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

March 31st, 2023: McStas 3.3 released

Dear all, The new McStas release v. 3.3 "next-generation" is built and ready for download!

McStas 3.3 is the fourth official release in the 3.x series, with a modernised code-generator and support for GPU acceleration on NVIDIA cards.

3.3 could have been considered a 'minor' update, but new built-in support for NeXus on all platforms and new SEARCH grammar warrant the .x increment.

Thanks to all members of the joint McStas-McXtrace team and input from our users via emails and GitHub issues alike!

Download and installation instructions are available via our GitHub INSTALL-doc pages.

Selected highlights from the releass are listed below. The full list changes is also available at

If you didn't start already, please start your migration to 3.x:

- If you are still in trouble, please write us a GitHub issue or an email to

Fixes of issues from last 3.x release:
A number of issues from 3.2 were addressed, see the relevant GitHub issues for details:
3.2 issue list

Release highlights

Our Docker and binder containers will be updated within the following weeks.

We hope you will enjoy this new release!!!

Previous news items: 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.