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Figure 1
The Ewald sphere construction for a beam with a bandwidth. (a) O is the origin of the reciprocal space. C1 and C2 are two Ewald sphere centers corresponding to the longest (λmax) and the shortest (λmin) wavelengths in the spectrum, respectively. When a reciprocal lattice point (shown as small dots) is located within a shell bounded by the two Ewald spheres (shaded gray), the Bragg condition is satisfied and diffraction occurs. P is one of the diffracting reciprocal lattice points. The region near P is magnified in (b), (c) and (d). (b) With a narrow bandwidth beam, the two Ewald spheres are very close and the shell is thin. In the rotation method, the reciprocal lattice point sweeps through the surface of the Ewald sphere as the reciprocal space rotates with the crystal. One can measure the full intensity. (c) In a still shot, only a fraction of the reciprocal lattice point (shaded black) can be excited; thus, the partiality is low. (d) With a wide-bandwidth beam, the shell is thicker. Thus, the partiality is higher even with a stationary crystal.

IUCrJ
Volume 8| Part 6| November 2021| Pages 853-854
ISSN: 2052-2525
https://doi.org/10.1107/S2052252521010794