An atom is aboutin size. X – rays have wavelength of about this order, X rays will therefore be scattered by the electron clouds around atoms in certain directions. By subjecting the sample to an intense beam of monochromatic x – rays (meaning x – rays of a fixed wavelength), rotating the sample, and analysing the angles of the scattered X rays, the internal structure of the material can be reconstructed.

One such obtained image is shown

Quite large molecules can be analysed in this way eg haemoglobin. The structure of DNA was found with the aid of X – ray crystallography. Hundreds of thousands of structures have now been found.

The reconstruction is a complex procedure and must necessarily be done with the aid of computers.