Edwin M. McMillan | Biography

Edwin M. McMillan's first important discovery was made in 1940 when he, Philip Abelson, and Glenn T. Seaborg (1912-1999)produced and identified samples of transuranium elements , later named neptunium and plutonium. After World War II, McMillan became involved in the development of particle accelerators. Simultaneously with but independent of the Russian physicist V. I. Veksler, McMillan found a way to compensate for the relativistic mass increase that occurs in high energy accelerators. He won a share of the 1951 Nobel Prize for chemistry (with Seaborg) for his discovery of neptunium and a share of the 1963 Atoms for Peace Award (with Veksler) for his work on accelerators.

McMillan was born in Redondo Beach, California, on September 18, 1907. His father was Edwin Harbaugh McMillan, a physician, and his mother was Anna Marie Mattison. The McMillan family moved to Pasadena when Edwin was a year old. He attended local primary and secondary schools, graduating from Pasadena High School in 1924.

After completing his B.S. and M.S. degrees at the California Institute of Technology in 1928 and 1929, McMillan enrolled at Princeton University for his graduate study. In 1932, he was awarded a Ph.D. degree for his thesis, entitled "Electric Field Giving Uniform Deflecting Force on a Molecular Beam." McMillan then received a National Research fellowship that allowed him to begin his postdoctoral studies at the University of California at Berkeley.

In 1934, Ernest Orlando Lawrence, inventor of the cyclotron, established the Berkeley Radiation Laboratory on the University of California campus and invited McMillan to join its staff. McMillan maintained his relationship with the laboratory (later renamed the Lawrence Radiation Laboratory) for the next 40 years. He was made associate director of the laboratory in 1954 and director in 1958, a post he held until his retirement in 1973.

In the late 1930s, McMillan turned his attention to one of the most exciting topics in scientific research at the time: the bombardment of atomic nuclei by neutrons. This type of research had been inspired by a series of experiments conducted by Enrico Fermi in the mid-1930s. Fermi had found that nuclei will often capture a neutron and undergo a nuclear transformation in which they are converted to a new element one place higher in the atomic table than the original element. Over a period of time, Fermi used this technique to transform more than 60 different elements.

The one element in which Fermi was most interested, however, was uranium. It was obvious that neutron capture by a uranium nucleus would result in the formation of the next heavier element, an element that does not exist naturally on Earth. When Fermi actually conducted this experiment, however, he obtained confusing results that could not be interpreted as the formation of a new element. A few years later, Otto Hahn, Fritz Strassmann, and Lise Meitner correctly interpreted Fermi's experiments, showing that the bombardment of uranium with neutrons had resulted in nuclear fission.

Working first with Abelson and later with Seaborg, McMillan repeated Fermi's original experiments. They bombarded uranium with neutrons and found that, while fission did occur, a small fraction of the uranium nuclei did undergo the kind of transformation to a heavier element that Fermi had anticipated. Later studies found that the uranium-235 isotope undergoes fission, while the uranium-238 isotope, under the proper conditions, is transformed to a heavier element. McMillan and Abelson suggested the name neptunium for the element after the planet Neptune, located one planet beyond Uranus, the namesake of uranium. A year later, McMillan and Seaborg found that the radioactive decay of neptunium produces yet another element, heavier than itself, an element they called plutonium. Again, the element's name was taken from that of a planet, Pluto, the farthest from the Sun. The two researchers were later to share the 1951 Nobel Prize in chemistry for their research on the transuranium elements.

With the onset of World War II, McMillan left Berkeley to conduct military research at the Massachusetts Institute of Technology, at the U.S. Navy Radio and Sound Laboratory in San Diego, and finally at the Manhattan Project laboratories at Los Alamos. At the war's conclusion, McMillan returned to Berkeley and the radiation laboratory, and immediately became immersed in problems of accelerator design. The cyclotron, invented by Lawrence in the early 1930s, had served the research community well for more than a decade, but the limits of the machine's usefulness were now becoming apparent. The most serious problem with traditional cyclotrons was relativistic mass increase.

Relativistic mass increase refers to the fact that as particles gain velocity in an accelerator, they also gain mass; the mass gain subsequently causes them to lose velocity. Before long, high-energy particles begin to fall out of phase with the electrical fields that are used to accelerate them, and they become lost inside the machine. McMillan's solution for this problem was simple and elegant. He modified the electrical field in the accelerator so that, as particles speed up and gain mass, the rate at which the electrical field changes direction slows down. In that way, the electrical field can be kept in phase with the particles even while they gain energy and mass.

For many years thereafter, this concept was employed in the development of more advanced circular accelerators, such as the synchrotron and synchrocyclotron. In 1963, McMillan was awarded a share of the Atoms for Peace Award with Veksler, who had developed the same concept at about the same time.

McMillan married Elsie Walford Blumer on June 7, 1941. She was the daughter of the former dean of the Yale University school of medicine and the sister of Mrs. Ernest Lawrence. The McMillans had three children, Ann, David, and Stephen. McMillan died of complications from diabetes on September 7, 1991, in El Cerrito, California.