Note on the aberrations of a fixed-angle energy-dispersive powder diffractometer

The geometrical and physical aberrations affecting the positions and breadths of diffraction maxima as determined by the energy distribution of photons diffracted through a fixed angle and analysed by a solid-state detector differ in many points of detail from those determined by the angular distribution of photons of fixed energy analysed by a conventional diffractometer. The main differences are investigated and the accuracy of spacing measurements is discussed. There is no simple analogue of the extrapolation method of reducing errors in spacing measurements.