Seth Neddermeyer

Seth Henry Neddermeyer (September 16, 1907 – January 29, 1988) was an American physicist who co-discovered the muon, and later championed the implosion-type nuclear weapon while working on the Manhattan Project at the Los Alamos Laboratory during World War II.

Early life Seth Henry Neddermeyer was born in Richmond, Michigan, on September 16, 1907. He attended Olivet College, a small college that his mother, older sister, and uncle had also attended, for two years before his family moved to California. He transferred to Stanford University, from which received his Bachelor of Arts (AB) degree in 1929. under the supervision of Carl D. Anderson. He confirmed the theory espoused by Niels Bohr for this process. He also noted large radiative energy losses of electrons in lead, in agreement with the theory propounded by Hans Bethe and Walter Heitler. That year, Neddermeyer and Anderson discovered the muon, using cloud chamber measurements of cosmic rays. Hideki Yukawa's 1935 theory of mesons had postulated a particle with a mass between that of the electron and the proton as mediating the nuclear force. For several years it was thought that the muon was this particle but it became clear that it could not be, since it did not interact with nuclear matter via the strong force. This was shown in an 1948 experiment carried out by Marcello Conversi, Oreste Piccioni, and Ettore Pancini. Yukawa's particle was the pi meson. The muon is now understood to be one of three charged leptons of the Standard Model.

Anderson and Neddermeyer collaborated with Millikan in high altitude studies of cosmic rays, which confirmed Robert Oppenheimer's theory that the air showers produced in the atmosphere by cosmic rays contained electrons. Although implosion was suggested by Richard Tolman as early as 1942 and discussed in the introductory lectures given to Los Alamos scientists by Robert Serber, Neddermeyer was one of the first to urge its full development.

Later years In 1946, after World War II ended, Neddermeyer left Los Alamos to become an associate professor at the University of Washington, where he would spend the rest of his career. In due course he became a full professor. He resumed his studies of cosmic rays using a cloud chamber and a new device that he invented to measure the speed of charged particles known as a "chronotron". He was particularly interested in the properties of the muon, and conducted experiments with muons at SLAC. He participated in the DUMAND Project, for which he helped design large-scale underwater neutrino detectors.

In later life, Neddermeyer was sometimes troubled by the nuclear weapons he had helped to invent.

Neddermeyer died in Seattle on January 29, 1988,

In popular culture Neddermeyer is portrayed by Colin Bennett in the 1980 BBC series Oppenheimer, by Joe D'Angerio in Fat Man and Little Boy, and by Devon Bostick in the Christopher Nolan-directed film Oppenheimer (2023).