Obituary : Professor Peter Fowler

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Peter Fowler was one of the outstanding physicists of his generation. His principal research field was that of elementary particles and cosmic rays, but he also made seminal contributions in many other areas, ranging from measurement of jet turbine blade temperatures to cancer therapy with particle beams.

The son of a prominent theoretical physicist, Sir Ralph Fowler, and the grandson of Lord Rutherford, the discoverer of the atomic nucleus, Peter Fowler was a Wykehamist whose first experiments in physics were as a radar officer in the wartime RAF (1942-46). Some time after D-Day, RAF bombers were having problems due to German jamming of their Gee navigation system. Fowler was able to detect the jamming signals and, by a clever analysis which was a real tour de force, to pin down the station responsible, which was then destroyed. Goering reportedly demanded a court martial over the breach of security, since he simply could not believe that the British were smart enough to deduce the location of the secret transmitter within a few days of its being switched on.

After taking his degree at Bristol, Fowler joined C.F. Powell's cosmic ray research group. This time in the late Forties was something of a golden era for physics in Britain, with startling new discoveries occurring almost daily.

Fowler was a leading figure in this research: among his notable achievements were the identification of the first example of a new type of "strange" elementary particle called a tau meson (one of his co-workers in this discovery was Rosemary Brown, who later became his wife) and the development of novel methods to measure the energies and electrical charges of the high energy primary cosmic ray nuclei, recorded on high-altitude balloon flights. The identification among these of the light elements lithium, beryllium and boron - almost completely absent in the stars - was the first proof that primary cosmic rays had been circling in the galaxy for millions of years, since such light nuclei could only have come from fragmentation of heavier nuclei in rare collisions in the interstellar medium. Fowler was also one of the first people to give the correct explanation of the aurora phenomenon, as due to light from atoms in the stratosphere excited by collisions with particles in the Van Allen radiation belts.

During the late Fifties and early Sixties, a long and systematic study of the characteristics of nuclear interactions at extremely high energies was undertaken using massive detectors carried in balloons and in proving flights of VC10 aircraft to Australia. This pioneer work of Fowler's laid the basis of later researches using particle accelerators. In 1961 he also wrote an important report for the Air Registration Board demonstrating that, contrary to what some scientists had asserted, the radiation levels due to solar flares in high altitude flights in Concorde across the North Atlantic would be no higher than in subsonic jets.

Peter Fowler's long-term interest in the nature of the cosmic radiation was pursued further using solid state detectors carried in very long balloon flights, and with gas scintillator detectors flown on the Ariel 6 satellite in the early Eighties. For the first time, significant results were obtained on the fluxes of atoms heavier than bismuth of the actinide series, such as thorium and uranium. The interest in these is that such nuclei can only be built from lighter elements by the rapid neutron capture processes unique to supernova explosions, the death throes of massive stars. The measurement by Peter Fowler of these "super heavy" nuclei is a very important marker for our understanding of the supernova mechanism.

One of the critical factors affecting the efficiency of aircraft jet engines is the temperature of the turbine blades, which is, however, difficult to measure directly when the engine is running. Fowler's ingenuity devised a neat way around this for Rolls Royce by exploiting the resonance capture of low energy neutrons in iron nuclei and the broadening of this resonance with the blade temperature, which could thus be measured in situ. His most recent research, in which he was active at the time of his death, was a novel application of these ideas to geology, by using neutron resonance directly to calibrate thermocouples at thousands of atmospheres pressure, such as obtain deep inside the earth's crust. An accurate temperature calibration is vital to understanding mineral reactions and cannot be obtained in any other way.

Appointed a Reader in Physics at Bristol in 1961, in 1964 Fowler was elected a Fellow of the Royal Society and subsequently as a Royal Society Research Professor in Physics. He served as chairman of the Medical Research Council Committee on Radiological Protection (1983-92), as a member of the Meteorological Committee (1983-93) and on the SERC Neutron Facilities Review Panel. He contributed a host of original papers to scientific literature and was joint author of several books, including, with Dr B. Foster, Forty Years of Particle Physics (1988).

Outside physics, his diverse interests included gardening (at which he was an expert) and meteorology, which for him was a lifelong hobby.

D. H. Perkins

Peter Howard Fowler, physicist: born 27 February 1923; Assistant Lecturer in Physics, Bristol University 1948-51, Lecturer 1951-61, Reader 1961- 64; Royal Society Research Professor in Physics 1964-81 (Emeritus); Visiting Professor, University of Minnesota 1956-57; FRS 1964; married 1949 Rosemary Hempson (nee Brown; three daughters); died Bristol 8 November 1996.