
Advertisement
Galbraith and Jelley performed their first experiments at the Atomic Energy Research Establishment (AERE), Harwell, Oxfordshire. They continued their investigations at an astronomical observatory on the Pic du Midi, a mountain in the French Pyrenees, to take advantage of more frequent nights with cler skies. Later, they operated more advanced “second-generation” cosmic ray detectors on the airfield of the RN air station at Culham, Oxfordshire.
The study of air showers is important in nuclear physics, astrophysics and cosmology. Galbraith’s pioneering work helped to establish cosmic-ray physics as a field of considerable international importance.
William Galbraith was born at Renfrew in 1925. His father, an accountant with the electrical company Stewart Raeburn (later taken over by GEC) was posted to Burma, and William spent his early years in Rangoon, returning to Scotland in 1932. He attended the Kelvinside Academy, Glasgow. In 1938 his father was transferred to GEC headquarters, and the family moved to London. Galbraith went to the Lower School of John Lyon (now the John Lyon School) at Harrow on the Hill.
Although he matriculated in 13 subjects, an unusually large number, he left school at 15 to join GEC as an export clerk, deciding whether materials of a strategic nature required an export licence — surprising responsibilities for one so young, and in wartime.
As part of his general training he learnt the elements of electrical engineering. Discovering that he had a natural aptitude for it he became a student assistant in the GEC research laboratories, Wembley, and attended evening classes at Chelsea Polytechnic, London. He then studied part-time for a BSc at Birkbeck College, working during the day on pre-production versions of valves for use in airborne and naval radars.
Advertisement
In 1948 he was given a post in the nuclear physics division at AERE Harwell. He conducted research to determine the spontaneous fission rates of uranium and plutonium isotopes. (Spontaneous fission is a form of radioactive decay.) A thesis based on this research earned him a University of London PhD. After this he switched to research on cosmic rays.
In 1956 he was elected to a Commonwealth Fund Fellowship and spent the next two years at the Radiation Laboratory of the University of California, Berkeley, working primarily on the decay of sub-atomic particles called kaons, or K-mesons. Returning to Harwell, he was involved in the construction and operation of Nimrod, the first circular proton accelerator in England.
In 1966 he was appointed Professor of High-Energy Physics at the University of Sheffield. There he continued his collaborative experimental work at CERN, European Organisation for Nuclear Research at Geneva. He was also one of the founders of research activities using the newly constructed particle accelerator (called Nina) at Daresbury, Cheshire.
He retired from Sheffield in 1988, after serving as dean of the faculty of Pure Science and as pro-vice chancellor, and was made professor emeritus.
Galbraith published more than 100 papers in scientific journals and book chapters. He wrote two monographs: Extensive Air Showers (1952), recognized as a classic, and High Energy and Nuclear Physics Data Handbook (1964).
Advertisement
He was an enthusiastic concert-goer, particularly in Sheffield, where he played a part in helping to set up the Sheffield Festival in the 1970s, and his support of local musicians, including the Lindsay String Quartet, helped to establish Sheffield as a cultural centre for the arts.
Galbraith’s wife predeceased him, and he is survived by one son and three daughters.
Professor William Galbraith, nuclear physicist, was born on May 31, 1925. He died on February 20, 2011, aged 85