Franck participated in theManhattan Project duringWorld War II as director of the chemistry division of theMetallurgical Laboratory. He was also the Chairman of the Committee on Political and Social Problems regarding theatomic bomb, which is best known for the compilation of theFranck Report, which recommended that the atomic bombs not be used on the Japanese cities without warning.
James Franck was born on 26 August 1882 inHamburg, Germany, into aJewish family, the second child and first son of Jacob Franck, a banker, and Rebecca Nachum Drucker.[3] He had an older sister, Paula, and a younger brother, Robert.[4] His father was a devout and religious man, while his mother came from a family ofrabbis.[3]
In 1891, Franck enrolled at theWilhelm-Gymnasium in Hamburg, which was then a boys-only school.[4] Hamburg had no university then, so prospective students had to attend one of the 22 universities elsewhere in Germany. Intending to study law and economics, In 1901, Franck entered theUniversity of Heidelberg, as it had a renowned law school.[5] He attended lectures on law, but was far more interested in those on science. While there, he metMax Born, who would become a lifelong friend. With Born's help, he was able to persuade his parents to allow him to switch to studying physics and chemistry.[6] He attended mathematics lectures byLeo Königsberger andGeorg Cantor, but Heidelberg was not strong on the physical sciences, so he decided to go to theUniversity of Berlin.[5]
At Berlin, Franck attended lectures byMax Planck andEmil Warburg.[7] For hisPh.D.,[8] Warburg suggested that he studycorona discharges. He found this topic too complex, so he changed the focus of his thesis.[9] TitledÜber die Beweglichkeit der Ladungsträger der Spitzenentladung (On the mobility ofions),[10] it would subsequently be published inAnnalen der Physik.[11]
With his thesis completed, Franck had to perform his deferred military service. He was called up on 1 October 1906 and joined the 1st Telegraph Battalion. He suffered a minor horse riding accident in December and was discharged as unfit for duty. He took up an assistantship at the Physikalische Verein inFrankfurt in 1907, but did not enjoy it, and soon returned to the University of Berlin.[12] At a concert, he met Ingrid Josefson, a Swedish pianist. They were married in a Swedish ceremony inGothenburg on 23 December 1907. They had two daughters: Dagmar "Daggie", who was born in 1909; and Elisabeth "Lisa", who was born in 1912.[13]
To pursue an academic career in Germany, having a doctorate was not enough; one needed avenia legendi, or habilitation. This could be achieved with either another major thesis or by producing a substantial body of published work. Franck chose the latter route. There were many unsolved problems in physics at the time, and by 1914 he had published 34 articles. He was the sole author of some, but generally preferred working in collaboration withEva von Bahr,Lise Meitner,Robert Pohl, Peter Pringsheim,Robert W. Wood,Arthur Wehnelt, andWilhelm Westphal. His most fruitful collaboration was withGustav Hertz, with whom he wrote 19 articles. He received his habilitation on 20 May 1911.[14]
Anode current (arbitrary units) versus grid voltage (relative to the cathode). This graph is based on the original 1914 paper by Franck and Hertz.
In 1914, Franck teamed up with Hertz to perform an experiment to investigatefluorescence. They designed avacuum tube for studying energeticelectrons that flew through a thin vapour ofmercury atoms. They discovered that when an electron collided with a mercury atom it could lose only a specific quantity (4.9 electronvolts) of itskinetic energy before flying away. A faster electron does not decelerate completely after a collision, but loses precisely the same amount of its kinetic energy. Slower electrons just bounce off mercury atoms without losing any significant speed or kinetic energy.[15][16]
These experimental results provided confirmation ofAlbert Einstein'sphotoelectric effect and Planck's relation (E =fh) linking energy (E) and frequency (f) arising from quantisation of energy with thePlanck constant (h). But they also provided evidence supporting themodel of the atom that had been proposed the previous year byNiels Bohr. Its key feature was that an electron inside an atom occupies one of the atom's "quantum energy levels". Before a collision, an electron inside the mercury atom occupies its lowest available energy level. After the collision, the electron inside occupies a higher energy level with 4.9 eV more energy. This means that the electron is more loosely bound to the mercury atom. There were no intermediate levels or possibilities.[15][17]
In a second paper presented in May 1914, Franck and Hertz reported on the light emission by the mercury atoms that had absorbed energy from collisions. They showed that thewavelength of thisultraviolet light corresponded exactly to the 4.9 eV of energy that the flying electron had lost. The relationship of energy and wavelength had also been predicted by Bohr.[15][18] Franck and Hertz completed their last paper together in December 1918. In it, they reconciled the discrepancies between their results and Bohr's theory, which they now acknowledged.[19][20] In his Nobel lecture, Franck admitted that it was "completely incomprehensible that we had failed to recognise the fundamental significance of Bohr's theory, so much so, that we never even mentioned it once".[21] On 10 December 1926, Franck and Hertz were awarded the 1925Nobel Prize in Physics "for their discovery of the laws governing the impact of an electron upon an atom".[2]
Franck enlisted in theGerman Army soon after the outbreak of theFirst World War in August 1914. In December, he was sent to thePicardy sector of theWestern Front. He became a deputy officer (offizierstellvertreter), and then a lieutenant (leutnant) in 1915.[22] In early 1915, he was transferred toFritz Haber's new unit that would introduce clouds of chlorine gas as a weapon.[23] WithOtto Hahn, he was responsible for locating sites for the attacks. He was awarded theIron Cross, Second Class, on 30 March 1915,[24] and the city of Hamburg awarded him theHanseatic Cross on 11 January 1916.[24] While in hospital withpleurisy, he co-wrote yet another scientific paper with Hertz, and he was appointed an assistant professor in his absence by Frederick William University on 19 September 1916. Sent to theRussian front, he came down withdysentery. He returned to Berlin, where he joined Hertz, Westphal,Hans Geiger, Hahn, and others at Haber'sKaiser Wilhelm Institute for Physical Chemistry and Electrochemistry, working on the development ofgas masks.[22] He was awarded the Iron Cross, First Class, on 23 February 1918. He was discharged from the army on 25 November 1918, soon after the war ended.[24]
With the war over, Haber's Kaiser Wilhelm Institute now returned to research, and Haber offered Franck a job. His new post came with more pay, but was not a tenured position. It did however allow him to pursue his research as he wished. Working with new, younger collaborators such asWalter Grotrian, Paul Knipping, Thea Krüger,Fritz Reiche, andHertha Sponer, his first papers at the Kaiser Wilhelm Institute examined atomic electrons in their excited state, results that would later prove important in the development of thelaser.[25] They coined the termmetastable for atoms spending an extended time in a state other thanthat of least energy.[26] When Niels Bohr visited Berlin in 1920, Meitner and Franck arranged for him to come to the Kaiser Wilhelm Institute to talk with the younger staff without the presence of thebonzen (bigwigs).[27]
In 1920, theUniversity of Göttingen offeredMax Born its Chair of Theoretical Physics, which had recently been vacated byPeter Debye. Göttingen was an important centre for mathematics, thanks toDavid Hilbert,Felix Klein,Hermann Minkowski, andCarl Runge, but not so much for physics. This would change. As part of his price for coming to Göttingen, Born wanted Franck to head experimental physics there. On 15 November 1920, he became Professor of Experimental Physics and Director of the Second Institute for Experimental Physics, a fully tenuredprofessor ordinarius. He was allowed two assistants, so he broughtHertha Sponer with him from Berlin to fill one of the positions, and Pohl, a gifted teacher, headed the First Institute and handled the lectures.[28][29] He refurbished the laboratory with the latest equipment using funds from his own pocket.[30]
Under Born and Franck, Göttingen was one of the world's great centres for physics from 1920 to 1933.[29][30] Although they published only three papers together, Born and Franck discussed every one of their papers with each other. Gaining admittance to Franck's laboratory became highly competitive. His doctoral students includedHans Kopfermann,Arthur R. von Hippel,Wilhelm Hanle,Fritz Houtermans,Heinrich Kuhn, andHeinz Maier-Leibnitz.[31] In supervising doctoral candidates, he had to ensure that thesis topics were well-defined, and would teach the candidate how to conduct original research, while still staying within the limits of the candidate's ability, the laboratory's equipment and the institute's budget.[32] Under his direction, research was carried out into the structure of atoms and molecules.[33]
In his own research, Franck developed what became known as theFranck–Condon principle, a rule inspectroscopy andquantum chemistry that explains the intensity ofvibronic transitions, simultaneous changes in electronic and vibrational energy levels of a molecule due to the absorption or emission of aphoton of the appropriate energy. The principle states that during anelectronic transition, a change from onevibrationalenergy level to another will be more likely to happen if the two vibrationalwave functions overlap more significantly.[34][35] The principle has since been applied to a wide variety of related phenomena.[36]
This period came to an end when theNazi Party won power in Germany inan election on 2 March 1933. The following month, it enacted theLaw for the Restoration of the Professional Civil Service, which provided for the retirement or dismissal of all Jewish civil servants, along with political opponents of the government. As a veteran of the First World War, Franck was exempt, but he submitted his resignation anyway on 17 April 1933.[38] He once commented that science was his god and nature was his religion. He did not require his daughters to attend religious instruction classes at school,[39] and even let them have a decorated tree at Christmas;[40] but he was proud of his Jewish heritage all the same.[39] He was the first academic to resign in protest over the law.[41] Newspapers around the world reported it, but no government or university protested.[42]
Franck assistedFrederick Lindemann in helping dismissed Jewish scientists find work overseas, before he left Germany in November 1933.[43] After a brief visit to the United States, where he measured the absorption of light inheavy water with Wood atJohns Hopkins University, he took up a position at theNiels Bohr Institute inCopenhagen.[44] He needed a new collaborator, so he took onHilde Levi, whose recent thesis had impressed him.[45] His original intention was to continue his research into the fluorescence of vapours and liquids, but under Bohr's influence they began to take an interest in biological aspects of these reactions, particularlyphotosynthesis, the process by which plants use light to convertcarbon dioxide and water into more organic compounds. Biological processes turned out to be far more complicated than simple reactions in atoms and molecules. He co-authored two papers with Levi on the subject, which he would return to over the following years.[44][46][47]
Franck found a position at thePolytekniske Læreanstalt in Copenhagen for Arthur von Hippel, who was now his son in law, having married his daughter Dagmar. He decided to provide financial security for his children by dividing his Nobel Prize money between them. The gold medal itself was entrusted to Niels Bohr for safekeeping.[48] When Germanyinvaded Denmark on 9 April 1940, the Hungarian chemistGeorge de Hevesy dissolved the gold medal, along with that ofMax von Laue inaqua regia to prevent the Germans from taking them. He placed the resulting solution on a shelf in his laboratory at the Niels Bohr Institute. After the war, he returned to find the solution undisturbed and precipitated the gold out of the acid. The Nobel Society then recast the Nobel Prize medals.[49][50]
In 1935, Franck moved to the United States, where he had accepted a professorship at Johns Hopkins University.[51] The laboratory there was poorly equipped compared to the one in Göttingen, but he received $10,000 for equipment from theRockefeller Foundation. A more intractable problem was that the university had no money to hire skilled staff. Franck was concerned about his family members remaining in Germany, and needed money to help them emigrate. He therefore accepted an offer from theUniversity of Chicago, where his work on photosynthesis had attracted interest, in 1938.[52]
Franck's first paper there, co-authored withEdward Teller, was on photochemical processes in crystals.[53]Hans Gaffron became his collaborator.[54] They were joined by Pringsheim, who escaped from Belgium after theGerman invasion. Franck arranged a position for Pringsheim at his laboratory.[55] Both his daughters and their families moved to the United States, and he was also able to bring out his elderly mother and aunt.[56] He became anaturalized US citizen on 21 July 1941,[24] so he was not anenemy alien when the United Statesdeclared war on Germany on 11 December 1941. His daughters still were, though, so they were restricted from travelling, and could not take care of their mother when she fell ill and died on 10 January 1942, although they were permitted to attend her funeral.[57]
In February 1942,Arthur Compton established itsMetallurgical Laboratory at the University of Chicago. As part of theManhattan Project, its mission was to buildnuclear reactors to createplutonium that would be used inatomic bombs.[58] The Metallurgical Laboratory's Chemistry Division was initially headed byFrank Spedding, but he preferred hands on work to administration. Compton then turned to Franck, with some trepidation owing to his German background.[59] Compton later wrote:
How Franck welcomed an invitation to join our project! It was a vote of confidence that far exceeded his hopes, and it gave him a chance to do his part for the cause of freedom. "It's not the German people I'm fighting", he explained. "It's the Nazis. They have a stranglehold over Germany. The German people are helpless until we can break the strength of their Nazi masters." The chemists welcomed Franck as an elder scientific statesman whose guidance they were glad to follow.[60]
In addition to heading the Chemistry Division, Franck was also the chairman of the Metallurgical Laboratory's Committee on Political and Social Problems regarding the atomic bomb, which consisted of himself andDonald J. Hughes,J. J. Nickson,Eugene Rabinowitch,Glenn T. Seaborg, J. C. Stearns andLeó Szilárd.[61] In 1945, Franck warnedHenry A. Wallace of their fears that "mankind has learned to unleash atomic power without being ethically and politically prepared to use it wisely."[62] The committee compiled what became known as theFranck Report. Finished on 11 June 1945, it recommended that theatomic bombs not be used on the Japanese cities without warning.[61] In any event, theInterim Committee decided otherwise.[63]
Franck marriedHertha Sponer in a civil ceremony on 29 June 1946,[64] after his first wife, Ingrid, died in 1942. In 1947, he became professor emeritus at theUniversity of Chicago, but continued to work there to tackle the problem of explaining the mechanism ofphotosynthesis. Meitner saw no break between his early and later work. She recalled that:
Franck enjoyed talking about his problems, not so much to explain them to others as to satisfy his own mind. Once a problem had aroused his interest he was completely captivated, indeed obsessed by it. Common sense and straight logic were his main tools, together with simple apparatus. His research followed an almost straight line, from his early studies of ion mobilities to his last work on photosynthesis; it was always the energy exchange between atoms or molecules that fascinated him.[65]
^Franck, J.;Hertz, G. (1914). "Über Zusammenstöße zwischen Elektronen und Molekülen des Quecksilberdampfes und die Ionisierungsspannung desselben" [On the collisions between electrons and molecules of mercury vapor and the ionization potential of the same].Verhandlungen der Deutschen Physikalischen Gesellschaft (in German).16:457–467.
^Franck, J.;Hertz, G. (1914). "Über die Erregung der Quecksilberresonanzlinie 253,6 μμ durch Elektronenstöße" [On the excitation of mercury resonance lines at 253.6 nm by electron collisions].Verhandlungen der Deutschen Physikalischen Gesellschaft (in German).16:512–517.
^Franck, J.;Hertz, G. (1919). "Die Bestätigung der Bohrschen Atomtheorie im optimalen Spektrum durch Untersuchungen der unelastischen Zusammenstöße".Physikalische Zeitschrift (in German).20:132–143.
^Van der Kloot, W. (2004). "April 1918: Five Future Nobel prize-winners inaugurate weapons of mass destruction and the academic-industrial-military complex".Notes Rec. R. Soc. Lond.58 (2):149–160.doi:10.1098/rsnr.2004.0053.S2CID145243958.
Lemmerich, Jost (2011).Science and Conscience: The life of James Franck. Translated by Ann M. Hentschel. Stanford, California: Stanford University Press.ISBN978-0-8047-7909-8.
Medawar, Jean; Pyke, David (2012).Hitler's Gift: The True Story of the Scientists Expelled by the Nazi Regime. New York: Arcade Publishing.ISBN978-1-61145-709-4.
James Franck on Nobelprize.org including the Nobel Lecture, 11 December 1926: "Transformation of Kinetic Energy of Free Electrons into Excitation Energy of Atoms by Impacts"
