TOWARDS GENERAL DIFFRACTOMETRY - I - NORMAL-BEAM EQUATORIAL GEOMETRY

Eulerian and kappa goniometers, as well as real diffractometers with u navoidable misalignments of their shafts, are described as special cas es of a general four-circle normal-beam equatorial diffractometer. The performance of these instruments can be improved by defining rotation s about their real axes. Methods for transformation of the setting ang les between the geometries based on different goniometer axes and proc edures for positioning reflections are described. Analytical solutions for the transformations between Eulerian and the general version of t he normal-beam equatorial diffractometer are presented.