Early years In 1913, Bothe joined the Physikalisch-Technische Reichsanstalt (PTR – now the
Physikalisch-Technische Bundesanstalt), where he stayed until 1930.
Hans Geiger had been appointed Director of the newly-established Laboratory for Radioactivity there in 1912; Bothe was an assistant to Geiger from 1913 to 1920, a scientific member of Geiger's staff from 1920 to 1927, and Director of the Laboratory for Radioactivity from 1927 to 1930—in succession to Geiger. In May 1914, Bothe volunteered for service in the German cavalry. He was taken prisoner by the Russians and incarcerated in Russia for five years. While there, he learned the Russian language and worked on theoretical physics problems related to his doctoral studies. He returned to Germany in 1920, with a Russian bride. In 1925, while still at the PTR, Bothe became a (unsalaried lecturer) at the
University of Berlin, and, in 1929, he became an (extraordinary professor) there. The study of cosmic radiation would be conducted by Bothe for the rest of his life. In 1932,
James Chadwick identified this radiation as the
neutron. even though its two most prominent supporters were the Lenard and
Johannes Stark. Supporters of
Deutsche Physik launched vicious attacks against leading theoretical physicists. While Lenard was retired from Heidelberg, he still had significant influence there. In 1934, Lenard had managed to get Bothe relieved of his directorship of the Physical and Radiological Institute, whereupon Bothe was able to become the Director of the Institute for Physics of the Kaiser-Wilhelm-Institut für medizinische Forschung (KWImF – Kaiser Wilhelm Institute for Medical Research) in
Heidelberg, replacing Karl W. Hauser, who had recently died.
Ludolf von Krehl, Director of the KWImF, and
Max Planck, President of the Kaiser-Wilhelm-Gesellschaft (KWG –
Kaiser Wilhelm Society), had offered the directorship to Bothe to ward off the possibility of his emigration. Bothe held the directorship of the Institute for Physics at the KWImF until his death in 1957. While at the KWImF, Bothe held an honorary professorship at Heidelberg, which he held until 1946. Fleischmann went with Bothe and worked with him there until 1941. To his staff, Bothe recruited scientists including
Wolfgang Gentner,
Heinz Maier-Leibnitz—who had done his doctorate with the Nobel Laureate
James Franck and was highly recommended by
Robert Pohl and
Georg Joos, and
Arnold Flammersfeld. Also included on his staff were Peter Jensen and Erwin Fünfer. In 1938, Bothe and Gentner published on the energy dependence of the nuclear photo-effect. This was the first clear evidence that nuclear absorption spectra are accumulative and continuous, an effect known as the dipolar giant nuclear resonance. This was explained theoretically a decade later by physicists
J. Hans D. Jensen, Helmut Steinwedel, Peter Jensen, Michael Goldhaber, and
Edward Teller. To facilitate the construction of the cyclotron, at the end of 1938 and into 1939, with the help of a fellowship from the Helmholtz Society, Gentner was sent to Radiation Laboratory of the University of California (now the
Lawrence Berkeley National Laboratory) in Berkeley, California. As a result of the visit, Gentner formed a cooperative relationship with
Emilio G. Segrè and
Donald Cooksey. It was during 1941 that Bothe had acquired all the necessary funding to complete construction of the cyclotron. The magnet was delivered in March 1943, and the first beam of deuteron was emitted in December. The inauguration ceremony for the cyclotron was held on 2 June 1944. While there had been other cyclotrons under construction, Bothe's was the first operational cyclotron in Germany. In any event, there were so few staff or groups that they could not repeat experiments to check results, although in fact a separate group at Gottingen, led by Wilhelm Hanle, determined the cause of Bothe's error: "Hanle's own measurements would show that carbon, properly prepared, would in fact work perfectly well as a moderator, but at a cost of production in industrial quantities ruled prohibitive by [German] Army Ordnance". By late 1941, it was apparent that the nuclear energy project would not make a decisive contribution to ending the war effort in the near term. HWA control of was relinquished to the RFR in July 1942. The nuclear energy project thereafter maintained its (important for the war) designation and funding continued from the military. However, the German nuclear power project was then broken down into the following main areas: uranium and heavy water production, uranium isotope separation, and the (uranium machine; i.e.,
nuclear reactor). Also, the project was then essentially split up between nine institutes, where the directors dominated the research and set their own research agendas. Bothe's Institute for Physics was one of the nine institutes. The other eight institutes or facilities were: the Institute for Physical Chemistry at the
University of Munich, the HWA (testing station) in Gottow, the KWIC, the Physical Chemistry Department of the
University of Hamburg, the (Kaiser Wilhelm Institute for Physics), the Second Experimental Physics Institute at the
University of Göttingen, the , and the Second Physical Institute at the
University of Vienna. At the end of 1957, Gentner was in negotiations with
Otto Hahn, President of the Max-Planck-Gesellschaft (MPG –
Max Planck Society; successor of the
Kaiser Wilhelm Society), and with the Senate of the MPG to establish a new institute under their auspices. Essentially, Bothe's Institute for Physics at the Max-Planck-Institut für medizinische Forschung (
Max Planck Institute for Medical Research), in Heidelberg, was to be spun off to become a full fledged institute of the MPG. The decision to proceed was made in May 1958. Gentner was named the director of the Max-Planck-Institut für Kernphysik (MPIK –
Max Planck Institute for Nuclear Physics) on 1 October, and he also received the position as an at the University of Heidelberg. Bothe had not lived to see the final establishment of the MPIK, as he had died in February of that year. Bothe was a German patriot who did not give excuses for his work with . However, his impatience with Nazi policies in Germany brought him under suspicion and investigation by the
Gestapo. == Personal life ==