A Measurement of the Polarization of Secondary X-Rays*

Abstract

It was observed by Barkla that the intensity of X-rays scattered from the second radiator perpendicular to the theoretical plane of polarization was about 1/3 as great as the intensity of the radiation in the plane. Since then evidence has accumulated that secondary X-rays even from light elements are not of the same wave-length as the primary rays. If this difference in wave-length is due to fluorescent radiation, it should result in an incomplete polarization of the scattered rays. The object of this experiment was to test this point by measurement of the degree of polarization of the scattered rays.Heterogeneous X-rays of an average wave-length of about 0.25 A were scattered by paper, aluminium and sulphur. A geometric correction was made for the lack of complete polarization due to the solid angles subtended by the radiators, and the results were extrapolated to zero thickness of the radiators. The experiments indicate that, within a probable error of 1 or 2 per cent, the radiation is completely polarized. This precludes the possibility of there being any considerable amount of fluorescent radiation emitted from the radiator.