Frédéric Joliot-Curie
After the armistice between France and Germany in the summer of 1940, Bothe and Gentner received orders to inspect the cyclotron Frédéric Joliot-Curie had built in Paris. While it had been built, it was not yet operational. In September 1940, Gentner received orders to form a group to put the cyclotron into operation. Hermann Dänzer from the University of Frankfurt participated in this effort. While in Paris, Gentner was able to free both Frédéric Joliot-Curie and Paul Langevin, who had been arrested and detained. At the end of the winter of 1941/1942, the cyclotron was operational with a 7-MeV beam of deuterons. Uranium and thorium were irradiated with the beam, and the byproducts were sent to Otto Hahn at the "Kaiser-Wilhelm Institut für Chemie" (KWIC, Kaiser Wilhelm Institute for Chemistry, today, the Max Planck Institute for Chemistry), in Berlin. In mid-1942, Gentner's successor in Paris, was Wolfgang Riezler from Bonn.