An der Schwelle zum Atomzeitalter. Die Vorgeschichte der Entdeckung der Kernspaltung im Dezember 1938

On the Threshold of the Atomic Age: The History of the Discovery of Nuclear Fission in December 1938: - Fifty years ago in mid-December 1938, Otto Hahn and Fritz Strassmann at the Kaiser Wilhelm Institute of Chemistry discovered nuclear fission by demonstrating, using chemical methods, the presence of barium in the decay products of neutron-irradiated uranium. This essay points out the constellation of conditions and prerequisites (Historischer Erfahrungsraum/“historical field of experience”) which led to the discovery of nuclear fission, and was constituted by specific components (“presentabilia”) both internal and external to science in general and to atomic research in particular. A decisive role was played by the constellation of the three members of the Berlin team and their personal situations under the political conditions of the 1930s. Further “presentabilia” were the institutional, instrumental and disciplinary conditions under which the team worked and the methods available to the individual members of the team. It was very important that some of the “presentabilia” were “not-present” to the members of the team. In particular, after Meitner's departure from Berlin Hahn and Strassmann had no access to methods and tools for proving the presence of alpha rays; nothing was known of the existence of actinides; no cyclotron or other source of neutrons more productive than those already in use in Berlin, Paris and Rome was available; it was very important that Strassmann and Hahn were not convinced of the strong validity of the resonance process induced by thermal neutrons; etc.