Dempster, Arthur Jeffrey
Dempster, Arthur Jeffrey (1886-1950), a United States physicist. He became noted for his study of isotopes of various elements. In 1935 he discovered uranium 235 (the isotope used in the first atomic bomb) and isolated plutonium. Dempster was one of the directors of the group at the University of Chicago that produced the first nuclear chain reaction in 1942.
Dempster was born in Toronto, Ontario, Canada. He graduated from the University of Toronto in 1909. In 1914 he came to the United States. Dempster received a Ph.D. from the University of Chicago in 1916 and began to teach physics there in 1917. In 1918 he became a United States citizen.