Absolute Wave-Lengths of the Copper and ChromiumK-Series

Abstract

In the measurement of x-ray wave-lengths by ruled gratings two principal difficulties have been discussed which may account for the difference observed between the wave-lengths determined by this method and those determined by using crystal gratings. They are, the periodic error in the grating, and the geometrical divergence of the x-ray beam. It is now shown that the effect of the periodic error can be determined by a study of the intensities of the optical ghost lines. For a good quality optical grating it has been found that the error in x-ray wave-lengths due to the periodic error in the grating is thus of no importance. By using a suitable disposition of apparatus the effect of the geometrical divergence of the x-ray beam can be made as small as desired. Thus it is concluded that ruled gratings can be used for precise wave-length measurements of x-ray spectra.