The Divergent Beam Diffractometer is the primary instrument at NIST used to certify powder SRMs for their X-ray diffraction properties. It is a custom-built instrument which provides a very highly-characterized angular scale in a well-controlled environment. It is a Bragg-Brentano instrument, usable with either open beam from a fine-focus copper X-ray tube, or using monochromated beam from a Ge(111) Johansson optic. The properties of this instrument are documented in a paper .
The DBD is equipped with a sample rotation stage that offers a precision in sample placement of better than 5 microns, critical for the operation of this instrument. Its rotation bearing is greater than 10 cm in diameter and the samples are retained magnetically. Recently installed was a robot arm that allows for remote sample changes. Two features of this arm are critical for its successful use in this application: The samples are retained with a vacuum chuck and the arm is both stiff and precise. These two features allow its use with our stage, with its magnetically retained samples, while assuring that powder samples are not disturbed during transfer.