THE PHI-EXTENT OF THE REFLECTION RANGE IN THE OSCILLATION METHOD ACCORDING TO THE MOSAICITY-CAP MODEL

New expressions for the cp extent of the reflection range in the oscil lation method are derived by the combination of analytical geometry wi th the reciprocal-space and Ewald-sphere formalisms. The effect of cry stal mosaicity is described by the extension of a reciprocal-lattice p oint into a cap. The effective cylindrical coordinates of the reciproc al-lattice point, corresponding to the cap points lying in the plane i n which the cap has its maximum cp extent, are introduced. The effect of beam divergence and wavelength spread are accounted for by consider ation of a nest of the Ewald spheres. The expressions for intersection of the mosaicity cap with the nest of the Ewald spheres are used to c heck whether a reflection is fully or partially registered during the crystal oscillations. The presented formulas have been incorporated in to software for processing area-detector data.