Johannes Hans Daniel Jensen

Education Johannes Hans Daniel Jensen was born on 25 June 1907 in Hamburg, Germany. From 1926 to 1931, Jensen studied physics, mathematics, physical chemistry, and philosophy at the University of Freiburg and the University of Hamburg. He received his Doctor rerum naturalium in 1932 and his habilitation in 1936, both from the University of Hamburg.

Career In 1937, Jensen became a docent at the University of Hamburg, and began working with Paul Harteck, Director of the University's Physical Chemistry Department and advisor to the (HWA – Army Ordnance Office) on explosives. Harteck and his teaching assistant, Wilhelm Groth, made contact with the (RKM – Reich Ministry of War) on 24 April 1939 to tell them of potential military applications of nuclear chain reactions. Military control of the German nuclear energy project, also known as the Uranverein (Uranium Club), began on 1 September 1939, the day that Nazi Germany initiated World War II by invading Poland. Harteck, one of the principals in the , brought Jensen into the project. Jensen's main thrust was on double centrifuges for separation of uranium isotopes (see the section below citing internal reports of the Uranverein). Harteck and Jensen developed a double centrifuge based on a rocking process to facilitate the separation effect.

In 1941, Jensen was appointed Professor of Theoretical Physics at Technische Hochschule Hannover (now Leibniz University Hannover). In 1949, he became a professor at the University of Heidelberg, where he remained until his retirement in 1969.

While all German universities were politicized, not all were as strict in carrying out this end as was the University of Hamburg, where Jensen received his doctorate and Habilitationsschrift. Upon his 1936 habilitation he had been a member of NSDDB for three years, the NSLB for two years, and a candidate for membership in NSDAP, which he received the next year. The university leader of NSLB had made it clear that active participation was expected from Jensen, and that is what they got.

After World War II the denazification process began. When Jensen faced the proceedings, he turned to Werner Heisenberg, a prominent member of the , for a testament to his character—a document known as a (whitewash certificate). Heisenberg was a particularly powerful writer of these documents; as he had never been a member of NSDAP, he had publicly clashed with NSDAP and the (SS), and was appointed by the British occupation authorities to the chair for theoretical physics and the directorship of the Max Planck Institute for Physics then in Göttingen. Heisenberg wrote the document and convinced the authorities that Jensen had joined the Party organizations only to avoid unnecessary difficulties in academia.

Honors Honors conferred upon Jensen include: Paul Harteck, Johannes Jensen, Friedrich Knauer, and Hans Suess Über die Bremsung, die Diffusion und den Einfang von Neutronen in fester Kohlensäure und über ihren Einfang in Uran G-36 (19 August 1940) Paul Harteck and Johannes Jesnsen Der Thermodiffusionseffekt im Zusammenspiel mit der Konvektion durch mechanisch bewegte Wände und Vergleich mit der Thermosiphonwirkung G-89 (18 February 1941) Johannes Jensen Über die Ultrazentrifugenmethode zur Trennung der Uranisotope G-95 (December 1941) Paul Harteck and Johannes Jensen Gerechnung des Trenneffektes und der Ausbeute verschiedner Zentrifugenanordnungen zur Erhöhung des Wirkungsgrades einer einselnen Zentrifuge G-158 (February 1943) Paul Harteck, Johannes Jensen, and Albert Suhr Über den Zusammenhang zwischen Ausbeute und Trennschärfe bei der Niederdruckkolonne G-159

Works Books Konrad Beyerle, Wilhelm Groth, Paul Harteck, and Johannes Jensen Über Gaszentrifugen: Anreicherung der Xenon-, Krypton- und der Selen-Isotope nach dem Zentrifugenverfahren (Chemie, 1950); cited in Walker, 1993, p. 278

Articles Otto Haxel, J. Hans D. Jensen, and Hans E. Suess On the "Magic Numbers" in Nuclear Structure, Phys. Rev. Volume 75, 1766 - 1766 (1949). Institutional affiliations: Haxel: Max-Planck Institut für Physik, Göttingen; Jensen: Institut für theoretische Physik, Heidelberg; and Suess: Inst. für physikalische Chemie, Hamburg. Received 18 April 1949. Helmut Steinwedel, J. Hans D. Jensen, and Peter Jensen Nuclear Dipole Vibrations, Phys. Rev. Volume 79, Issue 6, 1019 - 1019 (1950). Institutional affiliations: Steinwedel and J. H. D. Jensen - Institut für theoretische Physik, Universität Heidelberg and Peter Jensen - Physikalisches Institut, Universität Freiburg. Received 10 July 1950.