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.

Participation with the task: Development and optimization of high-resolution neutron scattering instruments dedicated to characterization and testing of materials of relevance to nuclear energy sector and related experiments in SANS, residual strain/stress and texture studies.

The aim of the submitted proposal is to get financial support for development of Monte Carlo methods for simulations of complex neutron optical systems, including their experimental validation and application to the research of dispersive multiple reflections of neutrons in elastically bent crystals. The new methods will be implemened in existing and well established software package RESTRAX, which has been developed at the NPI Řež. The results of experimental research of multiple Bragg reflections supported by Monte Carlo simulations will be employed in the development of high-resolution monochromators and analyzers. The ultimate goal of the proposed research is twofold: (a) Creation of an easy to use, validated and efficient software for modeling and optimization of neutron spectrometers employing advanced neutron optics elements and for data analysis; (b) Development and tests of dispersive multiple reflection monochromators suitable for ultra-high resolution measurements.

Participation on multilateral project with the task: Development and optimization of a curved wide wavelength band monochromator based on strongly cylindrically bent perfect Si-slabs in a sandwich for microfocusing small-angle neutron scattering (mfSANS) device.