A Computer-Controlled X-Ray Diffractometer for Texture Studies of Polycrystalline Materials

Abstract

AbstractThe Picker Four-Angle Computer System (FACS-1), a computercontrolled x-ray diffractometer originally designed for single crystal studies, has been adapted for use with polycrystalline samples. The system is controlled by a PDP-8S, a small time-sharing computer with teletype input and output. Programs have been written to take advantage of the high degree of flexibility inherent in online computer control. Four basic operations are possible: (a) simple 2θ step-scanning with variable step width; (b) 2θ stepscanning with randomization of orientation; (c) determination of Legendre expansion coefficients for oriented specimens; and (d) determination of pole figures. In operation (a), data is gathered at a series of 2θ values at a prefixed count and/or time. In (b), the sample is rotated to average out orientation, giving the “randomized” intensity (2θ) at various 2θ values. The on-line computer reads the scaler and timer every two degrees of x rotation and forms the appropriate integrals for calculating (2θ) as the sample rotates. Operation (c) is an extension of (b): not only is (2θ) determined, but also various moments of the orientation distribution of the form , where Pn is the nth order Legendre polynomial. Operation (d) may be used to measure pole figures of sheet specimens in reflection or transmission, or of fibers or small particles. Optional modes of operation allow for (a) use of the Ross “balanced filter” technique; (b) integration across diffraction peaks by continuous scanning in 2θ, with background correction; and (c) application of absorption corrections.