Otto Hahn

Otto Hahn discovered nuclear fission and spent the rest of his life campaigning against the weapons it made possible. Born in Frankfurt in 1879 to a glazier and workshop owner, he studied chemistry at Marburg intending to work in industry, and turned to radioactivity almost by accident while in London under William Ramsay, discovering a new substance he called radiothorium. He worked under Ernest Rutherford in Montreal, then joined the Kaiser Wilhelm Institute in Berlin. In 1907 he began a partnership with the Austrian physicist Lise Meitner that lasted thirty years; she was initially unpaid and barred from the main laboratory because she was a woman, working in a converted carpentry workshop. He served in the German army in the First World War in the gas warfare unit under Fritz Haber, which he later regarded with shame. After Enrico Fermi's neutron bombardment experiments, Hahn and Meitner, with Fritz Strassmann, spent four years investigating what uranium produced. Meitner, who was Jewish, fled to Sweden in July 1938 after the Anschluss stripped her of protection. In December 1938 Hahn and Strassmann found barium — an element about half the mass of uranium — where they expected something heavier, and Hahn wrote to Meitner because the chemistry made no sense. Meitner and her nephew Otto Frisch worked out the explanation over Christmas: the nucleus had split, releasing enormous energy, and they named it fission. Hahn published without her, and the 1944 Nobel Prize in Chemistry went to him alone, an omission long regarded as unjust. He was interned in England in 1945 and learned of Hiroshima there. He led German science after the war and campaigned against nuclear arms until his death in 1968.

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