PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

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The refractive index, n = (1–Nb c 2 /) ½ of Si for thermal neutrons equals unity to within about 1 part in 10 6 . This proposal can thus determine the refractive power, n–1±10 -6 , with a relative precision of a few parts in 10 6 , and hence the refractive index to a phenomenal precision of a few parts in 10 12 [156-157]. The refraction corrections of –2.7 * 10 -5 and –1.01x10 -5 fm to b c for {111} and {220} IFM reflections respectively, due to refraction at air-sample interfaces is of the same order as the Ioffe et al.’s experimentally determined b c precision of 5 parts in 10 5 . Therefore after refraction corrections, b c values in Ioffe’s measurement should be modified to 4.15101(21) and 4.15038 (21) instead of inferred 4.15102(21) and 4.15041(21) values corresponding to IFM reflections {220} with λ= 1.98 Å and {111} with λ= 2.7 Å, respectively. 5.1.2 Dual nondispersive phase shifter The dual nondispersive phase shifter comprising two identical and parallel phase shifters placed on one path, one before and the other after the mirror blade [Fig.55], in the nondispersive configuration has been recently proposed by Lemmel and Wagh [128]. The effective thickness of the phase shifter gets doubled which results in doubling of the neutron phase (D) and halving Ф/. The phase shift I( ) II ( ) , which now can be obtained in a single measurement with this dual phase shifter placed on a single beam path, is exactly nondispersive. Furthermore, the temporal as well as spatial displacements of the wave packet effected by the dual sample in the first gap get cancelled in the second, restoring full interference contrast. A long monolithic sample with a groove cut in the middle (Fig.56) to accommodate the mirror plate attains the exact parallelity and the identical thicknesses for its two segments. Both of these segments are mechanically and thermally coupled. The large nondispersive phase shift can be measured even 102
Fig.55 The experimental setup (schematic) employing a large symmetric LLL IFM with dual sample placed in subbeam II. 103
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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
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 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 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
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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