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Figure 4
X-ray centring. (a) Once optical centring is completed, a crystal in a loop (red) will rotate about the goniometer centre of rotation (ω). A mesh scan determines the horizontal and vertical translations required to bring the crystal to the centre of rotation at this angle using the goniometer horizontal translation and the centring-table motors (b, c). Rotating the spindle by 90° (d) and performing a vertical scan determines the final movement of the centring-table motors required to place the optimum diffraction volume of the crystal at the centre of rotation of the spindle (e, f). In cases where the centre of rotation of the spindle is not placed at the beam position, it is determined by two vertical scans separated by 180° (g, h). The difference in position between the scans determines the vertical displacement of the goniometer required to place the centre of rotation of the spindle on the beam position (i, j). This example shows values of ω of 0 and 90° for convenience; arbitrary starting values of ω can be used.

Journal logoSTRUCTURAL
ISSN: 2059-7983
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