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Edwin M. McMillan, 84, a professor emeritus of physics at the University of California at Berkeley who was a co-winner of the 1951 Nobel Prize for chemistry, died Sept. 7 at his home in El Cerrito, Calif. He had diabetes.

Upon learning of his death, his Nobel co-winner, Glenn T. Seaborg, noted that the two had been friends and colleagues since 1934, and added that "his important and versatile scientific contributions spanning physics, chemistry and engineering, and his great human qualities, form an important chapter in the history of science."

Seaborg and Dr. McMillan were awarded the prize for work in the 1930s and early 1940s discovering and isolating "transuranium" elements -- synthetic elements beyond uranium (element 92) on the periodic table. That work resulted in the discovery of plutonium (element 94), a crucial ingredient in the manufacture of atomic weapons and the operation of nuclear power plants.

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After wartime scientific work for the government, Dr. McMillan returned to Berkeley, where he had done research since the early 1930s, and developed what became the synchrotron, a high-energy accelerator that was a dramatic improvement on the cyclotron. This new tool made it possible for scientists to do research that led to the discovery of new atomic particles and antimatter.

In 1963, for his work on the synchrotron, he was named co-winner of the Atoms for Peace Award. He shared it with Soviet physicist Vladimir I. Veksler, who had done similar work independently. Their work in "phase stability," which led to the synchrotron, also made the giant linear accelerators of today possible.

Dr. McMillan began his career at Berkeley as a research fellow in 1932. He was named a full professor of physics in 1945 and retired as professor emeritus in 1973. Over the years, he also was affiliated with the university's Lawrence Radiation Laboratory, serving as assistant director from 1954 to 1958, then as lab director from 1958 to 1973.

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He was a member of the general advisory board of the Atomic Energy Commission from 1954 to 1958 and a trustee of Rand Corp. from 1959 to 1969. He also was a public voice for nuclear arms limitations.

Edwin Mattison McMillan was born Sept. 18, 1907, in Redondo Beach, Calif. When he was a year old, his family moved to Pasadena, Calif., where he became interested in physics. As a youth, he attended public lectures at the nearby California Institute of Technology. While an undergraduate at Cal Tech, he wrote a scientific paper on X-rays with an assistant professor named Linus Pauling.

Graduating with a degree in physics in 1928, Dr. McMillan received his master's degree in physics from Cal Tech in 1929. Three years later, he received his physics doctorate from Princeton University. He then went to Berkeley, and in 1934 he joined Ernest O. Lawrence, who was organizing the new radiation laboratory. He worked on Lawrence's revolutionary "atom-smasher," the cyclotron. He joined the Berkeley faculty in 1935.

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Dr. McMillan's work concerned studies of radioactivity and particle bombardment and led to his creating the first of the synthetic elements. In 1934, he and M. Stanley Livingston discovered oxygen-15. In 1940, he and Samuel Ruben discovered beryllium-10.

He showed that the neutron bombardment of uranium resulted not only in fission, but also in a new substance heavier than uranium. He named the new isotope neptunium 239. He called it neptunium (element 93) after Neptune, the planet beyond Uranus. Building on Dr. McMillan's work, a team led by Seaborg discovered the next element, 94. In keeping with Dr. McMillan's work, they named it plutonium, after Pluto, the planet beyond Neptune.

Dr. McMillan had been unable to continue the work resulting in plutonium himself because by 1940 he already was working on government scientific defense projects. During World War II, he was a leader in radar research at the Massachusetts Institute of Technology, and worked on the Navy's sonar research before he was recruited by a fellow Berkeley physicist, J. Robert Oppenheimer, to join the Manhattan Project's research efforts at Los Alamos, N.M. He was in charge of the early construction of the atomic bomb dropped on Hiroshima.

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Upon returning to Berkeley in 1945, he worked on the university's construction of a new cyclotron. Using Einstein's theory of relativity, he came up with his "theory of phase stability." It was used in adjusting the magnetic field of the new device, the synchrotron, thus achieving a machine twice as powerful as originally estimated. The new machine made it possible to create cosmic rays in the laboratory.

Dr. McMillan was a member of National Academy of Sciences, the American Philosophical Society and the Cosmos Club.

Survivors include his wife of 50 years, the former Elsie Walford Blumer, of El Cerrito; two sons, David, of Ancortes, Wash., and Steven, of El Cerrito; a daughter, Anne Chaikin of Bellingham, Wash.; and three grandchildren.

CLIFTON L. CLEVENGER

Construction Executive

Clifton L. Clevenger, 89, a retired area construction executive and founder of Clevenger Corp., a Beltsville commercial interior construction firm, died Sept. 6 at Montgomery General Hospital. He had pneumonia.

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Mr. Clevenger, who had lived in St. Michael's, Md., for 12 years, was born in West Virginia. He came to the Washington area in 1928 and lived in Laurel for 29 years before retiring to Florida in 1957. He returned to the Washington area the next year, then lived in Florida again for three years before moving to St. Michael's.

From about 1931 to 1957, he did sales work for John H. Hampshire Corp., a Bladensburg commercial construction company. He founded Clevenger Corp. in Florida in 1957, then moved it to the Washington area the next year. He retired as its president in 1967.

He held a patent for drywall movable partitions for use in commercial buildings.

Mr. Clevenger, an organizer of the Laurel Rescue Squad, was an unsuccessful candidate for the Republican nomination for Congress in Maryland's 5th District in the 1950s and early 1960s. He was a charter member of the Laurel Moose lodge and a member of the Lions Club in Laurel.

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Survivors include his wife of 61 years, Ella L.F. Clevenger of St. Michael's; four sons, Clifton Jr., of Annapolis, David O., of Highland, Md., Paul T., of Bladensburg, and John R., of Laurel; a brother, Lanie Clevenger of Cumberland, Md.; a sister, Edith Collins of Fairmont, W.Va.; six grandchildren; and five great-grandchildren.

ANNABELLE P. HOFFMAN

Sisterhood President

Annabelle Pepper Hoffman, 60, a past president of the sisterhood of the Arlington-Fairfax Jewish Congregation in Arlington, died Sept. 6 at Fairfax Hospital. She had diabetes.

Mrs. Hoffman, who lived in Alexandria, was a native of Pittsburgh. She came to the Washington area about 1965.

Survivors include her husband, Zelman, of Alexandria; a son, Lee, of Washington; and a brother, Leonard Pepper of Pittsburgh.

HELEN S. MULLINNIX

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Club Member

Helen S. Mullinnix, 91, a member of the Sulgrave and Army & Navy clubs in Washington, died Sept. 7 at a hospital in Harbor Beach, Mich., after a stroke. A resident of Washington, she was vacationing at the time of her death.

Mrs. Mullinnix had lived in the Washington area since 1935. She was born in Kansas and reared in Mississippi.

Her first marriage, to Gordon Hurlbutt, ended in divorce. Her second husband, retired Navy Rear Adm. Allen Mullinnix, died in 1978.

Survivors include two sons from her first marriage, Gordon Jr. and John Henry Hurlbutt, both of Tonganoxie, Kan.; three grandchildren; and a great-granddaughter.

THOMAS B. LAWRENCE

Washington Lawyer

Thomas B. Lawrence, 69, a lawyer in private general practice in Washington since the late 1940s, died of cancer Sept. 8 at his home in Rockville.

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Over the years, his clients had included the National Licensed Beverage Association. He had served as the association's counsel.

Mr. Lawrence, who came to the Washington area in the mid-1940s, was a native of St. Mary's County. He was a graduate of Loyola College of Baltimore and the Georgetown University law school. He served in the Navy in the Pacific during World War II.

He was a member of St. Elizabeth's Catholic Church in Rockville.

Survivors include his wife of 25 years, the former Joan Ryan, two sons, Quinn and Hugh, and two daughters, Suzanne and Monica Lawrence, all of Rockville; a brother, William S., of Bushwood, Md.; and two sisters, Margaret Kivlin of Greenbelt and Ann Abell of Leonardtown.

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