 Elastic Bragg scattering condition

For elastic scattering with $k-k^{\prime }=q\in {\Lambda }^{\ast }$ and $|k|=|k^{\prime }|=k$,The smallest nonzero diffraction angle is determined by the shortest reciprocal-lattice vector.

This reciprocal-lattice condition is equivalent to Bragg's law, expressed in terms of the lattice-plane spacing and the wavelength.