A Graphical Method for Selecting Suitable Radiations for the Precision Determination of Noncubic Lattice Constants and for Indexing Back-Reflection Lines in Powder X-Ray Photograms

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Abstract
A simple method by which the proper radiation or combination of radiations may be selected for the precision determination of hexagonal, rhombohedral, and tetragonal lattice constants is described and illustrated in detail. The method involves the use of specially prepared charts. With a knowledge of the approximate lattice constants, positions of diffraction lines with θ>60°; i.e., back-reflection lines, can be predicted directly from the charts for any common radiation. From the number, distribution, and indices of back-reflection lines, a suitable target may be chosen for an accurate determination of lattice constants. Furthermore, the charts are useful for predicting positions of beta-lines, and for indexing without calculation back-reflection lines in powder x-ray photograms of hexagonal, rhombohedral, or tetragonal lattices.