Ehrenhaft believed he had discovered a "sub-electron", smaller than anything measured by Robert Andrews Millikan.

[2] The double-focusing mechanism allowed for the separation and measurement of isotopes that could not be isolated by chemical means, and as such was a major contribution to nuclear physics.

[5] In 1938 Lise Meitner fled Germany after the Nazi occupation of Austria changed her citizenship from Austrian to German, making her subject to the antisemitic Nuremberg Laws of 1935.

[7] Josef Mattauch was appointed an associate professor of nuclear chemistry at the University of Berlin in 1940.

Hahn and Mattauch successfully sought funds for a major expansion for fundamental research in atomic physics.

[8] In 1942, the Minerva Project was approved, involving construction of a new building and addition of a cascade generator and particle accelerator.

[7][6] This included the director's house, one wing of the Institute, Mattauch's new mass spectrograph, and valuable research papers.

[8]: 283 The Institute was temporarily relocated to Tailfingen (now Albstadt) in the Württemberg district, in a textile factory belonging to the Ludwig Haasis company.

[7][6] On 1 April 1946, in Göttingen in the British zone of occupation, Otto Hahn became president of the Kaiser Wilhelm Society (Kaiser-Wilhelm-Gesellschaft, KWG).

[7][10] However, Mattauch suffered from tuberculosis[11] and spent much of his time seeking treatment, traveling and working abroad.

[6] Mattauch and Fritz Strassmann actively supported the proposed appointment of Lise Meitner as head of the physics department of the University of Mainz.

[14] Mattauch primarily focused on mass spectroscopy and research into the binding energy of atomic nuclei.

[7] In the early 1930s, at the University of Vienna, Mattauch worked with Richard F. K. Herzog on fundamental aspects of ion optics as they applied to mass spectroscopy.

[citation needed] He developed the Mattauch isobar rule ("Isobarenregel") in 1934, which was used to predict the radioactivity of the elements technetium and promethium.

[3][18] In the 1950s, a period of stability after the war, Mattauch was able to build a strong mass spectrometry program at the Max Planck Institute.