Hans Geiger was a German physicist who, with Ernest Rutherford devised in 1908 a method of detecting and counting alpha particles. This device, with modification, became the Geiger counter (or Geiger-Muller counter). Geiger and Ernest Marsden measured the deflection of alpha particles by thin metal foil in 1909 (see Rutherford's experiment and atomic model), and this phenomenon was the basis of Rutherford's discovery of the atomic nucleus.