PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

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Fig.20 Bragg reflection intensity fraction as a function of prism rotation for the asymmetric Bragg {111} prism reflection with asymmetry angles S and apex angles A being (a) 35° and 94° (b) 41° and 98°, respectively. 52
eference for the prism deflection measurement (Fig.18). Using an additional detector to record neutrons Bragg reflected from the prism, the few arcsec wide Bragg reflection of the prism was located and optimised by adjusting the prism tilt. The analyser rocking curves were recorded for several angles of incidence at the prism covering a span of about 40 arcsec centred at the total reflectivity domain. The direct and deflected neutron peaks were thus simultaneously recorded in each analyser scan. The Bragg reflection intensity of the prism was continuously monitored to confirm the stability of the prism orientation. The observed full width at half maximum (FWHM) of 6 arcsec for the Bragg reflection of the symmetric prism with apex angle A of 57° confirmed the absence of strains and defects in the prism (Fig.19a). However, the other symmetric prism (A = 90°) yielded a FWHM of 7.68 arcsec instead of 6 arcsec predicted by theory, indicating residual strain and a slight asymmetry ( S ≠ 0°) of the prism (Fig.19b). For the other two asymmetric Si {111} Bragg prisms with S of 35° and 41° and apex angles 94° and 98° respectively, the measured rocking curve FWHMS were 10.2 arcsec (Fig.20a) and 11.6 arcsec (Fig.20b) respectively in agreement with those expected for the corresponding asymmetry angles S of these prisms. The term ‘Convl Theory’ in Figs., signifies theoretical curves convoluted with 2 arcsec wide rectangular angular profile of the monochromated beam. 3.5 Results and Discussion The analyser rocking curve recorded at two typical incidence angles for a Bragg prism is displayed in Fig.21. Least-squares Voigt function fits (smooth curves) were made to the direct and deflected neutron peaks in the rocking curve. At each θ, the neutron deflection cr was determined from the angular shift between the fitted peaks for the direct and deflected beams. The area under the deflected peak corrected for the background was computed to infer the transmitted intensity 53
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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
Page 18 and 19:
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.
Page 24 and 25: spallation sources yield peak neutr
Page 26 and 27: SU(2) phase, and separation of geom
Page 28 and 29: [33-34,48]. The bi-refracting natur
Page 30 and 31: application of the dynamical theory
Page 32 and 33: I. One of the major disadvantages o
Page 34 and 35: nuclear physics very important as i
Page 36 and 37: potential for most nuclei in spite
Page 38 and 39: Due to the rapid strides made latel
Page 40 and 41: for a positive value of b c i.e. fo
Page 42 and 43: k b k O H . ni sin( B S) . (18)
Page 44 and 45: factor exp(-W). The centre, θ C ,
Page 46 and 47: exploiting multiple successive iden
Page 48 and 49: We shall confine our discussion hen
Page 50 and 51: The depth Z is measured from the in
Page 52 and 53: wings (large-y regions). The freque
Page 54 and 55: expressed as T(y, t )R(y, t )R(
Page 56 and 57: studies. With such beams, the and
Page 58 and 59: CHAPTER 3 Neutron forward diffracti
Page 60 and 61: eing the separation of points M and
Page 62 and 63: 3.1 Neutron forward diffraction Con
Page 64 and 65: excited by the incident wave (Fig.1
Page 66 and 67: Therefore, the forward diffracted i
Page 68 and 69: Fig.15 Calculated cr and I O for a
Page 70 and 71: (1 I ) D tan b . ID cot( B S)
Page 72 and 73: Fig.18 Experimental layout to measu
Page 76 and 77: fraction I O through the Bragg pris
Page 78 and 79: Fig.22 Experimental (points) and th
Page 80 and 81: Table 2: Observed deflection sensit
Page 82 and 83: total reflectivity domain. These ar
Page 84 and 85: Here the term C() accounts for the
Page 86 and 87: 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
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The refractive index, n = (1-Nb c
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with a white, and hence high-intens
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proposed dual sample. The dual samp
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The experiment was performed with =
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Fig.59 Typical interferograms for p
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Fig.63 Path I, II and I-II phases d
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Fig.65 Average intensity with the s
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Fig.69 New metrological mapping of
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Si at 26.2 o C, applying a correcti
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selected asymmetric Bragg prism may
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III. High precision determination o
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REFERENCES [1] H. Rauch and S. Wern
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[36] J. S. Nico and W. M. Snow, Ann
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[67] V. F. Sears, Can. J. Phys., 56
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[97] A. Cabello, S. Filipp, H. Rauc
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[127] A. Ioffe, D. L. Jacobson, M.
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2009, (Grenoble, France, 2010) 3-15
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PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

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