Arthur Jeffrey Dempster

Arthur Jeffrey Dempster ( born August 14, 1886 in Toronto, Ontario, † March 11, 1950 in Stuart, Florida) was a Canadian- American physicist.

Dempster studied at the University of Toronto with a Bachelor 's degree in 1909 and a master's degree in 1910, continued his studies in Germany and in 1916 received his doctorate at the University of Chicago. From 1919 he taught at the University of Chicago.

He developed the first modern mass spectrometer 1918 and 1936, as well as Kenneth Bainbridge and Joseph Mattauch a double focusing mass spectrometer. He turned to mass spectrometry for the determination and search of stable isotopes of chemical elements and to determine their relative frequencies. He discovered more isotopes than any other scientist with the exception of Francis William Aston, inventor of the principle. In 1935 he discovered the uranium isotope 235U.

During World War II Dempster worked in the Manhattan project.