Ewald's sphere
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Ewald's sphere is a geometric construct used in X-ray crystallography which neatly demonstrates the relationship between
- (a) the wavelength of the incident beams of light,
- (b) the angle of diffraction for a given reflection,
- (c) the unit cell and reciprocal unit cell of the crystal, and
- (d) the distance between the crystal and the film.
It was conceived by Paul Peter Ewald, a German physicist and crystallographer.
Ewald's sphere can be used to find the maximum resolution available for a given wavelength of light and the unit cell dimensions. It is often simplified to the two-dimensional "Ewald's circle" model.
Ewald's sphere is also known as the Ewald sphere.