The structure of polymers can be studied by the various techniques of diffraction, including diffraction by X rays, electrons, and neutrons. Of these, X-ray diffraction has been most widely used because of the high accuracy in the measurement of the lattice spacings. In electron diffraction, the lattice spacings cannot be measured with an accuracy of better than about 1%. However, sample size requirements are less stringent and electron microscope imaging can be performed at the same time. Also, electron scattering is stronger than X-ray scattering, and because the specimens are often very thin, the kinematical approximation can be made and therefore intensity calculations are more reliable. Neutron diffraction is usually expensive and is therefore used only for special studies to provide unique data (see also Neutron Scattering).