Dunning, John Ray (1907-1975), an American physicist, did research work that was important in developing the atomic bomb. With the cooperation of Alfred O. Nier, who separated small quantities of the isotopes (forms) of uranium known as U-235 and U-238 from each other, Dunning, E. T. Booth, and A. V. Grosse proved that slowly moving neutrons can cause U-235—but not U-238—to fission, or split (see Uranium (Fissionability)). Dunning also proved that nuclear forces depend partly upon magnetic properties of the neutron.
Dunning pioneered in research on the discharge of neutrons from uranium fission. During World War II, he directed research in isotope separation, which was put into large scale use at Oak Ridge, Tennessee.
Dunning was born on Sept. 24, 1907, in Shelby, Nebraska. He graduated from Nebraska Wesleyan University. He received his Ph.D. degree at Columbia University. Dunning began teaching physics at Columbia University in 1933. He was dean of the School of Engineering and Applied Science at Columbia from 1950 until 1969. He died on Aug. 25, 1975.
