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 Řež near Prague, Czech Republic

Reflectivity properties of bent perfect crystals

Output beam compression Output beam extention Assymetric diffraction geometries

Comparison on powder and solid  -Fe samples Missouri NPI

Dispersive Double-Crystal Monochromator

Experimental setup for the estimation of resolution of powder diffractometer under the dispersive setting of the double-crystal monochromator Dispersive Double-Crystal Monochromator

Mosaic Ge331) + bent Si(111) +  -Fe(220)

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 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

Fully asymmetric diffraction geometry

2d hkl  sin  hkl  =  hkl  =    =2d hkl Diffraction edge I( ) modulation Instrumental resolution  d/d=5.7x10 -4 Energy-Dispersive Neutron-Transmission Diffraction

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 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).

TOF experimental test

Experimental results

OTHER BRAGG DIFFRACTION OPTICS APPLICATIONS

Time focusing assembly