Calculation of the optimal specimen thickness for small-angle X-ray experiments with the use of polychromatic synchrotron radiation

An evaluation method of the optimal specimen thickness for small-angle X-ray experiments using polychromatic synchrotron radiation (SR) is put forward. Curves of the dependence of the optimal specimen thickness on various SR-spectra with a one-dimensional detector and Si(Li) SSD are calculated. The curves allow one to optimize an experiment by selecting either the optimal specimen thickness for an available SR-spectrum or the short-wave spectrum limit for a given specimen thickness (fibers, tissues, etc.). Besides increasing both precision and reproducibility of the X-ray experiments, the method gives the possibility either to increase the statistical precision within a given recording time of an X-ray pattern and/or to decrease the recording time with retention of the same statistical precision. It is shown that a deviation of 15–20% in the specimen thickness from the optimal thickness leads to a decrease in the scattering intensity of less than 2%.