Arthur Jeffrey Dempster (August 14, 1886 – March 11, 1950) was a Canadian-

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

physicist best known for his work in

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

and his discovery in 1935 of the uranium isotope ²³⁵U.

Early life and education

Dempster was born in Toronto, Ontario, Canada. He received his

bachelor's A bachelor's degree (from Middle Latin ''baccalaureus'') or baccalaureate (from Modern Latin ''baccalaureatus'') is an undergraduate academic degree awarded by colleges and universities upon completion of a course of study lasting three to six ye ...

and master's degrees at the University of Toronto in 1909 and 1910, respectively. He travelled to study in Germany, and then left at the outset of World War I for the United States; there he received his Ph.D. in physics at the University of Chicago.

Academic career

Dempster joined the physics faculty at the University of Chicago in 1916 and remained there until his death in 1950. During World War II he worked on the secret Manhattan Project to develop the world's first nuclear weapons. From 1943 to 1946, Dempster was chief physicist of the University of Chicago's

Metallurgical Laboratory The Metallurgical Laboratory (or Met Lab) was a scientific laboratory at the University of Chicago that was established in February 1942 to study and use the newly discovered chemical element plutonium. It researched plutonium's chemistry and m ...

or "Met Lab" which integrally related to the Manhattan Project and founded to study the materials necessary for the manufacture of atomic bombs. In 1946, he took a position as a division director at the

Argonne National Laboratory Argonne National Laboratory is a science and engineering research United States Department of Energy National Labs, national laboratory operated by University of Chicago, UChicago Argonne LLC for the United States Department of Energy. The facil ...

. Dempster died on March 11, 1950 in

Stuart, Florida Stuart is a city in and the seat of Martin County, Florida, United States. Located on Florida's Treasure Coast, Stuart is the largest of four incorporated municipalities in Martin County. The population is 17,425 according to the 2020 United State ...

at the age of 63.

Research

In 1918, Dempster developed the first modern mass spectrometer, a scientific apparatus allowing physicists to identify compounds by the mass of elements in a sample, and determine the isotopic composition of elements in a sample. Dempster's mass spectrometer was over 100 times more accurate than previous versions, and established the basic theory and design of mass spectrometers that is still used to this day. Dempster's research over his career centered on the mass spectrometer and its applications, leading in 1935 to his discovery of the uranium isotope ²³⁵U. This isotope's ability to cause a rapidly expanding

fission Fission, a splitting of something into two or more parts, may refer to: * Fission (biology), the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original * Nuclear fissio ...

nuclear chain reaction In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific nu ...

allowed the development of the atom bomb and nuclear power. Dempster was also well known as an authority on

positive ray An anode ray (also positive ray or canal ray) is a beam of positive ions that is created by certain types of gas-discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886. Later ...

References

{{DEFAULTSORT:Dempster, Arthur Jeffrey 1886 births 1950 deaths People from Old Toronto University of Toronto alumni University of Chicago alumni 20th-century American physicists American nuclear physicists Canadian physicists Canadian nuclear physicists Mass spectrometrists Manhattan Project people Fellows of the American Physical Society Members of the United States National Academy of Sciences Presidents of the American Physical Society Canadian emigrants to the United States