The nuclear physicist Sir John Hill was one of the pioneers of the early development of nuclear energy in the UK. During his career he held leading positions in the UK Atomic Energy Authority (UKAEA, formerly the Department of Atomic Energy), British Nuclear Fuels (BNFL), and Amersham International (a British pharmaceutical company acquired, in 2004, by the US group General Electric and incorporated into GE Healthcare).

John McGregor Hill was born in 1921 in Chester. From Richmond County Grammar School in Surrey he went to King's College London where he took a first in physics. He joined in 1941, serving in the RAF's Radar Branch. He was demobilised in 1946 with the rank of flight-lieutenant and went back to his education, this time at the Cavendish Laboratory, the University of Cambridge. He received his PhD in nuclear physics for research on radioactive isotopes having short lifetimes.

In 1948 he was appointed lecturer in physics at London University. In 1950 he began working for the Department of Atomic Energy of the Ministry of Supply, at the Windscale nuclear establishment, near the village of Seascale, Cumbria. There Hill was involved with the construction of Britain's first two nuclear reactors, or “piles” as they were then called. Housed in large, concrete buildings a few hundred metres apart, the reactors were moderated with graphite, cooled by air and fueled with natural uranium metal. They produced plutonium for Britain's early nuclear weapons.

On October 10, 1957, the graphite in one the reactors caught fire, releasing substantial amounts of radioactivity into the surrounding area. This was the world's worst reactor accident until the meltdown of a nuclear reactor at Three Mile Island, Pennsylvania, in 1979, and the much larger release of radioactivity in the Chernobyl disaster in 1986.

After the accident the name of the nuclear establishment was changed from Windscale to Sellafield. In 1954 the headquarters of the industrial section of the establishment moved to Risley near Warrington, and Hill became the manager of the production group. In this role he oversaw the operation of several facilities.

These included the uranium diffusion plant at Capenhurst, Chester, which produced enriched uranium; the fuel-manufacturing plant at Springfields, Lancashire, which produced fuel elements for reactors; the reprocessing plant at Windscale, which separated plutonium from spent reactor fuel elements; the reactor at Calder Hall, Sellafield, which produced plutonium for weapons and was also the world's first commercial nuclear power station; and finally the reactor at Chapelcross, Dumfriesshire, which also produced plutonium for nuclear weapons.

In 1964 Hill was appointed to the main board of the UKAEA and he rose rapidly to deputy director, then technical director, deputy managing director, managing director, and, in 1967, chairman, a post which he held until 1981.

In April 1971 Hill became chairman of British Nuclear Fuels (formerly the production group of UKAEA) and in 1975 he was appointed chairman of the Radiochemical Centre (later Amersham International). He retired as chairman of BNFL in 1983 and Amersham in 1988. He was chairman of Aurora Holdings, 1984-88, and of Rea Brothers Group, 1987-95.

Hill was knighted in 1969. He was elected Fellow of the Royal Society

in 1981 and Fellow of the Royal Academy of Engineering in 1982.

He was also a Fellow of the Institute of Physics and a Fellow of the Institute of Energy. He was an honorary Fellow of the Institute of Chemical Engineers (1977) and the Institute of Electrical Engineers (1981); and a foreign associate of the US Academy of Engineering (1976).

In 1974 he was awarded the Melchett Medal of the Institute of Energy and, in 1978, the Sylvanus Thompson Medal of the Institute of Radiology. In 1992 he was elected honorary lifetime member of the American Nuclear Society. In 1981 he was awarded an honorary doctorate by the University of Bradford.

Hill enjoyed gardening and golf. He was a member of Royal Mid-Surrey Golf Club in Richmond, serving as both captain and president.

His wife, two sons and a daughter survive him.

Sir John Hill, nuclear physicist, chairman of the UKAEA 1967-81, was born on February 21, 1921. He died on January 14, 2008, aged 86