Pavol Mikula and Michihiro Furusaka 1 Nuclear Physics Institute, v. v. i., Czech Academy of Sciences, Řež, Czech Rep.

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1 I-2. Development and optimization of a curved wide wavelength band monochromator based on strongly cylindrically bent perfect Si-slabs in a sandwich for minifocusing small-angle neutron scattering (mfsans) device Pavol Mikula and Michihiro Furusaka 1 Nuclear Physics Institute, v. v. i., Czech Academy of Sciences, Řež, Czech Rep. 1 Department of Mechanical Intelligence Engineering, Graduate School of Engineering, Hokkaido University, Japan Fax: , mikula@ujf.cas.cz Introduction SANS is a very powerful and popular technique to study nano-scale structure in a matter. Practically, every neutron facility over the world has at least one or two such instruments, but very often, they are over-subscribed and it is not so easy to obtain a beam time on these machines. The research group from Hokkaido University has been proposed a new and unconventional type of a high resolution SANS instrument called as Minifocusing small-angle neutron scattering instrument (mfsans) which can have a revolutionary impact on the instrumentation development namely at the medium and lower power neutron sources. Using a compact ellipsoidal mirror as a focusing device and high resolution position sensitive detectors, which have been developed in the last decade, it is possible to construct a very compact and versatile focusing-type SANS instrument. This development of the SANS device would permit to demonstrate an inexpensive instrument which can be designed and realized for operation at different neutron wavelengths. As the instrument can be designed at different wavelengths, then by using e.g. two or three instruments operating at different wavelengths one can substantially enlarge the range of momentum transfer with respect to conventional collimator SANS devices. It also permits one to enlarge the number of highly demanded neutron scattering instruments installed at the medium or low power pulsed or steady state neutron sources in a rather inexpensive way. The mock-up test experiments of the time-offlight type mfsans have been carried out at a small pulsed cold-neutron source at Hokkaido University. It is based on a 45 MeV electron linac combined with a high-performance solidmethane cold neutron moderator. In this case an ellipsoidal mirror with 4 m between focusing points is used with Ni coating on it. The actual length of the mirror was 900 mm and it has a cross section of 1/4 of a circle with radius of around 20 mm. At present a prototype of mfsans at the JRR-3 reactor position is under construction. In parallel to it works on a conceptual design of mfsans instruments at J-PARC are in progress. A wide wavelength band monochromator In the last two 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) and focusing in real space, one may obtain a high density monochromatic-beam comparable to that of the mosaic monochromators. Taking into account reflectivity and resolution properties of curved crystals, it has been demonstrated that the optimized curved crystals have monochromatization properties generally better than mosaic crystals. An increased interest in the reflectivity and focusing properties of curved perfect crystals has been evoked by a successful testing of the bent perfect crystals employed in double-monochromator systems, or for medium-resolution

2 small-angle scattering diffractometers [1-5]. Recently, favourable properties of bent Si crystal for short wavelength monochromatization have been reported and very efficient original double and triple axis arrangements employing bent perfect crystals have been proposed and then tested for residual stress measurements of polycrystalline materials. Recent instrumentation developments have been mainly oriented to medium-resolution small-angle scattering, high-resolution strain measurements, high-resolution powder diffractometry and TOF spectrometry. Our group together with the group at the Missouri University Research Reactor appears to be pioneers in the field of Bragg diffraction optics. Based on our ideas and experience, the first neutron optic elements have already been employed on instruments in PTB Braunschweig, HMI Berlin, ILL Grenoble, JAERI Tokai and KURRI Kumatori. In addition, our group has been asked to participate in an implementation of Bragg diffraction optics in LLB Saclay (France), Chalk River (Canada), GKSS Geesthacht, KAERI Daejon, ANSTO (Australia), Demokritos Athens, BARC Bombay and HMI Berlin. The most recent results related to the project are subject of publications [6-20]. Therefore, also in connection with the construction of the mfsans instrument our laboratory provides reflectivity and wavelength band calculations, know-how in the design and optimization performance of the required focusing monochromators. Furthermore, our laboratory provides Si-perfect crystals of a special cut for cylindrical bending according to the requirements. The main objectives of our contribution in the project can be summarized as follows: To improve neutron beam luminosity and resolution via exploitation of focusing devices and focusing monochromators. To participace on the development of the compact inexpensive small-angle neutron scattering instrument for installation at the medium or low power pulsed or steady state neutron sources The working plan for 2007: The design and preparation of the Si-crystal slabs for cylindrically bent focusing monochromator of a sandwich type for the SANS device, experimental tests of curved Si-crystal slabs on a cold neutron beam. The working plan for : The design and preparation other sets of Si-sandwich monochromators according to requirements coming from the first experience obtained on the prototype instruments as well as for other next phase instruments. If required, Monte Carlo simulations of the optimum design and performance of the small angle neutron scattering instrument implementing focusing elements can be carried out. This also covers training of users in manipulation with focusing bent perfect Si-crystal slabs and in optimization procedure. As a conclusion one can state that one of the most important concepts of "mfsans" is that one can install many such instruments on neutron guide-tubes at any reactors, or at beam lines of pulsed-neutron sources, either by putting wide-wavelength-band monochromators or by splitting a beam line by benders/splitters at a rather low cost. It opens up great opportunities in SANS measurements as it will result in creating new and exciting scientific fields. It also permits to expand a user base and to train people who could use such instruments or even build and maintain such instruments. Acknowledgement

3 The research in the field of Bragg diffraction optics is in the Czech Republic supported by the projects AV0Z , MSM and GA-CR 202/06/0601. References 1. P. Mikula, P. Lukáš and F. Eichhorn, New Version of a Medium Resolution Double- Crystal Diffractometer for the Study of a Small Angle Neutron Scattering (SANS), J. Appl. Cryst. 21 (1988) P. Mikula et al., A Highly Efficient Multicrystal Camera for SANS Studies, Physica B 156&157 (1989) P. Mikula, V. Wagner and R. Scherm, Focusing Double-Bent-Crystal (DBC) Diffractometer for Medium Resolution SANS Experiments, J. Appl. Cryst. 24 (1991) P. Lukáš et al., New SANS Diffractometer and Neutron Interferometric Device at NPI Řež,Physica B 180&181 (1992) P. Mikula, P. Lukáš, J. Kulda, P. Strunz, and J. Šaroun, Unconventional Double Bent Crystal (DBC) Diffractometer Equipped by Position Sensitive Detector (PSD), Proc. of SPIE's 1992 Symposium on Optical Applied Science and Engineering, X-Ray Optics, Vol. 1738, p P. Mikula, M. Vrána, M. Furusaka, Y. Yasushige, Fully Asymmetric Diffraction Geometry of a Bent Perfect Crystal Silicon Analyzer for High-Resolution TOF Spectrometry, In Proc. of the Int. Collaboration on Advanced Neutron Sources (ICANS XVI), May 12 15, 2003, Düsseldorf-Neuss, Germany, pp P. Mikula, M. Vrána and V. Wagner, On a possible use of multiple Bragg reflections for high resolution monochromatization of neutrons, Physica B, 350 (2004) e667-e M. Vrána, P. Mikula and B. Lebech, Direct comparison of plastically deformed Ge mosaic crystal and bent perfect Si crystal for neutron monochromatization, Physica B, 350 (2004) e663-e N. Achiwa, S. Kawano, M. Hino, P. Mikula, M. Ono, T. Ebisawa and T. Fukunaga, Si curved monochromator multi-counter neutron diffractometer installed at B4 supermirror thermal guide tube in KUR, Nucl. Instrum. Methods in Physics Research A 529 (2004) P. Mikula, M. Vrána, M. Furusaka, V. Wagner, Y. N. Choi, M.K. Moon, V.T. Em and C. H. Lee, Bragg Diffraction Optics Based on Cylindrically Bent Crystals in Neutron Scattering Instrumentation, Nucl. Instrum. Methods in Phys. Res., A 529 (2004) J. H. Kaneko, Y. Ohtake, H. Fujimoto, S. Kawamura, M. Watanabe, F. Fujita, T. Sawamura, P. Mikula, M. Furusaka, Investigation on possibility of neutron optical devices

4 based on piezoelectric single crystals, Nucl. Instrum. Methods in Phys. Res. A 529 (2004) M.K. Moon, C.H. Lee, V.T. Em, P. Mikula, et al., Optimization of Bent Perfect Si(311)- Crystal Monochromator for Residual Strain/Stress Instrument at HANARO Reactor - Part I, Physica B, 369 (2005) M.K. Moon, C.H. Lee, V.T. Em, P. Mikula, et al., Optimization of Bent Perfect Si(220)- Crystal Monochromator for Residual Strain/Stress Instrument- Part II, Physica B- Condensed Matter, 368 (2005) P. Mikula, M. Vrána, V. Wagner, D. Lott, Dispersive Monochromators/Analyzers Based on Cylindrically Bent Perfect Crystals (BPC) for High-Resolution TOF Spectrometry, In Proc. of the ICANS-XVII-17 th Meeting of the Int. Collaboration on Advanced Neutron Sources, April 25-29, 2005, Santa Fe, New Mexico. 15. P. Mikula, M. Vrána, D. Lott, V. Wagner, Neutron monochromator based on dispersive double-reflections excited in a cylindrically bent-perfect-crystal (BPC) slab, In Proc. of the ICNS 2005 Conference, Sydney, Nov. 27 Dec. 2, 2005, Physica B, (2006) S. Kawamura, J. H. Kaneko, H. Fujimoto, Y. Otake, F. Fujita, A.Homma, T. Sawamura, P. Mikula, M. Furusaka, Deformation experiment of piezoelectric single-crystals for neutronoptical-devices, In Proc. of the ICNS 2005 Conference, Sydney, Nov. 27 Dec. 2, 2005, Physica B, (2006) P. Mikula, M. Vrána, V. Wagner, High-resolution neutron diffraction performance for stress/strain measurements in polycrystalline materials, Zeitschrift für Kristallographie,, Suppl. 23 (2006) Y. N. Choi, S.A. Kim, S.K. Kim, S.B. Kim, C.H. Lee, P. Mikula, M. Vrána, Bent perfect crystal (BPC) monochromator at the monochromatic focusing condition, Zeitschrift für Kristallographie, Suppl. 23 (2006) M. Furusaka, K. Kamada, Y. Kiyanagi, F. Fumiyuki, A. Homma, K. Ikeda, K. Hirota, H. Shimizu, S. Satoh, P. Mikula, T. Satoh, K. Tanabe, K. Koyama, H. Takahashi, K. Fujita, T. Kamiyama, S. Naito, Y. Kawamura, H. Yoshizawa, S. Ikeda, First results from a minifocusing Small-Angle Neutron Scattering Instrument (mfsans) with an ellipsoidal mirror, In Proc. of the 18th Meeting of the Int. Collaboration on Advanced Neutron Sources (ICANS- XVIII), April 26-29, 2007, Dongguan City, Guangdong Province, China. 20. P. Mikula, M. Vrána, V. Wagner, M. Furusaka, Multiple reflections (MR) a new challenge for high-resolution neutron diffractometry and spektrometry, In Proc. of Int.

5 Workshop on Neutron Optics NOP07, PSI Willigen, March, 5-7, 2007, Nucl. Instrum. Methods, in print.