George Cowan, a chemist who helped build the first atomic bomb, detect the first Soviet nuclear explosion and test the first hydrogen bomb, died on Friday at his home in Los Alamos, N.M. He was 92.

The Santa Fe Institute, a scientific research center that Dr. Cowan headed and helped found, announced the death.

For his many contributions, Dr. Cowan was awarded the federal Energy Department’s highest honor, the Enrico Fermi Award, and the highest honor given by the Los Alamos National Laboratory, the Los Alamos Medal. The citation on his Los Alamos award called him “the driving force in the early radiochemical evaluations of nuclear weapons.”

Dr. Cowan began thinking about the possibility of a bomb in 1938, when he brought a clipping about nuclear fission to his physics professor and asked him to talk about the possibility of a weapon based on splitting the atom. His professor at Worcester Polytechnic Institute in Massachusetts made a convincing argument that it would not happen, but when Dr. Cowan graduated three years later, the professor referred him to Eugene Wigner, a physicist at Princeton....