Dear GSAS II developers ans users!

I'm using GSAS II for XRD analysis, thanks to Vadim Volochaev's warm advice. I found that it is indeed incredibly powerful and very flexible software. Thanks for the developing with open source!

Now I'm interested in the fitting of Anomalous Small-Angle X-ray Scattering (ASAXS) data of core-shell bimetallic particles, somewhat repeating the paper Haug2009 (doi:10.1088/0957-4484/20/50/505705). How do you think, is it possible to perform this task in GSAS with minor changes in codebase?

The general small-angle study is already implemented and we have integrated several 2D images in SASD curves of the same sample for different photon energies. In general: can I just use sequential fit over these patterns?
In more detail some questions appeared:
1) Does (anomalous) atomic factors are calculated independently for each dataset? I have a doubts, since "Anomalous density" shown in SASD > Substances window seems not to depend on the wavelength (energy). 2) Building of core-shell (spherical) model. As I understand, this requires two fit models: spheres of first substance (core) and spherical shells of the second substance. The addition of form-factors and volumes calculation for spherical shell seems to be pretty straightforward and I have put them in GSAS code by adding functions with simple subtraction of spherical FF/vol functions with different radii. 3) Finally, the model should be the same for all SASD curves, with changes in data described only by f' and f'' energy dependence. As I can see, it is impossible to add constraints of equivalence between SASD fitting parameters like it can be done in XRD analysis, is it? It is hard for me to estimate the amount of work to implement the SASD constraints, is it planned or too complex for current codebase state?

Thank you in advance,
Best wishes,

Dr. Leon Avakyan
Ass.Prof. Physics Faculty,
Southern Federal University,

Leon Avakyan

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