Neutron Scattering - JUWEL - Forschungszentrum Jülich

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KWS-1 & KWS-2 3 Fig. 1: Representation of the protein lysozyme, which has a very compact form. 1 Introduction Fig. 2: Schematic representation of a cylindrical micelle, which is composed of amphiphilic polymers. The objective of this lab course is to clarify the essential concepts of small-angle neutron scattering. Structures are only visible by a scattering experiment if there is an appropriate contrast. For neutrons one often uses the exchange of 1 Hby 2 H, i.e. deuterium. The scattering length density difference is responsible for the contrast of a small-angle neutron scattering experiment. We will investigate the protein Lysozyme in heavy water (Fig. 1) to obtain the information about the typical distance of the molecules. A second example is a micellar solution of the amphiphilic polymer POO10-PEO10 in heavy water (Fig. 2). The chosen contrast makes only the core of the micelle visible. The core is very compact because of the hydrophobic interaction. The aim of this second part is to determine the radius of the cylindrical structure. 2 The Protein Lysozyme in Water For this part of the experiment a Lysozyme solution of 0.02g per ml of water must be prepared. We will use deuterium oxide to prepare the solution of ca. 1ml. We will weigh exactly 0.02g of Lysozyme and put it into a new Packard glas. With an Eppendorf pipette we will add exactly 1 ml D2O. These pipettes are extremely accurate with respect to the volume. From the solution about 0.5 to 0.6ml are transferred to Hellma quartz cuvettes, which are 1mm thick. The experimental part in the chemistry lab is finished. 3 The Diblock Copolymer POO10-PEO10 This polymer is an amphiphilic diblock copolymer. It consists of the monomers octyl-oxide and ethylene oxide. The monomers were consecutively polymerized and are now forming polymers.
4 H. Frielinghaus, M.-S. Appavou The POO-block has a molar mass of 10kg/mol. The symmetrical polymer has about the same molecular weight in the PEO block. The PEO is deuterated in this polymer. Using heavy water especially the contrast of the POO-hydrophobic block to PEO and D2O is highlighted. This means that in the scattering experiment the micelle core will be particularly well visible, the corona will be not. Because these polymers are very expensive, a 0.1% solution is available for the scattering experiment. 4 The Measurement at KWS-1 and/or KWS-2 These two solutions are now being measured in the small-angle neutron scattering instrument KWS-1 (or KWS-2). The wavelength of neutrons is set to 7 ˚A. The collimation is fixed to 8m. The samples are placed as close as possible to the detector, to measure the largest Q values possible. Both samples will be measured at detector distances 2m and 8m. The offset between the sample position and the detector of about 30cm leads to effective detector distances of about 1.7m and 7.7m. The sample holder will be filled with the two samples. In addition, the empty beam and a plexiglass plate are measured for absolute calibration. For a good statistical measurement the following times are set: 8m detector distance for 20min, and 2m detector distance 10min. The total measuring time for the 4 positions will be about 2 hours. The measurement is typically started before lunch, and can be evaluated in the afternoon. It is quite likely that an internal employee will start separate measurements during the afternoon until the next morning in order to use the valuable measuring time overnight. 5 Evaluation of the <strong>Scattering</strong> Data: Absolute Calibration The measured data is raw data at first and describes the intensity on the detector. The data has to be corrected for the effectiveness of the different detector channels. Then the empty beam measurement is deducted to account for the zero effect of the instrument. Then the intensities are expressed as absolute units using Eq. 5.5 and are radially averaged, because for the isotropic scattering samples, the intensity does not depend on the polar angle. To perform all these steps we will be using a software available in our institute, called QtiKWS. However, since the understanding of the Eq. 5.5, as such, is more important than the exact technical understanding of the evaluation, the results are produced relatively quickly by the software, namely, dΣ/dΩ as a function of the scattering vector Q for our samples. This data will be provided for the students to do the final evaluation. In the following, this evaluation is described. 6 Evaluation of Lysozyme <strong>Scattering</strong> Curves The position of the maximum Qmax provides information on the typical distance of the proteins in solution. This can be calculated to ℓ =2π/Qmax. Knowing the weight of the protein in water (0.02g/cm 3 ) there is an alternative way to calculate the average distance. The molar
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Member of the Helmholtz Association
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Forschungszentrum Jülich GmbH Jül
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2 O. Sobolev, A. Teichert, N. Jünk
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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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Page 78 and 79: SPHERES Backscattering spectrometer
Page 80 and 81: SPHERES 3 1 Introduction Neutron ba
Page 82 and 83: SPHERES 5 Fig. 2: The monochromator
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Page 86 and 87: SPHERES 9 neutron is scattered, it
Page 88 and 89: SPHERES 11 The stationary equilibri
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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
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Page 128 and 129: ________________________ KWS-3 Very
Page 130 and 131: KWS-3 3 1 Introduction Ultra small
Page 132 and 133: KWS-3 5 2. The standard Q-range of
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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
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