GRASansP deals with many of the diverse requirements for analysis and reduction of SANS data using a general set of tools and reduction algorithms. Data from the two ILL SANS instruments, D11 and D22, as well as SANS instruments at some other neutron sources, are currently catered for in the GRASansP package. In principle the architecture and coding of GRASansP combined with the matrix handling abilities, graphics and other advantages of the Matlab™ environment should allow continued development of this software and be able to provide more general aspects of multi-detector and complex data set handling. The drive for producing such a suite of software came from the overwhelming need for a modern, complete and general-purpose package to deal with typical procedures required for analysis of two-dimensional SANS multidetector data.
By it’s very nature, two-dimensional data is often best appreciated in a graphical form. The birth of GRASansP came from the need for graphical inspection and ability to be able to quickly process and extract the scattered intensity, I(q), as a function of position on the multidetector (qx,qy) or as a function of sample environment conditions from a series of many measurement runs (e.g. temperature sweep, rocking curve etc.). This, combined with an interest in scientific software development and the abilities of the Matlab™ environment have brought GRASansP into it’s present state. SASfit calculates integral structural parameters like radius of gyration, scattering invariant, Porod constant.
Furthermore it can fit size distributions together with several form factors including different structure factors.
Additionally an algorithm has been implemented, which allows to simultaneously fit several scattering curves with a common set of (global) parameters. This last option is especially important in contrast variation experiments or measurements with polarised neutrons. The global fit helps to determine fit parameters unambiguously which by analyzing a single curve would be otherwise strongly correlated.
The program has been written to fulfill the needs at the Small Angle Neutron Scattering Facility at the Paul Scherrer Institute PSI. The numerical routines have been written in C whereas the menu interface has been written in Tcl, Tk. There are binary packages for Windows, Linux and MacOS (see Get SASfit and the project page ).