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

March 17th, 2017: Video presentation about using iFit with McStas by Emmanuel Farhi (ILL)

Dear all,

Emmanuel Farhi (McStas team & ILL Spectroscopy Group) visited the ESS DMSC in Copenhagen today and gave a nice talk about using iFit and McStas together. The presentation was recorded and is now available for viewing online here. Further information below:

Using iFit to control McStas simulations, and more.

The iFit tool will be presented. It is a generic data analysis and fitting infrastructure. A special focus will be put on the ability to launch McStas simulations, and retrieve the monitor data. The fitting capability of iFit allows to optimise a defined figure of merit (e.g. monitor or so) by changing the instrument parameters. This type feature is for instance used in the guide-bot from Mads Bertelsen, but it is applicable to any instrument model. Other features will be presented, such as the 4D convolution of a McStas TAS-type instrument with an 4D S(q,w) dispersion volume, which could be used for e.g. Bifrost. More on

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