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Optical effects on neutron guide tubes produced by collimation
Author(s) -
Margaça F. M. A.,
Falcão A. N.,
Sequeira A. D.,
Salgado J. F.
Publication year - 1991
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/s0021889890012158
Subject(s) - collimated light , optics , diaphragm (acoustics) , tube (container) , neutron , physics , collimator , detector , penumbra , beam (structure) , nuclear physics , materials science , acoustics , medicine , laser , ischemia , loudspeaker , cardiology , composite material
The collimation of a neutron beam carried by a guide tube is shown to produce extensive regions of umbra and penumbra on the inner walls of the guide tube whenever a diaphragm is used at the exit. The region of umbra renders useless a certain length of the guide‐tube end while in the region of penumbra the guide exhibits a faint luminosity. These optical effects are particularly important for stringent collimation. It is shown that these effects render impossible the implementation of the `equal‐flight‐paths' design currently used for small‐angle neutron scattering instruments, which use guide segments and a diaphragm in the collimation assembly. As a consequence, these operate most of the time in strongly unmatched configurations. It is shown that the optimized design formerly proposed by the authors, in which, whenever possible, the full luminous source area is used, not only avoids the optical effects mentioned but also guarantees the highest detector count rate.