Abstract
Small-angle neutron scattering (SANS) measurements from thin sections of rock samples such as shales demand as great a scattering vector range as possible because the pores cover a wide range of sizes. The limitation of the scattering vector range for pinhole SANS requires slit-smeared ultra-SANS (USANS) measurements that need to be converted to pinhole geometry. The desmearing algorithm is only successful for azimuthally symmetric data. Scattering from samples cut parallel to the plane of bedding is symmetric, exhibiting circular contours on a two-dimensional detector. Samples cut perpendicular to the bedding show elliptically dependent contours with the long axis corresponding to the normal to the bedding plane. A method is given for converting such asymmetric data collected on a double-crystal diffractometer for concatenation with the usual pinhole-geometry SANS data. The aspect ratio from the SANS data is used to modify the slit-smeared USANS data to produce quasi-symmetric contours. Rotation of the sample about the incident beam may result in symmetric data but cannot extract the same information as obtained from pinhole geometry.
Highlights
The typical range of scattering vectors measured on a pinhole small-angle neutron scattering (SANS) instrument is 10À3 < Q < 0.5 A À1, suitable for measuring correlations and dimensions in the range 10–1000 A
Ultra-small-angle neutron scattering (USANS) using a double-perfect-crystal diffractometer can measure in the scattering vector range of 10À5 < Q < 10À3 A À1 and examine dimensions in the range 0.1–10 mm (Agamalian et al, 1997; Barker et al, 2005)
This instrumental arrangement is different in concept from pinhole SANS in that it measures with high resolution in one direction only, while having a much broader angular acceptance in the
Summary
The typical range of scattering vectors measured on a pinhole small-angle neutron scattering (SANS) instrument is 10À3 < Q < 0.5 A À1, suitable for measuring correlations and dimensions in the range 10–1000 A. Ultra-small-angle neutron scattering (USANS) using a double-perfect-crystal diffractometer can measure in the scattering vector range of 10À5 < Q < 10À3 A À1 and examine dimensions in the range 0.1–10 mm (Agamalian et al, 1997; Barker et al, 2005). This instrumental arrangement is different in concept from pinhole SANS in that it measures with high resolution in one direction only, while having a much broader angular acceptance in the. The desmeared USANS intensity from systems that scatter with azimuthal symmetry may conveniently be concatenated with the azimuthally averaged data obtained from the accompanying SANS measurement. We investigate the information that might be gleaned from USANS data collected from such anisotropic systems by taking measurements from rock samples in different orientations
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