PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

CHAPTER 6
Conclusion and Future directions
The objective of this Chapter is to summarize the main findings of this thesis and to shed some
light on the future directions for the research work presented in Chapters 3, 4 and 5.
I. Neutron forward diffraction by Bragg prisms
In Chapter 3, we enunciated the theory of neutron forward diffraction by Bragg prisms and derived
analytic expressions for the intensity fraction and deflection of the forward diffracted neutron beam
within the framework of dynamical diffraction theory. In the vicinity of a Bragg reflection, the
neutron deflection deviates sharply from that for an amorphous prism reaching opposite extrema at
either end of the total reflectivity domain and exhibits several orders of magnitude greater
sensitivity to the incidence angle variation. Using a 2 arcsec wide 5.24 Å neutron beam from a 7-
bounce Bonse-Hart monochromator-analyser setup, we observed the variations of the deflection
and transmission of the neutron beam across a Bragg reflection, for several Bragg Si prisms. The
observed Bragg prism deflections deviate from amorphous prism deflections by up to 27% and
deflection sensitivities up to 0.43 arcsec per arcsec variation in the incidence angle are observed,
thus realising 3 orders of magnitude greater deflection sensitivity to the incidence angle variation
than that obtainable with amorphous prisms. The results agree well with the predictions of
dynamical diffraction theory.
The smooth deflection tuning ability and the several orders of magnitude higher sensitivity are the
key advantages of Bragg prisms over conventional prisms. These prisms can also be employed in
succession to achieve a larger deflection sensitivity, albeit with a concomitant intensity loss. The
theoretical prediction of a sign change of the deflection (Fig.16) on the low θ-side by a suitably
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