Gustav Hertz

German physicist

• Born: July 22, 1887
• Birthplace: Hamburg, Germany
• Died: October 30, 1975
• Place of death: Berlin, East Germany (now in Germany)

Hertz and his colleague James Franck received the Nobel Prize in Physics in 1926 for their spectroscopic experiments on mercury vapor bombarded with electrons. Their results were some of the first to confirm empirically the accuracy of Niels Bohr’s model of atomic structure as well as the hypothesis of Max Planck and Albert Einstein that atoms absorb energy in discrete quanta rather than continuously.

Early Life

Gustav Hertz (GEWS-tahf hehrts) was born to Auguste Hertz, née Arning, and the lawyer Gustav Hertz, brother of the famous expert on electromagnetic waves Heinrich Hertz. Little has been written about Hertz’s childhood, but it is known that Hertz attended the Johanneum School in Hamburg and at age nineteen began his studies at the University of Göttingen. He seems to have chosen a career as a scientist early in life, although it is not known to what extent the example of his distinguished uncle influenced his decision. The atomic scientist Arnold Sommerfeld probably had a more direct and significant impact as Hertz’s teacher when Hertz attended the University of Munich during the 1907 academic year.

After military service in 1908, Hertz went to Berlin to continue his studies and received a doctorate at the University of Berlin in 1911, after which he began working with another young scientist from Hamburg, James Franck. They experimented with, among other things, electron bombardment on mercury vapor. The spectroscopic results of their experiments were interpreted in several publications, and eventually the scientific community would recognize the significance of their work, as evinced by the selection of Hertz and Franck as recipients of the Nobel Prize in Physics in 1926.

Both Franck and Hertz left the University of Berlin at the outbreak of World War I and served in the army. Hertz was severely wounded in 1915 and recovered slowly. In 1917, he returned to Berlin as a privatdocent, or lecturer, at the university. As applied physics was his exclusive field of interest, Hertz did not hesitate in the following years to leave academic physics for private industry, although he would periodically return to Berlin to teach and to pursue research at one of the academic institutions there. In 1919, at the age of thirty-two, he married Ellen Dihlmann.

Life’s Work

When Hertz returned to the University of Berlin after World War I, he resumed work in the study of electron bombardments and the quantized energy exchanges that accompany them, and began to experiment with X-ray spectroscopy as well. Hertz was first and foremost a meticulous laboratory scientist. In 1920, he began a five-year sojourn as a researcher in Eindhoven, the Netherlands, at the Philips Incandescent Lamp Factory, which was one of the first industrial laboratories where basic research was pursued. Hertz devoted most of his time and energy to the problem of the separation of gases, that is, to obtaining pure forms of a given gas by diffusion.

In 1925, Hertz was asked to serve as director of the Physics Institute of the University of Halle; he accepted and remained there for three years. In these years, his work with Franck had become extremely well known, one result being an invitation in 1928 to return to Berlin as director of the Physics Institute at the Technische Hochschule of Berlin-Charlottenburg. In the early 1930’s, Hertz perfected a highly successful method for separating gaseous isotopes of helium and neon by diffusion. This technique, known as a diffusion “cascade,” was based on principles applicable to all types of isotopes. Hertz’s successes in this field would become especially important in the following decades, as he and other scientists began to investigate the uses of uranium isotopes in the creation of nuclear energy. Scientists in the United States used the method in developing the first atomic bombs.

Hertz refused to take a Nazi loyalty oath in 1934 and resigned his academic post to accept a position as chief physicist for Siemens Corporation in Berlin. Had it not been for his usefulness to Siemens, his future in Germany, as well as that of his wife, who was vocally pro-Allies, doubtlessly would have been far worse, since he was part Jewish. At Siemens, Hertz was encouraged to continue his work on the separation of isotopes, particularly heavy neon (neon 22).

As the decade of the 1930’s drew to a close, Hertz’s interest was consumed in spite of the growing necessity to oversee conventional weaponry projects at Siemens by problems associated with the actual creation of nuclear energy. The importance of Hertz’s method of separating isotopes was augmented considerably when a refugee from Austria, Lise Meitner, announced in 1939 in Sweden that she and her former collaborator in Germany, Otto Hahn, had split the atom, thus setting the stage for the possible creation of a chain reaction with uranium 235.

While Hertz had been indeed tolerated by Nazi authorities (he was a productive scientist with an impressive military record), the war years nevertheless were not free of tragedy. Ellen, his wife of twenty-two years, died in 1941. Their two sons, both of whom became professional scientists, would survive the war. In 1943, Hertz married Charlotte Jollasse. When the Red Army entered Berlin after World War II, Hertz agreed to join a research team in the Soviet Union. At first, it was reported that he had been coerced by the Soviets, but Werner Heisenberg revealed to the press in February of 1947 that Hertz and about two hundred other German scientists had joined the Soviet project willingly, accepting a stipend of six thousand rubles per month. Hertz and several of his colleagues and former pupils were given a manor house near Stochi on the Black Sea in which they constructed a laboratory for nuclear research and began planning for production of radioactive isotopes on a large scale.

In 1949-1950, when the Soviet Union acquired essential technical information for the construction of its own atomic bomb , Hertz’s skills were employed directly in the construction of nuclear weapons; he did not return to Germany until 1954, when he moved to Leipzig to teach experimental physics and serve as director of the Physics Institute. By 1957, it was widely known in the West that Hertz was one of the key minds behind the Soviet Union’s atomic weapons program, although little was known about the details of his work.

As a teacher at the University of Leipzig, Hertz saw the need for good textbooks on the specialized field of atomic physics and subsequently devoted much of his seemingly limitless energy to consolidating and compiling his knowledge of the structure of the atom. In 1957, he published a book on the principles and methods of nuclear physics (Grundlagen und Arbeitsmethoden der Kernphysik), which was followed by a three-volume compendium of nuclear science in 1958-1962 (Lehrbuch der Kernphysik). In 1961, Hertz withdrew from his post as director of the Physics Institute and began a much-deserved retirement. He died on October 30, 1975.

Significance

Meticulous laboratory work and cautious analysis of experimental data were Hertz’s métier; his contributions were not characterized by breathtaking originality but rather by painstaking accuracy and reliability. He helped to fill in the edifice of modern atomic theory. His scientific career was his life, and he managed, despite his religious background and political opinions, to remain in Germany and continue his work during the tribulations of the Nazi period. Moreover, he was able at the end of World War II to arrange for nearly ideal working conditions by going to work in the Soviet Union. Unlike his former colleague Franck, who fled Germany as early as 1933 and later worked on the first U.S. atomic bomb, Hertz never made known any problems he might have had with the political and ethical implications of a military use of nuclear power.

Hertz is often credited with leading the team that built Germany’s first cyclotron in the 1930’s. With this “atom-smashing” device, he wished to extend his early investigations on energy transfer in elastic collisions of electrons and atoms to inelastic collisions, that is, collisions in which an elementary particle fired at the atom is not absorbed but actually causes the breakup of the nucleus. The Nazi government did little to discourage his work in private industry. In time, he made considerable advances in the development of a method for the separation of the volatile isotope uranium 235.

After his retirement, Hertz was honored by his colleagues with a ceremony and Festschrift in celebration of his eightieth birthday in 1967. At that time, he was praised for the discovery of laws governing discrete energy transfer in electron collisions and for the invention and continual refinement of methods for separating isotopes, without which the use of nuclear power would have been impossible. In addition to the Nobel Prize shared with Franck, Hertz by the end of his life had received many other professional awards, including the Lenin Prize of the Soviet Union in 1955. He was a member of most scientific academies in the Eastern bloc, as well as the Göttingen Academy of Sciences in the West.

Bibliography

Barwich, Heinz, and Elfi Barwich. Das rote Atom. Munich: Scherz, 1967. Because of the paucity of materials on Hertz, this German book is noted here, since it is a standard work on the otherwise obscure history of atomic research in the Soviet Union following World War II. Barwich was a student of Hertz who also went to the Soviet Union after World War II. He fled the Eastern bloc in 1962.

Dardo, Mauro. Nobel Laureates and Twentieth-Century Physics. New York: Cambridge University Press, 2004. Chronicles major developments in physics since 1901, the year the first Nobel Prize in Physics was awarded. Includes information about the work of Hertz and James Franck and of other prizewinners.

Franck, James. “A Personal Memoir.” In Niels Bohr: A Centenary Volume, edited by Anthony P. French and P. J. Kennedy. Cambridge, Mass.: Harvard University Press, 1985. This reminiscence by Hertz’s colleague gives an interesting account of the experimental work that earned for them the Nobel Prize. Franck explains why he and Hertz were slow to realize the significance of their results for the tenability of the Bohr theory of the atom.

Heathcote, Niels Hugh de Vaudrey. Nobel Prize Winners in Physics, 1901-1950. New York: Henry Schuman, 1953. This valuable collection contains a straightforward treatment of the electron experiments of Hertz and Franck, based on selections from their Nobel Prize lectures.

Hermann, Armin. The Genesis of Quantum Theory, 1889-1913. Translated by Claude W. Nash. Cambridge, Mass.: MIT Press, 1971. Contains a useful discussion of contributions to quantum theory by Hertz and Franck. The author’s historical approach is intended not only for physicists but also for readers with a basic knowledge of science.

Holton, Gerald. “On the Recent Past of Physics.” American Journal of Physics 29 (1961): 805-810. This article, published in the year of Hertz’s retirement, mostly describes early reactions to Bohr’s atom model but briefly discusses the work of Hertz and Franck.