September 15, 2021   Read time 4 min
The American physicist Arthur Holly Compton performed the watershed X-ray scattering experiment that placed all of quantum mechanics on a sound experimental basis.

Compton was born on September 10, 1892, in Wooster, Ohio. His father, a professor at Wooster College, encouraged him to become a scientist. His older brother, Karl, who would eventually become president of the Massachusetts Institute of Technology, also kindled Arthur’s interest in physics by introducing him to the study of X-rays.

Compton completed his undergraduate education at Wooster College in 1913 and then followed his older brother to Princeton University. There, Arthur Compton received his M.A. degree in 1914 and his Ph.D. degree in 1916. For his doctoral research, Compton studied the angular distribution of X-rays reflected by crystals. Upon graduation from Princeton, he married Betty McCloskey, an undergraduate classmate from Wooster College. The couple had two sons.

After spending a year teaching physics at the University of Minnesota, Compton became an engineering physicist with the Westinghouse Lamp Company and lived for two years in Pittsburgh . In 1919, he received one of the first National Research Council fellowships. He used this prestigious award to study gamma ray scattering phenomena at the Cavendish Laboratory in England. While working with Ernest Rutherford (1871–1937), Compton was able to verify the puzzling results obtained by other physicists, such as Charles Barkla (1877–1944)—namely, that when scattered by matter, X-rays and gamma rays display an increase in wavelength as a function of scattering angle. At the time, classical physics could not satisfactorily explain how the wavelength of the high-frequency electromagnetic waves could change in such scattering interactions.

After a year of study in England, Compton returned to the United States and accepted a position as head of the department of physics at Washington University in Saint Louis, Missouri. There, using X-rays to bombard graphite (carbon), he resumed his investigation of the puzzling mystery of photon scattering and wavelength change. By 1922, Compton’s experiments revealed a definite, measurable increase of X-ray wavelength with scattering angle—a phenomenon now called the Compton effect. He applied special relativity and quantum mechanics to explain the results and presented his famous quantum hypothesis in “A Quantum Theory of the Scattering of X-rays by Light Elements,” a paper published in the May 1923 issue of The Physical Review. In 1927, Compton shared the Nobel Prize in physics with Charles Wilson (1869–1959) for his pioneering work that correctly explained the scattering of high-energy photons by electrons. In the process, Compton caused a revolution in quantum physics with his seemingly simple assumption that X-ray photons behave like particles and interact one-on-one as they scatter with free electrons in the target material.

Wilson’s cloud chamber helped to verify the presence of the recoil electrons predicted by Compton’s quantum scattering hypcloud tracks of recoiling electrons provided indisputable corroborating evidence of the particle-like behavior of electromagnetic radiation. Compton’s pioneering research implied that the scattered X-ray photons had less energy than the original X-ray photons. Compton became the first scientist to experimentally demonstrate the particlelike, or quantum, nature of electromagnetic waves. His book Secondary Radiations Produced by X-Rays, published in 1922, described much of this important research and his innovative experimental procedures. The discovery of the Compton effect served as the technical catalyst for the acceptance and rapid development of quantum mechanics in the 1920s and 1930s.

In 1923, Compton became a professor of physics at the University of Chicago. An excellent teacher and experimenter, he wrote the 1926 book X-Rays and Electrons to summarize and propagate his pioneering research experiences. From 1930 to 1940, Compton led a worldwide scientific study to measure the intensity of cosmic rays. His purpose was to determine any geographic variation in their intensity. Compton’s measurements showed that cosmic ray intensity correlated with geomagnetic latitude rather than geographic latitude. His results showed that cosmic rays were not electromagnetic in nature but, rather, very energetic charged particles capable of interacting with Earth’s magnetic field. During World War II, Compton played a major role in the development of the U.S. atomic bomb.

He served as a senior scientific advisor on the Manhattan Project and was director of the Metallurgical Laboratory at the University of Chicago. Under Compton’s leadership, the Italian-American physicist Enrico Fermi (1901–1954) was able to construct the world’s first nuclear reactor, which he first operated on December 2, 1942. This successful uranium-graphite reactor, Chicago Pile One, became the technical ancestor for the large plutonium-production reactors at Hanford, Washington. The Hanford reactors, in turn, produced the plutonium used in the world’s first atomic explosion, the Trinity device detonated in southern New Mexico on July 16, 1945, and in the Fat Man atomic weapon dropped on Nagasaki, Japan, on August 9, 1945.

Compton also encouraged the establishment of Argonne National Laboratory as a major postwar nuclear research facility. He described his wartime role and experiences in the 1956 book Atomic Quest: A Personal Narrative. Following World War II, Compton put aside high-energy physics research and followed his family’s strong tradition of Christian service to education by accepting the position of chancellor at Washington University. He served as chancellor until 1953 and then as a professor of natural philosophy until failing health forced him to retire in 1961. Compton died in Berkeley, California, on March 15, 1962. In the 1990s, the National Aeronautics and Space Administration (NASA) named its advanced highenergy astrophysics spacecraft the Compton Gamma Ray Observatory (CGRO) after him. Its suite of Compton effect gamma-ray detection instruments operated successfully from mid-1991 until June 2000, providing valuable astrophysical data.