Homogeneity of graphite-monochromated X-ray beams

The factors influencing the homogeneity of the incident X-ray beam when a graphite monochromator is applied are discussed, in particular the influence of the size and shape of the focal spot of the X-ray tube and the diffraction angle of the monochromator. Beam profiles have been measured for several commonly used X-ray tubes - with a fine or normal focus - and compared. It is shown that in certain cases the normal-focus X-ray tubes give a much broader high- intensity region of the incident beam than the fine- focus X-ray tubes.