1882-1945

German nuclear physicist who developed various instruments and techniques for measuring charged nuclear particles—the most famous of which is the Geiger-Müller counter, commonly referred to as the Geiger counter. Geiger invented an alpha-particle detector in 1908 that allowed him and Ernst Rutherford to show alpha-particles to be helium nuclei. In 1909 Geiger performed his now famous alpha-particle scattering experiments with Ernest Marsden. Their results directly led to Rutherford's nuclear theory of the atom.