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Diffraction by solids 29

fulfilled, and reflections are seen at all possible values of θ.
Modern diffractometers use scintillation detectors which sweep
an arc of angle 2θ around the sample, giving a measure of X-ray
intensity as a function of the angle 2θ. The diffraction pattern
which is obtained must be correlated with the unit cell of the
sample. By obtaining the angles for which reflections occur, the
2
ratios of the values of sin θ may be directly correlated to the
values of h, k, and l in a process known as indexing.
Related topics Crystalline solids (A5)

Radiation for diffraction by solids

Diffraction takes place when a wave interacts with a lattice whose dimensions are of the
same order of magnitude as that of the wavelength of the wave. The lattice scatters the
radiation, and the scattered radiation from one point interferes with the radiation from
others so as to either enhance the amplitude of the radiation (constructive interference),
or to reduce it (destructive interference) (Fig. 1). The pattern of constructive and
destructive interference yields information about molecular and crystal structure.