Considerations in the Design of Goniometers for Use in X-Ray Powder Diffractometers

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Abstract
Most modern X-ray powder diffraction work is carried out using the parafocusing powder diffractometer. The typical instrument employs a mechanical goniometer to control the basic geometric movements required for recording diffraction data. Modern trends toward high speed data acquisition and computerized analytical procedures make the need for a well designed and well maintained goniometer system increasingly critical. This paper reviews the mechanical design parameters of typical goniometer systems in light of their influence on the accuracy and precision obtainable in diffraction data. Data on typical vertical and horizontal goniometer systems are compared, along with bench tests using a state of the art “anti-backlash” gearing system. By examining the nature of the errors typically encountered in today's goniometers it becomes evident why the next major improvement will likely be in software rather than hardware.