Carl David Anderson Biography

Anderson was born in New York City on September 3, 1905. He earned his bachelor of science degree in physics and engineering at the California Institute of Technology in 1927 and his Ph.D. from the same institution three years later. Upon graduation, Anderson was appointed to the faculty at Cal Tech and became professor of physics there in 1939. During World War II he served with the Cal Tech Artillery Rocket Project. After the war, he used military B-29 aircraft in his studies of cosmic radiation. He returned to Cal Tech and served as chairman of the division of physics, mathematics, and astronomy from 1962 to 1970. He retired from Cal Tech in 1976 and died in San Marino, California on January 11, 1991.

Anderson is best known for his discoveries of the positive electron ( positron) in 1932 and the meson in 1935. Both discoveries came about as a result of his research on cosmic rays begun in 1930. Cosmic rays are highly energetic forms of electromagnetic radiation originating from far beyond the earth 's atmosphere. When they enter the atmosphere, they collide with atoms and molecules, tearing them apart and producing a variety of secondary particles.

The nature of these secondary particles can be studied in a cloud chamber. Their mass and energy can be determined by the paths they leave in the chamber. One problem in using a conventional cloud chamber in this research, however, is the enormous energy carried by cosmic rays. The secondary particles they produce are often moving so fast that they are deflected only slightly as they pass through the chamber.

Anderson solved this problem by inserting a lead plate in the cloud chamber. The lead plate slows down cosmic ray secondaries and makes it easier to interpret their paths.

The first discovery Anderson made with his modified chamber was a particle whose mass was the same as that of the electron, but whose charge was positive rather than negative. He suggested calling the particle a positron, a name that has been universally adopted. For his discovery of the positron, Anderson shared the Nobel Prize for physics in 1936 with Victor Franz Hess.

Around the same time, Anderson discovered a second new particle. While studying cosmic radiation on Pike's Peak in Colorado, Anderson identified the track of a particle that was more massive than the electron, but only a quarter as massive as the proton. The particle had a lifetime of only a few millionths of a second. Anderson suggested calling the particle a mesotron, but its name was soon shortened to meson. Later research has shown the meson to be a very heavy particle related to the electron.