<P> In December 1942, during World War II, Charles Allen Thomas, a chemist and director of research at Monsanto in St. Louis, joined the National Defense Research Committee (NDRC) as the deputy chief of its Division 8, which was responsible for propellants, explosives and the like . Early in 1943, he traveled to the east with Richard C. Tolman, a member of the NDRC, and James B. Conant, the president of Harvard University and the chairman of the NDRC, to witness a demonstration of a new underwater explosive . Conant and Tolman took the opportunity to quietly investigate Thomas' background . He was then invited to a meeting in Washington D.C., with Brigadier General Leslie R. Groves, Jr., the director of the wartime Manhattan Project responsible for building an atomic bomb . When he got there, Thomas found Conant was also present . </P> <P> Groves and Conant were hoping to harness Thomas's industrial expertise for the benefit of the project . They offered him a post as a deputy to Robert Oppenheimer, the director of the Los Alamos Laboratory in New Mexico, but he did not wish to move his family or give up his responsibilities at Monsanto . Instead he accepted the role of coordinating the plutonium purification and production work being carried out at Los Alamos, the Metallurgical Laboratory in Chicago, Radiation Laboratory in Berkeley, and Ames Laboratory in Iowa . Chemistry and metallurgy at Los Alamos would be led by the youthful Joseph W. Kennedy . </P> <P> At Los Alamos, physicist Robert Serber proposed that instead of relying on spontaneous fission, the chain reaction inside the atomic bomb should be triggered by a neutron initiator . The best - known neutron sources were radium - beryllium and polonium - beryllium . The latter was chosen, as polonium has a 138 - day half - life, which made it intense enough to be useful but not long - lived enough to be stockpiled . Thomas took charge of the development of techniques to industrially refine polonium for use with beryllium in the "urchin" internal neutron initiators . This effort became the Dayton Project . </P> <P> Thomas brought in key personnel from Monsanto's Thomas and Hochwalt Laboratories in Dayton, Ohio, including Caroll Hochwalt, James Lum and Nicholas Samaras . Thomas became Director of the Dayton Project, with Hochwalt as Assistant Project Director and Lum as Laboratory Director . They decided that about twelve chemists would be required, and Lum set about recruiting professors, graduate students and industrial chemists from universities and laboratories in the area . The first of these recruits commenced in August 1943, but few had any experience with radiochemistry . Numbers increased from 46 full - time employees at the end of 1943 to 101 at the end of 1944, 201 at the end of 1945, and 334 at the end of 1946, including 34 members of the Army's Special Engineer Detachment . </P>

Who invented the trigger for the atomic bomb