Dear FLUKA users,

It is our pleasure to announce that a new minor release of the FLUKA code, version 4-5.2, has been issued and can be downloaded from the Official CERN FLUKA website: https://fluka.cern

See the release notes at the bottom of this message for a detailed account of all novelties.

For consistency, please update to the latest version of Flair, available from https://flair.cern 

With our kindest regards,

The FLUKA developer team at CERN and Collaborating Institutes

=== Fluka-4.5.2 ===

As of this minor release, running and building FLUKA is now supported with gfortran version 8.1 and above, while support for gfortran 7 has been discontinued.

Neutron data libraries for JEFF-4.0, ENDF/B-VIII.1, and JENDL-5.0 are now available via https://flukafiles.web.cern.ch/neutron JEFF-3.3 remains the default neutron data library in this minor release.

PHYSICS IMPROVEMENTS:

• In low-energy-neutron-induced fission, the relaxation of excited fission fragments is now performed by FLUKA's gamma de-excitation module (which provides a correlated gamma cascade), instead of relying on evaluated nuclear databases (which just provide inclusive photon spectra).

TECHNICAL IMPROVEMENTS:

• Unstructured meshes:
      - NASTRAN format and the new compact format of ANSYS are now supported.
      - In ANSYS unstructured meshes, an additional transition body is sometimes interspersed between tetrahedral and hexahedral regions. This transition body was inadvertently parsed as a new FLUKA region. As of this release, it is instead embedded in the hexahedral region.
      - Added a procedure to directly sample (without rejection) uniformly distributed points inside unstructured-mesh regions. See the source_newgen.f manual page for details.
      - Version 1.4 of the FLUKA meshing tool (FLUKA_mesh_fix.py), available for download from this page, now runs on Windows and MacOS. Access to both meshing kernels of the Gmsh API (GEO and OCC) is provided. Furthermore, it is now capable of producing unstructured meshes which can be readily concatenated. Finally, it now supports MeshLib v3.1.1.211, addressing the issue raised in this forum thread. Note, however, that this version of MeshLib is not backwards compatible with earlier versions.
• Point-wise neutron interactions below 20 MeV:
      - The codebase of FLUKA's point-wise low-energy-neutron event handling (elastic scattering, radiative capture, inelastic interactions, and fission) has been migrated to a modern C++ framework, transparent for the users, in view of the ongoing evolution towards the next generation of the FLUKA code.
      - In absence of prescission-neutron multiplicity information, no prescission neutron is emitted, as opposed to earlier code versions where an ad-hoc model was invoked.
• Automatic importance biasing: Maps can now be written out at the end of each cycle, as detailed in the manual.

BUG FIXES:

• Point-wise neutron interactions below 20 MeV:
      - Fixed a bug which led to spurious polar-angle and energy sampling for ejectiles of inelastic channels when the parent neutron energy was barely above reaction threshold.
      - Fixed a rare bug wherein for final states encoded in the MT=57 section (n,anything) of neutron library files the multiplicity of charged particles was sampled incorrectly (while that of neutrons was unaffected).
      - Fixed a bug whereby in absence of prompt-fission-neutron multiplicity as a function of the parent-neutron energy a single neutron was emitted. This affected a few exotic nuclei. Global multiplicity information is now used if available.
      - Improved the transition from resolved to unresolved resonance region in case a dedicated junction point was not clearly identified in the evaluated data libraries. This inadvertently accentuated/suppressed the cross section after the last resonance during Doppler broadening.
      - Fixed the bug triggering an abort for DPA scoring when pointwise fission events occur, reported in this forum thread.
• Tracking in electromagnetic fields:
      - Fixed a bug whereby energy update in electric field tracking was overridden under certain conditions, thus resolving the issue reported in this forum thread.
      - Fixed a bug in the implementation of the horn magnetic field.
• Other:
      - Fixed a bug which led to spurious gamma de-excitation emission for triton.
      - If DOSE-H2O scoring is requested (without further radiobiological scoring), the radiobiological file is no longer requested and the code no longer halts, thus resolving the issue reported in this forum thread.   
      - Erratum: the fixed rejection of deuteron nuclear interactions on deuterium which led to an overestimation of the D(d,n) in version 4-5.1 also improved the T(d,n) channel.