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Figure 2
One reciprocal-space plane, illustrating the scattering geometry. Each color denotes one X-ray energy, for which the area detector measures scattering on a Ewald sphere centered on the tail of the diffracted wavevector kf; ki is the incident wavevector. Scattering into the detector's center, corresponding to the head of kf, shifts radially in reciprocal space as energy changes. The circle represents a sphere of diffuse scattering, with a Bragg reflection G at its center. Bragg scattering from misoriented portions of the sample falls on a sphere of mosaic spread, centered on the origin of reciprocal space. The intersection of the mosaic spread with the Ewald sphere corresponds to an arc on the detector which is close to a horizontal line (Fig. 1[link]). For E = EBragg, both diffuse scattering and mosaic spread are centered on the Bragg reflection. For E < EBragg, diffuse scattering is at higher scattering angles than observed for the Bragg reflection at the Bragg energy, with mosaic spread at still higher angles [Fig. 1(c)[link]]. For E > EBragg, diffuse scattering is at lower angles, with mosaic spread at even lower angles [Fig. 1(d)[link]].

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