[NOBUGS] McStas and McXtrace 3.9.0 released

[Peter Kjær Willendrup]

October 5th, 2026: McStas and McXtrace 3.9.0 released
Changes in McStas/McXtrace 3.9.0

Covers everything since the previous "announced" release, 3.8.4.

Highlights

  *   MPI is now enabled by default when compiling instruments. Multi-core runs work out of the box, and a long-standing hang in MPI runs with empty event lists is fixed. By @willend<https://github.com/willend>.
  *   NCrystal everywhere: NCrystal materials can now be used in Union, and PowderN / Single_crystal accept multiphase and single-crystal NCrystal materials. New components: Union_NCrystal_material and NCrystal_filter. By @tkittel<https://github.com/tkittel> and @mads-bertelsen-agentic<https://github.com/mads-bertelsen-agentic>.
  *   Union framework simplified: Union_init and Union_stop are no longer needed in your instruments, the framework is now self-contained (@mads-bertelsen-agentic<https://github.com/mads-bertelsen-agentic> and @g5t<https://github.com/g5t>). Also new: Union_abs_logger_nD_scintillator (@MilanKlausz<https://github.com/MilanKlausz>, with @tkittel<https://github.com/tkittel>).
  *   MCViNE sample kernels in McStas: 16 sample kernels from MCViNE (S(Q), S(Q,E), phonon, SANS and more), each available both as a standalone sample component and as a Union process. Contributed by @Fahima-Islam<https://github.com/Fahima-Islam>.
  *   New Dispersion_relation sample component for phonon or magnon scattering from tabulated (numerical) dispersion relations, tested against Phonon_simple and SpinWave_BCO. By Daniel Lomholt Christensen (@lomholy-agentic<https://github.com/lomholy-agentic>) and Kim Lefmann.
  *   Full component settings in NeXus output: in NeXus output mode, every component variable is now embedded in the output file with its actual runtime setting, so each simulation fully documents how its components were configured. By @willend<https://github.com/willend>, with related fixes by @tkittel<https://github.com/tkittel>.
  *   Much faster mcdisplay-webgl: the 3D instrument viewer no longer depends on Vite/npm and now starts up much faster. By @willend<https://github.com/willend>.
  *   Models of NeXT, the ILL neutron + X-ray imaging instrument, in both packages: ILL_H521_NeXT (neutron branch) in McStas and ILL_NeXT_Xray (X-ray branch) in McXtrace. Both were "vibe-coded" by @willend<https://github.com/willend> with Claude, starting from the instrument's webpage and the existing ILL information in McStas.
  *   New SOLEIL beamlines for McXtrace: SIRIUS, SAMBA and PUMA, plus fixes to CRISTAL. By @farhi<https://github.com/farhi>, with PUMA written by Uxue Saez Fernandez.
  *   Another big documentation round: refreshed manuals, new Union chapters, web versions of the manuals, and updated documentation for every component and instrument. By @willend<https://github.com/willend>, AI-assisted.

What's Changed

The full, categorised list of changes, common to McStas and McXtrace as well as specific to each, is in the McCode v3.9.0 release notes on GitHub<https://github.com/mccode-dev/McCode/releases/tag/v3.9.0>.

New Contributors

  *   @NoeB<https://github.com/NoeB> made their first contribution in #2697<https://github.com/mccode-dev/McCode/pull/2697>
  *   @lomholy-agentic<https://github.com/lomholy-agentic> made their first contribution in #2694<https://github.com/mccode-dev/McCode/pull/2694>
  *   @mccode-registrar[bot]<https://github.com/apps/mccode-registrar> made its first contribution in #2695<https://github.com/mccode-dev/McCode/pull/2695>

Full Changelog: https://github.com/mccode-dev/McCode/compare/v3.8.4...v3.9.0

Peter Kjær Willendrup
Forskningsingeniør, Specialkonsulent

DTU Physics

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Technical University of Denmark


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Department of Physics
Fysikvej
Building 307
DK-2800 Kongens Lyngby

Main office at
ESS DMSC
Building 305
DK-2800 Kongens Lyngby

Direct +45 2125 4612
Mobil +45 2125 4612
Fax +45 4593 2399
pkwi at fysik.dtu.dk

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