Anderson, Carl David (1905-1991), an American physicist, discovered two subatomic particles—the positron and the muon. He identified these particles while studying cosmic rays with the aid of a Wilson cloud chamber (see Cosmic rays ). For his discovery of the positron, Anderson shared the 1936 Nobel Prize in physics with Victor F. Hess.
The positron, which Anderson discovered in 1932, was the first known antiparticle (see Antimatter ). The British physicist Paul Dirac had predicted its existence in 1931. The positron has a mass equal to that of the negatively charged electron, but its electric charge is positive. In 1937, Anderson discovered the particle known as the mu-meson, or muon. Muons have positive or negative charges and closely resemble positrons and electrons. But the mass of a muon is about 207 times as great as that of an electron.
Anderson was born on Sept. 3, 1905, in New York City. In 1930, he received a Ph.D. degree in physics from the California Institute of Technology. He died on Jan. 11, 1991.
