Hahn, Otto (ôˈtō hän) [key], 1879–1968, German chemist and physicist. His important contributions in the field of radioactivity include the discovery of several radioactive substances, the development of methods of separating radioactive particles and of studying chemical problems by the use of radioactive indicators, and the formation of artificial radioactive elements by bombarding uranium and thorium with neutrons. He received the 1944 Nobel Prize in Chemistry for splitting the uranium atom (1939) and discovering the possibility of chain reactions. The development of the atomic bomb was based on this work. Hahn was a member of the Kaiser Wilhelm Institute of Chemistry, Berlin, from 1912 and director from 1928 to 1944. He was in Allied custody (1944–46) and on his return to Germany became head of the Kaiser Wilhelm Gesellschaft, Göttingen (later reorganized as the Max Planck Gesellschaft).