Journal of large-scale research facilities, 1, A4 (2015) http://dx.doi.org/10.17815/jlsrf-1-23 Published: 18.08.2015 RESI: Thermal neutron single crystal di�rac- tometer Heinz Maier-Leibnitz Zentrum Ludwig-Maximilians-Universität München Technische Universität München Instrument Scientists: - Bjørn Pedersen, Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Garching, Germany, phone: +49(0) 89 289 14707, email: bjoern.pedersen@frm2.tum.de Abstract: The di�ractometer RESI, which is operated by the Department für Geo- und Umweltwissen- schaften Sektion Kristallographie, Ludwig-Maximilians-Universität München and the Technische Uni- versität München, is designed for high q-resolution, low background and best �ux usage allowing opti- mum measurements of weak di�raction phenomena in a large portion of the reciprocal space on single crystalline samples. 1 Typical Applications Structure analysis with thermal neutrons (λ = 0.8 Å to 2 Å) is complementary to structure analysis with X-rays. The measurement possibilities provided by this instrument are crucial for many scienti�c questions: • Structure analysis, bonding theory, electron densities: Due to the interaction with atomic cores and the di�raction angle independence of the atomic form factor, it is possible to measure Bragg scattering up to high di�raction angles. • Real crystals and compounds of interest for material science are often not perfectly ordered. The elucidation of these real structures requires the analysis of the corresponding di�use scattering. The di�use scattering - o� the Bragg re�ections - is normally di�erentially weak and distributed continually (anisotropic) in the reciprocal space. • Partially crystalline compounds, like �bre structures, show a speci�c scattering, which is highly anisotropic and continously distributed in the reciprocal space. Therefore, di�ractometers with area detectors like RESI are best suited for this kind of problems. • Structural phase transitions can be accompanied by continuous re�ection shifting. 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-1-23 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 1, A4 (2015) http://dx.doi.org/10.17815/jlsrf-1-23 Figure 1: Instrument RESI with focusing guide (left), Eulerian cradle (middle, front), area detector (mid- dle, back) and single counter (right); (Copyright by W. Schürmann, TUM). • Modulated structures show satellite re�ections at “incommensurable” positions. Both areas require analysis of large portions of the reciprocal space. • A new class of aperiodic crystals (“quasi crystals”) show dense, but discrete re�ex patterns, where more than 90% of the re�exes are very weak. Additionally, due to the fact that quasi crystals often contain two or more transition metals (which are almost isoelectronic), neutrons o�er much higher contrast than X-ray methods. • Twinned crystals and multi-domain/multi-phase crystals are often di�cult to measure on single-counter instruments. The area detector at RESI allows for easy detection and in many cases separation of re�ections in such systems. The advantages of the high-resolution area detector can be utilised best, if the reciprocal space is not too empty. That means, that RESI is optimal for cells of ca. 1000 Å3 to ca. 20000 Å3. Typical crystal sizes range from 5 mm3 to 25 mm3. 2 Sample Environment Dedicated sample environment of RESI: • Oxford Cryosystems Cryostream 700 temperature range 100 K - 400 K consumption 20 l L-N2/d • Oxford Instruments Helijet temperature range 15 K - 100 K consumption 2 l L-He / h sample size 1 x 1 x 1 mm3 max. Standard sample environment usable with RESI: • Closed-cycle cryostat CC, 2.5 K – 300 K • Closed-cycle cryostat CCR, 3 K – 100 K using 3He insert, 500 mK – 4 K using 3He/4He dilution, 50 mK – 1 K • Vacuum furnace, 340 K – 2100 K • Mirror furnace, RT – 1250 K 2 http://dx.doi.org/10.17815/jlsrf-1-23 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-1-23 Journal of large-scale research facilities, 1, A4 (2015) Figure 2: Schematic drawing of RESI. 3 Technical Data 3.1 Primary beam • Beam tube SR-8b • Neutron guide Length: 12 m, focussing vertical / horizontal section: 70 x 40 mm → 60 x 30 mm • Coatings: m = 3 top/bottom; m = 1 side 3.2 Monochromators Vertically focussing lamella type, �xed take-o� 90° • Cu-422, 20’ mosaic, 1 Å: 2 · 106 n cm-2 s-1 • Ge-511, 25’ mosaic (deformed wafer stack) 1.5 Å: 6 · 106 n cm-2 s-1 3.3 Secondary neutron guide Vertically focussing ellipitical guide-in-guide • Length: 1 m • Focus 400 mm after guide exit • Coating: m = 5 3 http://dx.doi.org/10.17815/jlsrf-1-23 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 1, A4 (2015) http://dx.doi.org/10.17815/jlsrf-1-23 3.4 Available goniometers • Kappa-Goniometer: Bruker-Nonius Mach3 carrying capacity: max 100 g • Eulerian cradle Huber 420: higher carrying capacity, e.g. for closed-cycle cryostat • Huber 2-circle goniometer: with tilting head highest carrying capacity, e.g. for CCR with 3He insert 3.5 Available detectorss • MAR345 image plate detector: 345 mm diameter, N-sensitive image plate • Single counter 3He with optional analyzer for pure elastic scattering 4 http://dx.doi.org/10.17815/jlsrf-1-23 https://creativecommons.org/licenses/by/4.0/ Typical Applications Sample Environment Technical Data Primary beam Monochromators Secondary neutron guide Available goniometers Available detectorss