X-Ray Goniometer

a device that permits the simultaneous recording of the direction of X rays diffracted by a specimen under study and of the position of the specimen at the time of diffraction. An X-ray goniometer can be an independent device recording the diffraction pattern on photographic film; in this case it is an X-ray camera. The term “X-ray goniometer” is also applied to goniometric devices that are components of X-ray diffractometers and are used for mounting the specimen and detector in positions corresponding to the conditions necessary for the occurrence of X-ray diffraction.

In photorecording X-ray goniometers for the investigation of single crystals or textures, a diffraction cone corresponding to the crystallographic plane under study is isolated by means of a slotted screen. The photographic film and specimen are moved synchronously; one of the coordinates on the film therefore corresponds to the azimuth angle of the diffracted ray, and the other corresponds to the angle of rotation of the specimen. The Weissenberg X-ray goniometer (Figure 1) operates in this way, as does the Zhdanov texture X-ray goniometer.

Figure 1. Schematic of a Weissenberg X-ray goniometer: (S) specimen under study, (CC) cylindrical cassette with X-ray film; the synchronous movement of the specimen and cassette is provided by gearing and a drive screw

A similar scheme can be used in X-ray goniometers for dif-fractometers. In this case, however, the angle of rotation of the specimen and the angles of rotation and inclination of the detector are read directly from graduated circles or sensing elements mounted on the corresponding shafts. In X-ray diffrac-tometers an equatorial geometry is used for the investigation of single crystals and textures: the counter moves only in one plane, and the specimen must be rotated about three mutually perpendicular axes so that the diffracted beam strikes the plane of motion of the counter. The positions of the specimen (the angles λ, Φ, and ω of its rotation about the axes of rotation) and counter (the angle 20) at the time of diffraction are read from the graduated circles (Figure 2).

Figure 2. Schematic of an equatorial four-circle goniometer for the investigation of single crystals: (1) graduated circle measuring Φ, the angle of rotation of the crystal about the axis of the goniometric head; (2) graduated circle recording x, the angle of inclination of the Φ-axis; (3) graduated circle measuring ω, the angle of rotation of the crystal with respect to the principal axis of the goniometer; (4) graduated circle measuring 20, the angle of rotation of the counter

Powder specimens are investigated by means of a slightly divergent beam of X rays that converges at a single point after diffraction by the object. In this case, the Bragg-Brentano photographic scheme is used, wherein the plane of the specimen divides the scattering angle in half (Figure 3), and of the Zeeman-

Figure 3. Schematic of ray focusing in a Bragg-Brentano X-ray goniometer for the investigation of powder specimens: (F) focus of X-ray tube, (S) flat specimen, (D) slit of counter, (C) counter, (20) angle of reflection

Bolin scheme, wherein the focus of the X-ray tube, the specimen, and the detector slit are located on a single circle (Figure 4).

Figure 4. Schematic of ray focusing in a Zeeman-Bolin X-ray goniometer: (F) focus of X-ray tube, (S) curved specimen, (D) slits of counters, (C) counters

X-ray goniometers also include systems that form the primary beam—such as collimators and monochromators—and moving systems for measuring integrated intensity.