Monte Carlo neutron ray-tracing simulations
Authors:3rd party code used in RESTRAX
The software package RESTRAX is a tool for neutron ray-tracing simulations of neutron scattering instruments. It is useful for instrument design, optimization of experimental conditions and analysis of experimental data. RESTRAX permits to run fast simulations of neutron beam on a regular desktop computer or laptop thanks to several sampling optimization techniques used to improve sampling efficiency.
The package includes two programs:
SIMRES - general ray-tracing code
This program permits to run simulations for most of the present neutron scattering instruments using unpolarized beams, both monochromatic and time-of-flight. It is an alternative and in part complementary to the other neutron simulation programs (McStas, VITESS, NISP). SIMRES can simulate neutron flux and its distribution in both real and momentum subspaces as well as resolution functions. It comes with a user friendly GUI which allows for setting up and control of the virtual instrument, 3D visualization and export of graphs and data output. Advanced features such as scanning of instrument parameters, numerical optimization as well as script recording and execution helps to carry out rather complex tasks needed during an instrument design. The ability to propagate neutron trajectories in reverse direction (sample to source) makes it particularly useful for simulation of configurations with very small and collimated beams and small samples, allowing for much higher simulation speed than in the down-stream mode. SIMRES newly permits also to import/export neutron events using the MCPL library and thus binding with other program. For example, simulations running SIMRES for the primary beam and calling McStas to propagate neutrons further through the sample and secondary spectrometer are feasible.
RESTRAX for Three Axis Spectrometers
This vesion specially designed for three-axis spectrometers (TAS) is equiped with simplified (but faster) ray-tracing code for simulation of TAS resolution functions and additional tools for data analysis. It provides graphical representation of resolution functions as well as both simulated and experimental scattering functions. The non-linear least-squares fitting routine is available with variety of scattering models and a possibility to add other models created by users as a library linked dynamically to the main program. The program has been equiped with intuitive graphical user interface written in Java (portabe across platforms)