 President Harry S. Truman did not sign the act creating the Atomic Energy Commission into law until 1 August 1946, and it did not become active until 1 January 1947.In the meantime, Groves' legal authority to act was limited.Most of the scientists at Los Alamos were eager to return to their laboratories and universities, and by February 1946 all of the wartime division heads had left, but a talented core remained.