Precision γ-Ray Wavelength Measurement by Crystal Diffraction

Abstract

The double flat crystal spectrometer was used as early as 1917 by A. H. Compton 1a to study the reflectivity of X-rays by crystals. In the following ten years the spectrometer was used by many workers for comparing X-ray wavelengths1. In particular the careful analysis of the two crystal geometry by Davis and Purks (1927)2 and independently by Ehrenberg and Mark (1927)3 showed that the spectrometer could be used for precision measurement. By 1930 Marst and Von Susich, and Allison and Williams 1b, used a two crystal spectrometer with an angular precision of a fraction of a second of arc to study the relative shapes of X-ray lines. With such precision, X-ray wavelengths could be compared with a standard error of a few parts in 105. In recent years, the double crystal spectrometer, supplemented by modern technical development, has been found useful for the precise comparison of nuclear radiations, which have wavelengths 10 to 200 times shorter than the standard (Mo Kα) X-ray4.