Walther Wilhelm Georg Bothe

Walther Wilhelm Georg Bothe (1891-1957), German physicist, mathematician, chemist, and Nobel Prize winner. Bothe developed the coincidence method of particle detection and used it to study interactions between elementary particles. He shared the 1954 Nobel Prize in physics with German-born British physicist Max Born.

Born in Oranienburg, Germany, Bothe attended the University of Berlin from 1908 to 1912. He received his doctorate in 1914 under the German physicist Max Planck for the study of the molecular theory of refraction, reflection, scattering, and absorption of light rays (see Optics). Bothe served in the Germany Army during World War I (1914-1918) and was captured and held as a prisoner of war in Russia from 1915 to 1920. While he was a prisoner, he managed to keep studying theoretical physics and learn Russian. In 1920 he accepted an invitation from Hans Geiger, a fellow German physicist, to work at the radioactivity laboratory of the Physikalisch-Technische Reichsanstalt (State Physical-Technical Institute). Bothe went on to teach physics at the University of Berlin from 1920 to 1931, and at the University of Giessen from 1931 to 1934. In 1934 he became director of the Max Planck Institute at Heidelberg, where he remained until his death.

Bothe's international recognition began with his development of mathematical expressions for the scattering patterns of various rays and particles. This research served as foundation for his studies on collisions between X rays and electrons in matter, in which the electrons are knocked away from their atoms and the X rays are scattered. Earlier physicists had theorized that individual collisions did not necessarily conserve momentum and energy—that is, the momentum and energy of the incoming X ray did not have to equal the combined momentum and energy of the electron and the scattered X ray after the collision. This idea was contrary to the fundamentals of classical physics.

Geiger and Bothe believed they could test this theory experimentally by using electrical counters to examine particle emissions. The most widely used electrical counter was the Geiger-Müller tube.

With his knowledge of the tube, Bothe invented a system in 1925 in which two counters were connected to a common amplifier. The device registered pulses only when particles triggered both counters simultaneously. This new process, called the coincidence method, allowed Bothe and Geiger to study the coincidences between the scattered X ray and the recoiling electron, leading them to discover small-scale conservation of energy and momentum, thus refuting the quantum theory of radiation.

Bothe continued his work in experimental and theoretical physics, working on cosmic rays (high-energy, fast moving subatomic particles that come through the earth's atmosphere from outer space), discovering a new type of radiation later found to be the neutron, and working on the German government's radiation and nuclear energy projects.