Edward Mills Purcell
Purcell, Edward Mills (1912-1997) was an American physicist who received the 1952 Nobel Prize in physics for developing and applying a simple, precise method for determining the magnetic properties of atomic nuclei. He shared the prize with American physicist Felix Bloch, who had independently developed a similar method.
Purcell was born on Aug. 30, 1912, in Taylorville, Illinois, to Edward A. Purcell and Mary Elizabeth (Mills) Purcell. He attended public schools in Taylorville and Mattoon and received a B.S. degree in electrical engineering from Purdue University in Lafayette, Indiana, in 1933. After a year as an exchange student at the technical university in Karlsruhe, Germany, Purcell began graduate studies in physics at Harvard University, where he received his M.A. degree in 1936 and his Ph.D. degree in 1938. He remained at Harvard as an instructor until 1940. In 1946, he became an associate professor of physics, and in 1949 he became a full professor.
During World War II (1939-1945), Purcell supervised a group at the Massachusetts Institute of Technology Radiation Laboratory that was developing techniques for producing and detecting microwaves (short radio waves). He worked with Austrian-born American physicist Isidor Isaac Rabi.
In the 1930's, Rabi developed a technique for measuring magnetic moments, but his method required turning the sample to vapor. Purcell sought to develop a better technique. At about the same time, Bloch began working on the same problem at Stanford University in California.
The magnetic moment of a nucleus causes it to precess in a magnetic field. Precession is the rotation of a spinning rigid body that has been tipped from its vertical axis by an external force acting on it. This phenomenon is illustrated by the wobble of a top and the gyration of the earth's axis. The rate of nuclear precession depends on the strength of the magnetic field and on the magnetic moment of the particular nucleus. Purcell and Bloch knew that if the strength of the field is known and the precession frequency rate can be determined, the magnetic moment could be calculated.
In the 1940's, Purcell and Bloch both found a way to measure the magnetic field of nuclei. The technique Purcell developed involved placing a substance in a strong magnetic field and exposing it to radio waves. They discovered that the waves interacted with the nuclei of the substance's atoms. This discovery became known as nuclear magnetic resonance (NMR).
Chemists soon began using NMR as an analytic tool. In addition, researchers began to use NMR to study living organisms without causing damage. In the 1970's, NMR scanners were created that could show specific chemical reactions within the body. Magnetic resonance imaging (MRI), based on NMR, has become a highly useful technique for doctors to gain images of tissues inside the body. They use these images to diagnose certain diseases, disorders, and injuries.
Purcell also made important contributions to radio astronomy. In 1951, his investigations using NMR revealed that hydrogen atoms in space give off electromagnetic radiation of a certain radio frequency. Purcell helped build the first radio telescope. Radio telescopes collect and measure faint radio waves given off by objects in space. His work also pointed the way for the use of microwaves in telephonic and television communication.
In 1958, Purcell became Donner Professor of Science at Harvard. He served as a scientific adviser to the United States government on science policy in the 1950's and 1960's. In 1960, he became the Gerhard Gade University Professor at Harvard, a position he held until his retirement. In 1980, he became emeritus professor.
Purcell wrote the textbook Electricity and Magnetism (1965), widely regarded as a classic. He also made important contributions to science education at the high school and college levels.
He received the National Medal of Science of the National Science Foundation in 1980. He was a member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Physical Society, of which he was president in 1970.