Presentation on theme: "Focusing monochromators/analyzers Asymmetric diffraction geometry of the monochromator Dispersive double crystal monochromator Two wavelength sandwich."— Presentation transcript:
Focusing monochromators/analyzers Asymmetric diffraction geometry of the monochromator Dispersive double crystal monochromator Two wavelength sandwich monochromator FAD geometry of the monochromator Dispersive „umweganregung“ monochromator Energy dispersive neutron diffraction transmission Bent perfect crystals in TOF diffractometry? Other applications and proposals ? Possible contribution of NPI Rez Neutron Bragg Diffaction Optics for High-Resolution Neutron Scattering Instrumentation Pavel Mikula Nuclear Physics Institute, Academy of Sciences of the Czech Republic 250 68 Řež near Prague, Czech Republic
Reflectivity properties of bent perfect crystals
Horizontally focusing two wavelength sandwich monochromator Sandwich monochromator Si111(2.7 A) & Si220(1.65 A) Si111(2.7 A) & Ge311(1.45 A) hkl 1 hkl 2 2 1 Advantage: For strain measure- ments of two phase materials, composi- tes etc.
FADG Two possible scans: -scan, k ┴ -2 scan, k || Special case of single crystal diffractometry
Schematic drawing of the case of the symmetric diffraction geometry – (a) and of the fully asymmetric diffraction geometry – (b). Comparison of two diffraction geometries
Diffraction profiles as imaged by IP for curved crystals set in the symmetric diffraction geometry (R=8.8 m) and the fully asymmetric diffraction geometry (R=7.5 m). Beam profiles at the sample position
“Umweganregung“ monochromator Double reflection realized on (h 2,k 2,l 2 ) and (h 3,k 3,l 3 ) in a bent perfect or mosaic single crystal simulates the forbidden one corresponding to (h 1,k 1,l 1 ) and can provide a good intensity of highly monochromatic and highly collimated beam for a further use. Relation for scattering vectors
scan taken with the Si crystal slab set for 222 diffraction in symmetric transmission geometry; guide tube, 3x3 m 2 Cd slit “Umweganregung“ monochromator
scan taken with the Si crystal slab set for 222 diffraction in symmetric transmission geometry and bending dependences taken with on the umweg-peak at =47.9 o.
“Umweganregung“ monochromator scan taken with the Si crystal slab set for 002 diffraction in symmetric transmission geometry
Bragg diffraction edge of a 8 mm thick standard sample. Sample thickness dependence of A o FWHM=5.7x10 -4 rad FWHM=12.5x10 -4 rad EDNTD examples
High resolution bent perfect crystal analyzer in fully asymmetric diffraction geometry Extremely low attenuation factor for neutrons in the wavelength range of 0.15-0.4 nm
TOF experimental test Generally, different lattice planes (hkl) at different asymmetry angles can operate simultaneously. The beam that should be analyzed enters the bent crystal slab through its end face and passes along its longest edge. Due to the bending, on the path through the crystal it meets homogeneously changing diffraction angle hkl with respect to the planes (hkl).