Method of determining the specimen-surface displacement of an X-ray diffractometer

A simple method of determining the specimen-surface displacement of an x-ray diffractometer is described. The position of the specimen surface is compared with the position of a glass slide of known specimen-surface displacement by means of a travelling microscope. The displacement of a specimen is found to 0.006 mm which corresponds to a maximum angular error of 0.004° in 2θ for the Philips diffractometer used, radius 17 cm. The displacement is shown to be critically dependent on the method of locking the specimen holder. This is overcome by performing the various steps of the locking procedure in a certain fixed order. The effect of movement of the specimen holder shaft on the displacement is discussed.