In 1911 Geiger and John Mitchell Nuttall discovered the Geiger–Nuttall law (or rule) and performed experiments that led to Rutherford's atomic model.[5] In 1928 Geiger and his student Walther Müller created an improved version of the Geiger tube, the Geiger–Müller tube.[6][7] Geiger also worked with James Chadwick. In 1912 he became leader of the Physical-Technical Reichsanstalt in Berlin, 1925 professor in Kiel, 1929 in Tübingen, and from 1936 in Berlin.