On March 2 1997, J. Carson Mark, leader of the Theoretical (T) Division at Los Alamos Scientific (later National) Laboratory for 26 years, died at a Los Alamos nursing home. He was 83.

Mark, who was born July 6, 1913, in Lindsay, Ontario, Canada, first came to Los Alamos in 1945 as part of the British Mission to the Manhattan Project during World War II. He joined the Laboratory staff permanently in 1946 and became leader of T Division the following year. During the 1950s he became a naturalized U.S. citizen, and he remained T Division leader until his retirement in 1973.

Mark earned a bachelor's degree from the University of Western Ontario in 1935 and a doctorate in mathematics from the University of Toronto in 1938. He taught math at the University of Manitoba from 1938 to 1943 and was a scientist for the Canadian National Research Council from 1943 to 1945.

At the Laboratory, he was involved in the development of various weapons systems, including thermonuclear bombs. He had a broad range of research interests, including hydrodynamics, neutron physics and transport theory.

One of Mark's most notable achievements was in heading the Panda Committee that designed and developed the world's first "true" H-Bomb, that is, one which operated on the Teller-Ulam principles. This device, called the Sausage, was detonated in the Ivy Mike test on 31 October 1952, 19:14:59.4 (GMT), with a yield of 10.4 megatons. A crater 6240 feet across was left on the island of Elugelab at Eniwetak Atoll.

Frank Harlow, who joined T Division in 1953 and was appointed by Mark as a group leader in 1959, said Mark enjoyed working in the rapidly growing field of computing. "Carson personally took a lot of interest in working with computers," Harlow said. "He was right there in the thick of things. He made major contributions to the continuing progress of our nuclear weapons program at that time."

Mark led the division during a period of significant transition, Harlow said. A major part of the weapons program had been in T Division, but by the 1960s, much of the weapons work had been relocated and the division had entered a period of diversification that involved working with outside agencies and private industry.

Mark was actively involved in issues related to disarmament and nonproliferation after his retirement. Recent publications on on-proliferation include Explosive Properties of Reactor-Grade Plutonium,; Science and Global Security, Vol. 4, No. 1 (1993). "Can Terrorists Build Nuclear Weapons?" by J. Carson Mark, Theodore Taylor, Eugene Eyster, William Maraman, and Jacob Wechsler, excerpted from Preventing Nuclear Terrorism is on-line at the Nuclear Control Institute.

He served on the Nuclear Regulatory Commission's Advisory Committee on Reactor Safeguards and was a member of the American Mathematical Society and the American Physical Society.

Mark is survived by his wife Kathleen Abbott Mark of Los Alamos; three daughters, Joan Mark Neary of Tesuque, Elizabeth Mark Smith of Davis, Calif., and Mary Ellen Mark of Albuquerque; three sons, Thomas Mark of Newport, Ore., and Graham Mark and Christopher Mark, both of Los Alamos; 13 grandchildren; and three great-grandchildren. The principle source of this article was the Daily News Bulletin of the Los Alamos National Laboratory for March 4, 1997.