Focusing monochromators/analyzers Asymmetric diffraction geometry of the monochromator

1. Neutron Bragg Diffaction Optics for High-Resolution Neutron Scattering Instrumentation Pavel Mikula Nuclear Physics Institute, Academy of Sciences of the Czech Republic250 68 Řež near Prague, Czech Republic Possible contribution of NPI Rez • 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 ?

2. Reflectivity properties of bent perfect crystals

3. Assymetric diffraction geometries Output beam compression Output beam extention

4. Comparison on powder and solid a-Fe samples Missouri Missouri NPI NPI

5. Dispersive Double-Crystal Monochromator

6. Dispersive Double-Crystal Monochromator

7. Dispersive Double-Crystal Monochromator

8. Dispersive Double-Crystal Monochromator

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

10. Mosaic Ge331) + bent Si(111) + g-Fe(220)

11. Horizontally focusing two wavelength sandwich monochromator l1 l2 Sandwich monochromator Si111(2.7 A) & Si220(1.65 A) Si111(2.7 A) & Ge311(1.45 A) hkl1 hkl2 Advantage: For strain measure- ments of two phase materials, composi- tes etc.

12. Special case of single crystal diffractometry FADG • Two possible scans: • w-scan, Dk┴ • w-2w scan, Dk||

13. Comparison of two diffraction geometries Schematic drawing of the case of the symmetric diffraction geometry – (a) and of thefully asymmetric diffraction geometry – (b).

14. Beam profiles at the sample position Diffraction profiles as imaged by IP for curved crystalsset inthe symmetric diffraction geometry (R=8.8 m) and the fully asymmetric diffraction geometry (R=7.5 m).

15. “Umweganregung“ monochromator  Relation for scattering vectors Double reflection realized on (h2,k2,l2) and (h3,k3,l3) in a bent perfect or mosaic single crystal simulates the forbidden one corresponding to (h1,k1,l1) and can provide a good intensity of highly monochromatic and highly collimated beam for a further use.

16. “Umweganregung“ monochromator q-2q scan taken with the Si crystal slab set for 222 diffraction in symmetric transmission geometry; guide tube, 3x3 m2 Cd slit

17. “Umweganregung“ monochromator q-2q 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 q=47.9o.

18. “Umweganregung“ monochromator q-2q scan taken with the Si crystal slab set for 002 diffraction in symmetric transmission geometry

19. Fully asymmetric diffraction geometry

20. Energy-Dispersive Neutron-Transmission Diffraction 2dhklsin Q hkl=l Q hkl=90o l =2dhkl Diffraction edge I(l) modulation Instrumental resolution Dd/d=5.7x10-4

21. EDNTD examples FWHM=5.7x10-4 rad Sample thickness dependence of Ao FWHM=12.5x10-4 rad Bragg diffraction edge of a 8 mm thick standard sample.

22. 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

23. TOF experimental test Generally, different lattice planes (hkl) at different asymmetry angles y 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 qhkl with respect to the planes (hkl).

24. TOF experimental test

25. Experimental results

26. Experimental results

27. OTHER BRAGG DIFFRACTION OPTICS APPLICATIONS

28. Time focusing assembly