Strain and texture measurements on geological samples using neutron diffraction at IBR-2, Joint Institute for Nuclear Research, Dubna (Russia)

Abstract

Information on texture and residual stress in geological samples is very important for the calculation of physical properties connected with the evaluation of the geomechanical behavior of parts of the earths’s crust in connection with processes from human activities (mining, tunnelling) and natural processes of deformation (seismicity, earthquakes). Texture and stress are not independent of each other and in the general case should be analyzed together. Complications arise because geological samples are generally composed of several phases (minerals) whose elastic constants may be significantly different. Nevertheless, modern neutron diffractometers such as SKAT and EPSILON-MDS at the fast pulsed reactor IBR-2 at the FLNP of the JINR make it possible to obtain the needed diffraction patterns. This was shown especially for texture measurements on samples with quartz as the main component as well as for mica, feldspar, amphibole, and several other minerals. In order to extend strain measurements beyond samples composed of quartz, dolomite, and/or anhydrite to such frequently occurring minerals as feldspars and mica it would be necessary on the one hand to use Rietveld refinement with corrections due to texture and anisotropic peak broadening. With an increase in the number of mineral phases suitable for these diffractometers, it is in general necessary to improve the experimental conditions for SKAT and EPSILON-MDS, especially to significantly raise the flux of incident neutrons on the sample.