Arthur Jeffrey Dempster

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Arthur Jeffrey Dempster
Arthur Jeffrey Dempster - Portrait.jpg
BornAugust 14, 1886
Toronto, Ontario, Canada
DiedMarch 11, 1950(1950-03-11) (aged 63)
Stuart, Florida, United States
Alma materB.S. University of Toronto
M.S. University of Toronto
Ph.D. University of Chicago
Known forDeveloped the first modern mass spectrometer, discovered 235U (used in atomic bombs)
Awards Newcomb Cleveland Prize (1929)
Scientific career
External video
Dempster mass spectrum.gif
Nuvola apps kaboodle.svg Michael A. Grayson, Discovery of Isotopes of Elements (Part I: Arthur Jeffrey Dempster), Profiles in Chemistry, Chemical Heritage Foundation

Arthur Jeffrey Dempster (August 14, 1886 – March 11, 1950) was a Canadian-American physicist best known for his work in mass spectrometry and his discovery in 1935 of the uranium isotope 235U. [1]

Canadians citizens of Canada

Canadians are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, several of these connections exist and are collectively the source of their being Canadian.

United States federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

Physicist scientist who does research in physics

A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate causes of phenomena, and usually frame their understanding in mathematical terms. Physicists work across a wide range of research fields, spanning all length scales: from sub-atomic and particle physics, through biological physics, to cosmological length scales encompassing the universe as a whole. The field generally includes two types of physicists: experimental physicists who specialize in the observation of physical phenomena and the analysis of experiments, and theoretical physicists who specialize in mathematical modeling of physical systems to rationalize, explain and predict natural phenomena. Physicists can apply their knowledge towards solving practical problems or to developing new technologies.


Early life and education

Dempster's 180 degree magnetic sector mass analyzer. Dempster Mass Spectrometer.gif
Dempster's 180 degree magnetic sector mass analyzer.

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

Toronto Provincial capital city in Ontario, Canada

Toronto is the provincial capital of Ontario and the most populous city in Canada, with a population of 2,731,571 in 2016. Current to 2016, the Toronto census metropolitan area (CMA), of which the majority is within the Greater Toronto Area (GTA), held a population of 5,928,040, making it Canada's most populous CMA. Toronto is the anchor of an urban agglomeration, known as the Golden Horseshoe in Southern Ontario, located on the northwestern shore of Lake Ontario. A global city, Toronto is a centre of business, finance, arts, and culture, and is recognized as one of the most multicultural and cosmopolitan cities in the world.

Bachelors degree Undergraduate academic degree

A bachelor's degree or baccalaureate is an undergraduate academic degree awarded by colleges and universities upon completion of a course of study lasting three to seven years. In some institutions and educational systems, some bachelor's degrees can only be taken as graduate or postgraduate degrees after a first degree has been completed. In countries with qualifications frameworks, bachelor's degrees are normally one of the major levels in the framework, although some qualifications titled bachelor's degrees may be at other levels and some qualifications with non-bachelor's titles may be classified as bachelor's degrees.

A master's degree is an academic degree awarded by universities or colleges upon completion of a course of study demonstrating mastery or a high-order overview of a specific field of study or area of professional practice. A master's degree normally requires previous study at the bachelor's level, either as a separate degree or as part of an integrated course. Within the area studied, master's graduates are expected to possess advanced knowledge of a specialized body of theoretical and applied topics; high order skills in analysis, critical evaluation, or professional application; and the ability to solve complex problems and think rigorously and independently.

Academic career

Dempster joined the physics faculty at the University of Chicago in 1916 and remained there until his death in 1950.

Physics Study of the fundamental properties of matter and energy

Physics is the natural science that studies matter and its motion and behavior through space and time and that studies the related entities of energy and force. Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.

During World War II he worked on the secret Manhattan Project to develop the world's first nuclear weapons.

World War II 1939–1945 global war

World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China. It included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, and the only use of nuclear weapons in war.

Manhattan Project research and development project that produced the first atomic bombs

The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs. The Army component of the project was designated the Manhattan District; Manhattan gradually superseded the official codename, Development of Substitute Materials, for the entire project. Along the way, the project absorbed its earlier British counterpart, Tube Alloys. The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US$2 billion. Over 90% of the cost was for building factories and to produce fissile material, with less than 10% for development and production of the weapons. Research and production took place at more than 30 sites across the United States, the United Kingdom, and Canada.

Nuclear weapon Explosive device that derives its destructive force from nuclear reactions

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or from a combination of fission and fusion reactions. Both bomb types release large quantities of energy from relatively small amounts of matter. The first test of a fission ("atomic") bomb released an amount of energy approximately equal to 20,000 tons of TNT (84 TJ). The first thermonuclear ("hydrogen") bomb test released energy approximately equal to 10 million tons of TNT (42 PJ). A thermonuclear weapon weighing little more than 2,400 pounds (1,100 kg) can release energy equal to more than 1.2 million tons of TNT (5.0 PJ). A nuclear device no larger than traditional bombs can devastate an entire city by blast, fire, and radiation. Since they are weapons of mass destruction, the proliferation of nuclear weapons is a focus of international relations policy.

From 1943 to 1946, Dempster was chief physicist of the University of Chicago's Metallurgical Laboratory or "Met Lab" which integrally related to the Manhattan Project and founded to study the materials necessary for the manufacture of atomic bombs.

Metallurgical Laboratory former laboratory at the University of Chicago, part of the Manhattan Project

The Metallurgical Laboratory 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 metallurgy, designed the world's first nuclear reactors to produce it, and developed chemical processes to separate it from other elements. In August 1942 the lab's chemical section was the first to chemically separate a weighable sample of plutonium, and on 2 December 1942, the Met Lab produced the first controlled nuclear chain reaction, in the reactor Chicago Pile-1, which was constructed under the stands of the university's old football stadium, Stagg Field.

In 1946, he took a position as a division director at the Argonne National Laboratory.

Argonne National Laboratory science and engineering research national laboratory in Lamont, IL, United States

Argonne National Laboratory is a science and engineering research national laboratory operated by the University of Chicago Argonne LLC for the United States Department of Energy located in Lemont, Illinois, outside Chicago. It is the largest national laboratory by size and scope in the Midwest.

Dempster died on March 11, 1950 in Stuart, Florida at the age of 63.


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. [2] 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. [3] [4] This isotope's ability to cause a rapidly expanding fission nuclear chain reaction allowed the development of the atom bomb and nuclear power. Dempster was also well known as an authority on positive rays.

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  1. Allison, Samuel K. (1952). "Arthur Jeffrey Dempster 1886–1950" (PDF). National Academy of Sciences . Retrieved 13 December 2012.
  2. Dempster, A. J. (April 1918). "A New Method of Positive Ray Analysis" (PDF). Phys. Rev. 11 (4): 316–325. Bibcode:1918PhRv...11..316D. doi:10.1103/PhysRev.11.316 . Retrieved 2007-11-24.
  3. "Today in Science History".
  4. Armstrong, David; Burke, Monte (December 23, 2002). "85 Innovations 1917-193". Forbes. Retrieved 13 December 2012.