Multichannel collimation for SANS instruments

A contribution to the practical implementation of a variable-geometry converging multichannel collimator for SANS

“…The advantages of the converging multichannel collimator (CMC) in small-angle neutron scattering (SANS) have been reported by several authors (Nunes, 1974;Carpenter & Faber, 1978;Margac Ëa et al, 2000;Falca Ä o et al, 2002). The essential idea is to split the incoming beam using a number of elementary channels so that actual source and sample are divided into an equal number of independent elementary data-generating channels of smaller cross section.…”

“…If the elementary channels have the same geometry, the instrument resolution will be essentially that of a single channel whereas the detector count rate will be the channel count rate multiplied by the number of channels. A SANS instrument equipped with a CMC with N identical channels is equivalent to N SANS instruments sharing a common detector and offers considerable count-rate gains when compared with the single-channel arrangement using the same source and with equal resolution (Margac Ëa et al, 2000).…”

Guidelines for the implementation ofXYvariable-geometry converging multichannel collimation in a specific SANS facility

“…The principle of converging multichannel collimation applied to a SANS arrangement has been shown to present signi®cant advantages over the one-channel collimator arrangement as far as count rate at constant resolution and accessed Q range are concerned (Nunes, 1974;Ishikawa et al, 1986;Mildner & Carpenter, 1987;Margac Ëa et al, 2000). This requires that all the elementary channel walls converge at one and the same point on the detector plane.…”

Intensity and resolution effects in converging multichannel collimators for SANS by Monte Carlo simulation

“…The advantages of converging multichannel collimators (CMCs) in small-angle neutron scattering (SANS) were reported several years ago (Nunes, 1974;Carpenter & Faber, 1978;Mildner & Carpenter, 1984, 1987. The essential idea is to split the incoming beam using a number of elementary channels so that the actual source and sample are divided into an equal number of independent elementary data-generating channels of smaller size (Margac Ëa et al, 2000;Falca Ä o et al, 2000). The composite sample thus offers a larger area than that in the otherwise equivalent single-channel arrangement.…”

“…If the elementary channels have the same geometry, the instrument resolution will be that of a single channel, 1 whereas the detector count rate will be the channel count rate multiplied by the number of channels. A SANS instrument equipped with a CMC with N identical channels is equivalent to N SANS instruments sharing a common detector and offers considerable count-rate gains when compared with the single-channel arrangement using the same source and with equal resolution (Margac Ëa et al, 2000). In the above it is assumed that the sample scattering function does not change signi®cantly over the angular range of the¯ight directions of the neutrons passing through the CMC and impinging on the sample.…”