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Improving X-ray absorption correction and absolute scaling in SAXS and SWAXS measurements
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.
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.