The Distribution of Energy between the Modified and the Unmodified Rays in the Compton Effect

Intensity ratio of modified to unmodified scattered x-rays as a function of scattering angle.—Using small tubes of the Compton type and Soller collimators, reliable measurements of the intensity of scattered x-rays were obtained from five radiators—paraffin, wood, carbon (graphite), aluminium and sulfur. An ionization spectrometer (ethyl bromide) with a large calcite crystal was employed. Since the wave-length range investigated was small, the relative energy of each spectrum was obtained, to a close approximation, by integrating with a planimeter the area under the ionization curve which represented the line. The results of this measurement are as follows: where $\varphi$ represents the scattering angle and $R$ the intensity ratio of the modified to the unmodified line. The values of $R$ increase with angle of scattering for a given element in the general manner predicted by Jauncey's theory, but the numerical values given by the theory are 20 to 50 percent too large. For a given angle, the values of $R$ increases as the atomic number decreases, being greatest for paraffin which contains relatively more hydrogen than does wood. Experiments were also performed with a lithium radiator kept in a lead cell filled with hydrogen, on which two mica windows (about 0.005 mm in thickness) were provided so that one of them allowed the primary ray to fall on the scatterer and the other permitted the secondary ray to pass into the collimator. With a scattering angle of 110°, the unmodified line was practically absent, certainly less than 4 percent of the modified. This seems to prove that the Compton effect cannot be attributed to anything other than true scattering. This also favors the hypothesis, suggested by A. H. Compton, that the unmodified line occurs when the energy imparted to the electron during the process of scattering is insufficient to eject it from the atom.