Program interní podpory projektů mezinárodní spolupráce AV ČR (spolupráce ÚJF AV ČR, v.v.i. a KAERI Daejeon)

In the last decades many papers have been published in which successful employment of curved perfect Si crystals as neutron monochromators or analyzers in particular diffraction experiments has been reported. It has been found that due to the spatial condensation of neutrons (because of asymmetric diffraction geometry or focusing in real space), one may obtain a high monochromatic-beam density comparable to that of the mosaic monochromators. Taking into account reflectivity and the resolution properties of curved crystals Popovici et. al. (Missouri University) demonstrated a feasibility of the optimized curved crystal three axis spectrometer having the properties generally better than those of spectrometers employing flat mosaic crystals. New interest in the reflectivity and focusing properties of curved  perfect crystals has been evoked also by successful testing of the bent  perfect crystals employed in double-monochromator systems, or for medium-resolution small-angle scattering diffractometers. Favourable properties of bent Si crystals for short wavelength monochromatization have been reported and very efficient original double and triple axis arrangements employing the bent perfect crystals have been proposed and then tested for residual stress measurements of polycrystalline materials. In the last decade the neutron diffraction group of NPI ASCR, v.v.i. has been concentrated on the development of new unconventional types of neutron monochromators permitting significantly to increase figure of merit of some dedicated neutron scattering instruments. In this way a cooperation with colleagues from HANARO Centre in KAERI has appeared very fruitful.