Arthur Holly Compton (September 10, 1892 – March 15, 1962) was an American physicist who shared the 1927 Nobel Prize in Physics with C. T. R. Wilson for his discovery of the Compton effect, which demonstrated the particle nature of electromagnetic radiation. It was a significant discovery at the time; the wave nature of light had been well-demonstrated, but the idea that light had both wave and particle properties was not easily accepted.
In 1919, Compton was awarded one of the first two National Research Council Fellowships that allowed students to study abroad. He chose to go to the University of Cambridge's Cavendish Laboratory in England, where he studied the scattering and absorption of gamma rays. Further research along these lines led to the discovery of the Compton effect.
Compton used X-rays to investigate ferromagnetism, concluding that it was a result of the alignment of electron spins, and studied cosmic rays, discovering that they were made principally of positively charged particles.
During World War II, Compton was a key figure in the Manhattan Project that developed the first nuclear weapons. His reports were important in launching the project. In 1942, he became a member of the S-1 Executive Committee, and then head of the "X" projects overseeing the Metallurgical Laboratory, with responsibility for producing nuclear reactors to convert uranium into plutonium, finding ways to separate the plutonium from the uranium and to design an atomic bomb. Compton oversaw Enrico Fermi's creation of Chicago Pile-1, the first nuclear reactor, which went critical on December 2, 1942. The Metallurgical Laboratory was also responsible for the design and operation of the X-10 Graphite Reactor at Oak Ridge, Tennessee. Plutonium began being produced in the Hanford Site reactors in 1945.
After the War, Compton became Chancellor of Washington University in St. Louis. During his tenure, the university formally desegregated its undergraduate divisions, named its first female full professor, and enrolled a record number of students after wartime veterans returned to the United States.
Education
Arthur Holly Compton was born on September 10, 1892, in Wooster, Ohio, the son of Elias Compton and Otelia Catherine Augspurger, who was named American Mother of the Year in 1939 and was of German Mennonite descent. They were an academic family. Elias was Dean of the University of Wooster (now the College of Wooster), which Arthur also attended. Arthur's eldest brother, Karl, who also attended Wooster, earned a Ph.D. in physics from Princeton University in 1912, and was President of the Massachusetts Institute of Technology from 1930 to 1948. His second brother, Wilson, likewise attended Wooster, earned his Ph.D. in economics from Princeton in 1916 and was President of the State College of Washington (now Washington State University) from 1944 to 1951. All three brothers were members of the Alpha Tau Omega fraternity.
Compton was initially interested in astronomy, and took a photograph of Halley's Comet in 1910. Around 1913, he described an experiment where an examination of the motion of water in a circular tube demonstrated the rotation of the earth, a device now known as the Compton generator. That year, he graduated from Wooster with a B.S. and entered Princeton, where he received his M.A. in 1914. Compton then studied for his Ph.D. in physics under the supervision of Hereward Lester Cooke, writing his thesis titled The Intensity of X-Ray Reflection, and the Distribution of the Electrons in Atoms.
When Arthur Compton earned his Ph.D. in 1916, he, Karl, and Wilson became the first group of three brothers to earn PhDs from Princeton. Later, they would become the first such trio to simultaneously head American colleges. Their sister, Mary, married a missionary, C. Herbert Rice, who became the Principal of Forman Christian College in Lahore. In June 1916, Compton married Betty Charity McCloskey, a Wooster classmate and fellow graduate. They had two sons, Arthur Alan Compton and John Joseph Compton.
In 1916, Compton became a physics instructor at the University of Minnesota. In 1917, he became a research engineer at the Westinghouse Lamp Company in Pittsburgh, where he worked on the development of the sodium-vapor lamp. During World War I, he developed aircraft instrumentation for the Signal Corps.
In 1919, Compton was awarded one of the first two National Research Council Fellowships that allowed students to study abroad. He chose to go to the University of Cambridge's Cavendish Laboratory in England. Working with George Paget Thomson, the son of J. J. Thomson, Compton studied the scattering and absorption of gamma rays. He observed that the scattered rays were more easily absorbed than the original source. Compton was greatly impressed by the Cavendish scientists—especially Ernest Rutherford, Charles Galton Darwin, and Arthur Eddington—and he ultimately named his second son after J. J. Thomson.
From 1926 to 1927, Compton taught at the Department of Chemistry of the University of the Punjab where he was a Guggenheim Fellow.
For a time, Compton was a deacon at a Baptist church. "Science can have no quarrel", he said, "with a religion which postulates a God to whom men are as His children."
Career and research Compton effect
Returning to the United States, Compton was appointed Wayman Crow Professor of Physics, and head of the Department of Physics at Washington University in St. Louis in 1920. In 1922, he found that X-ray quanta scattered by free electrons had longer wavelengths and, in accordance with Planck's relation, less energy than the incoming X-rays, the surplus energy having been transferred to the electrons. This discovery, known as the "Compton effect" or "Compton scattering", demonstrated the particle concept of electromagnetic radiation.
In 1923, Compton published a paper in the Physical Review that explained the X-ray shift by attributing particle-like momentum to photons, something Einstein had invoked for his 1905 Nobel Prize-winning explanation of the photoelectric effect. First postulated by Max Planck in 1900, these were conceptualized as elements of light "quantized" by containing a specific amount of energy depending only on the frequency of the light. In his paper, Compton derived the mathematical relationship between the shift in wavelength and the scattering angle of the X-rays by assuming that each scattered X-ray photon interacted with only one electron. His paper concludes by reporting on experiments that verified his derived relation:
where is the initial wavelength, is the wavelength after scattering, is the Planck constant, is the electron rest mass, is the speed of light, and is the scattering angle.
The quantity is known as the Compton wavelength of the electron; it is equal to . The wavelength shift lies between zero (for ) and twice the Compton wavelength of the electron (for ). He found that some X-rays experienced no wavelength shift despite being scattered through large angles; in each of these cases the photon failed to eject an electron. Thus the magnitude of the shift is related not to the Compton wavelength of the electron, but to the Compton wavelength of the entire atom, which can be upwards of 10,000 times smaller.
"When I presented my results at a meeting of the American Physical Society in 1923", Compton later recalled, "it initiated the most hotly contested scientific controversy that I have ever known." The wave nature of light had been well demonstrated, and the idea that it could have a dual nature was not easily accepted. It was particularly telling that diffraction in a crystal lattice could only be explained with reference to its wave nature. It earned Compton the Nobel Prize in Physics in 1927. Compton and Alfred W. Simon developed the method for observing at the same instant individual scattered X-ray photons and the recoil electrons. In Germany, Walther Bothe and Hans Geiger independently developed a similar method.
X-rays
In 1923, Compton moved to the University of Chicago as Professor of Physics, a position he would occupy for the next 22 years. In 1925, he demonstrated that the scattering of 130,000-volt X-rays from the first sixteen elements in the periodic table (hydrogen through sulfur) were polarized, a result predicted by J. J. Thomson. William Duane from Harvard University spearheaded an effort to prove that Compton's interpretation of the Compton effect was wrong. Duane carried out a series of experiments to disprove Compton, but instead found evidence that Compton was correct. In 1924, Duane conceded that this was the case.
Compton investigated the effect of X-rays on the sodium and chlorine nuclei in salt. He used X-rays to investigate ferromagnetism, concluding that it was a result of the alignment of electron spins. In 1926, he became a consultant for the Lamp Department at General Electric. In 1934, he returned to England as Eastman visiting professor at Oxford University. While there, General Electric asked him to report on activities at General Electric Company plc's research laboratory at Wembley. Compton was intrigued by the possibilities of the research there into fluorescent lamps. His report prompted a research program in America that developed it.
Compton's first book, X-Rays and Electrons, was published in 1926. In it he showed how to calculate the densities of diffracting materials from their X-ray diffraction patterns. He revised his book with the help of Samuel K. Allison to produce X-Rays in Theory and Experiment (1935). This work remained a standard reference for the next three decades.
Cosmic rays By the early 1930s, Compton had become interested in cosmic rays. At the time, their existence was known but their origin and nature remained speculative. Their presence could be detected using a spherical "bomb" containing compressed air or argon gas and measuring its electrical conductivity. Trips to Europe, India, Mexico, Peru and Australia gave Compton the opportunity to measure cosmic rays at different altitudes and latitudes. Along with other groups who made observations around the globe, they found that cosmic rays were 15% more intense at the poles than at the equator. In September 1932, Compton attributed this to the effect of cosmic rays being made principally of charged particles, rather than photons as Robert Millikan had suggested, with the latitude effect being due to Earth's magnetic field. This resulted in a public altercation between Millikan and Compton in December. Ultimately, Compton was proven correct.
Manhattan Project
In April 1941, Vannevar Bush, head of the wartime National Defense Research Committee (NDRC), created a special committee headed by Compton to report on the NDRC uranium program. Compton's report, which was submitted in May 1941, foresaw the prospects of developing radiological weapons, nuclear propulsion for ships, and nuclear weapons using uranium-235 or the recently discovered plutonium. In October he wrote another report on the practicality of an atomic bomb. For this report, he worked with Enrico Fermi on calculations of the critical mass of uranium-235, conservatively estimating it to be between and . He also discussed the prospects for uranium enrichment with Harold Urey, spoke with Eugene Wigner about how plutonium might be produced in a nuclear reactor, and with Robert Serber about how the plutonium produced in a reactor might be separated from uranium. His report, submitted in November, stated that a bomb was feasible, although he was more conservative about its destructive power than Mark Oliphant and his British colleagues.