GB613107A - Improvements in and relating to means for orienting irregular quartz crystals - Google Patents

Abstract

613,107. X-ray crystalography. BRITISH THOMSON-HOUSTON CO., Ltd. June 5 1944, No. 10749. Convention date, June 5, 1943. [Classes 97 (iii), 98 (i) and 98 (ii)] To orient an irregular quartz or other crystal for cutting, the crystal is mounted in a goniometer with its approximate optic axis perpendicular to a light-sensitive film and a collimated beam of X-rays is projected through the film and on to the crystal so that from examination of the back reflected X-ray pattern recorded on the film the true direction of the axis is found. As shown in Fig. 1, the crystal 12 is cemented to a plate 38 with its optic axis, as approximately determined for example by polarized light, parallel to a rod 13 supported in a frame 40 by means of a split chuck operated by a nut 48 to permit sliding adjustment of the rod. The frame 40 carries blocks 41, 42 for sliding movement along semicircular slides 29, 30, the latter carrying a graduated scale 36. One side of the rod 13 is milled flat and slidably keyed thereto is a circular scale 16 supported by arms 52. Knobs 44, 55 are provided for clamping the members. The slides 29, 30 are supported by pillars 31 on a ring 32 rotatable about a graduated scale 34 supported by a plate 17 movable along bearings 27 in a frame 18 which may slide along a reference bar 11 fixed to the operating table. The crystal may thus be rotated about three axes and is vertically adjusted by the sliding rod 13. The X-ray camera 19 comprises shells 71, 72, Figs. 4, 5, of copper or moulded resin which are clamped together by latches 73 in each shell engaging corresponding studs 75 in the other shell. The shell 71 carries holes 77 in its lower rim arranged to coincide with holes 86 in the shell 72, and holes 78 to engage three studs 68 to permit accurate registration of the members. The circular film 70 has notches 81 to engage the registering pins 68 and an aperture 80 for the passage of the trays. The latch yokes 74 have internal bores 82 connected to tubes 83 to allow developing and treating liquids to be forced into the camera after exposure without opening the camera. When the film has been inserted and the shells latched together, the camera is placed upon a non-metallic plate 20 which has holes 67 to receive the registering pins 68 and an aperture 62 through which X-rays may pass from a tube 61, the X-ray beam being collimated by a brass tube 88 fixed to a lead protection sheet in the shell 72 and carrying centrally placed apertures at each end. The top of the tube 88 is closed by aluminium foil as is the aperture 21 in the shell 71. In operation, the frame 40, the rod 13 and the ring 32 are all located at the zeros of their respective scales and the lower point of the crystal is placed in contact with the aperture 21. An exposure is made and the film processed. For determining the necessary angles to set on the three scales to orient the optic axis of the crystal accurately vertically the goniometer 100, Fig. 6, is employed. This comprises a box having a central circular aperture beneath which is a lamp. Rotatable on the box is a circular slide 103 which in turn carries a slide 105 moving in bearings 117. An anti-clockwise degree scale 102 is carried by the box and the slide 103 carries a scale 104. Rotatable on the linearly moving slide 105 is a ring 107 carrying a radial straight edge 108 and a line 122 marking the centre of the ring 107. The X-ray film after focusing is located over the aperture by pins 114 corresponding to the registering pins 68. By adjustment of the slides 103, 105 and the ring 108 various angular and linear measurements are carried out on the X-ray diffraction pattern which permit calculation of the angles to be set on the scales 16, 30, 34 of the crystal support to orient the optic axis, or the mechanical or electric axes of the crystal in given direction. Such measurements are described in detail in the Specification. When the crystal has been oriented with its optic axes vertical, it may be cemented to a suitably located plate to permit sections of the crystal to be cut along the optic axis.