Neutron Scattering - JUWEL - Forschungszentrum Jülich

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KWS-3 3 1 Introduction Ultra small angle (USANS) and small angle neutron scattering (SANS) experiments are performed by two different types of instruments to cover a combined Q-range from 10 -5 Å -1 up to 1Å -1 . Double crystal diffractometers are used for USANS experiments, whereas the "standard" SANS experiment is performed using a pinhole camera. In principle, the Q-range of both instrument classes overlaps. Typical USANS instruments like S18 (ILL) or PCD (NIST) may reach maximum Q-vectors of 5�10 -3 Å -1 . The disadvantage of these instruments is that they do not allow taking a full area image on a 2D position sensitive detector. On the other hand, the well-known pinhole instrument D11 at Institut Laue-Langevin (France) reaches a minimum Q-vector of 3�10 -4 Å -1 by use of largest possible wavelength 22Å and sample-to-detector distances (>40 m). But the required instrumental settings push both types of instruments to their limits, mainly due to signal-to-noise level and the reduced flux at sample position. The use of neutron lenses as additional elements of a pinhole SANS instrument has been tested to overcome this intensity problem [1]. An alternative design is realized by the KWS-3 instrument [2]. The principle of this instrument is a one-to-one image of an entrance aperture onto a 2D position-sensitive detector by neutron reflection from a double-focusing elliptical mirror. It permits to perform SANS studies with a scattering wave vector resolution between 10 -4 and 10 -3 Å -1 with considerable intensity advantages over conventional pinhole-SANS instruments and double crystal diffractometers. Therefore it perfectly bridges the "Q-gap" between USANS and SANS: Very Small Angle <strong>Scattering</strong> (VSANS). The increasing need for these intermediate Q-vectors arises from the growing interest in biological and colloidal samples, which partially deal with length scales in the �m range. An investigation of the multilevel structures in partially crystalline polymer solutions performed using a combination of those three above depicted types of SANS instruments can be found in [3]. Figure 1: Focused VSANS fills space between USANS (double crystal diffractometer) and classical SANS instruments. The main innovation and challenge of KWS-3 was to build a large mirror having a shape as close as possible to an ellipsoid and with a surface roughness less than 5 Å. The mirror is a
4 Vitaliy Pipich 1.2 m long, 0.12 m wide and 0.05m thick toroidal double focusing mirror of 11 m focal length. At such a short mirror length with respect to the focal length, the toroidal shape is a good enough approximation to an elliptical shape. The reflection plane has been chosen to be horizontal, reducing the deterioration of the image due to gravity. A photo of the mirror is given in Figure 1. Figure 2:(left) layout of KWS-3;(right) toroidal mirror installed in vacuum its chamber. KWS-3 is optimized for very small angle scattering range from 10 -4 to 3·10 -3 Å -1 . For last cold source filling and instrument configuration the flux at the sample position (and detector) is near 11500 counts per full sample area by use 12.5Å wavelength with 20% wavelength spread, 2x2 mm 2 entrance aperture and 20x100 mm 2 beam size sample-to-detector distance at 9.5 meters. 2 VSANS applications All applications of the classical SANS could be investigated by VSANS by taking into account Q-resolution of VSANS. The conventional fields of application of very small angle scattering studies are: � particles in solution [protein aggregates, polymers, micelles, ceramics]; � porous materials [cement, paste, rocks, coal etc.]; � inhomogeneous metallic alloys; � bulk samples with artificial regular structure [phase gratings]; and other inhomogeneities on a size range from 50 nm to 5 �m, often in addition to SANS spectra, but also diffraction, reflection and refraction studies on surfaces. 3 Preparatory Exercises 1. The contrast variation (CV) is a very important feature of the neutron scattering. What is the scattering length density (SLD) �? How to calculate the SLD? What is the definition of the scattering contrast ��? How to carry out the contrast variation experiment in case of an aqueous solution of particles?
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Member of the Helmholtz Association
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Forschungszentrum Jülich GmbH Jül
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�� 1 PUMA
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2 O. Sobolev, A. Teichert, N. Jünk
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2 POWDER DIFFRACTOMETER SPODI Conte
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14 POWDER DIFFRACTOMETER SPODI neut
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2 M. Meven Contents 1 Introduction
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4 M. Meven a (hkl) Plane. Each plan
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6 M. Meven wavelengths � in the s
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10 M. Meven This has to be taken in
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12 M. Meven 4 Sample Section 4.1 In
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14 M. Meven Fig. 8 (a) orthorhombic
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16 M. Meven 4.3 Oxygen Position The
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18 M. Meven To direct the secondary
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20 M. Meven For a given spectrum
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22 M. Meven References [1] Th. Hahn
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SPHERES Backscattering spectrometer
Page 80 and 81: SPHERES 3 1 Introduction Neutron ba
Page 82 and 83: SPHERES 5 Fig. 2: The monochromator
Page 84 and 85: SPHERES 7 While the primary spectro
Page 86 and 87: SPHERES 9 neutron is scattered, it
Page 88 and 89: SPHERES 11 The stationary equilibri
Page 90 and 91: SPHERES 13 4. Summarize the tempera
Page 92 and 93: ________________________ DNS Neutro
Page 94 and 95: DNS 3 1 Introduction Polarized neut
Page 96 and 97: DNS 5 Monochromator horizontal- and
Page 98 and 99: DNS 7 3 Preparatory Exercises The p
Page 100 and 101: DNS 9 important and always necessar
Page 102: DNS 11 Contact �� Phone:
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Page 128 and 129: ________________________ KWS-3 Very
Page 132 and 133: KWS-3 5 2. The standard Q-range of
Page 134 and 135: KWS-3 7 Table 2. Samples for practi
Page 136 and 137: KWS-3 9 References [1] Eskilden, M.
Page 138 and 139: ________________________ RESEDA Res
Page 140 and 141: RESEDA 3 1 Introduction Neutrons ar
Page 142 and 143: RESEDA 5 various length values l ac
Page 144 and 145: RESEDA 7 In this expression, a norm
Page 146 and 147: RESEDA 9 spin flip from up to down
Page 148 and 149: RESEDA 11 The neutrons are counted
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Neutron Scattering - JUWEL - Forschungszentrum Jülich

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