A New X-Ray Synthesis

Abstract

S. H. Yü has recently developed a synthesis of X-ray intensity data which, it is claimed, has certain advantages over the Patterson synthesis. An account of the method has been published in NATURE (June 6, 1942, p.638). S. H. Yu and C. P. Ho have illustrated the synthesis by a detailed treatment of iron pyrites (Science Records, Academica Sinica, 1 ; 1942). In a further study, submitted to NATURE, they have investigated the effect of the approximations necessary in practice, and the conditions for obtaining satisfactory results from the new method. It is necessary to use a mean value for the variation of atomic structure factor with angle; that given by the Thomas-Fermi atom proves to be a sufficient approximation. For a good determination of the atomic parameters the edge of the unit cell must be divided into at least 100 parts. For the synthesis described in NATURE it is necessary to know at least 13 orders of h00 to get a good result, but it is shown that it is possible to modify the method so that it is applicable to a smaller number. Yü and Ho are to be congratulated on maintaining scientific research in China in difficult circumstances, and the application of the method to unknown structures will be awaited with interest.