PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

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an overall compression factor of 14.78 for each peak. Each of these I H (θ H ) peaks drops to zero intensity at |y|=1 incidence due to the onset of total reflectivity regime and tails towards the other peak. The tails can be clipped by cutting the side face of the prism parallel to the I H beam direction, beyond a preset depth (cf. Fig.26). Neutrons incident at large |y| and propagating at large enough angles Δ reach this specially cut part of the side face, with an effective apex angle A'=θ B +θ S , which forbids them from exiting into the I H beam. This side-face cut approach proposed in [138], has been employed extensively over the past two decades by experimenters in Vienna, Berlin, Mumbai and ILL (cf., [111-112]) to attain Bonse-Hart angular profiles free of I H beam contamination. Each I H (θ H ) peak thus drops to zero intensity for incidence beyond ±y C , say, as well. The critical incidence angles -y C , y C and the corresponding exit angles θ H1 and θ H2 beyond which the I H peak becomes zero are geometrically determined by the distance of closest neutron incidence from the apex. By locating the incident beam optimally between 9 and 32 mm from the prism apex and applying the special cut to the side face beyond a depth of 5 mm from the incidence face, we attain θ H1 θ H | y= –1. The net peak made up of a smaller peak pair of 0.26 arcsec FWHM each (Fig.32) dropping to zero intensity on either side is hence contained completely within the full width at bottom equal to (θ H | y=1 – θ H | y= –1). The configuration has been optimised to make these two peaks add to a tail-free and nearly flat-topped single peak of 0.53 arcsec FWHM (Fig.33) dropping to zero intensity at angular deviations from the centre greater than 0.43 arcsec on either side. Similarly, a Bragg prism analyser configuration of opposite asymmetry with the optimum angles A=16 o and θ S =−51 o , the θ B +θ S cut made at depths beyond 8.3 mm and beam incidence between 34 and 67 mm from the prism apex, is expected to accept two 0.22 arcsec wide neutron peaks separated by 2.13 arcsec (Fig.34). The convolution of the monochromator peak with this analyser acceptance curve, constituting a pair of peaks with an FWHM of 0.57 arcsec each, separated by 70
2.35 arcsec, is also displayed in Fig.34. Fig.35 depicts our SUSANS experimental setup incorporating this optimised Bragg prism monochromator-analyser pair [146-149]. Fig.35 SUSANS experimental arrangement of the optimised monochromator-analyser pair of Si {111} Bragg prisms. A translation of the monochromator chooses between its Bragg reflection and prism diffraction to illuminate the analyser. Cd sheet downstream of the analyser can be translated to allow or forbid the analyser Bragg reflection into the detector (not shown). 71
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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
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 74 and 75: Fig.20 Bragg reflection intensity f
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 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 138 and 139: Fig.69 New metrological mapping of
Page 140 and 141: 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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