13  SasView/sasmodels form factors: small-angle scattering

This chapter documents the sasmodels category: a large set of small-angle scattering (SANS/USANS) form-factor models, generated automatically from the open-source SasView/sasmodels project (https://github.com/SasView/sasmodels) and exposed to McStas as individual SasView_* components (each wrapping one sasmodels kernel; they supersede the older, generic SasView_model component, which is now in the obsolete category). This gives access to the same, actively maintained library of scattering-law implementations used for SANS data fitting in SasView itself, directly as McStas sample components, without needing to hand-implement each form factor.

Most models exist in a plain (orientation-averaged, i.e. powder/isotropic) form and, where the shape has a well-defined orientation, an _aniso variant that additionally accepts orientation parameters. For the underlying physics of any individual model (defining equation, parameter meaning, validity range), consult the corresponding page in the SasView documentation (https://www.sasview.org/docs/); the parameter tables below are generated directly from each component’s McDoc header and give the McStas-specific parameter names, units and defaults.

See also Templates/templateSasView and Templates/Test_SasView_guinier in the example instrument library for worked examples, and the samples/SANS_* and contrib/SANS* components (documented in the Samples chapter) for McStas’s own, native (non-SasView-derived) SANS sample models.