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The spatial condensation of the neutron beam by an asymmetric diffraction in thermal‐neutron monochromatization
Author(s) -
Mikula P.,
Kulda J.,
Horalík L.,
Chalupa B.,
Lukáš P.
Publication year - 1986
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889886089288
Subject(s) - monochromator , bent molecular geometry , optics , neutron , monocrystalline silicon , beam (structure) , crystal (programming language) , radius , neutron diffraction , diffraction , condensation , neutron flux , mosaicity , perfect crystal , neutron radiation , materials science , schlieren , monochromatic color , physics , silicon , nuclear physics , x ray crystallography , optoelectronics , wavelength , computer security , computer science , composite material , thermodynamics , programming language
A thermal‐neutron monochromator based on an elastically bent perfect silicon crystal in a strongly asymmetric diffraction geometry used for the spatial condensation of the output neutrons is presented and discussed. Its effective `mosaic spread' δ h θ can be easily controlled by a simple choice of the bending radius and the length of the irradiated part of the crystal plate. A theoretical analysis shows that a gain in the flux density of monochromatic neutrons in the fully asymmetric case in comparison with the symmetric one is equal to the ratio of the width of the incident polychromatic beam and the thickness of the crystal. The experimental integrated reflectivity and focusing obtained are found to be in good agreement with theoretical predictions. The asymmetric arrangement of the bent crystal seems to be suitable for use at a source with a large incident‐beam cross section when δ h θ may achieve a value of about 10 −2 rad and an effective neutron flux at the sample position may achieve the fluxes obtained by the best mosaic monochromator.