Carl David Anderson died on this date in 1991. He was an American physicist who is best known for his discovery of the positron in 1932, an achievement for which he received the 1936 Nobel Prize in Physics. He also discovered the muon in 1936. Anderson was born in New York City, the son of Swedish immigrants. He studied physics and engineering at Caltech (B.S., 1927; Ph.D., 1930). Under the supervision of Robert A. Millikan, he began investigations into cosmic rays during the course of which he encountered unexpected particle tracks in his (modern versions now commonly referred to as an Anderson) cloud chamber photographs that he correctly interpreted as having been created by a particle with the same mass as the electron, but with opposite electrical charge. This discovery announced in 1932 and later confirmed by others, validated Paul Dirac’s theoretical prediction of the existence of the positron. Anderson first detected the particles in cosmic rays. He then produced a more conclusive proof by shooting gamma rays produced by the natural radioactive nuclide ThC into other materials, resulting in the creation of positron-electron pairs. For this work, Anderson shared the 1936 Nobel Prize in Physics with Victor Hess. Also in 1936, Anderson and his first graduate student, Seth Neddermeyer, discovered the muon (or ‘mu-meson’, as it was known for many years), a subatomic particle 207 times more massive than the electron, but with the same negative electric charge and spin 1/2 as the electron, again in cosmic rays. Anderson and Neddermeyer at first believed that they had seen the pion, a particle which Hideki Yukawa had postulated in his theory of the strong interaction. When it became clear that what Anderson had seen was not the pion, the physicist I. I. Rabi, puzzled as to how the unexpected discovery could fit into any logical scheme of particle physics, quizzically asked “Who ordered that?” (sometimes the story goes that he was dining with colleagues at a Chinese restaurant at the time). The muon was the first of a long list of subatomic particles whose discovery initially baffled theoreticians who could not make the confusing “zoo” fit into some tidy conceptual scheme. Willis Lamb, in his 1955 Nobel Prize Lecture, joked that he had heard it said that “the finder of a new elementary particle used to be rewarded by a Nobel Prize, but such a discovery now ought to be punished by a 10,000 dollar fine.” Anderson spent all of his academic and research career at Caltech. During World War II, he conducted research in rocketry there. He was elected a Fellow of the American Academy of Arts and Sciences in 1950. He died on January 11, 1991, and his remains were interred in the Forest Lawn, Hollywood Hills Cemetery in Los Angeles, California. His wife Lorraine died in 1984.
Isidor Isaac Rabi died on this date in 1986. He was a Polish-born American physicist and Nobel laureate, recognised in 1944 for his discovery of nuclear magnetic resonance, which is used in magnetic resonance imaging. He was also involved in the development of the cavity magnetron, which is used in microwave radar and microwave ovens. Born into a traditional Jewish family in Rymanów, Galicia, in what was then part of Austria-Hungary, Rabi came to the United States as a baby and was raised in New York’s Lower East Side. He entered Cornell University as an electrical engineering student in 1916 but soon switched to chemistry. Later, he became interested in physics. He continued his studies at Columbia University, where he was awarded his doctorate for a thesis on the magnetic susceptibility of certain crystals. In 1927, he headed for Europe, where he met and worked with many of the finest physicists of the time. In 1929 Rabi returned to the United States, where Columbia offered him a faculty position. In collaboration with Gregory Breit, he developed the Breit-Rabi equation and predicted that the Stern–Gerlach experiment could be modified to confirm the properties of the atomic nucleus. He developed techniques for using nuclear magnetic resonance to discern the magnetic moment and nuclear spin of atoms. This work led to his being awarded the Nobel Prize in Physics in 1944. Nuclear magnetic resonance became an important tool for nuclear physics and chemistry. The subsequent development of magnetic resonance imaging from it has made it important to medicine as well. During World War II he worked on radar at the Massachusetts Institute of Technology Radiation Laboratory and on the Manhattan Project. After the war, he served on the General Advisory Committee (GAC) of the Atomic Energy Commission and was chairman from 1952 to 1956. He also served on the Science Advisory Committee (SAC) of the Office of Defense Mobilization and was Science Advisor to President Dwight D. Eisenhower. He was involved with the establishment of the Brookhaven National Laboratory in 1946, and later, as United States delegate to UNESCO, with the creation of CERN in 1952. When Columbia created the rank of University Professor in 1964, Rabi was the first to receive such a chair. A special chair was named after him in 1985. He retired from teaching in 1967 but remained active in the department and held the title of University Professor Emeritus and Special Lecturer until his death.