<P> The same year, his doctoral student James Chadwick discovered the neutron, which was immediately recognized as a potential tool for nuclear experimentation because of its lack of an electric charge . Experimentation with bombardment of materials with neutrons led Frédéric and Irène Joliot - Curie to discover induced radioactivity in 1934, which allowed the creation of radium - like elements at much less the price of natural radium . Further work by Enrico Fermi in the 1930s focused on using slow neutrons to increase the effectiveness of induced radioactivity . Experiments bombarding uranium with neutrons led Fermi to believe he had created a new, transuranic element, which was dubbed hesperium . </P> <P> But in 1938, German chemists Otto Hahn and Fritz Strassmann, along with Austrian physicist Lise Meitner and Meitner's nephew, Otto Robert Frisch, conducted experiments with the products of neutron - bombarded uranium, as a means of further investigating Fermi's claims . They determined that the relatively tiny neutron split the nucleus of the massive uranium atoms into two roughly equal pieces, contradicting Fermi . This was an extremely surprising result: all other forms of nuclear decay involved only small changes to the mass of the nucleus, whereas this process--dubbed "fission" as a reference to biology--involved a complete rupture of the nucleus . Numerous scientists, including Leó Szilárd, who was one of the first, recognized that if fission reactions released additional neutrons, a self - sustaining nuclear chain reaction could result . Once this was experimentally confirmed and announced by Frédéric Joliot - Curie in 1939, scientists in many countries (including the United States, the United Kingdom, France, Germany, and the Soviet Union) petitioned their governments for support of nuclear fission research, just on the cusp of World War II, for the development of a nuclear weapon . </P> <P> In the United States, where Fermi and Szilárd had both emigrated, this led to the creation of the first man - made reactor, known as Chicago Pile - 1, which achieved criticality on December 2, 1942 . This work became part of the Manhattan Project, a massive secret US government military project to make enriched uranium by building large reactors to breed plutonium for use in the first nuclear weapons . The US tested atom bombs and eventually these weapons were used to attack the cities of Hiroshima and Nagasaki . </P> <P> In 1945, the first widely distributed account of nuclear energy, in the form of the pocketbook The Atomic Age, discussed the peaceful future uses of nuclear energy and depicted a future where fossil fuels would go unused . Nobel laurette Glenn Seaborg, who later chaired the Atomic Energy Commission, is quoted as saying "there will be nuclear powered earth - to - moon shuttles, nuclear powered artificial hearts, plutonium heated swimming pools for SCUBA divers, and much more". </P>

When did the first nuclear reactor go online