Enrico Fermi and moved to the Argonne Woods site. There Fermi directed experiments on nuclear reactions, revelling in the opportunities provided by the reactor's abundant production of free neutrons. The laboratory soon branched out from physics and engineering into using the reactor for biological and medical research. Initially, Argonne was run by Fermi as part of the University of Chicago, but it became a separate entity with Fermi as its director in May 1944. When the air-cooled X-10 Graphite Reactor at Oak Ridge went critical on 4 November 1943, Fermi was on hand just in case something went wrong. The technicians woke
Nuclear reactor new type of reactor using uranium came from the discovery by Lise Meitner, Fritz Strassmann and Otto Hahn in 1938 that bombardment of uranium with neutrons (provided by an alpha-on-beryllium fusion reaction, a "neutron howitzer") produced a barium residue, which they reasoned was created by the fissioning of the uranium nuclei. Subsequent studies in early 1939 (one of them by Szilárd and Fermi) revealed that several neutrons were also released during the fissioning, making available the opportunity for the nuclear chain reaction that Szilárd had envisioned six years previously. On 2 August 1939 Albert Einstein signed a letter to President