PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

Fig.10 Boundary conditions on wave vectors dictate the allowed wave vectors at
incidence and exit faces of an amorphous prism in reciprocal space. 38
Fig.11 Calculated variation of δ am with incidence angle for A=90 o and n=1-10 -5 , exhibits
a minimum when both the incidence and exit angles equal. 39
Fig.12 Bragg diffraction of a neutron beam from a thick single crystal in real space. 40
Fig.13 Bragg diffraction of a neutron beam in reciprocal space. At each incidence angle,
continuity of tangential components of wave vectors across the incidence and exit
faces of the prism yields unique tie points as well as internal and emergent wave
vectors (see text). 41
Fig.14 Variation of the diffracted (I D ) and transmitted (I O ) beam intensities with the angle
of incidence for different apex angles A. 43
Fig.15 Calculated δ cr and I O for a symmetric Bragg prism. 46
Fig.16 Calculated δ cr and I O for an asymmetric Bragg prism. 46
Fig.17 Calculated
b
δ
cr
and
b
I
cr
for an asymmetric Bragg prism. 48
Fig.18 Experimental layout to measure neutron deflection and transmission by a Bragg
prism. The set up employs 7X7 reflections each in the monochromator and
analyser channel-cut crystals of a 5.24 Å neutron beam with a silicon prism
suspended in each crystal between 3 rd and 4 th reflections and sample (Bragg prism)
was placed between the monochromator and analyser. 50
Fig.19 Bragg reflection intensity fraction as a function of prism rotation for the
symmetric Bragg {111} prism reflection with apex angles A of (a) 56.7 o and (b)
90 o , respectively. 51
Fig.20 Bragg reflection intensity fraction as a function of prism rotation for the