Patent GB-948673-A (GB)
Title: X-ray diffraction apparatus
IPC: G01N23/201
Filed: 1961-09-29
Abstract: 948,673. X-ray diffraction apparatus. APPLIED RESEARCH LABORATORIES Inc. Sept. 29, 1961 [Dec. 8, 1960], No. 35336/61. Heading H5R. [Also in Division F2] An X-ray diffraction apparatus incorporates a mechanical linkage having an apex point equispaced from its opposite ends and means for locating the ends of the linkage for travel along a pair of straight ways inclined to each other at an angle which is half the angle subtended at the apex by the ends of the ways; the diffraction element is secured at one end of the linkage, and the detector slit at the end of a radius arm connected to the apex; as the focal circle in effect rolls about the point corresponding to the specimen under examination, the diffracting element and the slit remain on the circle, and the apex itself moves in a circular path about the specimen. Fig. 2 shows diagrammatically how the linkage arrangement is set out in relation to an X-ray monochromator. The X-rays from the specimen 32 are diffracted by the curved crystal 10 and pass through an exit slit 20 to a detector 22. The isosceles triangle linkage 30 has its apex 44 at the centre of the focal circle 18 and the ends of its base 28 also lying on the circle. At one end of the base is mounted the crystal 10. The ends of the base are constrained to move along straight ways 36, 38 respectively, which, extended, meet at the specimen 32 and form an angle # thereat. The apex angle 44 of the triangle is thus 2#. As the base ends of the triangle move along the ways, the apex 44 describes a circular path about centre 32. The detector 22 is slidably mounted on an arm 50 pivoted at the farther base end of the triangle, and a constant length cable arrangement maintains the distance from crystal 10 to exit slit 20 the same as the distance from crystal 10 to specimen 32. A rigid arm 52 links slit 20 to the apex point 44, so that as the triangle moves, the slit 20 follows the lemniscate path 26. Fig. 4 shows a practical embodiment. The isosceles triangle 30 of Fig. 2 here takes the form of a T-bar 64, the cross-piece 66 forming the base of the triangle, and the tip 68 the apex (44 on Fig. 2). The assembly is mounted on a base-plate 60. A slot 62 in the plate forms one guiding way (36, 40 in Fig. 2) and a track 72 fixed to the plate forms the other guiding way (38, 42 in Fig. 2). The two guide ways are in this case inclined at 45 degrees, so that the T-bar defines a right-angled isosceles triangle. One end of the T-bar carries a roller 70 which runs in track 72, held there by a spring 74. The other end carries a pivot 76 projecting through slot 62. This is rotatable in a slide 78, which can be guided smoothly along slot 62 by means of a drive screw 81, power-driven via a gear train 82. The crystal 10 is fixed at the end of pivot 76. The slit 20 and detector 22 are mounted on a slide bar 90 (equivalent of 50 in Fig. 2) which turns on pivot 76 at the crystal position, and is urged away from the crystal 10 by a tension spring 92. Its travel is controlled by the constant length cable 54, both ends of which are anchored on a pin 100, and which has two flights trained round pulleys pivoted at 76 and a bight portion passing round an idler pulley fixed to the assembly 20, 22 (Fig. 8, not shown). This maintains the distances exit slit to crystal to specimen constant, as described above. The equivalent of the link arm 52 in Fig. 2 is provided by bar 98.