American physicist · 1907–1991
Edwin McMillan
Edwin McMillan made the first element heavier than uranium. His discovery of neptunium in 1940 opened the door to the transuranium elements, and he shared the 1951 Nobel Prize in Chemistry with Glenn Seaborg.
- Elements credited
- 2
- Discoveries
- 1940
- Co-discoverers
- 4
- Where
- United States
The work
Studying uranium fission at Berkeley in 1939, McMillan noticed that some radioactivity stayed in the thin uranium foil instead of flying out with the fission fragments. It had a half-life of 2.3 days and did not behave like any fission product.
In 1940 he and Philip Abelson showed chemically that it was a new element, 93, formed when uranium-238 captures a neutron and then emits an electron. They named it neptunium, after Neptune, the planet beyond Uranus. McMillan also saw signs of the next element, which Seaborg’s group identified as plutonium.
Neptunium and Plutonium side by side
Life and career
McMillan was born in Redondo Beach, California, and studied at Caltech and Princeton before joining Ernest Lawrence’s Radiation Laboratory at Berkeley. During the war he worked on radar and sonar and then at Los Alamos.
In 1945 he discovered the principle of phase stability, which made the synchrotron possible, the type of accelerator still used in physics labs today. He later directed the Lawrence Radiation Laboratory from 1958 to 1973.
Also known for
- Phase stability and the synchrotron
- 1951 Nobel Prize in Chemistry