A goniometer for large single crystals

A highly accurate goniometer head for large single crystals was designed using the principle of two rotational axes (Denne, 1971). This device is better than any other classically designed goniometer of the same size, giving an accuracy of 0.1 ° without the need of a Nonius scale. It is mainly used in our laboratory for orienting large single crystals by means of the photographic method. Detailed drawings are given in Fig. 1 and the very simple calculations necessary for its adjustment are described below. The goniometer consists of three round parts of 58 mm diameter. Two parts have a wedge-shaped cross section inclined 9 ° , while the third part is flat (see Fig. la). Part C is the rigid component and can be attached to any stationary apparatus by the thread hole T. It should be mounted so that its base stands perpendicular to the incident Xray beam. Parts A and B rotate and are held together and to part C by retention grooves and locking screws. The crystal holder is connected to part A by the screw S. Part A has four fiducial marks 90 ° apart. The wide side of part B is engraved on both edges in 2 ° divisions from zero to 180 °. Part C has two fiducial marks 180 ° apart. The engraving positions are shown in Fig. lb. The angular range of this" device is _+ 18 °. The calculations for the adjustment of the moving parts for a film-to-crystal distance of 30 mm are described with the aid of the stereogram in Fig. 2. Point O is the center of the photographic film to which the required Laue point L should