XRD Theory

Single Diffraction

The simplest X-ray diffraction system consists of a power supply, X-ray tube, collimating slits, nickel filter, a crystal holder, a goniometer head for measurement and a suitable X-ray detector. This type of system is only capable of determining the Bragg angle to about ±2 minutes, this being entirely too inaccurate for the orientation of most piezoids.

Double Diffraction

The use of a double diffraction X-ray has become the standard in the crystal industry. In this system an additional crystal called the reference or collimating crystal is used to provide a highly directional, monochromatic X-ray beam. When radiation is directed at the reference crystal, only the wavelengths that satisfy the Bragg relation will be reflected from the crystal and be directed to the unknown crystal. By utilizing this type of system, no nickel filter is required. With the proper goniometer head, accuracy within of a 1/4 minute or better is possible.