John Alexander Simpson (November 3, 1916 – August 31, 2000) was an American physicist and science educator. He was deeply committed to educating the public and political leaders about science and its implications, most notably as a principal founder of the Bulletin of the Atomic Scientists and a long-time member of the organizations Board of Sponsors.
He is known for inventions such as the gas flow α-particle proportional counter (for measuring plutonium yields in the presence of high intensity fission products), and the neutron monitor, and for having several of the instruments he created launched into space, such a dust flux monitor aboard the Stardust spacecraft.
