Gustav Herts German physicist, nephew of Heinrich Hertz. Together with Frank, he measured the energy of a quantum and discovered the law of collision of an electron with an atom. Nobel Prize Laureate Date of Birth: 22.07.1887 Country: Germany

Biography of Gustav Ludwig Hertz

Gustav Ludwig Hertz was a German physicist and the nephew of Heinrich Hertz. Together with James Franck, he measured the energy of the quantum and discovered the law of electron collision with an atom. He was awarded the Nobel Prize.

Early Life and Education
Gustav Ludwig Hertz was born in Hamburg, Germany, to lawyer Gustav Hertz and Augusta (Arning) Hertz. His uncle, Rudolf Heinrich Hertz, was one of the most prominent physicists of the late 19th century. Hertz completed his secondary education at the Johanneum School in Hamburg. In 1906, he enrolled at the University of Göttingen, where he studied mathematics and mathematical physics under David Hilbert and Carl Runge. He then continued his studies at the University of Munich under Arnold Sommerfeld, where he became interested in the then-new quantum theory, and at the University of Berlin under James Franck and Robert Pohl, where he developed an interest in experimental physics. In 1911, Hertz defended his dissertation at the University of Berlin on the infrared absorption of carbon dioxide and obtained his doctorate.

Contribution to Quantum Theory
In 1913, Hertz was appointed as an assistant at the Physical Institute of the University of Berlin, where he collaborated with James Franck on researching the energy changes during the collision of atoms with electrons. Their work provided direct confirmation of Niels Bohr's atomic model, although they were not yet familiar with it. According to Bohr's theory, electrons could only orbit the nucleus in "allowed" orbits, each corresponding to a specific energy state of the electron. According to Bohr, when an electron absorbs a discrete amount of energy, or quantum, it "jumps" to an orbit corresponding to higher energy and located farther from the nucleus. When an electron transitions from a higher to a lower orbit, it emits a quantum. The energy of the quantum is equal to the difference in energy between the orbits. Bohr's model partially explained the previously mysterious line spectra of elements. When a gas is excited, such as by passing an electric discharge through it, the atoms release excess energy in the form of light. Each element emits light of specific colors corresponding to characteristic frequencies and wavelengths for that element. A spectroscope can separate these frequencies and produce a series of colored lines, or line spectrum, characteristic of the element. Max Planck, the founder of quantum theory, demonstrated in 1900 that the frequency is proportional to the energy of the light quantum. Therefore, according to Bohr's theory, each spectral line corresponds to the difference in energy between two orbits. Thus, line spectra serve as a kind of key to the atomic structure.

Measurement of Quantum Energy
To measure the energy of the quantum, Hertz and Franck applied a positive voltage to an electrode opposite the electron source and accelerated the electrons in a sealed tube. The electrons, whose maximum kinetic energy was known (equal to the product of the potential difference and the electron charge), passed through a highly rarefied pair of mercury atoms. Another electrode could detect the energy losses of the electrons due to collisions with mercury atoms. It was found that the energy losses were negligible until the potential difference reached 4.9 volts. This discovery, which showed that the atom absorbed energy in only certain portions, confirmed one aspect of Bohr's theory. Similar results were obtained for other gases, such as helium and neon. Hertz and Franck calculated the frequency corresponding to the quantum with an energy equal to the electron energy of 4.9 electron volts and found that it coincided with the frequency of one of the mercury's line spectra (in the ultraviolet range). However, since Bohr's theory was only a few months old at the time and much was still unclear, Hertz and Franck mistakenly interpreted 4.9 volts as the ionization potential, i.e., the energy required to remove an electron from the atom. The loss of an electron disrupts the neutrality of the atom, which is a balance between negative electrons outside the nucleus and positive protons in the nucleus, and leads to the formation of a positively charged ion. Hertz and Franck believed that the ultraviolet mercury line was emitted when an ion captured an electron and filled a vacancy. The main problem was that Bohr's model predicted an ionization potential of 10.36 volts. After some confusion, a better understanding of Bohr's model was achieved, and it was then revealed that the line in question corresponded to the transition of an electron between two lower orbits in the spectral series, rather than the loss of an outer electron and its capture. The value of 4.9 volts turned out to be the excitation potential, i.e., the energy (or quantum) required to excite an electron - its transition from one energy level to another, higher one, without detaching it from the atom. Improving the experimental technique, Hertz, Franck, and other researchers measured several other (higher) excitation potentials. It turned out that the obtained potential values corresponded to the lines observed in the mercury spectrum. The predicted value of the ionization potential was also confirmed. Hertz and Franck became the first physicists to directly measure the energy of the quantum.

Later Life and Career
During World War I, Hertz and Franck served in the German army. In 1915, Hertz was severely wounded. After a lengthy recovery, he became an adjunct professor at the University of Berlin in 1917. From 1920 to 1925, Hertz worked at the physical laboratory of the Philips incandescent lamp factory in Eindhoven, Netherlands. Philips was one of the first private companies to fund fundamental research. In 1925, Hertz became a professor of physics at the University of Halle and the director of the Physical Institute at the same university. Three years later, he returned to Berlin as the director of the Physical Institute at the Charlottenburg Technical University. During this period, one of Hertz's most significant scientific achievements was the development of the gas diffusion method for separating neon isotopes. When the Nazis came to power in Germany in 1933, Hertz refused to swear allegiance to the Führer and was forced to resign in 1934. Until the end of World War II, he worked as the director of the research laboratory of Siemens and Halske in Berlin. It is unclear why Hertz, whose father was Jewish and whose first wife was against Nazism, was allowed to hold such an important position.

After the war, Hertz was among a group of German scientists who were sent to the Soviet Union under a ten-year contract. During his visit to the United States in 1939, Hertz told his friends that the level of physics research in America was very high, but he felt that he would be more useful in the Soviet Union. Hertz hoped that his family would be able to integrate into Soviet society. However, both Hertz and other German scientists were isolated in a laboratory complex. In the Soviet Union, Hertz led research on atomic energy and radar in a laboratory located in Sukhumi. He further improved his method of isotope separation to the point where it became possible to conduct separation on an industrial scale. In 1955, Hertz returned to Leipzig, where he became a professor at Karl Marx University. As the director of the Physical Institute at Leipzig University, Hertz supervised the construction of a new institute building to replace the one destroyed during the war. In 1961, Hertz retired and settled in East Berlin, where he spent the last 14 years of his life. In 1919, Hertz married Ellen Dillman, with whom he had two sons, both of whom became physicists. In 1943, two years after the death of his first wife, he entered into a second marriage with Charlotte Jollasse. Hertz was a reserved individual, and little is known about his views and hobbies, except that he was a proficient photographer.

Achievements and Recognition
In addition to the Nobel Prize, Hertz received numerous honorary awards, including the Max Planck Medal from the German Physical Society and the Lenin Prize from the Soviet government. He was elected a member of the German Academy of Sciences in Berlin and the Göttingen Academy of Sciences, as well as the academies of sciences in Hungary, Czechoslovakia, and the Soviet Union.