McStas - A neutron ray-trace simulation package

McStas is a general tool for simulating neutron scattering instruments and experiments. It is actively supported by DTU Physics, NBI KU, ESS, PSI and ILL.

Simulated scattering from a hollow-cylinder vanadium sample.

The plot shows the intensity of scattered neutrons (red is highest intensity). The sample is at the center of the sphere with the neutron beam coming from the left. Clearly seen is the shadowing effect of the sample causing a lower intensity opposite the beam. Also seen is the effect of the non-symmetric geometry of the sample, causing lower intensity directly above and to the side of the sample.

Recent news

Migrating from McStas 2.x to 3.x? - Use the wiki-based guides

January 7th, 2026: McStas and McXtrace 3.6.5 released

McStas and McXtrace release 3.6.5 is now available.
McStas installation instructions are found on GitHub .

What's Changed - Main Changes:

Bugfixes, new features, all common to McStas and McXtrace:

macOS bundles in 3.6.1 did not actually install that version but something earlier. Fixed by pinning in yml file, @willend in #2285
PDF manuals had wrong version numbers, @willend in #2285
Allow mcrun / mcdisplay to run / visualize without access to .c/.instr by @willend in #2281
mcgui/mxgui editable font colors, handle long filenames without extreme window resizing by @willend in #2275
Fix cross-platform sort-order issue in PowderN by @willend in #2272
Platform-independent reflection list sort in Single_crystal by @willend in #2273
mcrun/mxrun: feature addition - scan by seed by @willend in #2276
Add mcplot toggle to "plot 1D-curves from 0-value" in linear mode by @willend in #2278
Add commentstring to vim editor by @Lomholy in #2284

Other stuff

%Example adjustments, McXtrace by @willend in #2269
Test_SANS/Test_SAXS, supplement stats by x10 SPLIT by @willend in #2270
Use ${{ matrix.mpi }} to ensure different output dirs by @willend in #2271
Fix indentation bug - issue #2279 by @willend in #2280
Temporarily disable this instr from McXtrace tests by @willend in #2283

Full Changelog:https://github.com/mccode-dev/McCode/compare/v3.6.1...v3.6.5

Previous news items: 2025, 2024, 2023, 2022, 2021,2020,2019, 2018, 2017, 2016, 2015, 2014, 2013, 2012, 2011, 2010, 2009, 2008, 2007, 2006, 2005, 2004, 2003, 2002, 2001, 2000, 1999, 1998.