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 oscillation method are derived by the combination of analytical geometry with the reciprocal-space and Ewald-sphere formalisms. The effect of crystal mosaicity is described by the extension of a reciprocal-lattice point into a cap. The effective cylindrical coordinates of the reciprocal-lattice point, corresponding to the cap points lying in the plane in which the cap has its maximum cp extent, are introduced. The effect of beam divergence and wavelength spread are accounted for by consideration 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 check whether a reflection is fully or partially registered during the crystal oscillations. The presented formulas have been incorporated into software for processing area-detector data.