Walther Wilhelm Georg Bothe (German: [ˈvaltɐ ˈboːtə]; 8 January 1891 – 8 February 1957) was a German experimental physicist who shared the 1954 Nobel Prize in Physics with Max Born "for the coincidence method and his discoveries made therewith."

Bothe served in the military during World War I from 1914 and was captured by the Russians, returning to Germany in 1920. After returning to his laboratory, he developed and used coincidence circuits to study nuclear reactions, such as the Compton effect, cosmic rays, and the wave–particle duality of radiation.

In 1930, Bothe became a Full Professor and Director of the Physics Department at the University of Giessen. In 1932, he became Director of the Physical and Radiological Institute at the University of Heidelberg. He was forced to leave this position because of the Deutsche Physik movement. To prevent him from leaving Germany, he was appointed Director of the Physics Institute at the Kaiser Wilhelm Institute for Medical Research in Heidelberg. There, he built the first operational cyclotron in Germany. Additionally, he was a key leader in the German nuclear energy project, also known as Uranverein, which began in 1939 under the Army Ordnance Office.

In 1946, along with his role as Director of the Physics Institute at the KWImf, Bothe was reinstated as a professor at the University of Heidelberg. From 1956 to 1957, he was a member of the Nuclear Physics Working Group in Germany.

One year after Bothe’s death, his Physics Institute at the KWImf was renamed as a new institute under the Max Planck Society and became the Max Planck Institute for Nuclear Physics. Its main building was later named the Bothe Laboratory.

Education

Walther Wilhelm Georg Bothe was born on 8 January 1891 in Oranienburg, Germany. His parents were Friedrich Bothe and Charlotte Hartung. Between 1908 and 1912, he studied at the University of Berlin. In 1913, he became Max Planck's teaching assistant. He received his Ph.D. under Planck the following year.

Career and research

In 1913, Bothe joined the Physikalisch-Technische Reichsanstalt (PTR – now the Physikalisch-Technische Bundesanstalt), where he worked until 1930. Hans Geiger had become the Director of the newly created Laboratory for Radioactivity there in 1912. Bothe worked as Geiger’s assistant from 1913 to 1920, as a scientific member of Geiger’s team from 1920 to 1927, and as the Director of the Laboratory for Radioactivity from 1927 to 1930, taking over from Geiger.

In May 1914, Bothe volunteered to serve in the German cavalry. He was captured by the Russians and held in Russia for five years. During this time, he learned Russian and studied theoretical physics topics related to his doctoral research. He returned to Germany in 1920, bringing his Russian wife with him.

After returning from Russia, Bothe continued working at the PTR under Hans Geiger in the Laboratory for Radioactivity. In 1924, Bothe published research on his coincidence method. The Bothe–Geiger coincidence experiment studied the Compton effect and the wave–particle duality of light. Bothe’s coincidence method and its applications earned him the Nobel Prize in Physics in 1954.

In 1925, while still working at the PTR, Bothe became a Privatdozent (unsalaried lecturer) at the University of Berlin. In 1929, he became an ausserordentlicher Professor (extraordinary professor) there.

In 1927, Bothe began studying how light elements change when bombarded with alpha particles. In 1928, Bothe and H. Fränz linked the results of nuclear reactions to nuclear energy levels.

In 1929, Bothe worked with Werner Kolhörster and Bruno Rossi (who were visiting his laboratory at the PTR) to study cosmic rays. He continued this research for the rest of his life.

In 1930, Bothe became an ordentlicher Professor (ordinary professor) and Director of the Physics Department at the University of Giessen. That same year, Bothe and Herbert Becker bombarded beryllium, boron, and lithium with alpha particles from polonium and observed a new type of radiation. In 1932, James Chadwick identified this radiation as the neutron.

In 1932, Bothe took over as Director of the Physical and Radiological Institute at the University of Heidelberg after Philipp Lenard. Rudolf Fleischmann became Bothe’s teaching assistant. When Adolf Hitler became Chancellor of Germany in 1933, the idea of Deutsche Physik (Aryan Physics) gained popularity. This movement opposed theoretical physics, including quantum mechanics and nuclear physics. Political influence replaced academic ability in universities, even though its main supporters were Philipp Lenard and Johannes Stark. Supporters of Deutsche Physik attacked leading theoretical physicists.

In 1934, Lenard forced Bothe to leave his directorship at the Physical and Radiological Institute. Bothe then became Director of the Institute for Physics at the Kaiser-Wilhelm-Institut für medizinische Forschung (KWImF – Kaiser Wilhelm Institute for Medical Research) in Heidelberg, replacing Karl W. Hauser. Ludolf von Krehl, Director of the KWImF, and Max Planck, President of the Kaiser-Wilhelm-Gesellschaft (KWG – Kaiser Wilhelm Society), offered Bothe the position to prevent him from leaving Germany. Bothe remained Director of the Institute for Physics at the KWImF until his death in 1957. He also held an honorary professorship at Heidelberg until 1946. Fleischmann worked with Bothe there until 1941. Bothe recruited scientists such as Wolfgang Gentner, Heinz Maier-Leibnitz, Arnold Flammersfeld, Peter Jensen, and Erwin Fünfer to his team.

In 1938, Bothe and Gentner published research on the energy dependence of the nuclear photo-effect. This was the first clear evidence that nuclear absorption spectra are continuous and accumulative, an effect later called the dipolar giant nuclear resonance. This was explained theoretically by physicists J. Hans D. Jensen, Helmut Steinwedel, Peter Jensen, Michael Goldhaber, and Edward Teller.

Also in 1938, Maier-Leibnitz built a cloud chamber. Images from the cloud chamber were used by Bothe, Gentner, and Maier-Leibnitz to publish the Atlas of Typical Cloud Chamber Images in 1940. This became a standard reference for identifying scattered particles.

By the end of 1937, Bothe and Gentner’s success with a Van de Graaff generator led them to plan building a cyclotron. By November 1937, they had sent a report to the President of the KWG and began seeking funding. A magnet was ordered from Siemens in September 1938, but funding became difficult. Gentner continued his research on the nuclear photo-effect using the upgraded Van de Graaff generator, which produced energies just under 1 MeV. After completing his research on the Li (p, gamma) and B (p, gamma) reactions and the nuclear isomer Br, Gentner focused on building the cyclotron.

To help build the cyclotron, Gentner traveled to the Radiation Laboratory at the University of California (now the Lawrence Berkeley National Laboratory) in 1938–1939 with a fellowship from the Helmholtz Society. He formed a partnership with Emilio G. Segrè and Donald Cooksey.

After the armistice between France and Germany in 1940, Bothe and Gentner were ordered to inspect the cyclotron built by Frédéric Joliot-Curie in Paris. The cyclotron was not yet operational. In September 1940, Gentner was ordered to form a team to start operating it. Hermann Dänzer from the University of Frankfurt helped with this effort. While in Paris, Gentner helped free

Personal life

Because he was held captive in Russia during World War I, Bothe met Barbara Below and married her in 1920. They had two children. Barbara died before Bothe.

Bothe was a skilled painter and musician. He played the piano.

Works

The following reports were published in Kernphysikalische Forschungsberichte (Research Reports in Nuclear Physics), an internal publication of the German Uranverein. The reports were classified as Top Secret, had very limited distribution, and the authors were not allowed to keep copies. The reports were taken during the Allied Operation Alsos and sent to the United States Atomic Energy Commission for evaluation. In 1971, the reports were no longer kept secret and returned to Germany. The reports are now available at the Karlsruhe Nuclear Research Center and the American Institute of Physics.

• Walther Bothe Die Diffusionslänge für thermische Neutronen in Kohle G12 (7 June 1940)
• Walther Bothe Die Abmessungen endlicher Uranmaschinen G-13 (28 June 1940)
• Walther Bothe Die Abmessungen von Maschinen mit rücksteuendem Mantel G-14 (17 July 1941)
• Walther Bothe and Wolfgang Gentner Die Energie der Spaltungsneutronen aus Uran G-17 (9 May 1940)
• Walther Bothe Einige Eigenschaften des U und der Bremsstoffe. Zusammenfassender Bericht über die Arbeiten G-66 (28 March 1941)
• Walther Bothe and Arnold Flammersfeld Die Wirkungsquerschnitte von 38 für thermische Neutronen aus Diffusionsmessungen G-67 (20 January 1941)
• Walther Bothe and Arnold Flammersfeld Resonanzeinfang an einer Uranoberfläche G-68 (8 March 1940)
• Walther Bothe and Arnold Flammersfeld Messungen an einem Gemisch von 38-Oxyd und –Wasser; der Vermehrungsfaktor K und der Resonanzeinfang w. G-69 (26 May 1941)
• Walther Bothe and Arnold Flammersfeld Die Neutronenvermehrung bei schnellen und langsamen Neutronen in 38 und die Diffusionslänge in 38 Metall und Wasser G-70 (11 July 1941)
• Walther Bothe and Peter Jensen Die Absorption thermischer Neutronen in Elektrographit G-71 (20 January 1941)
• Walther Bothe and Peter Jensen Resonanzeinfang an einer Uranoberfläche G-72 (12 May 1941)
• Walther Bothe and Arnold Flammersfeld Versuche mit einer Schichtenanordnung von Wasser und Präp 38 G-74 (28 April 1941)
• Walther Bothe and Erwin Fünfer Absorption thermischer Neutronen und die Vermehrung schneller Neutronen in Beryllium G-81 (10 October 1941)
• Walther Bothe Maschinen mit Ausnutzung der Spaltung durch schnelle Neutronen G-128 (7 December 1941)
• Walther Bothe Über Stahlenschutzwände G-204 (29 June 1943)
• Walther Bothe Die Forschungsmittel der Kernphysik G-205 (5 May 1943)
• Walther Bothe and Erwin Fünfer Schichtenversuche mit Variation der U- und D2O-Dicken G-206 (6 December 1943)
• Fritz Bopp, Walther Bothe, Erich Fischer, Erwin Fünfer, Werner Heisenberg, O. Ritter, and Karl Wirtz Bericht über einen Versuch mit 1.5 to D2O und U und 40 cm Kohlerückstreumantel (B7) G-300 (3 January 1945)

• Walther Bothe and Hans Geiger Ein Weg zur experimentellen Nachprüfung der Theorie von Bohr, Kramers und Slater, Z. Phys. Volume 26, Number 1, 44 (1924)
• Walther Bothe Theoretische Betrachtungen über den Photoeffekt, Z. Phys. Volume 26, Number 1, 74–84 (1924)
• Walther Bothe and Hans Geiger Experimentelles zur Theorie von Bohr, Kramers und Slater, Die Naturwissenschaften Volume 13, 440–441 (1925)
• Walther Bothe and Hans Geiger Über das Wesen des Comptoneffekts: ein experimenteller Beitrag zur Theorie der Strahlung, Z. Phys. Volume 32, Number 9, 639–663 (1925)
• W. Bothe and W. Gentner Herstellung neuer Isotope durch Kernphotoeffekt, Die Naturwissenschaften Volume 25, Issue 8, 126–126 (1937). Received 9 February 1937. Institutional affiliation: Institut für Physik at the Kaiser-Wilhelm Institut für medizinische Forschung.
• Walther Bothe The Coincidence Method, The Nobel Prize in Physics 1954, Nobelprize.org (1954)

• Walther Bothe Der Physiker und sein Werkzeug (Gruyter, 1944)
• Walther Bothe and Siegfried Flügge Kernphysik und kosmische Strahlen. T. 1 (Dieterich, 1948)
• Walther Bothe Der Streufehler bei der Ausmessung von Nebelkammerbahnen im Magnetfeld (Springer, 1948)
• Walther Bothe and Siegfried Flügge (editors) Nuclear Physics and Cosmic Rays FIAT Review of German Science 1939–1945, Volumes 13 and 14 (Klemm, 1948)
• Walther Bothe Theorie des Doppellinsen-b-Spektrometers (Springer, 1950)
• Walther Bothe Die Streuung von Elektronen in schrägen Folien (Springer, 1952)
• Walther Bothe and Siegfried Flügge Kernphysik und kosmische Strahlen. T. 2 (Dieterich, 1953)
• Karl H. Bauer and Walther Bothe Vom Atom zum Weltsystem (Kröner, 1954)