What is it about?
Accurate correction for X-ray absorption is essential for quantitative SAXS and SWAXS measurements, particularly when samples differ strongly in their X-ray attenuation. We developed a numerical angle-dependent correction for line-collimated measurements in cylindrical capillaries. The method accounts for the actual illuminated scattering volume, experimentally measured primary-beam profiles, and absorption in both the sample and the capillary wall. It provides calculated transmission factors that can be applied directly during data reduction when conventional experimentally measured scalar transmission factors become unreliable.
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Why is it important?
Incorrect absorption correction can propagate directly into background subtraction and absolute intensity scaling. In our measurements of strongly absorbing nonafluorotert-butanol, the conventional scalar primary-beam transmission correction produced non-physical negative intensities after empty-capillary subtraction, whereas the numerical correction enabled physically meaningful data reduction. Importantly, we also show that absorption-related bias is not restricted to such extreme samples: it can affect routine water-based absolute-scale calibration when the absorption of the water-filled and empty capillaries differs substantially.
Perspectives
This work originated from a practical data-reduction problem encountered in our laboratory: conventional transmission correction failed for a strongly absorbing fluorinated liquid. What initially appeared to be an isolated instrumental problem led us to examine the absorption correction more systematically. The resulting approach combines established path-length-based absorption modelling with experimentally measured beam profiles and the actual line-collimated geometry of our SWAXS instrument. Particularly interesting to us was the finding that the same issue can also introduce a measurable bias in the much more routine procedure of absolute scaling using water as a secondary standard.
Matija Tomšič
University of Ljubljana
Read the Original
This page is a summary of: Angle-dependent X-ray absorption correction in small- and wide-angle X-ray scattering: accounting for constrained scattering volume, beam profiles and capillary wall attenuation, Journal of Applied Crystallography, August 2026, International Union of Crystallography,
DOI: 10.1107/s1600576726006837.
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