Fermi left Italy in 1938 to escape new Italian racial laws that affected his Jewish wife , Laura Capon . He emigrated to the United States , where he worked on the Manhattan Project during World War II . Fermi led the team that designed and built Chicago Pile-1 , which went critical on 2 December 1942 , demonstrating the first human-created , self-sustaining nuclear chain reaction . He was on hand when the X-10 Graphite Reactor at Oak Ridge , Tennessee , went critical in 1943 , and when the B Reactor at the Hanford Site did so the next year . At Los Alamos , he headed F Division , part of which worked on Edward Teller 's thermonuclear " Super " bomb . He was present at the Trinity test on 16 July 1945 , where he used his Fermi method to estimate the bomb 's yield
Trinity test
Trinity (nuclear test)
Enrico Fermi