Carl Friedrich von Weizsaecker, a physicist

Carl Friedrich von Weizsaecker, a physicist who helped research atomic weapons for the Nazis during World War II but later dedicated his life to pacifism and philosophy, has died.

Dr. Weizsaecker's family said he had been gravely ill for a long time.

Born in Kiel, Germany, into a prominent family of jurists and theologians, Dr. Weizsaecker studied physics and mathematics in Leipzig, Berlin and Goettingen and went on to become a professor of physics. His brother Richard served as German president from 1984 until 1994.

Dr. Weizsaecker said he worked on the atomic bomb to avoid being conscripted into the German army. He also insisted in postwar interviews that he was grateful that nuclear technology was never used by the Nazis.

After the war, Dr. Weizsaecker dedicated his energies to philosophy and physics as a professor and researcher.

A dedicated pacifist, he continually pressed for scientists to take moral responsibility for the results of their work. He wrote several books that analyzed the dangers of war in the contemporary world.