Arthur H. Crompton (1892-1962): Experimentalist who proved wave-particle dualism

ARTHUR H. CROMPTON graduated from College of Wooster in 1913, he entered Princeton University for a master's degree. Two years later, Compton earned the doctorate for a dissertation on the interaction of X-rays with matter.

He was an outstanding graduate student, a ``whiz'' at problem solving. He perfected a laboratory method at his home to measure latitude and the earth's rotation independently of astronomical observations.

He started his career as an instructor in physics at the University of Minnesota (1916-17), where he did research on X- rays. He next spent two years as a research engineer in the newly established laboratory of Westinghouse Electric Company. He did original work on the sodium-vapour lamp and developed instrumentation for aircraft.

Change-over to pure research

Compton left Westinghouse because he came to recognize that fundamentally his interest was not in industrial but pure research.

Anxious to pursue his X-ray studies further, Compton applied for a fellowship to work with Ernest Rutherford (1871-1937) at the Cavendish Laboratory in England. Since the laboratory did not have high-voltage X-ray equipment, Compton studied the scattering and absorption of gamma rays; the latter are energetic X-rays emitted by radioactive nuclei.

Compton returned to the U.S. in 1920 and became chairman of the physics department at Washington University, St. Louis, where he performed his most famous experiments. This was suggested by his earlier work with gamma rays at Cambridge.

Using Bragg's crystal spectrometer, Compton made precise measurements of the wavelength of X-rays that had been scattered from a target. This was of two types, one with the same wavelength as that of the primary rays and the other with a longer wavelength. The increase in wavelength was proportional to the angle of scattering.

Applying quantum theory to results

Compton's results defied explanation in terms of classical physics, but now he took the bold step of applying quantum theory to explain the increase in wavelength. He viewed X-rays as particle (or quantum) and described the phenomenon as an elastic collision taking place between two particles, an electron and the light quantum. As the particle gives up some of its energy to the electron, it has a lower energy after the collision, corresponding to a longer wavelength of radiation. He also found a formula connecting wavelength change with angle of scattering.

Since light, like X-rays, is a form of electromagnetic radiation the Compton effect provided strong support for Einstein's theory (1905) that light behaves like a particle as well as a wave. It paved the way for de Broglie's hypothesis that matter can show a wave-particle dualism (1925).

The particle aspect is demonstrated by the interaction of X-rays with the electrons. The functioning of the spectrometer can be explained only by considering x-rays to be waves.

Compton's quantum interpretation created a stir among physics because it conflicted with the ideas of J.J. Thomson (1856-1940), the discoverer of electron.

Compton published his results in 1923, which marked a turning point in his career. He accepted a position as professor of physics at the University of Chicago, where he spent the next twentytwo years. For the great series of experiments on the Compton effect and their theoretical interpretation, he shared (1927) the Nobel Prize in Physics with C.T.R. Wilson (The Hindu, April 6, 2000).

Work on cosmic rays

The other most important activity of Compton after going to Chicago was his work on cosmic rays. Realising their importance for cosmological theories, Compton developed a greatly improved detector and convinced the Carnegie Institution to fund a world survey during 1931-1934.

The globe was divided into nine regions and roughly 100 physicists, carrying identical detectors, traversed continents to measure cosmic-ray intensities.

The most significant conclusion was that the intensity of cosmic rays at the surface of the earth steadily decreases as one goes from either pole to the Equator (called latitude effect).

Compton's survey proved that the earth's magnetic field deflects most of the incident cosmic rays, which is only possible if they are charged particles. His reports on these measurements often appeared as letters in the ``Physical Review''.

Development of the atomic bomb

World War II brought about a complete change in physics research on 6 November 1941, Compton presented a report on the military potentialities of atomic energy.

This report had been prepared in collaboration with Ernest O. Lawrence (The Hindu, July 12, 2001) who had informed Compton of the discovery of plutonium at the Radiation Laboratory, University of California in Berkley.

Compton gave up all his other activities to organise and direct the Metallurgical Laboratory at the University of Chicago, which was responsible for the production of plutonium. He was in charge when the first successful nuclear chain with uranium was accomplished by Enrico Fermi and others on 2 December 1942.

As the war reached its end, Compton accepted the position of Chancellor of Washington University (1945-53) which change surprised many of his colleagues. His ties with Washington University were very strong. He continued with great distinction through his teaching, writing and public service. His most notable contribution is the book ``Atomic Quest'' which gives a complete and generous account of the activities of all his colleagues in the Manhattan Project.

Compton was elected to the National Academy of Sciences at the young age of 35. Compton was an inspiring teacher. his contagious enthusiasm, friendliness and great mental powers made his classes memorable experiences to the students who attended them.

He shared most generously all his knowledge with his students and younger colleagues. He was professor-at- large, dividing his time between Washington University_ and Wooster College till his sudden end at the age of 70 (March 15, 1962).

R. PARTHASARATHY

Send this article to Friends by E-Mail

Section  : Science & Tech
Previous : Question Corner
Next     : Saving the light combat aircraft