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McStas - Simulated exp.

A series of short movies showing how neutron experiments are prepared or performed. Some of these movies have an historical interest since they captured important moments in the life of the ILL.

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Films and animations


Simulating neutron instruments and experiments by means of a Monte Carlo ray tracing technique

Why simulate neutron instruments and experiments ?

Simulating a complex instrument means simulating the path of neutrons through all of its components (e.g. neutrons guides, monochromators, choppers, anlysers, etc.) from the source to the detector. This is a very valuable technique to improve or optimize existing instruments or to design new ones.
Simulating an experiment is quite similar, but puts the focus on the physics of the sample rather than the optics of the instrument. A measured spectrum or diagram is always a mixture of several neutron scattering processes (sample), parasitic scatterings (sample environment), and background scattering (instrument environment) combined with the optical imperfections of the instrument. A strong point of simulations: they make it possible to separate all these contributions and to better understand their interaction - a very valuable tool in optimizing experiment parameters. The simulation of model samples is also very helpful in understanding results from true samples.

The animation below was developed for the ILL's Open Day (16 June 2007). It shows how McStas simulates the behavior of both a neutron spectrometer (here, a time-of-flight spectrometer) and its sample (here, a liquid) by means of a Monte-Carlo ray tracing technique.
- The first part of the movie shows the simulated trajectories of neutrons through the components of the instrument.
- The second part show the results of the simulation which mimics the results of a true experiment.
We intentionally kept the cursor motion and transitory images of popup menus to remind you that the images come from a computer simulation.

Reference: McStas

Movie by E. Farhi and A. Filhol

© 2006-2007, Institut Laue-Langevin, Grenoble, France.

Movie files (864x656 pixels, duration 1'06): .mp4 (1.5 Mb), .webm (5.8 .Mb)
Movie files (640x480 pixels, duration 1'06): .mp4 (1.5 Mb), .webm (4.3 .Mb).

English checked by: Ronen Ghosh, June 2007.
Updates: A.Filhol, 18 June 2007, 9 Sept 2009, 15 May 2012.

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