[Feature request]: TsPhotoneutron behavior

[Sberth]

Feature request

Dear all,

I am currently working on photonuclear reactions with OpenTOPAS V.4.0. I have noticed a suprinsing behavior in the TsPhotoneutron module.
Indeed, i ran several simulations using the TsPhotoneutron module, and observed the neutron spectrum resulting from photonuclear reactions on various materials for incident gamma energies ranging from 10 to 250 MeV. It appears, that the produced neutron energy spectrum remains unchanged for energies higher than 150 MeV.

This results seems to be correlated with the fact, that nuclear data stored in the LEND data file (from ENDF/-B.VII.0), which are used by the TsPhotoneutron module, are evaluated only up to 150 MeV. However, it seems that the final state is still produced using nuclear data from the B.VII.0 files, even when the simulation involves at energies higher than the limit of G4LENDorBERTModel of 40 MeV.
For incident energies above 150 MeV, such as 250 MeV, the produced neutron spectrum seems identical to the one obtains for a incident energy of 150 MeV. This behavior isn't it inconsistent with the use of the bertini model which should produce neutrons with an energy higher than ~ 150 MeV ?

The graph shows the neutron energy spectrum between 20 and 250 MeV with two calculations, one with tsphotoneutron at 150 MeV and the other at 250 MeV.

Thank you in advance for your helps,
Sylvain,

TOPAS category

Physics

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• No indexed TOPAS references available here: The prompt says “no relevant references found,” so I can’t verify the intended/actual behavior of TsPhotoneutron, its model switching thresholds, or how it selects Geant4 photonuclear models/data in OpenTOPAS v4.0 from documentation/source. Any detailed claim would be unverified.

• What your observed “spectrum freezes above 150 MeV” usually indicates (generic Geant4/TOPAS-stack guidance):

  • A data-driven final-state model is being used beyond its evaluated range (e.g., 0–150 MeV), with the code effectively clamping to the highest available dataset or otherwise reusing the last valid distribution.
  • The intended handoff to a cascade model (e.g., Bertini) may not be happening for gamma-nuclear in your configuration, or the high-energy model is not active for that channel/region/material.

• Practical debugging checklist (log-first):

  • In the TOPAS run log, search for lines that list registered processes/models for gamma and specifically the photonuclear process. Confirm which model is assigned in the 150–250 MeV range.
  • Enable any available verbose process/model reporting (Geant4 process verbosity via TOPAS/Geant4 settings if your build supports it) and re-run at 150 vs 250 MeV; check whether the same model name appears.
  • Confirm you are using an appropriate physics list for photonuclear reactions and that TsPhotoneutron isn’t overriding it in a way that pins you to LEND throughout.

• Feature request outcome (generic):

  • If TsPhotoneutron is forcing LEND final states above 150 MeV, that’s a valid feature request: add/ensure model handoff above the LEND limit and/or emit a warning when incident energies exceed the evaluated data range.

[JoseRamosMendez]

Hi Silvain,
The TsPhotoNeutron module was implemented for x-rays/photons within about clinical energies and for the supported materials in B.VII. Thus, it's performance for energy range above this limit (~20-35 MeV) was not tested neither its integration/compatiblity with other hadronic modules/constructors. For the moment, if you need to go higher in energy then you can try other Geant4 physics constructor.
Best.

[Sberth]

Hi,

I see, thank you for your reply.
Then i will see what i can do.
Best regards,