James Franck

James Franck was born on 26 August 1882 in Hamburg, Germany, into a Jewish family, the second child and first son of Jacob Franck, a banker, and Rebecca Nachum Drucker. He had an older sister, Paula, and a younger brother, Robert. His father was a devout and religious man, while his mother came from a family of rabbis. In 1891, Franck enrolled at the Wilhelm-Gymnasium in Hamburg, which was then a boys-only school. 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 the University of Heidelberg, as it had a renowned law school. He attended lectures on law, but was far more interested in those on science. While there, he met Max 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. He attended mathematics lectures by Leo Königsberger and Georg Cantor, but Heidelberg was not strong on the physical sciences, so he decided to go to the University of Berlin. At Berlin, Franck attended lectures by Max Planck and Emil Warburg. For his Ph.D., Warburg suggested that he study corona discharges. He found this topic too complex, so he changed the focus of his thesis. Titled Über die Beweglichkeit der Ladungsträger der Spitzenentladung (On the mobility of the charge carriers of the peak discharge), it would subsequently be published in Annalen der Physik.{{cite journal 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 in Frankfurt in 1907, but did not enjoy it, and soon returned to the University of Berlin. At a concert, he met Ingrid Josefson, a Swedish pianist. They were married in a Swedish ceremony in Gothenburg on 23 December 1907. They had two daughters: Dagmar "Daggie", who was born in 1909; and Elisabeth "Lisa", who was born in 1912. To pursue an academic career in Germany, having a doctorate was not enough; one needed a habilitation (Dr. habil.). 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 with Eva von Bahr, Lise Meitner, Robert Pohl, Peter Pringsheim, Robert W. Wood, Arthur Wehnelt, and Wilhelm Westphal. His most fruitful collaboration was with Gustav Hertz, with whom he wrote 19 articles. He received his habilitation on 20 May 1911. == Franck–Hertz experiment ==

In 1914, Franck teamed up with Hertz to perform an experiment to investigate fluorescence. They designed a vacuum tube for studying energetic electrons that flew through a thin vapour of mercury atoms. They discovered that when an electron collided with a mercury atom it could lose only a specific quantity (4.9 electronvolts) of its kinetic 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. These experimental results provided confirmation of Albert Einstein's photoelectric effect and Planck's relation () linking energy (E) and frequency (f) arising from quantisation of energy with the Planck constant (h). But they also provided evidence supporting the model of the atom that had been proposed the previous year by Niels 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. 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 the wavelength of this ultraviolet 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. 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. 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". On 10 December 1926, Franck and Hertz were awarded the 1925 Nobel Prize in Physics "for their discovery of the laws governing the impact of an electron upon an atom". == World War I ==

Franck enlisted in the German Army soon after the outbreak of the First World War in August 1914. In December, he was sent to the Picardy sector of the Western Front. He became a deputy officer (offizierstellvertreter), and then a lieutenant (leutnant) in 1915. In early 1915, he was transferred to Fritz Haber's new unit that would introduce clouds of chlorine gas as a weapon. With Otto Hahn, he was responsible for locating sites for the attacks. He was awarded the Iron Cross, Second Class, on 30 March 1915, and the city of Hamburg awarded him the Hanseatic Cross on 11 January 1916. While in hospital with pleurisy, 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 the Russian front, he came down with dysentery. He returned to Berlin, where he joined Hertz, Westphal, Hans Geiger, Hahn, and others at Haber's Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry, working on the development of gas masks. 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. 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 as Walter Grotrian, Paul Knipping, Thea Krüger, Fritz Reiche, and Hertha 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 the laser. They coined the term metastable for atoms spending an extended time in a state other than that of least energy. 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 the bonzen (bigwigs). == Career in Göttingen ==

, James Franck, and Robert Pohl (the bonzen) in 1923 In 1920, the University of Göttingen offered Max Born its Chair of Theoretical Physics, which had recently been vacated by Peter Debye. Göttingen was an important centre for mathematics, thanks to David Hilbert, Felix Klein, Hermann Minkowski, and Carl 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 tenured professor ordinarius. He was allowed two assistants, so he brought Hertha Sponer with him from Berlin to fill one of the positions, and Pohl, a gifted teacher, headed the First Institute and handled the lectures. He refurbished the laboratory with the latest equipment using funds from his own pocket. Under Born and Franck, Göttingen was one of the world's great centres for physics from 1920 to 1933. The principle has since been applied to a wide variety of related phenomena. For his work during this time period, Franck was elected to the American Academy of Arts and Sciences in 1929. == Middle life ==

This period came to an end when the Nazi Party won power in Germany in an election on 2 March 1933. The following month, it enacted the Law 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. 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, and even let them have a decorated tree at Christmas; but he was proud of his Jewish heritage all the same. Franck found a position at the Polytekniske 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. When Germany invaded Denmark on 9 April 1940, the Hungarian chemist George de Hevesy dissolved the gold medal, along with that of Max von Laue in aqua 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. In 1935, Franck moved to the United States, where he had accepted a professorship at Johns Hopkins University. The laboratory there was poorly equipped compared to the one in Göttingen, but he received $10,000 for equipment from the Rockefeller 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 the University of Chicago, where his work on photosynthesis had attracted interest, in 1938. Franck's first paper there, co-authored with Edward Teller, was on photochemical processes in crystals. Hans Gaffron became his collaborator. They were joined by Pringsheim, who escaped from Belgium after the German invasion. Franck arranged a position for Pringsheim at his laboratory. Both his daughters and their families moved to the United States, and he was also able to bring out his elderly mother and aunt. He became a naturalized US citizen on 21 July 1941, In any event, the Interim Committee decided otherwise. == Later life ==

, James Franck, Albert Einstein, and Isidor Rabi in 1954 Franck married Hertha Sponer in a civil ceremony on 29 June 1946, after his first wife, Ingrid, died in 1942. In 1947, he became professor emeritus at the University of Chicago, but continued to work there to tackle the problem of explaining the mechanism of photosynthesis. Meitner saw no break between his early and later work. She recalled that: Franck died suddenly of a heart attack while visiting Göttingen on 21 May 1964 at the age of 81. He is buried in Chicago with his first wife. == Recognition ==

Awards Memberships == Commemoration ==

In 1967, the University of Chicago named the James Franck Institute after him. A lunar crater has also been named in his honour. His papers and recast Nobel Prize medal are located in the University of Chicago Library. == See also ==