Klaus Clusius
Klaus Paul Alfred Clusius (19 March 1903 – 28 May 1963) was a German physical chemist from Breslau (Wrocław), Silesia. During World War II, he worked on the German nuclear energy project, also known as the Uranium Club; he worked on isotope separation techniques and heavy water production. After the war, he was a professor of physical chemistry at the University of Zurich. He died in Zurich. Education. Clusius studied at the "Technische Hochschule Breslau" (today, the Wrocław University of Technology) from 1922 to 1926. He received his doctorate in 1926, under Arnold Eucken, who was the director of  the physicochemical institute there; his thesis was on the specific heat of solids at low temperatures. From 1926 to 1929, he was Eucken's teaching assistant. From 1929 to 1930, under a Rockefeller Foundation Fellowship, he did postdoctoral studies and research at the University of Oxford, with Cyril Norman Hinshelwood, and at the Leiden University. He completed his Habilitation, in 1931, at the "Georg-August-Universität Göttingen" under Eucken, who had been the director of the physicochemical institute there since 1929. He then became Eucken's teaching assistant. Career. In 1934, Clusius became an "ausserordentlicher Professor" (extraordinarius professor) at the  University of Würzburg. From 1936, he was an "ordentlicher Professor" (ordinarius professor) at the "Ludwig Maximilian University of Munich". At that time or later, he became Director of the "Physikalisch-Chemisches Institut der Universität München" (Physical Chemistry Institute of the University of Munich). At the University, he conducted major experiments on heavy water, and he developed a thermodiffusion isotope separation tube, in 1938, with his younger colleague Gerhard Dickel. In December 1938, the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to "Naturwissenschaften" reporting they had detected the element barium after bombarding uranium with neutrons; simultaneously, they communicated  these results to Lise Meitner, who had in July of that year fled to The Netherlands and then went to Sweden. Meitner, and her nephew Otto Robert Frisch, correctly interpreted these results as being nuclear fission. Frisch confirmed this experimentally on 13 January 1939. Paul Harteck was director of the physical chemistry department at the University of Hamburg and an advisor to the "Heereswaffenamt" (HWA, Army Ordnance Office). On 24 April 1939, along with his teaching assistant Wilhelm Groth, Harteck made contact with the "Reichskriegsministerium" (RKM, Reich Ministry of War) to alert them to the potential of military applications of  nuclear chain reactions. Two days earlier, on 22 April 1939, after hearing a colloquium paper by Wilhelm Hanle on the use of uranium fission in a "Uranmaschine" (uranium machine, i.e., nuclear reactor), Georg Joos, along with Hanle, notified Wilhelm Dames, at the "Reichserziehungsministerium" (REM, Reich Ministry of Education), of potential military applications of nuclear energy. The communication was given to Abraham Esau, head of the physics section of the "Reichsforschungsrat" (RFR, Reich Research Council) at the REM. On 29 April, a group, organized by Esau, met at the REM to discuss the potential of a sustained nuclear chain reaction. The  group included the physicists Walther Bothe, Robert Döpel, Hans Geiger, Wolfgang Gentner (probably sent by Walther Bothe), Wilhelm Hanle, Gerhard Hoffmann, and Georg Joos; Peter Debye was invited, but he did not attend. After this, informal work began at Göttingen by Joos, Hanle, and their colleague Reinhold Mannfopff; the group of physicists was known informally as the first "Uranverein" (Uranium Club) and formally as "Arbeitsgemeinschaft für Kernphysik". The group's work was discontinued in August 1939, when the three were called to military training. The second "Uranverein" began after the HWA squeezed out the RFR of the REM and started  the formal German nuclear energy project under military auspices. The second "Uranverein" was formed on 1 September 1939, the day World War II began, and it had its first meeting on 16 September 1939. The meeting was organized by Kurt Diebner, former student of Gerhard Hoffmann the University of Halle and advisor to the HWA, and held in Berlin. The invitees included Walther Bothe, Siegfried Flügge, Hans Geiger, Otto Hahn, Paul Harteck, Gerhard Hoffmann, Josef Mattauch, and Georg Stetter. A second meeting was held soon thereafter and included Klaus Clusius, Robert Döpel, Werner Heisenberg, and Carl Friedrich von Weizsäcker. Also  at this time, the "Kaiser-Wilhelm Institut für Physik" (KWIP, Kaiser Wilhelm Institute for Physics, after World War II the Max Planck Institute for Physics), in Berlin-Dahlem, was placed under HWA authority, with Diebner as the administrative director, and the military control of the nuclear research commenced. In 1939, Clusius and Dickel announced the separation of chlorine isotopes, an accomplishment which had been sought for decades. That same year, Clusius, Paul Harteck, Rudolf Fleischmann, Wilhelm Groth and others initiated experiments with the Clusius-Dickel thermodiffusion isotope separation tube with uranium hexafluoride. In 1942, with about four physical chemists, Clusius  further explored isotope separation and conducted experiments on heavy water production problems. During World War II, Clusius gave talks outside of the Third Reich, just as did Werner Heisenberg. From 1947 to 1963, Clusius was an ordinarius professor of physical chemistry at the "Universität Zürich". The research he directed included the separation and enrichment of stable isotopes, among them those of rare gases (except for helium) using cascaded Clusius-Dickel separation columns. These isotopes, which were in much demand, were supplied to a number of research laboratories. Further research was high-precision calorimetry, elucidation of chemical reaction pathways using 15 -nitrogen, electrochemical and low temperature fractionation methods for large scale production of nitrogen and oxygen isotopes. His research activities in Zürich are best described in. Clusius mentored a large number of graduate students and postdoctoral associates, among them several with future careers in academia. Among these was Ernst Schumacher, who became a professor at the University of Bern, where he in turn mentored a large number of students and associates. Another student was Horst Meyer (physicist) professor at Duke University. Among the postdoctoral assistants was Michael Hoch, who became professor of Chemical Engineering at the University of Cincinnati. Honors. Clusius  received honors which included: Internal Reports. The following reports were published in "Kernphysikalische Forschungsberichte" ("Research Reports in Nuclear Physics"), an internal publication of the German "Uranverein". The reports were classified Top Secret, they had very limited distribution, and the authors were not allowed to keep copies. The reports were confiscated under the Allied Operation Alsos and sent to the United States Atomic Energy Commission for evaluation. In 1971, the reports were declassified and returned to Germany. The reports are available at the Karlsruhe Nuclear Research Center and the American Institute of Physics.