HAHN, OTTO

(b. Frankfurt am Main, Germany, 8 March 1879, d. Göttingen, Germany, 28 July 1968)

radiochemistry. For the original article on Hahn see DSB, vol. 6.

Hahn was an exceptionally prominent public figure in postwar Germany, known for the discovery of nuclear fission, for his principled conduct during National Socialism, and for his leadership in the rehabilitation of German science. For decades he was the subject of admiring media attention and much biographical material, including his own two autobiographies and a posthumously published memoir, but significant aspects of his life and work remained largely exempt from critical historical examination until well after his death. This supplement focuses on the scientific and political context for the fission discovery, Hahn’s wartime involvement in the German nuclear fission project, and his postwar advocacy for the German scientific community.

The Discovery of Nuclear Fission: December 1938 . Like many conservative academics in the interwar period, Hahn was dismayed by the loss of the imperial monarchy and dismissive of the Weimar Republic. His first reaction to the National Socialist regime was to hope for a national revival, but he was appalled by the purge of Jewish scientists and soon found himself, probably for the first time, in a nonconformist political position. He was concerned for dismissed Jewish colleagues, maintained contact with émigré friends, and at the end tried to intervene on behalf of several Jewish friends who faced deportation. It helped that the Kaiser Wilhelm Institute (KWI) for Chemistry, of which Hahn was director, was privately funded by the chemical industry and therefore was somewhat insulated, at least at first, from direct control by the government. Thus Lise Meitner, Hahn’s closest colleague and head of the institute’s nuclear physics section, was not dismissed in 1933, although she was of Jewish origin, and Hahn was able to retain Fritz Strassmann, a promising young chemist whose anti-Nazi position made him virtually unemployable outside the institute. From 1934 to 1938 Hahn, Meitner, and Strassmann investigated the radioactive species, thought to be transuranium elements, which were produced by the neutron bombardment of uranium. The work was interdisciplinary, requiring nuclear physics for the reaction processes and chemistry and radiochemistry for analyzing the many radioactive products.

Meitner fled Germany for Sweden in July 1938, but she and Hahn were able to maintain contact by mail. In November 1938 they met secretly in Copenhagen, soon after Hahn and Strassmann found several new activities among the uranium products, which they attributed to isotopes of radium. To Meitner and other physicists it seemed impossible that slow neutrons could cause uranium to lose two alpha particles and form radium, and Meitner pressed Hahn to rigorously reexamine the new activities. Hahn and Strassmann then began a series of fractional crystallization and indicator experiments designed to verify the radium by separating it from the barium that they had used as a carrier. When they could not separate it, the chemists concluded that their “radium” was in fact an isotope of the much lighter element barium—the first indication that uranium nuclei had split. Hahn informed Meitner toward the end of December

1938, asking her to find some “fantastic explanation” for the surprising result. She and her physicist nephew Otto Robert Frisch provided the first theoretical interpretation, calculated the energy released, and named the process nuclear fission.

In Germany the discovery came at a time of heightened political tension, and Hahn, regarded as politically unreliable, was suddenly threatened with the loss of his institute. When he and Strassmann published the barium finding in early January 1939, physicists worldwide greeted it as sensational news, but for Hahn it was also a “heaven-sent gift” that he urgently hoped would protect him and his institute. Afraid that others would learn that he had continued to collaborate with Meitner in exile and that he had informed her of the barium before publication, he insisted that the discovery resulted solely from chemical experiments that he and Strassmann had done in December, and that physics had played no part. In the end, Hahn and his institute were safe. But historians have come to regard his effort to distance the discovery from physics and himself from Meitner as an injustice to her and a misrepresentation of the interdisciplinary nature of the scientific work. At the very least, this can be seen as an instance in which normal standards of scientific attribution were compromised by the effects of anti-semitism, forced emigration, and fear.

Wartime Fission Research in Germany . In March 1939 Frédéric Joliot and his group in Paris reported that secondary neutrons are released during uranium fission, raising the possibility of an energy-producing chain reaction.

The German military took notice, and just after the war began in September 1939 the Army Ordnance unit for high explosives convened a group of leading atomic scientists to explore the military potential of nuclear fission. Hahn, still concerned for his institute, was eager to participate and committed the KWI for Chemistry to the fission project. Hahn later recalled that the first mention of an atomic bomb gave him a “terrible fright” but that he resolved to go on with his research as before.

The field was new, and much fundamental research was indeed necessary, but German scientists, like their Allied counterparts, quickly understood that weapons could in principle be made from two fissile nuclides: the rare isotope of uranium, uranium-235, and the transuranium element 94. Accordingly, the German fission project focused on building a nuclear reactor, for energy and to breed element 94, and on developing methods for separating uranium-235 from natural uranium. Neither goal was met. The German project was active and well supported, but it was far smaller in scale than the corresponding Allied effort.

The KWI for Chemistry was involved in every major aspect of the project and was classified at the highest level of importance to the war effort until the end. Institute physicists investigated neutron reaction processes and the properties of moderators, essential for bomb physics and for the theory and design of the reactor under construction at the nearby KWI for Physics. A sizable group worked on mass spectroscopic methods for isotope separation. Chemists analyzed and purified uranium and its compounds for the reactor, prepared a small amount of element 93 (later named neptunium) and attempted to find element 94 (plutonium). Hahn and Strassmann characterized a large number of fission fragments, data that would have been essential for the operation of a working reactor. With few exceptions, the results were unpublished, circulating as secret reports within the fission project.

After the war Hahn repeatedly stated that he had done only basic research, citing his work on fission fragments, most of which was openly published, and the work on elements 93 and 94. No doubt Hahn preferred to think of himself as a simple scientist engaged in fundamental research, but during the war his primary role was to head an institute that made its scientific expertise available to the state. The institute thrived, and Hahn became one of the Nazi regime’s technocratic and military elites, was permitted to travel in occupied Eastern Europe to promote German “cultural influence,” and was even allowed to visit neutral Sweden, where he was made a foreign member of the Royal Academy of Sciences, a prelude to the Nobel Prize. In 1943 he received a high-ranking civilian award for his contributions to the war effort. After air raids destroyed the institute buildings in Berlin Dahlem in February–March 1944, Hahn and the KWI for Chemistry relocated to southern Germany, where the work continued until the war’s end.

Postwar . Hahn dedicated himself to the rebuilding effort, serving as president of the Kaiser Wilhelm Gesellschaft (KWG) and its successor, the Max Planck Gesellschaft, from 1946 to 1960. To an entire generation of German scientists, he was an iconic figure, the prototype of the decent German, a Nobel laureate whose most famous discovery was the result of basic research, a man known for his upright stance during National Socialism. As spokesperson for the KWG and, by extension, for the scientific community, Hahn projected an image of German science as undiminished in excellence and uninvolved in politics or the war. Particularly in the precarious early postwar years, his leadership succeeded in fostering solidarity among scientists and drawing support from the Allied occupation authorities.

As with most Germans of his generation, however, Hahn’s advocacy meant rewriting the history of the recent past. In his public statements and autobiographical writings, Hahn described his wartime work as unfettered fundamental research that was unrelated to the war effort, never examining his part in the fission project as a whole, the secret research in his institute, or its ties to industry, government, and the military. Like other fission scientists, he misrepresented the objective of the fission project, claiming that it was never directed toward a bomb but only to a nuclear reactor for energy production. Similarly, Hahn depicted the KWG under National Socialism as a haven for free, independent science, even though he was quite aware of the KWG’s ties to the Hitler regime and the military, and its opportunistic expansion into German-occupied Europe.

Hahn’s postwar efforts to distance himself and his institutions from National Socialism were typical of the self-portrayals of his generation. With his prominence, reputation, and the sheer quantity of his writings, he created a widely accepted narrative that obscured rather than illuminated the realities of scientific structures in the National Socialist state. It was only after the late twentieth century that historians had the necessary documentation and critical distance to explore the accommodation and collaboration of science in this period.

SUPPLEMENTARY BIBLIOGRAPHY

By far the most important archival source for Otto Hahn is the collection of his personal and professional papers in the Archiv zur Geschichte der Max-Planck-Gesellschaft, Berlin. A list of Hahn’s publications and selected secondary literature has been assembled by his grandson and published in Otto Hahn: Erlebnisse und Erkenntnisse, edited by Dietrich Hahn, Düsseldorf: Econ Verlag, 1975, which includes Hahn’s frankest memoir, written in 1945 and published posthumously, together with selected correspondence and postwar writings.

WORKS BY HAHN

A Scientific Autobiography, translated and edited by Willy Ley. London: MacGibbon & Kee, 1967.

My Life. Translated by Ernst Kaiser and Eithne Wilkins. New York: Herder and Herder, 1968.

OTHER SOURCES

Berninger, Ernst, ed. Otto Hahn—Eine Bilddokumentation: Persönlichkeit, wissenschaftliche Leistung, Öffentliches Wirken. Munich: H. Moos Verlag, 1969.

Crawford, Elisabeth, Ruth Lewin Sime, and Mark Walker. “A Nobel Tale of Wartime Injustice.” Nature 382 (1996): 393–395.

Gerlach, Walther, and Dietrich Hahn, ed. Otto Hahn: Ein Forscherleben unserer Zeit. Stuttgart: Wissenschaftliche Verlagsgesellschaft, 1984.

Hahn, Dietrich, ed. Otto Hahn Begründer des Atomzeitalters, Eine Biographie in Bildern und Dokumenten. Munich: List Verlag, 1979.

———. Otto Hahn: Leben und Werken in Texten und Bildern. Frankfurt/Main: Insel, 1988.

Krafft, Fritz. Im Schatten der Sensation: Leben und Wirken von Fritz Straæmann. Weinheim: Verlag Chemie 1981.

Sime, Ruth Lewin. Lise Meitner: A Life in Physics. Berkeley: University of California Press, 1996.

———. “The Politics of Memory: Otto Hahn and the Third Reich.” Physics in Perspective 8 (2006): 3–51.

———. “Otto Hahn and the Kaiser-Wilhelm-Institut für Chemie in World War II.” In Gemeinschaftsforschung, Bevollmächtigte und der Wissenstransfer. Die Organisation kriegsrelevanter Forschung und die Kaiser-Wilhelm-Gesellschaft im NS-System, edited by Helmut Maier. Wallstein: Göttingen, 2007.

Walker, Mark. German National Socialism and the Quest for Nuclear Power 1939–1949. Cambridge, U.K.: Cambridge University Press, 1989.

———. “Otto Hahn: Responsibility and Repression.” Physics in Perspective 8 (2006): 116–163.

Ruth Lewin Sime