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. His interest in physics was inspired by the work of Robert A. Millikan, and he enrolled in graduate school at California Institute of Technology (Caltech), where he wrote his 1935 PhD thesis on "The absorption of high energy electrons", 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. Neddermeyer contributed to the research which led to the 1932 discovery of the positron, for which Anderson was awarded the Nobel Prize in Physics in 1936. That year, Neddermeyer and Anderson discovered the muon, using cloud chamber measurements of cosmic rays. Their discovery predated Hideki Yukawa's 1935 theory of mesons that postulated the particle as mediating the nuclear force. 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. They also obtained the first evidence that gamma rays can generate positrons. Manhattan Project work In early 1941, with World War II raging in Europe but the United States not yet a belligerent, Neddermeyer joined a team led by Charles C. Lauritsen and William A. Fowler at the Department of Terrestrial Magnetism at the Carnegie Institution of Washington, and then at the National Bureau of Standards in Washington, D.C., that worked on the photoelectric proximity fuze. After this work was completed, Neddermeyer was recruited by Oppenheimer to work at the Manhattan Project's Los Alamos Laboratory. Neddermeyer was an early advocate for the development of an implosion technique for assembling a critical mass in an atomic bomb. Although implosion was suggested by Richard Tolman as early as 1942 and discussed in the introductory lectures given