Over the past 50 years, research by academic and industrial scientists in microelectronics, plastics, pharmaceuticals and other fields has depended on the technique of neutron scattering to reveal the detailed arrangements of atoms in solids and liquids.
Clifford Shull, who died on March 31st aged 85, was a pioneer of this method of unlocking the most intimate secrets of the structure of materials that were difficult to investigate by any other means. He shared the Nobel Prize for physics in 1994 for his discoveries.
His research in neutron scattering began in 1946 at the American Atomic Energy Commission laboratory at Oak Ridge, Tennessee, using one of the first nuclear reactors. He and his colleagues devised a way of deflecting neutrons ejected in the nuclear reactions into a beam that they then aimed at the material they wanted to study. By analysing the pattern of neutrons bouncing off the material, they were able to discover the juxtaposition of atoms in a range of materials.
Neutron scattering overcame the limitations of X-rays in analysing many materials and was the first technique to detect the position of hydrogen atoms and measure magnetic fields around atoms.
He shared his Nobel Prize with Bertram Brockhouse, who had independently invented a variation of the same technique. The Shull method answered the question of where atoms "are"; Brockhouse's told us what atoms "do".
Clifford Shull was born in Pittsburgh, Pennsylvania, the youngest of three children. His father owned a small hardware store. He began to take a serious interest in physics in his final year at high school and in 1933 won a scholarship to the Carnegie Institute of Technology, in Pittsburgh, to study physics. The institute had a strong reputation in engineering and physical sciences and he was initially drawn toward aeronautical engineering as a possible career.
His interest in physics sharpened under the tuition of a brilliant lecturer, Harry Hower, then head of the physics department. He graduated in 1937, and took a research and teaching post at New York University, where he was encouraged to join a research project of a nuclear physics group headed by Frank Myers and Robert Huntoon, who were building a generator for accelerating deuterons.
He was later involved in accelerating beams of electrons for experiments, for which he got his PhD in 1941, and researching an early approach to using neutron interactions with materials as a method of analysis.
The idea of using neutrons to unlock the secrets of the atomic nucleus was first recognised by physicists in 1932, when Chadwick discovered the neutron. Since it had no electric charge, the neutron could easily penetrate the charged nucleus, although the big breakthrough had to wait until streams of thermal, slow-moving neutrons were available from nuclear reactors.
In 1941, Clifford Shull joined the Texas Company research laboratories, which specialised in developing high-performance aviation fuels and lubricants. The work became increasingly important after the United States entered the second World War that December.
He wanted to join the Manhattan Project, developing the atomic bomb, but was obliged to stay at the Texas Company throughout the war years. Once hostilities had ceased, however, he got a job at Oak Ridge, pursuing the exciting developments in nuclear physics going on within the Manhattan Project. He joined Ernest Wollan, who had been at the laboratory since its formation and who had assembled a rudimentary device for obtaining neutron diffraction patterns of crystals and materials.
Between them they created the techniques that would earn him a Nobel Prize. Then, in 1955, he left for academic life and a highly productive research career at Massachusetts Institute of Technology.
The techniques he and Ernest Wollan developed made neutron scattering a revolutionary research tool, which, in recent times, has led to the construction of high-tech ceramic superconductors and the detailed study of the structure of viruses, which could improve medical treatment for many illnesses. But by first studying simple compounds, such as table salt, they discovered that neutrons were deflected in a distinctive pattern when they struck a sample of material. It was this that allowed the researchers to determine the sample's atomic structure.
He also initiated studies with neutron diffraction to investigate the properties of metals, including how they became magnetised. That research led to new magnetic materials for products ranging from computer, audio and video components to refrigerator magnets.
Clifford Shull is survived by his wife, Martha-Nuel Summer, and three sons.
Clifford Glenwood Shull: born 1915; died, March 2001