Experimental methods available at the Neutron Physics Laboratory
Neutron Bragg diffraction optics
Experimental investigations in this field are concentrated on experimental studies of the dispersive monochromators providing high and ultra-high angular and/or energy resolution. We have done several tests of ultra-high resolution dispersive monochromators based on multiple reflections excited in elastically deformed perfect crystals. High-resolution monochromatic neutron beams also opened new possibilities of application for an alternative radiography technique, for the so called phase contrast radiography.
Investigation of internal strains in polycrystals
Because of their high penetration ability into most materials thermal neutrons have been found very useful probe in measurements of internal strains in polycrystalline samples. The neutron diffraction technique can provide information on both macro- and micro-strains. The determination of macrostrains (e =Δd/do) is based on the measurement of small angular shifts of diffraction peaks caused by small lattice-parameter variations of Δd in a sampled volume with respect to the stress-free lattice spacingdo. The magnitude of stress can be calculated by using appropriate elastic moduli. Investigation of microstrains is based on the analysis of the shape of broadened diffraction profiles. Two high-resolution neutron strain scanners are available at the medium-power reactor LVR-15 in NPI Řež. The instruments are equipped with curved Si and Ge monochromators and with linear high-resolution position-sensitive detectors for fast recording of diffraction profiles.
Small-angle neutron scattering (SANS)
Small-angle neutron scattering ranks among several techniques (e.g. X-ray small angle scattering, electron microscopy) widely used for investigation of condensed matter structure. The SANS technique is concerned with the measurement of structures within the size range 30-105 Å. This size range corresponds to momentum transfer Q values ranging from 105 to 0.3 Å-1. For measurements in the range of small Q values, we employ the double-crystal (DC) nondispersive setting using elastically bent perfect crystals.