Extinction in time-of-flight neutron powder diffractometry

Time-of-flight data have been collected from polycrystalline specimens of magnesium oxide in which the grain size distribution is known. These data were obtained at scattering angles of 150, 90 and 60°. A primary extinction factor given in an analytical form by Sabine [Acta Cryst. (1988), A44, 368-373] is included in a Rietveld program. The experimental data from the two high-angle histograms are refined to give an effective mosaic block size and overall temperature factors. The effective mosaic block size is used in the calculation of an extinction factor for each reflection. This factor is then compared with the ratio of measured integrated intensities. The theoretical form of the extinction factor is verified to a level of 0.30. The temperature factors measured from each specimen are identical and in agreement with the best literature value.