Potential of full pattern fit methods for the texture analysis of geological materials: implications from texture measurements at the recently upgraded neutron time-of-flight diffractometer SKAT

Abstract

The application of Rietveld texture analysis (RTA) to time-of-flight (TOF) neutron diffraction data allows complex materials with many diffraction peaks to be investigated, for example, rocks composed of different minerals. At the recently upgraded SKAT texture diffractometer at the JINR in Dubna (Russia), which provides three alternative multidetector systems, resolution and accessible range of latticedspacings can be adapted to sample requirements. In order to infer the optimum experimental setup and the reliability of texture estimates from complicated TOF patterns, the influence of counting statistics and various spectral resolutions on texture deconvolution was investigated. Comparing the results obtained at different resolutions and from different sections of thedpatterns indicates that the textures of a four-phase sample can be determined, but using a section at smalldspacings with a larger number of peak overlaps leads to smoother textures. A complex seven-phase sample shows orientation differences in addition to the smoothing effect. Weak textures and textures of the minor rock constituents are inaccurate owing to multiple peak overlaps. Consequently, good resolution is essential for RTA on such samples. Grid thinning tests confirmed that no more than 150 diffraction spectra are needed to characterize the texture of a monomineralic sample, and approximately 350 spectra are sufficient for a four-phase sample. The irregular grid point arrangement caused by the SKAT geometry has no negative consequences.