John Ray Dunning
Dunning, John Ray (1907-1975) was an American physicist whose work in the 1930's and 1940's helped lay the groundwork for the practical use of nuclear power. He helped prove that bombarding uranium U-235 with slowly moving neutrons can set off fission, a process fundamental in producing nuclear energy.
Dunning was born in Shelby, Nebraska, in 1907. He graduated from Nebraska Wesleyan University in 1929 and received his Ph.D. degree from Columbia University in 1934. Dunning began teaching physics at Columbia University in 1933.
During World War II (1939-1945), Dunning was involved in the Manhattan Project, the topsecret United States government project to build the first atomic bomb. With his colleagues at Columbia University, he proved that U-235, an isotope of uranium, can be made to undergo fission (splitting) when struck by slowly moving neutrons. When U-235 is split, it releases energy. A continuous series of such fissions, called a chain reaction, produces the energy used in atomic bombs and nuclear power plants.
For the project, Dunning directed research in producing a pure form of U-235. In its natural state, U-235 is found in combination with another form of uranium, U-238. Dunning used a process called gaseous diffusion to separate U-235 from U-238. He and his team targeted a gas compound containing both forms of uranium at a barrier with very fine filters. The molecules containing lighter U-235 atoms moved faster and passed more easily through the filters than those with U-238. After repeating this process many times, Dunning and his team found they could separate a useful amount of U-235 from the compound. The process was used to produce U-235 for atomic bombs.
Dunning served as dean of Columbia's School of Engineering from 1950 until 1969. Throughout his career, he worked to educate the public on nuclear energy and the challenges of using it.