The φ Extent of the Reflection Range in the Oscillation Method According to the Mosaicity-Cap Model

New expressions for the φ 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 φ 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.