J. Hans D. Jensen

Infobox Scientist
name = Johannes Hans Daniel Jensen
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caption = Johannes Hans Daniel Jensen
birth_date = June 25, 1907
birth_place = Hamburg
death_date = February 11, 1973
death_place = Heidelberg
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nationality = German
ethnicity =
field = physics
work_institutions =
alma_mater = University of Hamburg
doctoral_advisor = Wilhelm Lenz
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Johannes Hans Daniel Jensen (June 25, 1907 in Hamburg – February 11, 1973 in Heidelberg) was a German nuclear physicist. During World War II, he worked on the German nuclear energy project, also know as the Uranium Club, in which he made contributions to the separation of uranium isotopes. After the war, he was a professor at the University of Heidelberg. He was a visiting professor at the University of Wisconsin–Madison, the Institute for Advanced Study, Indiana University, and the California Institute of Technology. Jensen shared half of the 1963 Nobel Prize for Physics with Maria Göppert-Mayer for their proposal of the shell nuclear model.

Education

Jensen studied physics, mathematics, physical chemistry, and philosophy at the " Albert-Ludwigs-Universität Freiburg" and the University of Hamburg from 1926 to 1931, and he received his doctorate at the latter in 1932 under Wilhelm Lenz. Jensen completed his Habilitation in 1936 at the University of Hamburg. [ [http://nobelprize.org/nobel_prizes/physics/laureates/1963/jensen-bio.html Johannes Jensen] – Nobel Prize Biography (1963).] [ Hentschel and Hentschel, 1996, 363-364 and Appendix F; see the entry for Johannes Jensen.]

Career

In 1937, Jensen was Privatdozent (unpaid lecturer) at the University of Hamburg and began collaboration there with Paul Harteck, who was director of the physical chemistry department at there and also advisor to the "Heereswaffenamt" (HWA, Army Ordnance Office) on explosives. Harteck and his teaching assistant Wilhelm Groth made contact with the "Reichskriegsministerium" (RKM, Reich Ministry of War) on 24 April 1939 to alert them to the potential of 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. Harteck, one of the principals in the "Uranverein", 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 ("Schaukelverfahren") to facilitate the separation effect. [ [http://nobelprize.org/nobel_prizes/physics/laureates/1963/jensen-bio.html Johannes Jensen] – Nobel Prize Biography (1963).] [ Hentschel and Hentschel, 1996, 363-364 and Appendix F; see the entries for Harteck and Johannes Jensen.] [ Walker, 1993, 121-122.]

In 1941, Jensen became an extraordinarius professor of theoretical physics at the "Technische Hochschule Hannover" (today, the University of Hanover), and in 1946 he became an ordinarius professor there. In 1949, he was appointed ordinarius professor at the Ruprecht Karl University of Heidelberg; since 1969 he was emeritus praecox. He was a guest professor at the University of Wisconsin–Madison (1950), the Institute for Advanced Study (1952), and Indiana University and the California Institute of Technology (1953). [ [http://nobelprize.org/nobel_prizes/physics/laureates/1963/jensen-bio.html Johannes Jensen] – Nobel Prize Biography (1963).] [ Hentschel and Hentschel, 1996, 363-364 and Appendix F; see the entry for Johannes Jensen.]

In 1963, Jensen shared half of the Nobel Prize in Physics with Maria Göppert-Mayer for their proposal of the shell nuclear model; the remaining half of the prize was awarded to Eugene Wigner for unrelated work in nuclear and particle physics, especially through the application of fundamental symmetry principles.

Party memberships

Adolf Hitler took power on 30 January 1933. On 7 April, the Law for the Restoration of the Professional Civil Service was enacted; this law, and its subsequent related ordnances, politicized the education system in Germany. Other factors enforcing the politicization of education were " Nationalsozialistische Deutsche Arbeiterpartei" (NSDAP, National Socialist German Workers Party) organizations in academia and the rise of the " deutsche Physik" movement, which was anti-Semitic and had a bias against theoretical physics, especially including quantum mechanics. The Party organizations were the "Nationalsozialistischer Deutscher Studentenbund" (NSDStB, National Socialist German Student League) founded in 1926, the "Nationalsozialistischer Lehrerbund" (NSLB, National Socialist Teachers League) founded in 1927, and the "Nationalsozialistischer 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 an "Habilitationsschrift", which was a prerequisite to attaining the rank of "Privatdozent" necessary to becoming a university lecturer. [ Walker, 1993, 192-204. In these pages, Mark Walker puts into perspective the motivations of and the pressures on the students and scientists in the early years of National Socialism in Germany. He addresses the general situation, the "Uranverein" scientists as a group, and particular cases, e.g., Johannes Jensen, Wilhelm Groth, Karl Wirtz, and Wolfgang Gentner.] [ Hentschel, 1996, Appendix C; see the entries the NSDDB, NSDStB, and the NSLB.] [ Hoffmann, Dieter "Between Autonomy and Accommodation: The German Physical Society during the Third Reich", "Physics in Perspective" 7(3) 293-329 (2005).] [ Beyerchen, 1977, 123 – 167.]

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 Jensen’s "Habilitation" in 1936, he had been a member of the NSDDB for three years, the NSLB for two years, and a candidate for membership in the NSDAP, which he received the next year. The leader of the NSLB at the University had made it clear that active participation was expected from Jensen, and that is what they got. [ Walker, 1993, 195-196.] [ Hentschel and Hentschel, 1996, Appendix F; see the entry for Johannes Jensen.]

After World War II, the denazification process began. When Jensen faced the proceedings, he turned to Werner Heisenberg, a prominent member of the "Uranverein", for a testament to his character – a document known as a "Persilschein" (whitewash certificate). [ "Persilschein" a play on words using the name of the German detergent "Persil".] Heisenberg was a particularly powerful writer of these documents, as he had never been a member of the NSDAP, he had publicly clashed with the NSDAP and the Schutzstaffel (SS), and he had been appointed by the British occupation authorities to the chair for theoretical physics and the directorship of the " Max-Planck Institut für Physik" then in Göttingen. Heisenberg wrote the document and convinced the authorities that Jensen had only joined the Party organizations to avoid unnecessary difficulties in academia. [ Walker, 1993, 192-204.]

Honors

Honors conferred upon Jensen include: [ [http://nobelprize.org/nobel_prizes/physics/laureates/1963/jensen-bio.html Johannes Jensen] – Nobel Prize Biography (1963).] [ Hentschel and Hentschel, 1996, 363-364 and Appendix F; see the entry for Johannes Jensen.]

*1947 – Honorary professor at the University of Hamburg

*1963 – Nobel Prize in Physics

*1964 – Honorary doctorate from the "Technische Universität Hannover" (today, the University of Hanover)

*1969 – Honorary citizen of Fort Lauderdale, Florida

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. [ Hentschel and Hentschel, 1996, Appendix E; see the entry for "Kernphysikalische Forschungsberichte".] [ Walker, 1993, 268-274.]

*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

elected Literature

*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.

Bibliography

*Beyerchen, Alan D. "Scientists Under Hitler: Politics and the Physics Community in the Third Reich" (Yale, 1977) ISBN 0-300-01830-4

*Hentschel, Klaus, editor and Ann M. Hentschel, editorial assistant and Translator "Physics and National Socialism: An Anthology of Primary Sources" (Birkhäuser, 1996) ISBN 0-8176-5312-0

*Hoffmann, Dieter "Between 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" [http://nobelprize.org/nobel_prizes/physics/laureates/1963/jensen-lecture.pdf (12 December 1963)]

*Stech, Berthold "J.H.D. Jensen: Personal recollection" [http://www.thphys.uni-heidelberg.de/home/info/historie_dir/jensen_stech.html University of Heidelberg]

*Walker, Mark "German National Socialism and the Quest for Nuclear Power 1939–1949" (Cambridge, 1993) ISBN 0-521-43804-7

Notes