Small-angle scattering data analysis in GSAS-II

The General Structure Analysis System II (GSAS-II) now contains modules for the analysis of small-angle X-ray scattering data. This includes processing of two-dimensional images to create corrected one-dimensional patterns, analysis via maximum entropy or total nonnegative least-squares methods of the size distribution, assuming polydispersity, in the dilute limit, and modeling of the one-dimensional data with combinations of Guinier/Porod, Porod, both dilute and condensed populations of scattering objects, and Bragg scattering components; slit smearing corrections can be applied where needed. GSAS-II can apply these modeling tools over a sequence of data collected while some experimental condition is varied. This sequential refinement result can then be subjected to a post refinement analysis to determine global parameters encompassing the entire experiment.