Lattice-parameter determination for powders using synchrotron radiation

The Daresbury station 8.3 powder diffractometer has been used to determine the lattice parameter of tungsten powder to about 3–6 p.p.m. with respect to the National Institute of Standards and Technology SRM640B silicon de facto standard. The measurement and analysis algorithms that have been developed indicate that there are no X-ray optical systematic errors, that the mean deviation between calculated and measured 2θ ranges from 0.0003 to 0.0005° (corresponding to the absolute precision claimed for the optical angle encoder by the manufacturer) and that the lattice parameter of tungsten powder at 298 K is 3.165269 (19) Å. Two different wavelengths were used, λ ≃1 and λ ≃1¼ Å, but the analysis algorithm is wavelength independent; no measurement of or assumption about the X-ray wavelength is required.