About John A. Simpson

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Professor John Alexander Simpson was a scientific group leader for the Manhattan Project, co-founder of the Bulletin of the Atomic Scientists and pioneering physicist who flew the first cosmic-ray experiments to Mars, Jupiter, Mercury and Saturn.  Simpson came to the University of Chicago in 1943, shortly after Enrico Fermi and his team achieved the first controlled nuclear chain reaction on campus as part of the top-secret Manhattan Project.

On Aug. 7, 1945, the day after the United States dropped the atomic bomb on Hiroshima, Simpson and his colleagues organized the Atomic Scientists of Chicago to campaign for the peaceful use of nuclear power under international control. Simpson served as the group’s first chairman. Along with two of his University of Chicago colleagues, Simpson stated the case in an article that filled two pages of the Oct. 29, 1945 issue of LIFE magazine. In December 1945, Simpson co-founded the Bulletin of the Atomic Scientists.

In late 1945, Simpson also became an unofficial adviser to U.S. Sen. Brien McMahon of Connecticut, who chaired the Senate Special Committee on the Control of Atomic Energy. Together they and others worked successfully to promote and develop the McMahon Act of 1946, which provided for the civilian control of atomic energy.

Simpson soon turned his attention to cosmic rays, subatomic particles that constantly bombard Earth from all directions at nearly the speed of light. He began studying cosmic rays shortly after World War II, first with instruments aboard B-29s, then aboard helium balloons and a naval vessel that sailed to the Antarctic to learn why their intensities varied widely.

In 1948, Simpson invented the cosmic ray neutron intensity monitor. By 1951 he had set up five monitoring stations from the city of Chicago to the magnetic equator in Peru, allowing him to use the Earth’s own magnetic field as an analyzer. All but the highest-energy cosmic rays are deflected into space near the equator, where the magnetic field is strong and nearly parallel to the Earth’s surface. But as the field becomes more vertical toward the poles, lower-energy particles are able to penetrate the atmosphere.

Simpson received his bachelor’s degree from Reed College in Portland in 1940, then attended New York University, where he earned his master’s degree in 1942 and his doctorate in 1943. He served as a scientific group leader for the Manhattan Project at the University of Chicago from 1943 to 1946. He became an Instructor in Physics at the University in 1946, Assistant Professor in 1947, Associate Professor in 1949, Professor in 1954, Edward L. Ryerson Distinguished Service Professor in 1968, Arthur H. Compton Distinguished Service Professor in 1974 and Arthur H. Compton Distinguished Service Professor Emeritus in 1987. He also held appointments as Chairman of the Committee on Instruction in Biophysics from 1951 to 1952, and as Director of the Enrico Fermi Institute from 1973 to 1978.