German physical chemist and Nobel laureate, whose greatest contributions were in the field of radioactivity. Hahn was born in Frankfurt-on-Main and educated at the Universities of Marburg and Munich. In 1911 he became a member of the Kaiser Wilhelm Institute for Physical Chemistry in Berlin and served as director of the institute from 1928 to 1945, when it was taken into Allied custody after World War II. In 1918 he discovered, with the Austrian physicist Lise Meitner, the element protactinium. Hahn, with his co-workers Meitner and the German chemist Fritz Strassmann, continued the research started by the Italian physicist Enrico Fermi in bombarding uranium with neutrons. Until 1939 scientists believed that elements with atomic numbers higher than 92 (known as transuranic elements) were formed when uranium was bombarded with neutrons. In 1938, however, Hahn and Strassmann, while looking for transuranic elements in a sample of uranium that had been irradiated with neutrons, found traces of the element barium. This discovery, announced in 1939, was irrefutable evidence, confirmed by calculations of the energies involved in the reaction, that the uranium had undergone fission, splitting into smaller fragments consisting of lighter elements. Hahn was awarded the 1944 Nobel Prize for Chemistry for his work in nuclear fission. It was proposed in 1970 that the newly synthesized element number 105 be named hahnium in his honour, but another naming system was adopted for transuranic elements beyond 104.
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