Clifford G. Shull
1915–2001, Pittsburgh, Pennsylvania, USA, Medford, Massachusetts, USA
American physicist who shared the 1994 Nobel Prize in Physics for developing neutron diffraction, revealing atomic and magnetic structures in crystals.
Born in Pittsburgh, Shull earned his PhD at New York University in 1941 studying electron diffraction. After wartime work at the Texas Company researching catalysts, he joined the Clinton Laboratory (Oak Ridge) in 1946, where with Ernest Wollan he built the first instruments to diffract reactor neutrons off crystals. Neutrons — sensitive to light atoms and to magnetic moments — let him determine hydrogen positions and discover antiferromagnetic ordering. In 1955 he moved to MIT, retiring in 1986; the Nobel came when he was 79, among the longest delays in the prize's history.
Nobel-winning work
At Oak Ridge's graphite reactor, Shull and Wollan showed in 1946 that thermal neutrons — de Broglie wavelength ~0.1 nm — diffract from crystals just as X-rays do, but with scattering amplitudes set by nuclei rather than electron clouds. This made neutrons uniquely sensitive to light atoms (especially hydrogen) invisible to X-rays.
Because the neutron also carries a magnetic moment, Shull demonstrated magnetic scattering and mapped antiferromagnetic ordering in MnO (1949) — opening neutron crystallography as the definitive tool for magnetic structures and hydrogen positions.
Workplaces: Massachusetts Institute of Technology, Oak Ridge National Laboratory
United States