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DISCOVERY OF THE COMPTON EFFECT. First edition, journal issue in original printed wrappers, of the Compton effect, which demonstrated the existence of quanta of electromagnetic radiation, later called photons. "This discovery created a sensation among the physicists of the time. There were the inevitable controversies surrounding a discovery of such major proportions. Nevertheless, the photon idea was rapidly accepted. Sommerfeld incorporated the Compton effect in his new edition of Atombau und Spektrallinien with the comment, It is probably the most important discovery which could have been made in the current state of physics " (Pais, Subtle is the Lord, p. 414). "Arthur Holly Compton will always be remembered as one of the world s great physicists. His discovery of the Compton effect, so vital in the development of quantum physics, has ensured him a secure place among the great scientists" (DSB). The explanation and measurement of the Compton effect earned Compton a share of the Nobel Prize in physics in 1927. Compton (1892-1962) received his PhD from Princeton in 1916 for research on the intensity distribution of X-rays reflected from crystals. After a period working for the Westinghouse Company he returned to fundamental research in 1919, when he obtained one of the first National Research Council Fellowships (established by Millikan). He used it to spend a year at the Cavendish Laboratory in Cambridge, where he continued his experiments on the scattering of radiation. In 1920 Compton moved to Washington University in St. Louis, where he continued his work on X-ray scattering, using a Bragg spectrometer he had brought from Cambridge. By this time it had become apparent that the scattered radiation had a wavelength longer than that of the primary radiation, and that the shift of wavelength varied with the scattering angle: this became known as the Compton effect. "It was only late in 1922, when considering all data available to him, that Compton saw the necessity for a light quantum with energy and momentum to explain the scattering of X-rays. Compton read a paper entitled A quantum theory of the scattering of X-rays by light elements at a meeting of the American Physical Society in Chicago, which took place on 1 and 2 December 1922. Its abstract begins as follows: The hypothesis is suggested that when an X-ray quantum is scattered it spends all its energy and momentum upon some particular electron. The electron in turn scatters the ray to some definite direction. The change in momentum of the X-ray quantum due to the change in direction of its propagation results in a recoil of the scattering electron. The energy in the scattered quantum is thus less than the energy of the primary quantum by the kinetic energy of recoil of the scattering electron. "The full paper was published a little later [the offered paper]. It contains … the calculation of the shift in wavelength between primary and secondary radiation as a function of scattering angle. Compton had data for only one scattering angle, 90 degrees, for which he had measured the spectrum. It was obtained with a primary radiation which was the K? radiation of molybdenum produced by an X-ray tube with a molybdenum anticathode" (Brandt, The Harvest of a Century, Chapter 31). "The Compton effect, aptly characterized by Karl K. Darrow as one of the most superbly lucid processes in nature, is now part of the fabric of physics; and it is of interest to recall its influence on the development of the quantum theory during the years 1923 1930. "In the first place, it provided conclusive proof that Einstein s concept of a photon as having both energy and directed momentum was essentially correct. Einstein himself brought considerable attention to Compton s discovery by his discussions at the Berlin seminars. Interest was also high at Gottingen, Munich, Zurich, Copenhagen, and other Continental centers where theoretical physics was rapidly developing. "However, the quantita.
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