Powder processing
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Fraunhofer scattering
Particles interrupt the incident beam, leaving secondary wavelets from surrounding regions to reinforce in certain directions, in a similar way to that observed with a diffraction grating. As in that case, the directions in which this occurs are inclined at greater angles to the incident direction when spacings (particle sizes) are smaller. The scattering angle, θ, is given by
\[\sin \theta = \frac{{1.22\lambda }}{d}\]
where λ is the wavelength and d is the particle size. The scattering angle θ is thus larger for smaller particles.