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Edwin McMillan and Glenn Seaborg, Discoverers of New Elements and Isotopes

by William Watson on Mon, October 16, 2017

To celebrate 70 years of advancing scientific knowledge, OSTI is featuring some of the leading scientists and works particularly relevant to the formation of DOE, OSTI, and their predecessor organizations and is highlighting Nobel laureates and other important research figures in DOE’s history.  Their accomplishments were key to the evolution of the Department of Energy, and OSTI’s collections include many of their publications.

In 1951, Edwin M. McMillan and Glenn T. Seaborg were jointly awarded the Nobel Prize in Chemistry for discovering that the list of chemical elements, previously thought to end with the most massive known element, uranium, was actually longer and included elements whose atoms were even more massive.  Unlike most other elements, the new ones discovered by McMillan and Seaborg were not found ready-made in nature, but were produced artificially.

Edwin McMillan and Glenn Seaborg

McMillan had discovered the first transuranium element and named it “neptunium” after Neptune, the next planet beyond Uranus (for which uranium had been named).  McMillan and his coworkers also produced a second new element, but when McMillan left that project to help develop radar in World War II, he left it to others to confirm that the element was indeed a new one.  Seaborg led the group that finished this job and named the new discovery “plutonium,” after what was then considered the next planet after Neptune.  Seaborg went on to become a lead discoverer or co-discoverer of another three elements by 1951 and of six other elements after that.

The new elements’ existence had implications beyond nuclear physics.  By the time McMillan and Seaborg were awarded their Nobel Prize, the chemical properties of the elements they had already discovered (neptunium, plutonium, americium, curium, and berkelium) were unexpectedly found to be more similar to those of the rare-earth elements promethium through terbium than to those of the transition metals rhenium through gold.  This clarified important details of the way chemical properties repeat throughout the list of elements, as expressed in the periodic table.  Put another way, the periodic table turned out to have a different structure for the heaviest elements from the structure that had generally been expected before.

Edwin McMillan was born in 1907 at Redondo Beach, California.  After his undergraduate and master’s work at the California Institute of Technology and his doctoral research at Princeton, he began his work at the University of California, Berkeley, which included the synthesis of neptunium and plutonium.  After McMillan’s subsequent contributions to develop radar (and sonar) for national defense, he helped establish the Manhattan Project’s Los Alamos laboratory as J. Robert Oppenheimer’s first recruit, and participated in teams that developed both uranium and plutonium nuclear weapons.  After World War II, McMillan co-invented the synchrotron, a machine that could (among other things) accelerate subatomic particles into nuclei at higher energies than the cyclotron he had used to produce neptunium, and he returned to Berkeley’s Radiation Laboratory to build synchrotrons.  McMillan eventually succeeded Ernest O. Lawrence as the Lab’s director after Lawrence’s death in 1958, serving until his own retirement in 1973.  McMillan was awarded the National Medal of Science the year before his death in 1991.  Further details of McMillan’s biography are available through DOE R&D Accomplishments; some of the reports McMillan wrote or coauthored can be found through SciTech Connect.

Glenn Seaborg was born in 1912 in Ishpeming, Michigan.  Seaborg earned his bachelor’s degree from the University of California at Los Angeles and his doctorate from the University of California, Berkeley.  His collaborations with others to alter atomic nuclei not only produced new chemical elements but also new radioactive isotopes of many already-known elements, eight of which produce radiations that are now used to diagnose and treat serious illnesses.  Seaborg worked on the Manhattan Project, was a professor and Chancellor of UC Berkeley, chaired the Atomic Energy Commission for a decade, advised ten U.S. Presidents in various capacities, and was awarded the National Medal of Science in 1991.  One of the ten elements that he was involved in discovering was officially recognized as “seaborgium” by the International Union of Pure and Applied Chemistry in 1997 before Seaborg’s death in 1999.  SciTech Connect includes many reports by Seaborg, and a short lecture about his life is available through DOE R&D Accomplishments.

Reports of research sponsored by the Department of Energy and its predecessor agencies are freely available to the public through SciTech Connect; besides reports by McMillan and Seaborg, these include many other reports about research on elements in the periodic table beyond uranium and radioisotopes.

Page last updated on 2017-10-17 15:40