Release of FLUKA 4-4.0

Dear FLUKA users,

It is our pleasure to announce that a new major release of the FLUKA code, version 4-4.0, has been issued and can be downloaded from the Official CERN FLUKA website:

Please see the release notes at the bottom of this message for a detailed account of all new features, among which we wish to highlight a new model for nuclear elastic scattering of protons below 250 MeV, as well as the improved gamma spectra from thermal neutron capture, and the ability to sample thermal-neutron scattering laws from user-supplied files in ACE format.

We wish to make you especially aware of the following changes:

1) Point-wise neutron interactions below 20 MeV are now on by default for DAMAGE, NEW-DEFA, and PRECISIOn DEFAULTS.
In order to benefit from this rich physics feature, neutron data libraries need to be downloaded and installed, as detailed here, otherwise your runs will stop with an error message.
Should you instead have good reason to still need group-wise low-energy neutron interactions, see the manual.
Please be aware that group-wise interactions offer a rather coarse account: they lack an explicit tracking of charged secondaries, have discrete angular distributions for secondary neutrons, have uncorrelated sampling of residual nuclei, and have Doppler broadening only at a few temperatures, among other. Point-wise interactions, instead, do not suffer from these shortcomings and should be preferred, at modest CPU penalty.
2) WHAT(2) in the MATERIAL card (material atomic weight) has been deprecated due to its recurrent misuse as mass number, despite the manual indications. Should your inputs have this field filled, please clear it (or, if really justified, modify it according to the updated manual instructions).

To comfortably profit from the new features, please update to the latest Flair v3.3-0.3, available from the Official Flair site.
NB: the Flair support of ACE file loading shall be issued in an upcoming release.

With our kindest regards,

The FLUKA developer team at CERN and Collaborating Institutes


=== Fluka-4.4.0 ===

This major release offers new significant physics ingredients, including an improved model for nuclear elastic scattering of low-energy protons and refined gamma spectra from thermal neutron capture, along with a series of technical improvements and due bug fixes, detailed below.

We'd like to especially highlight that point-wise neutron interactions below 20 MeV are henceforth automatically activated for the DAMAGE, NEW-DEFA, and PRECISIOn DEFAULTS (as well as in the absence of the DEFAULTS card, corresponding to the NEW-DEFA implicit choice), requiring the download and installation of neutron data libraries as detailed here.



  • A new model for the nuclear elastic scattering of protons has been implemented, relying on partial-wave analyses and experimental angular distributions, significantly improving FLUKA's description of proton elastic scattering near Coulomb barrier and up to 250 MeV for target nuclei with A>1. Proton-proton nuclear elastic scattering remains unaltered with respect to previous FLUKA versions.
  • The reaction cross section for protons on 11B at low energies has been further refined, and now features a broad peak of 900 mb at ~650 keV as well as a narrow peak of 100 mb at ~150 keV.
  • A correction has been made to FLUKA's deuteron reaction model below 150 MeV/n: in earlier versions, when a neutron was stripped to the continuum, the remaining proton was subject to an excessive Coulomb barrier when attempting to penetrate the target nucleus. This spurious effect (now corrected) led to a significant underestimation of channels such as (d,2n), especially on heavy target nuclei at deuteron energies up to 10s of MeV, as reported in this and this forum thread.
  • Point-wise thermal neutron scattering laws S(a,b,T) can now be imported directly from ACE-formatted files (see the LOW-PWXS card documentation in the manual). FLUKA neutron library packages do not provide ACE files. It is up to the user to retrieve them if needed, e.g. from the following repositories
    to name but a few. Use of external ACE files should be duly quoted and referenced when employed through FLUKA.

  • Correlated gamma emission spectra following the capture of thermal neutrons have been included from ENSDF for the following isotopes: 1H, 12C, 14N, 16O, 17O, 21Ne, 24Mg, 28Si, 29Si, 39K, 41Ca, 42Ca, 43Ca, 46Ti, 48Ti, 49Ti, 52Cr, 53Cr, 57Fe, 60Ni, 61Ni, 67Zn, 83Kr, 90Zr, 91Zr, 94Mo and 95Mo, now better reproducing experimental gamma line energies and intensities, thus overcoming the issue raised in this forum thread.
  • Point-wise (n,inl) interactions reaching a final state with excitation energy above the neutron separation energy are now resampled to avoid excessive excitation energy going into the gamma de-excitation stage.


  • The (already discouraged) use of WHAT(2) in the MATERIAL card (material atomic weight) has been deprecated due to frequent inadvertent misuse as mass number. Should your inputs have this field filled, please clear it, or refer to the manual to intentionally overwrite default values.
  • The AUXSCORE card has been provided with the additional option RESNUCLEi, enabling the scoring of residual nuclei filtered by the projectile particle species.
  • A profiler is now included, allowing the user to resolve the CPU time spent per region and per particle species on every cycle. See the PROFILE card documentation in the manual.
  • In the source_newgen.f user routine:
    - A new sampling function has been added to sample from external files containing discrete energy lines and their relative intensities.
    - From now on it is possible to use the same sampling function with up to 100  files simultaneously.

  • A new command-line utility,, is available in the bin/ folder as an additional tool for a simplified post-processing of FLUKA scoring of the output files.


  • Fixed a bug in the synchrotron-radiation emission module (activated by the SYRASTEP card), which led to cumulative path lengths for emitting particles other than e- and e+ to be erroneously taken from the electromagnetic particle stack. This fix addresses the issue raised in this forum thread.
  • Fixed the crash reported in this forum thread, which was related to a region-flagging issue for low-energy neutron secondaries, impacting biological dose scoring.
  • Relaxed an excessively strict abort condition evaluating the range of heavy ions, fixing the issues raised in this and this forum threads.     
  • Reinstated the USDRAW calls from e+ annihilation in-flight events (ICODE=214) and from muon pair production by photons (ICODE=237), which were unfortunately inactive in earlier versions, preventing the user from intercepting these events in the mgdraw.f user routine.
  • Fixed the bug reported in this forum thread, whereupon relative paths are now accepted (in the form of strings between quotation marks) as #define variable values.
  • Fixed a bug whereby incomplete $start_translate directives erroneously inherited values from previous $start_translate directives.
  • Fluence scoring with USRYIELD has been deactivated. It led to erroneously mix up angles with respect to the beam direction (which USRYIELD is designed to use) and angles with respect to the scoring boundary (required for fluence evaluation purposes).