Johannes Hans Daniel Jensen was born on 25 June 1907 inHamburg, Germany.
From 1926 to 1931, Jensen studied physics, mathematics, physical chemistry, and philosophy at the Universities ofFreiburg andHamburg, receiving hisdoctorate from the latter in 1932 underWilhelm Lenz.
In 1932, Jensen became Scientific Assistant in the Institute for Theoretical Physics at theUniversity of Hamburg, and completed hishabilitation there in 1936.[2][3]
In 1937, Jensen became adocent at the University of Hamburg and began working withPaul Harteck, Director of the University's Physical Chemistry Department and advisor to theHeereswaffenamt (HWA – Army Ordnance Office) on explosives. Harteck and his teaching assistant,Wilhelm Groth, made contact with theReichskriegsministerium (RKM – Reich Ministry of War) on 24 April 1939 to tell them of potential military applications ofnuclear chain reactions. Military control of theGerman nuclear energy project, also known as theUranverein (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 theUranverein, brought Jensen into the project. Jensen's main thrust was on doublecentrifuges forseparation ofuranium isotopes (see the section below citing internal reports of theUranverein). Harteck and Jensen developed a double centrifuge based on a rocking process (Schaukelverfahren) to facilitate the separation effect.[2][4][5]
In 1941, Jensen became Professor of Theoretical Physics atTechnische Hochschule Hannover (nowUniversität Hannover). In 1949, he was appointed Professor of Physics at theUniversity of Heidelberg, becomingemeritus praecox (early retiree) in 1969.
Adolf Hitler took power on 30 January 1933. On 7 April of that year theLaw for the Restoration of the Professional Civil Service was enacted; this law, and its subsequent related ordinances, politicized the education system in Germany. Other factors enforcing the politicization of education wereNationalsozialistische Deutsche Arbeiterpartei (NSDAP – National Socialist German Workers Party) organizations in academia and the rise of theDeutsche Physik (Aryan Physics) movement, which wasanti-Semitic and had a bias againsttheoretical physics, especially includingquantum mechanics. The Party organizations were theNationalsozialistischer Deutscher Studentenbund (NSDStB – National Socialist German Student League) founded in 1926, theNationalsozialistischer Lehrerbund (NSLB,National Socialist Teachers League) founded in 1927, and theNationalsozialistischer Deutscher Dozentenbund (NSDDB –National Socialist German University Lecturers League) founded in 1933. While membership in the NSDDB was not mandatory, it was tactically advantageous, if not unavoidable, as the district leaders had a decisive role in the acceptance of aHabilitationsschrift, which was a prerequisite to attaining the rank ofPrivatdozent necessary to becoming a university lecturer.[6][7][8][9]
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 andHabilitationsschrift. Upon his 1936habilitation 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.[10][11]
AfterWorld War II thedenazification process began. When Jensen faced the proceedings, he turned toWerner Heisenberg, a prominent member of theUranverein, for a testament to his character—a document known as aPersilschein (whitewash certificate).[12] 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 theSchutzstaffel (SS), and was appointed by the British occupation authorities to the chair for theoretical physics and the directorship of theMax 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.[13]
Paul Harteck, Johannes Jensen,Friedrich Knauer, andHans SuessÜber 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 JesnsenDer Thermodiffusionseffekt im Zusammenspiel mit der Konvektion durch mechanisch bewegte Wände und Vergleich mit der Thermosiphonwirkung G-89 (18 February 1941)
Johannes JensenÜber die Ultrazentrifugenmethode zur Trennung der Uranisotope G-95 (December 1941)
Paul Harteck and Johannes JensenGerechnung des Trenneffektes und der Ausbeute verschiedner Zentrifugenanordnungen zur Erhöhung des Wirkungsgrades einer einselnen Zentrifuge G-158 (February 1943)
Paul Harteck, Johannes Jensen, and Albert SuhrÜber den Zusammenhang zwischen Ausbeute und Trennschärfe bei der Niederdruckkolonne G-159
Konrad Beyerle,Wilhelm Groth,Paul Harteck, and Johannes JensenÜber Gaszentrifugen: Anreicherung der Xenon-, Krypton- und der Selen-Isotope nach dem Zentrifugenverfahren (Chemie, 1950); cited in Walker, 1993, p. 278
Otto Haxel, J. Hans D. Jensen, andHans E. SuessOn 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, andPeter JensenNuclear 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.
^Walker, 1993, pp. 192-204. In these pages, Mark Walker puts into perspective the motivations of and the pressures on students and scientists in the early years of National Socialism in Germany. He addresses the general situation, theUranverein scientists as a group, and particular cases, e.g., Johannes Jensen,Wilhelm Groth,Karl Wirtz, andWolfgang Gentner.
^Hentschel, 1996, Appendix C; see entries for NSDDB, NSDStB, and the NSLB.
Beyerchen, Alan D.Scientists Under Hitler: Politics and the Physics Community in the Third Reich (Yale, 1977)ISBN0-300-01830-4
Hentschel, Klaus, editor and Ann M. Hentschel, editorial assistant and TranslatorPhysics and National Socialism: An Anthology of Primary Sources (Birkhäuser, 1996)ISBN0-8176-5312-0
Hoffmann, DieterBetween Autonomy and Accommodation: The German Physical Society during the Third Reich,Physics in Perspective 7(3) 293-329 (2005)
Jensen, J. Hans D.Glimpses at the History of the Nuclear Structure Theory,The Nobel Prize in Physics 1963 (12 December 1963)J. Hans D. Jensen on Nobelprize.org
Schaaf, MichaelHeisenberg, Hitler und die Bombe. Gespräche mit Zeitzeugen (GNT-Verlag, Diepholz 2018)ISBN978-3-86225-115-5
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