The Scattering of Unpolarized X-rays

Abstract

Unpolarized x-rays from an x-ray tube excited at 90 to 125 kv and filtered through aluminum and copper were scattered by paraffin at angles of 75°, 97°30′ and 120°. The intensity of the scattered rays was measured by the ionization produced in a chamber containing air saturated with (1) methyl iodide (2) ethyl bromide. It was found very necessary to keep the temperature of the ionization chamber and the voltage on the x-ray tube constant during an experiment. The results are expressed by the ratios of the ionization currents produced at scattering angles of 97°30′ and 120° respectively to the current produced at an angle of 75°. The wave-lengths present in the primary x-rays were determined by measuring the absorption of x-rays in a series of thicknesses of aluminum, the x-rays entering the same ionization chamber as that which was used in the scattering experiment. The absorption curve so obtained was found to consist of two exponential curves which correspond to two wave-lengths, the intensity of the shorter wave-length being much greater than that of the longer. With these wave-lengths and their relative intensities and taking account of the change of absorption in the ionization chamber due to the Compton change of wave-length the theoretical values for the above ratios were calculated by use of (1) the Dirac scattering formula and (2) the Compton formula. The agreement between the ratios calculated from the Dirac formula and the experimental ratios was excellent. The wave-lengths when methyl iodide was in the chamber were 0.205A and 0.39A and when ethyl bromide was in the chamber were 0.26A and 0.47A. At these wave-lengths the difference between the Dirac and the Klein and Nishina formulas is so small that experimental discrimination between them was not possible.