Oak Ridge National Laboratory was completed, later renamed to "Oak Ridge National Laboratory". The site was chosen for the X-10 Graphite Reactor, used to show that plutonium can be created from enriched uranium. Enrico Fermi and his colleagues developed the world's second self-sustaining nuclear reactor after Fermi's previous experiment, the Chicago Pile-1. The X-10 was the first reactor designed for continuous operation. After the end of World War II the demand for weapons-grade plutonium fell and the reactor and the laboratory's 1000 employees were no longer involved in nuclear weapons. Instead, it was used for scientific research. In 1946 the first medical isotopes were
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