McStas - Monte Carlo simulation of neutron instruments

McStas is an ongoing project to create a general tool for simulating neutron scattering instruments. The project is a collaboration between DTU Physics (formerly RISØ DTU and RISØ Natnl. Lab), University of Copenhagen, Paul Scherrer Institute and Institut Laue-Langevin.

The Risø efforts have historically been funded through multiple EU programs.

The software is freely available and can be downloaded from this site.

McStas is based on a compiler that reads a high-level specification language defining the instrument to be simulated and produces C code that performs the Monte Carlo Simulation. The system is very fast in use, both when setting up the instrument definition and when doing calculations. Typical figures are 500000 neutron histories per second on a fast PC.

McStas supports triple-axis,  time-of-flight instruments, and polarised neutrons. It comes with a comprehensive manual and a library of well-tested components that include most standard elements of neutron scattering instruments, including steady-state and pulsed sources, monochromators/analysers, guides, collimators, vanadium and powder samples, velocity selectors and choppers, and a variety of detectors.

McStas has been found to run on all existing computer systems (Unix/Linux, Windows, MacOS). Please refer to the platform requirements and tests page.

This software required a substantial effort to be brought to you. If you enjoy this software, please use the folowing references in your work: