Sir Francis Simon CBE (2 July 1893 – 31 October 1956), was a German and later British physical chemist and physicist who devised the gaseous diffusion method, and confirmed its feasibility, of separating the isotope Uranium-235 and thus made a major contribution to the creation of the atomic bomb.

In 1936 despite being supported by Einstein, Nernst, Planck and Rutherford he was unsuccessful in beating Mark Oliphant for the Chair of Physics at Birmingham University.

In 1940 in collaboration with Nicholas Kurti and Heinrich Gerhard Kuhn, he was commissioned by the MAUD Committee to investigate the feasibility of separating uranium-235 by gaseous diffusion.

He initially adapted his wife's wire kitchen strainer to assist in this work before commissioning a membrane from ICI containing 160,000 holes to the square inch.

His resulting conclusions on the separation of uranium isotopes was transferred to the Manhattan Project and was the basis of the process that produced sufficient U235 to make the atomic bomb.

Upon the retirement of Lord Cherwell he became Dr Lee's Professor of Experimental Philosophy and head of the Clarendon Laboratory in 1956, one month before his death from coronary disease.