The determination of unit-cell parameters from a Laue diffraction pattern

Single-crystal Laue diffraction patterns have not hitherto been used for the precise determination of unit-cell dimensions, although axial ratios and interaxial angles have frequently been derived. Here, we use an attenuator such as 0.1 mm palladium foil in the white synchrotron-radiation beam incident on the crystal; the absorption edge (e.g. palladium at 0.509 Å) then sharply defines the minimum wavelength present. With gnomonic projections in the manner described by Carr, Cruickshank & Harding [J. Appl. Cryst. (1992), 25, 294-308], the unit-cell dimensions on an absolute scale can be derived. Three tests show that these dimensions are correct to circa 0.5%.