Diffraction can occur whenever Bragg's law is satisfied. With monochromatic radiation, an arbitrary setting of a single crystal in an x-ray beam will not generally produce any diffracted beams. There would therefore be very little information in a single crystal diffraction pattern from using monochromatic radiation.

This problem can be overcome by continuously varying l or q  over a range of values, to satisfy Bragg's law. Practically this is done by: • using a range of x-ray wavelengths (i.e. white radiation), or • by rotating the crystal or, using a powder or polycrystalline specimen. By selecting combinations of x-ray ranges and specimen types, discover the different techniques used in x-ray diffraction.

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Why is it not useful to use white radiation with a polycrystalline specimen?