PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

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Fig.69 New metrological mapping of the Si dual sample. IFM and the sample position for path I and II was set at the centre of the intensity plateau obtained for the respective path. During the first week of the experiment, it was difficult to obtain interferograms with good and stable contrasts, due to a vacuum pump inadvertently placed over the IFM cabin roof by the reactor operational staff members. On isolating its vibrations from the cabin, 116
we were able to achieve empty IFM contrasts up to about 75 %. On placing the sample in path I or II, the intensity dropped only by about 5% (Fig.65) and the interference contrast remained essentially unaltered over a majority of scans (Fig.66). We note that the actual neutron path length of 58.5 mm within the Si dual sample though very large, still yielded a very good contrast underscoring the importance of measurements in nondispersive sample configuration. Further, small intensity decrease in measurements made with the sample IN positions compared to sample OUT scans is due to the incoherent scattering and absorption of neutrons within sample. The phases extracted from interferograms acquired at several rotations ε and tilts γ of the sample in path I and II were fitted to parabolic curves (Fig.67). The sample was then set to the correct orientation (ε 0 , γ 0 ) where the phase magnitude exhibited a minimum. A large number of successive sample-in and -out interferometric scan pairs were then made alternately for path I and II. A typical interferogram for this set of measurements is shown in Fig.68. The regulated air flow within the temperature-controlled aluminium enclosure yielded good interference contrasts, but also reduced the relative air humidity to between 5 and 10% which, in turn, led to a large variation in the measured phases. The frequency of interference oscillations remained fairly constant throughout the measurements. To arrive at the correct phase, we carefully analysed the temperature and humidity data. We observed that the measured phases on either path remained closely constant when thermal gradients in the IFM vicinity were low and the relative humidity inside the IFM cabin ranged between 35 and 40%. From 95 such interferograms for paths I and II and using the previous measurements of b c for Si [127], we deduced phases of – 455 X 360 – 54.811 0.154 deg and + 455 X 360 – 256.49 0.117 deg for paths I and II respectively so that Φ I-II = – 455 X 720 + 201.679 0.193 deg. After considering a 1μm uncertainty in the sample thickness of 35.96 mm (Fig.69), thermal expansion of 117
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Studying neutron dynamical diffract
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DECLARATION I, hereby declare that
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ACKNOWLEDGEMENTS I sincerely, thank
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Fig.10 Boundary conditions on wave
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Fig.28 Theoretical curves for Si {1
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sample. Least-squares fit to the sa
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Fig.62 Interference contrast and av
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3.4 Experimental 49 3.5 Results and
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SYNOPSIS The present thesis aims to
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analytic expressions for intensity
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Research A, 634 (2011) S41. [9] S.
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spallation sources yield peak neutr
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SU(2) phase, and separation of geom
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[33-34,48]. The bi-refracting natur
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application of the dynamical theory
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I. One of the major disadvantages o
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nuclear physics very important as i
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potential for most nuclei in spite
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Due to the rapid strides made latel
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for a positive value of b c i.e. fo
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k b k O H . ni sin( B S) . (18)
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factor exp(-W). The centre, θ C ,
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exploiting multiple successive iden
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We shall confine our discussion hen
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The depth Z is measured from the in
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wings (large-y regions). The freque
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expressed as T(y, t )R(y, t )R(
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studies. With such beams, the and
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CHAPTER 3 Neutron forward diffracti
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eing the separation of points M and
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3.1 Neutron forward diffraction Con
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excited by the incident wave (Fig.1
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Therefore, the forward diffracted i
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Fig.15 Calculated cr and I O for a
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(1 I ) D tan b . ID cot( B S)
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Fig.18 Experimental layout to measu
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Fig.20 Bragg reflection intensity f
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fraction I O through the Bragg pris
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Fig.22 Experimental (points) and th
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Table 2: Observed deflection sensit
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total reflectivity domain. These ar
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Here the term C() accounts for the
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Fig.28 Theoretical curves for Si {1
Page 88 and 89: I H (θ H ) peaks of 0.18 height an
Page 90 and 91: other with a compression factor lim
Page 92 and 93: an overall compression factor of 14
Page 94 and 95: 4.3 Experimental 4.3.1 Bragg prism
Page 96 and 97: 4.3.2 Experiment The experiment was
Page 98 and 99: Fig.38 Bragg reflection rocking cur
Page 100 and 101: 4.4 Applications of novel SUSANS se
Page 102 and 103: Fig.42 First Q ~ 10 -6 Å -1 SUSANS
Page 104 and 105: 2 (1) -(δk i .Δ i ) /2 Γ (Δ) =
Page 106 and 107: 2 I( ) A( ) . (76) The least squa
Page 108 and 109: Fig.46 Analyser rocking curve for a
Page 110 and 111: This instrument was also employed t
Page 112 and 113: Fig.48 Theoretical flat-topped angu
Page 114 and 115: difference between the two neutron
Page 116 and 117: Fig.52 Phase dispersion in a 26.5 m
Page 118 and 119: the beam and remains visible up to
Page 120 and 121: cos bc 4NDd1 1 2cot 2 III 2 2
Page 122 and 123: yield about an order of magnitude r
Page 124 and 125: The refractive index, n = (1-Nb c
Page 126 and 127: with a white, and hence high-intens
Page 128 and 129: proposed dual sample. The dual samp
Page 130 and 131: The experiment was performed with =
Page 132 and 133: Fig.59 Typical interferograms for p
Page 134 and 135: Fig.63 Path I, II and I-II phases d
Page 136 and 137: Fig.65 Average intensity with the s
Page 140 and 141: Si at 26.2 o C, applying a correcti
Page 142 and 143: selected asymmetric Bragg prism may
Page 144 and 145: III. High precision determination o
Page 146 and 147: REFERENCES [1] H. Rauch and S. Wern
Page 148 and 149: [36] J. S. Nico and W. M. Snow, Ann
Page 150 and 151: [67] V. F. Sears, Can. J. Phys., 56
Page 152 and 153: [97] A. Cabello, S. Filipp, H. Rauc
Page 154 and 155: [127] A. Ioffe, D. L. Jacobson, M.
Page 156: 2009, (Grenoble, France, 2010) 3-15
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PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

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