Geiger, Hans Wilhelm (1882-1945) was a German physicist who invented the Geiger counter for detecting radioactivity. Geiger was born at Neustadt, Rheinland-Pfalz, on 30 September 1882. He studied physics at the Universities of Munich and Erlangen, obtaining his PhD from the latter institution in 1906 with a dissertation on gaseous ionization. In 1906 he became assistant to Arthur Schuster (1851-1934), Professor of Physics at the University of Manchester. Ernest Rutherford (1871-1937) succeeded Schuster in 1907 and Geiger stayed on as his assistant. They were later joined by Ernest Marsden, with whom Geiger collaborated. In 1912 Geiger became head of the Radioactivity Laboratories at the Physikalische Technische Reichsanstalt in Berlin, after declining the offer of a post at the University of Tübingen. He established a successful research group, which was joined by such eminent scientists as Walther Bothe (1891-1957) and James Chadwick (1891-1974). Geiger served in the German artillery during World War I, and then returned to the Reichsanstalt in Berlin. In 1925 Geiger accepted a post as Professor of Physics at the University of Kiel. He moved in 1929 to the University of Tübingen, and in 1936 he became head of Physics at the Technical University of Charlottenberg- Berlin as well as the editor of the Zeitschrift für Physik. Illness reduced the pace of his scientific activities during most of World War II and then he lost his home and belongings during the Allied occupation of Germany. Geiger died a few months later on 24 September 1945 at Potsdam. Geiger's early postdoctoral work in Manchester involved the application of his expertise in gaseous ionization to the field of radioactive decay. One direction which his work took was the development in 1908 of a device that counted alpha particles. The counter consisted of a metal tube containing a gas at low pressure and thin wire in the centre of the tube. The wire and tube were under a high voltage and each alpha particle arriving through a window at one end of the tube caused the gas to ionize, producing a momentary flow of current. The resulting electric signals counted the number of alpha particles entering the tube. With this counter, Geiger was able to show that approximately 3.4 x 10(to the power of 10) alpha particles are emitted per second by a gram of radium, and that each alpha particle has a double charge. Rutherford later demonstrated that the doubly charged alpha particle was in fact a helium nucleus. In 1909, Marsden and Geiger studied the interactions of alpha particles from radium with metal reflectors. They found that most alpha particles passed straight through the metal, but that a few were deflected at wide angles to the beam. They showed that the amount of deflection depended on the metal that the reflector was made of and that it decreased with a lowering of atomic weight. They used metal reflectors of different thicknesses to demonstrate that the deflection was not caused merely by some surface effect. This work led directly to Rutherford's proposal in 1911 that the atom consists of a central, positively charged nucleus surrounded by electron shells. The observed deflection of the alpha particles was due to the positively charged particle interacting with the positively charged nuclei in the metal and being deflected by repulsive forces. Geiger and Marsden later published the mathematical relationship between the amount of alpha scattering and atomic weight. Other subjects which Geiger studied under Rutherford included the relationship between the range of an alpha particle and its velocity in 1910; the various disintegration products of uranium in 1910 and 1911; and the relationship between the range of an alpha particle and the radioactive constant, which was determined with John Nuttall (1890-1958) in 1911. In 1912, upon his return to Germany, Geiger began the first of many refinements to his radiation counter, enabling it to detect beta particles and other kinds of radiation as well as alpha particles. The modern form of the instrument was finally developed with Walther Müller in 1928, and it is now usually known as the Geiger-Müller counter. It can be operated so that radioactivity causes it to emit audible clicks which can be recorded automatically. Geiger used this instrument to confirm the Compton effect in 1925 and to study cosmic radiation from 1931 onwards. Cosmic rays became a prolonged source of interest which occupied him for most of the rest of his career. Geiger's contribution to science in discovering a simple and reliable way of detecting radiation not only enabled discoveries to be made in nuclear physics, but also afforded an instant method of checking radiation levels and finding radioactive minerals. Author not available, Geiger, Hans Wilhelm (1882-1945). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998. |