Arthur Jeffrey DempsterBorn 14 Aug 1886; died 11 Mar 1950 at age 63.Canadian-American physicist who in 1918 built the first mass spectrometer (based on the invention of Francis W. Aston) and discovered isotope uranium-235 (1935). The mass spectrometer is an instrument that uses electric and magnetic fields to separate and measure a sample's atoms according to their mass and relative quantity. In 1935, he discovered that naturally occurring uranium, though mostly uranium-238, contained 0.7% U-235 (later used as the primary fuel in atomic bombs and reactors after Niels Bohr predicted it could be used to produce a chain reaction releasing huge amounts of nuclear fission energy). During WW II, Dempster worked with the secret Manhattan Project that developed the world's first nuclear weapons.« |
