In December 1940 Bacher joined the Radiation Laboratory at MIT, but did not immediately cease his research. He reached an arrangement with its director, Lee Alvin DuBridge, to return to Cornell for four days every three weeks until it was completed. He was researching the neutron cross section of cadmium, a topic of interest to Enrico Fermi, who was attempting to build a nuclear reactor, but whose figures did not agree with Bacher's. Bacher carefully checked his results, and Fermi, convinced of their correctness, urged Bacher to publish them. Bacher submitted a paper to the Physical Review with instructions to withhold publication until after the war, and the paper was not published until 1946.