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Bragg Reflection in Mosaic Crystals. II. Neutron Monochromator Properties

Bragg Reflection in Mosaic Crystals. II. Neutron Monochromator Properties In the preceding article, the general solution of the Darwin equations has been obtained for a mosaic crystal slab for both the Laue case (transmission geometry) and the Bragg case (refection geometry). This now allows the calculation, for the first time, of the reflectivity of an absorbing crystal of finite thickness in situations where the Bragg planes make an arbitrary angle with the surface of the crystal. In this paper, these results are applied to a numerical calculation of the reflecting properties of a number of commonly used neutron monochromator crystals. The incident-neutron flux is taken to be Maxwellian with an epithermal tail and it is investigated how the various properties depend on the neutron wavelength, the crystal thickness, the mosaic spread and the angle that the Bragg planes make with the surface of the crystal. It is found, for example, that for asymmetrical reflections gains in flux of 25 to 50% or more can easily be achieved for a wide range of wavelengths in crystals with the kinds of thickness and mosaic spread that are available in practice. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Crystallographica Section A: Foundations of Crystallography International Union of Crystallography

Bragg Reflection in Mosaic Crystals. II. Neutron Monochromator Properties

Bragg Reflection in Mosaic Crystals. II. Neutron Monochromator Properties


Abstract

In the preceding article, the general solution of the Darwin equations has been obtained for a mosaic crystal slab for both the Laue case (transmission geometry) and the Bragg case (refection geometry). This now allows the calculation, for the first time, of the reflectivity of an absorbing crystal of finite thickness in situations where the Bragg planes make an arbitrary angle with the surface of the crystal. In this paper, these results are applied to a numerical calculation of the reflecting properties of a number of commonly used neutron monochromator crystals. The incident-neutron flux is taken to be Maxwellian with an epithermal tail and it is investigated how the various properties depend on the neutron wavelength, the crystal thickness, the mosaic spread and the angle that the Bragg planes make with the surface of the crystal. It is found, for example, that for asymmetrical reflections gains in flux of 25 to 50% or more can easily be achieved for a wide range of wavelengths in crystals with the kinds of thickness and mosaic spread that are available in practice.

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Publisher
International Union of Crystallography
Copyright
Copyright (c) 1997 International Union of Crystallography
ISSN
0108-7673
eISSN
1600-5724
DOI
10.1107/S0108767397099984
Publisher site
See Article on Publisher Site

Abstract

In the preceding article, the general solution of the Darwin equations has been obtained for a mosaic crystal slab for both the Laue case (transmission geometry) and the Bragg case (refection geometry). This now allows the calculation, for the first time, of the reflectivity of an absorbing crystal of finite thickness in situations where the Bragg planes make an arbitrary angle with the surface of the crystal. In this paper, these results are applied to a numerical calculation of the reflecting properties of a number of commonly used neutron monochromator crystals. The incident-neutron flux is taken to be Maxwellian with an epithermal tail and it is investigated how the various properties depend on the neutron wavelength, the crystal thickness, the mosaic spread and the angle that the Bragg planes make with the surface of the crystal. It is found, for example, that for asymmetrical reflections gains in flux of 25 to 50% or more can easily be achieved for a wide range of wavelengths in crystals with the kinds of thickness and mosaic spread that are available in practice.

Journal

Acta Crystallographica Section A: Foundations of CrystallographyInternational Union of Crystallography

Published: Jan 1, 1997

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