In 1911 Geiger and John Mitchell Nuttall discovered the Geiger–Nuttall law (or rule) and performed experiments that led to Rutherford's atomic model. In 1928 Geiger and his student Walther Müller created an improved version of the Geiger tube, the Geiger–Müller tube. 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.