Neutron Scattering - JUWEL - Forschungszentrum Jülich

More documents

Recommendations

Info

J-NSE 3 1 Introduction Aim of the experiment is to study the dynamics of a polymer chain in solution with <strong>Neutron</strong> Spin Echo spectroscopy (NSE), the technique which offers the highest energy resolution in neutron scattering. The technique is well suited for soft matter systems where the molecules or nanoscopic structures like membranes or micelles exhibit fluctuating Brownian motions, driven by the thermal energy. NSE is able to analyze these fluctuations on the nanosecond and nanometer time- and lengthscale. In this neutron course experiment PEP (poly(ethylene propylene)) with a molecular weight of 70 kg/mol is dissolved in deuterated decane with a concentration of 3 %. The dynamics of the polymer in solution will be studied here at room temperature. The results will be interpreted in terms of the Zimm model which allows to draw conclusions about the internal motions of the polymer chains. 2 <strong>Neutron</strong> Spin Echo Spectroscopy The neutron spin echo technique uses the neutron spin as an indicator of the individual velocity change the neutron suffered when scattered by the sample. Due to this trick the instrument accepts a broad wavelength band and at the same time is sensitive to velocity changes down to 10−5 . However the information carried by the spins can only be retrieved modulo an integer number of spin precessions as intensity modulation proportional to the cosine of a precession angle difference. The measured signal is the cosine transform I(Q, t) of the scattering function S(Q, ω). All spin manipulations only serve to establish this special type of velocity analysis. For details see Reference [1]. Due to the intrinsic Fourier transform property of the NSE instrument it is especially suited for the investigation of relaxation-type motions that contribute at least several percent to the entire scattering intensity at the momentum transfer of interest. In those cases the Fourier transform property yields the desired relaxation function directly without numerical transformation and tedious resolution deconvolution. The resolution of the NSE may be corrected by a simple division. For a given wavelength the Fourier time range is limited to short times (about 3 ps for the FRM II-setup) by the lower limit of the field integral and to long times by the maximum achievable field integral J = � Bdl. The lower limit results from the lowest field values that are needed as “guide” field in order to prevent neutrons from depolarization effects. The upper limit results either from the maximum field that can be produced by the main solenoid, powersupply and cooling combination or by the maximum field integral inhomogeniety (→ variation of precession angle between different paths within the neutron beam) that can be tolerated respectively corrected for, depending which condition applies first. The Fourier time is proportional to J ·λ3 . The J-NSE may achieve a J =0.5Tm corresponding to t =48nsatλ =8 ˚A. The instrument itself (see Figure 1) consists mainly of two large water-cooled copper solenoids that generate the precession field. The precession tracks are limited by the π/2-flippers in front of the entrance respectively exit of the first and second main solenoids and the π-flipper near the sample position. The embedding fields for the flippers are generated by Helmholtz-type coil
4 O. Holderer, M. Zamponi and M. Monkenbusch pairs around the flipper locations. After leaving the last flipper the neutrons enter an analyzer containing 60 (30 x 30 cm 2 ) magnetized CoTi supermirrors located in a solenoid set. These mirrors reflect only neutrons of one spin direction into the multidetector. By the addition of compensating loops the main coils and the analyzer coil are designed such that the mutual influence of the different spectrometer components is minimized. Fig. 1: Working principle of the NSE spectrometer [2]. Depending on its velocity, each neutron undergoes a number of precessions in the first solenoid before hitting the sample. The second solenoid after the scattering process rewinds exactly these precessions for elastically scattered neutrons, whereas inelastically scattered neutrons collect a different phase angle of rotation, ΔΨ � Δv/v 2 γJ, with γ =2π ×2913.06598×10 −4 s −1 T −1 . The distribution of velocity changes Δv of the neutrons suffer during scattering at the sample –in terms of it’s cos-Fourier transform– ismeasured as polarization of the neutron beam at the end of the second solenoid after the last π/2-flipper. The small velocity changes are proportional to the small energy changes �ω, ω being the frequency of the Fourier transform. The time parameter (Fourier time) is proportional to λ 3 J and here in first instance is controlled by the current setting of the main coils (i.e. J). The polarization then is determined by scanning the magnetic field in one of the main coils slightly with the so called phase coil. If first and second arm are symmetric, a maximum of the polarization is measured, if the phase of the spins is shifted by 180 degree by variation of the field of one coil, one gets to a minimum of intensity. With a 360 degree variation one gets to the next maximum and so on. These oscillations are shown in Figure 2. The amplitude of this echo is normalized to the difference between maximum intensity (up-value), where all flippers are switched off, and the minimum intensity where only the π-flipper is switched on (down-value). Assuming that this normalization accounts for all imperfections of the polarization analysis in the instrument, the result yields the desired degree of polarization reduction due to inelastic/quasielastic scattering of the sample. Since the thus determined polarization reduction also contains the effects due to field integral inhomogeniety a further renormalization step is needed, which is equivalent to a resolution deconvolution in a spectroscopic instrument as e.g. the backscattering spectrometer. In order to be able to perform this resolution correction the same experimental and data treatment procedure has to be carried out with an elastic scatterer.
Page 1 and 2:
Member of the Helmholtz Association
Page 4 and 5:
Forschungszentrum Jülich GmbH Jül
Page 6:
�� 1 PUMA
Page 9 and 10:
2 O. Sobolev, A. Teichert, N. Jünk
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
10 O. Sobolev, A. Teichert, N. Jün
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
2 POWDER DIFFRACTOMETER SPODI Conte
Page 25 and 26:
4 POWDER DIFFRACTOMETER SPODI 2. Ba
Page 27 and 28:
6 POWDER DIFFRACTOMETER SPODI Ewald
Page 29 and 30:
8 POWDER DIFFRACTOMETER SPODI Powde
Page 31 and 32:
10 POWDER DIFFRACTOMETER SPODI Rela
Page 33 and 34:
12 POWDER DIFFRACTOMETER SPODI Prof
Page 35 and 36:
14 POWDER DIFFRACTOMETER SPODI neut
Page 37 and 38:
16 POWDER DIFFRACTOMETER SPODI The
Page 39 and 40:
18 POWDER DIFFRACTOMETER SPODI 4 U
Page 41 and 42:
20 POWDER DIFFRACTOMETER SPODI 7. E
Page 43 and 44:
22 POWDER DIFFRACTOMETER SPODI Figu
Page 45 and 46:
24 POWDER DIFFRACTOMETER SPODI Cont
Page 47 and 48:
2 M. Meven Contents 1 Introduction
Page 49 and 50:
4 M. Meven a (hkl) Plane. Each plan
Page 51 and 52:
6 M. Meven wavelengths � in the s
Page 53 and 54:
8 M. Meven intensities (I~Z 2 ) tha
Page 55 and 56: 10 M. Meven This has to be taken in
Page 57 and 58: 12 M. Meven 4 Sample Section 4.1 In
Page 59 and 60: 14 M. Meven Fig. 8 (a) orthorhombic
Page 61 and 62: 16 M. Meven 4.3 Oxygen Position The
Page 63 and 64: 18 M. Meven To direct the secondary
Page 65 and 66: 20 M. Meven For a given spectrum
Page 67 and 68: 22 M. Meven References [1] Th. Hahn
Page 69 and 70: 24 M. Meven
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
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:
Page 105: 2 O. Holderer, M. Zamponi and M. Mo
Page 109 and 110: 6 O. Holderer, M. Zamponi and M. Mo
Page 111 and 112: 8 O. Holderer, M. Zamponi and M. Mo
Page 113 and 114: 10 O. Holderer, M. Zamponi and M. M
Page 119 and 120: 2 H. Frielinghaus, M.-S. Appavou Co
Page 121 and 122: 4 H. Frielinghaus, M.-S. Appavou Th
Page 123 and 124: 6 H. Frielinghaus, M.-S. Appavou Fi
Page 125 and 126: 8 H. Frielinghaus, M.-S. Appavou mo
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
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
Page 150: RESEDA 13 Contact ��
Page 153 and 154: 2 S. Mattauch and U. Rücker Conten
Page 155 and 156: 4 S. Mattauch and U. Rücker Fig. 2
Page 157 and 158:
6 S. Mattauch and U. Rücker 4 Expe
Page 159 and 160:
8 S. Mattauch and U. Rücker Contac
Page 161 and 162:
2 H. Morhenn, S. Busch, G. Simeoni
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 178 and 179:
Schriften des Forschungszentrums J
Page 180 and 181:
Page 182 and 183:
show all

Neutron Scattering - JUWEL - Forschungszentrum Jülich

Create successful ePaper yourself

Delete template?

Save as template?