Smearing effects introduced by the response function of position-sensitive gas detectors in SAXS experiments

The response of gas-filled position-sensitive detectors consists not only of the main Gaussian response (FWHM similar to 0.1 mm) but also of a linear exponential term measurable up to 7 mm from the excitation, superimposed on an incoherent background. This effect depends on gas type and pressure and is due to fluorescence of the detection gas. The consequences of this effect on some standard experimental methods used in small-angle X-ray scattering (SAXS), i.e. Porod limit and Guinier radii determination, are investigated.