The system of neutron optics for the diffractometer E PSILON and SKAT

1. The system of neutron optics for the diffractometer EPSILON and SKAT Walther A. Bulkin Frischbutter V. Kudryashov Ch. Scheffzük F. Schilling

2. V. Zhuravlov A. Sirotin E. Shabalin I. Natkaniec S. Manoshin S. Kulikov A. Belushkin A. Balagurov Thanks to:

3. 1983 - reactor IBR-2 became critically 1983 – the diffractometer NSWR, built in the workshop of the TU Dresden, was mounted at beamline 7 1983 - first plans for a long flight path for an inelastic spectrometer with inverted geometry 1984 - idea for an additional multipurpose- instrument: quasi-elastic scattering high resolution diffraction texture investigation Historical review(1):

4. 1985 - sputtering of glass with Cr/Ni and production of the glass segments for both guides in the workshop of the FLNP 1986 - commissioning of the instrument NSWR at the long flight path for the multi-purpose instrument it was realised only the texture unit 1995 - early variant of EPSILON 1996 - replacement of NSWR by SKAT 2007 - begin of the reconstruction of the former neutron guide 7A Historical review(2):

6. Good spectral resolution Good spatial resolution High intensity Low background Good sample environment What do we expect from a good diffractometer?

7. In order to reduce the attenuation due to absorption and scattering at this side should be built in an evacuated tube Start of the neutron guides as near as possible to the chopper built in of a guide splitter In-pile improvements for high intensity:

12. Pulse reactor IBR works as a low power steady state reactor (≈ 100 kW) Every 200 ms a high power neutron pulse is generated (≈ 1000 MW) Reduction of the background with a background chopper

13. Flight path: 102≤l1+l2≤110 m resulting velocity for travelling within 200 ms 510≤v≤550 m/s cut-off wavelength due to frame overlapping: λc-o =7.75Å and 7.19Å, respectively opening in the chopper disk (dist. = 5.5m) 19.4° and 18°, respectively opening of the chopper 10.8 ms and 10 ms, respectively (for a beam of zero width) Backgroundchopper(1)

14. Background chopper(2) Calculations of the transmission function of the background chopper were done for: • “Standard” (old) mounting: chopper axis is below the entrance windows of the guides • edges radial • edges parallel • “alternative” mounting: chopper axis is at the same height but aside the entrance windows • edges radial • edges parallel

15. Guide splitter(1) • All guides start closer to the moderator • The three guides do not “disturb” each other • at the end of the guide splitter 3 separate neutron guides will start • all guides are evacuated.

16. Lambda-chopper(1) • The 7th beam line will have partial sight on the cold source • There is a need to have neutrons beyond the frame overlapping, both for EPSILON and SKAT due to the large unit cells of some minerals • Every second power pulse could be eliminated by an additional chopper • The back ground chopper should provide this extended wavelength range too

17. Lambda-chopper(2)

18. Lambda-chopper(3)

19. Lambda-chopper(4)

20. Neutrons are classical mechanical particles They have a mass mo They have a velocity v They have a momentum p Neutron guide and some fundamental mathematics

21. Neutron guide and some fundamental mathematics(2) • Neutrons are waves • They have a wave length The wave length λ is connected with the flight time t by

22. Neutron guide and some fundamental mathematics(3) In time-of-flight diffraction patterns you see peaks in a distribution of the number of diffracted neutrons (intensity) over the wavelength for a given scattering angle ϑ. According to BRAGG‘s law we get

24. Spectral Resolution Spectral resolution can be improved by increasing the flight path!

25. Classical neutron guides are based on the phenomena „total reflection“ like fibre optics Small total reflection angles in the order of minutes of arc Only few minerals/elements are of interest Angle of total reflection is proportional to the wavelength Angle of total reflection of Ni with natural abundance of isotopes defines the value m=1.0 which corresponds αtot=0.1° Ni58 corresponds m=1.2 Neutron guides

26. Neutron guides are built of well aligned glass sections The surface of the glass should have nearly no roughness Boron glass meets the requirements Neutron guides for thermal neutrons are bent in the most cases Neutron guides(2)

28. Neutron guides are built of well aligned glass sections The surface of the glass should have nearly no roughness Boron glass meets the requirements Neutron guides for thermal neutrons are bent in the most cases Neutron guides(2)

29. The neutron guides for EPSILON and SKAT are built up of sections 1 m long The sections are 95 mm high and 50 mm wide The first part (within the splitter) is straight The next part about 80 m length is bent; radius of curvature:13 400 m Bent neutron guides transport only neutrons with a wavelength greater the critical wavelenght, which depends on the width and the radius of bending.The critical wavelength is 1.58 Å In order to homogenize the flux across the section the last part are straight Neutron guides(3)

33. After realization the new neutron guides and the chopper system there are created two high level diffractometers for long wavelength diffraction Outlook and conclusion

34. Acknowledgment • the BMBF Germany, • FLNP Dubna • Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences • Karlsruhe Institute for Technology • for support