PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

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Table 2: Observed deflection sensitivities, corresponding transmissions and percentage variations in the deflections for various Bragg prisms from their respective amorphous prisms. Bragg Prisms Sensitivity |d cr /dθ| Transmission I O 100·(| cr – am |/ | am |) max. (arcsec/arcsec) (%) Sym. (θ S =0°) and A=56.7° Sym. (θ S =0°) and A=90° Asym. (θ S =35°) and A=94° Asym. (θ S =41°) and A=98° 0.16 0.78 27 0.22 0.47 29.5 0.43 0.96 27 0.23 0.88 19 The best results however, were observed with the asymmetric prism of θ S =35° and A=94°, exhibiting cr deviation from am by upto 27% with sensitivities |d cr /dθ| upto 0.43 arcsec/arcsec corresponding to a transmission of 0.96. These observed sensitivities |d cr /dθ| are several orders of magnitude greater than those obtainable with amorphous prisms [139-145]. Encouraged by this experimental verification of predictions of the dynamical diffraction theory, we designed, fabricated and successfully operated a super-collimator monochromator delivering a Bragg prism diffracted (I H ) neutron beam of sub-arcsec angular width described in Chapter 4. 58
CHAPTER 4 First sub-arcsec collimation of a monochromatic neutron beam 4.0 Introduction I present in this chapter, a novel device producing a tail-free plane-wave-like neutron beam of subarcsec angular width. Neutrons incident on a single crystal prism in an asymmetric Bragg configuration undergo, in addition to the Bragg reflection, diffraction at the exit face [138] of the prism. Two small diffraction peaks I H , one on either side of the Bragg reflection, appear outside the Fig.26 Asymmetric Bragg prism diffraction (schematic). Outside the total reflectivity domain, unreflected neutrons traverse the prism at an angle Δ to the incidence surface and exit the side face in diffracted (I H ) and forward diffracted (I O ) beams. At large enough angles Δ, neutrons reach the part of the side face cut along the diffracted beam direction and exit wholly into the I O beam, thus truncating I H on the larger-|y| side as well to yield a tail-free, sharp angular profile. 59
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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
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 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 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 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
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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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