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

February 27th, 2020: McStas 3.0beta bugfixes etc

February 25th, 2020: McStas 3.0beta technology preview available!

Dear all,

A technology preview for the forthcoming McStas 3.x series is now available for testing!

Main highlights of the release are:

For more details and instructions, please refer to this document on our Wiki

Thanks to:

January 24th, 2020: McStas 2.6 release!

Dear all,

A new release of McStas, v. 2.6 has been built and is ready for download!

Download and installation instructions are available via our GitHub download pages.

Selected highligts from the release are listed below. The full list of changes is also available at

Changes in McStas v.2.6, January 24th, 2020

- Most other new datafiles are directly related to component- or instrument-additions and have been mentioned above.

We hope you will enjoy this new release!!!

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