# Latest **URL:** https://geant4-forum.web.cern.ch/latest.md [Latest](https://geant4-forum.web.cern.ch/latest.md) · [Categories](https://geant4-forum.web.cern.ch/categories.md) --- ## [Tips for effective and successful posting](https://geant4-forum.web.cern.ch/t/tips-for-effective-and-successful-posting/11004)
**Author:** [@bmorgan](https://geant4-forum.web.cern.ch/u/bmorgan)\ **Replies:** 0\ **Last updated:** [August 24, 2023, 1:55pm UTC](https://geant4-forum.web.cern.ch/t/tips-for-effective-and-successful-posting/11004 "2023-08-24T13:55:15Z")
This forum is intended to help with problems and answer questions on the Geant4 toolkit, whether that be to develop applications using it, to request or contribute new features, or generally discuss and communicate about… --- ## [How to post code snippets](https://geant4-forum.web.cern.ch/t/how-to-post-code-snippets/9944)
**Author:** [@bmorgan](https://geant4-forum.web.cern.ch/u/bmorgan)\ **Replies:** 0\ **Last updated:** [February 13, 2023, 2:06pm UTC](https://geant4-forum.web.cern.ch/t/how-to-post-code-snippets/9944 "2023-02-13T14:06:27Z")
To effectively help with coding/output problems, we need to see that code or output clearly. Discourse provides all the tools here to make this easy once you know how to use them. There are really only two simple guideli… --- ## [Crash in geant4.11.4.3 when a track starts outside the world](https://geant4-forum.web.cern.ch/t/crash-in-geant4-11-4-3-when-a-track-starts-outside-the-world/15433)
**Author:** [@arce](https://geant4-forum.web.cern.ch/u/arce)\ **Replies:** 1\ **Last updated:** [November 12, 2026, 1:11pm UTC](https://geant4-forum.web.cern.ch/t/crash-in-geant4-11-4-3-when-a-track-starts-outside-the-world/15433 "2026-11-12T13:11:00Z")
Please fill out the following information to help in answering your question, and also see tips for posting code snippets. If you don’t provide this information it will take more time to help with your problem! Geant4 V… --- ## [G4GammaGeneralProcess: Rayleigh scattering apparently omitted above 1.022 MeV (Geant4 11.4)](https://geant4-forum.web.cern.ch/t/g4gammageneralprocess-rayleigh-scattering-apparently-omitted-above-1-022-mev-geant4-11-4/15428)
**Author:** [@Berfin\_Turkoglu](https://geant4-forum.web.cern.ch/u/Berfin_Turkoglu)\ **Replies:** 5\ **Last updated:** [November 11, 2026, 7:04pm UTC](https://geant4-forum.web.cern.ch/t/g4gammageneralprocess-rayleigh-scattering-apparently-omitted-above-1-022-mev-geant4-11-4/15428 "2026-11-11T19:04:14Z")
Geant4 Version:11.4.0 Operating System: Windows 11 Compiler/Version: Visual Studio 2022 / MSVC CMake Version: 4.0.1 Hello, I noticed a difference in uncollided gamma transmission depending on whether G4GammaGeneral… --- ## [Multi threading changes simulation result](https://geant4-forum.web.cern.ch/t/multi-threading-changes-simulation-result/15425)
**Author:** [@Enrico\_Pierobon](https://geant4-forum.web.cern.ch/u/Enrico_Pierobon)\ **Replies:** 4\ **Last updated:** [November 6, 2026, 1:21pm UTC](https://geant4-forum.web.cern.ch/t/multi-threading-changes-simulation-result/15425 "2026-11-06T13:21:44Z")
Dear Geant4 forum, I am experiencing issues with multi threading. It seems that running my simulation with more than 1 thread, like using: /run/numberOfThreads 4 changes the output. Let me take one step back. I am va… --- ## [Recommendation for Event Generator like baising](https://geant4-forum.web.cern.ch/t/recommendation-for-event-generator-like-baising/15427)
**Author:** [@papawan](https://geant4-forum.web.cern.ch/u/papawan)\ **Replies:** 0\ **Last updated:** [November 6, 2026, 11:51am UTC](https://geant4-forum.web.cern.ch/t/recommendation-for-event-generator-like-baising/15427 "2026-11-06T11:51:52Z")
Hello, Wanted to get some advice on specific biasing scenario I was hoping to achive. For context we can assume my detector is a target material sandwiched by two scintillators. I am hoping to my signal sample which i… --- ## [Need advice on G4AutoLock in primary generator](https://geant4-forum.web.cern.ch/t/need-advice-on-g4autolock-in-primary-generator/15421)
**Author:** [@Vyacheslav\_Porosev](https://geant4-forum.web.cern.ch/u/Vyacheslav_Porosev)\ **Replies:** 2\ **Last updated:** [November 4, 2026, 8:18am UTC](https://geant4-forum.web.cern.ch/t/need-advice-on-g4autolock-in-primary-generator/15421 "2026-11-04T08:18:18Z")
Please fill out the following information to help in answering your question, and also see tips for posting code snippets. If you don’t provide this information it will take more time to help with your problem! Geant4 V… --- ## [NeutronHP in QGSP\_BERT\_HP across Geant4 versions](https://geant4-forum.web.cern.ch/t/neutronhp-in-qgsp-bert-hp-across-geant4-versions/15236)
**Author:** [@Heiley\_Wong](https://geant4-forum.web.cern.ch/u/Heiley_Wong)\ **Replies:** 2\ **Last updated:** [October 29, 2026, 3:43am UTC](https://geant4-forum.web.cern.ch/t/neutronhp-in-qgsp-bert-hp-across-geant4-versions/15236 "2026-10-29T03:43:39Z")
Please fill out the following information to help in answering your question, and also see tips for posting code snippets. If you don’t provide this information it will take more time to help with your problem! Geant4 V… --- ## [Segmentation fault after many geometry reinitializations](https://geant4-forum.web.cern.ch/t/segmentation-fault-after-many-geometry-reinitializations/15411)
**Author:** [@dima51](https://geant4-forum.web.cern.ch/u/dima51)\ **Replies:** 3\ **Last updated:** [October 27, 2026, 7:31am UTC](https://geant4-forum.web.cern.ch/t/segmentation-fault-after-many-geometry-reinitializations/15411 "2026-10-27T07:31:05Z")
Hi! It seems there is a problem with many geometry reinitializations in MT mode. My application (9 logical volumes, local field managers, 16 threads) segfaults in G4LogicalVolume::GetFieldManager() after about 900–2300 … --- ## [Hadrontherapy example (CATANA): nozzle brass tubes, modulator wheel position and the clinical SOBP modulator file](https://geant4-forum.web.cern.ch/t/hadrontherapy-example-catana-nozzle-brass-tubes-modulator-wheel-position-and-the-clinical-sobp-modulator-file/15413)
**Author:** [@Ava\_Rasta](https://geant4-forum.web.cern.ch/u/Ava_Rasta)\ **Replies:** 0\ **Last updated:** [October 25, 2026, 8:16pm UTC](https://geant4-forum.web.cern.ch/t/hadrontherapy-example-catana-nozzle-brass-tubes-modulator-wheel-position-and-the-clinical-sobp-modulator-file/15413 "2026-10-25T20:16:22Z")
Hello, I am using the advanced example Hadrontherapy (Geant4 11.3) to model the CATANA 62 MeV passive proton beamline, for the U87 cell irradiations of Chaudhary et al. (2014), done around 2012-2014. I have three short … --- ## [Low Energy Positron Implantation, Artefact Creation](https://geant4-forum.web.cern.ch/t/low-energy-positron-implantation-artefact-creation/15267)
**Author:** [@Constantin\_Luy](https://geant4-forum.web.cern.ch/u/Constantin_Luy)\ **Replies:** 4\ **Last updated:** [October 20, 2026, 6:30am UTC](https://geant4-forum.web.cern.ch/t/low-energy-positron-implantation-artefact-creation/15267 "2026-10-20T06:30:35Z")
Geant4 Version: 11.4.1 Operating System:Ubuntu 24.04 under WSL2 on Windows Compiler/Version: GCC/G++ 13.3.0 CMake Version: 3.28.3 Hello, I am currently building an application to run positron implantation simulatio… --- ## [Inclusion of Particle spectra in PrimaryGenerator Action class](https://geant4-forum.web.cern.ch/t/inclusion-of-particle-spectra-in-primarygenerator-action-class/15406)
**Author:** [@amandubey](https://geant4-forum.web.cern.ch/u/amandubey)\ **Replies:** 2\ **Last updated:** [October 19, 2026, 9:50am UTC](https://geant4-forum.web.cern.ch/t/inclusion-of-particle-spectra-in-primarygenerator-action-class/15406 "2026-10-19T09:50:09Z")
Please fill out the following information to help in answering your question, and also see tips for posting code snippets. If you don’t provide this information it will take more time to help with your problem! Geant4 V… --- ## [Possible reactant/input-order dependence in Geant4-DNA IRT-sync — clarification requested](https://geant4-forum.web.cern.ch/t/possible-reactant-input-order-dependence-in-geant4-dna-irt-sync-clarification-requested/15373)
**Author:** [@Mehmet\_Karabuga](https://geant4-forum.web.cern.ch/u/Mehmet_Karabuga)\ **Replies:** 7\ **Last updated:** [October 19, 2026, 7:56am UTC](https://geant4-forum.web.cern.ch/t/possible-reactant-input-order-dependence-in-geant4-dna-irt-sync-clarification-requested/15373 "2026-10-19T07:56:30Z")
Geant4 version: 11.4.2 Chemistry model: IRT\_syn Platform: macOS 12.7.6, Intel x86\_64 Hello Geant4-DNA developers, We are investigating reactant-order invariance in the Geant4-DNA IRT-sync chemistry model. As a base… --- ## [How to create pure MuonToMuonPairProduction events?](https://geant4-forum.web.cern.ch/t/how-to-create-pure-muontomuonpairproduction-events/15397)
**Author:** [@papawan](https://geant4-forum.web.cern.ch/u/papawan)\ **Replies:** 6\ **Last updated:** [October 16, 2026, 6:28pm UTC](https://geant4-forum.web.cern.ch/t/how-to-create-pure-muontomuonpairproduction-events/15397 "2026-10-16T18:28:51Z")
Hi everyone, I’m trying to implement a program to study muon (lepton) pair production from muon-nucleus scattering. Just for context, I implemented a simple geometry with a block of Tungsten. For testing, I have a ver… --- ## [G4Exception : PART122 errror](https://geant4-forum.web.cern.ch/t/g4exception-part122-errror/10657)
**Author:** [@dogukkann](https://geant4-forum.web.cern.ch/u/dogukkann)\ **Replies:** 3\ **Last updated:** [October 14, 2026, 10:54pm UTC](https://geant4-forum.web.cern.ch/t/g4exception-part122-errror/10657 "2026-10-14T22:54:52Z")
How can I solve this error? \*\*\* G4Exception : PART122 issued by : G4ParticleTable::Insert() The particle Cs133 has already been registered in the Particle Table \*\*\* Fatal Exception \*\*\* core dump \*\*\* Waiting for sug… --- ## [How to Extract First-Generation Fe PKA Energy and Depth Spectra from 10 MeV Proton Irradiation Using G4ScreenedNuclearRecoil?](https://geant4-forum.web.cern.ch/t/how-to-extract-first-generation-fe-pka-energy-and-depth-spectra-from-10-mev-proton-irradiation-using-g4screenednuclearrecoil/15403)
**Author:** [@Zeenat\_Ullah](https://geant4-forum.web.cern.ch/u/Zeenat_Ullah)\ **Replies:** 0\ **Last updated:** [October 13, 2026, 4:23pm UTC](https://geant4-forum.web.cern.ch/t/how-to-extract-first-generation-fe-pka-energy-and-depth-spectra-from-10-mev-proton-irradiation-using-g4screenednuclearrecoil/15403 "2026-10-13T16:23:31Z")
Dear Geant4 Experts, I am conducting research on ion-induced primary knock-on atom (PKA) production in reactor structural materials, with the broader goal of establishing a computational framework for selecting ion irra… --- ## [Nuclear Quenching Factor?](https://geant4-forum.web.cern.ch/t/nuclear-quenching-factor/15399)
**Author:** [@raadshaikh](https://geant4-forum.web.cern.ch/u/raadshaikh)\ **Replies:** 6\ **Last updated:** [October 8, 2026, 8:02pm UTC](https://geant4-forum.web.cern.ch/t/nuclear-quenching-factor/15399 "2026-10-08T20:02:21Z")
I apologise if this isn’t the right place to ask this… When energy is deposited in a scintillator and scintillation light is produced, the amount of light depends on the particle type (e.g. alphas produce less light tha… --- ## [Text colour of /vis/scene/add/date](https://geant4-forum.web.cern.ch/t/text-colour-of-vis-scene-add-date/15394)
**Author:** [@Johan\_Nyberg](https://geant4-forum.web.cern.ch/u/Johan_Nyberg)\ **Replies:** 3\ **Last updated:** [October 4, 2026, 8:55pm UTC](https://geant4-forum.web.cern.ch/t/text-colour-of-vis-scene-add-date/15394 "2026-10-04T20:55:14Z")
Please fill out the following information to help in answering your question, and also see tips for posting code snippets. If you don’t provide this information it will take more time to help with your problem! Geant4 V… --- ## [Fast neutrons from reaction of deutrons (energy up to 2 MeV) with 7Li/6Li](https://geant4-forum.web.cern.ch/t/fast-neutrons-from-reaction-of-deutrons-energy-up-to-2-mev-with-7li-6li/15375)
**Author:** [@Victor\_Bobrovnikov](https://geant4-forum.web.cern.ch/u/Victor_Bobrovnikov)\ **Replies:** 7\ **Last updated:** [October 2, 2026, 10:00am UTC](https://geant4-forum.web.cern.ch/t/fast-neutrons-from-reaction-of-deutrons-energy-up-to-2-mev-with-7li-6li/15375 "2026-10-02T10:00:11Z")
Please fill out the following information to help in answering your question, and also see tips for posting code snippets. If you don’t provide this information it will take more time to help with your problem! Geant4 V… --- ## [Mie scattering has no effect on Cherenkov photons produced by muon propagation](https://geant4-forum.web.cern.ch/t/mie-scattering-has-no-effect-on-cherenkov-photons-produced-by-muon-propagation/15388)
**Author:** [@Timur\_Gromov](https://geant4-forum.web.cern.ch/u/Timur_Gromov)\ **Replies:** 0\ **Last updated:** [September 30, 2026, 12:09pm UTC](https://geant4-forum.web.cern.ch/t/mie-scattering-has-no-effect-on-cherenkov-photons-produced-by-muon-propagation/15388 "2026-09-30T12:09:48Z")
Geant4 Version: 11.3.2 Operating System: Ubuntu 24.04.4 LTS Compiler/Version: GCC 13.3.0 CMake Version: 3.28.3 Hello! I am studying the effect of light scattering on event reconstruction accuracy for the Baikal-GVD… --- ## [Coupling realistic pulsed beam temporal structures (micro/macro-pulses) with molecularDNA for DNA damage scoring and RBE estimation](https://geant4-forum.web.cern.ch/t/coupling-realistic-pulsed-beam-temporal-structures-micro-macro-pulses-with-moleculardna-for-dna-damage-scoring-and-rbe-estimation/15380)
**Author:** [@chuanye90](https://geant4-forum.web.cern.ch/u/chuanye90)\ **Replies:** 3\ **Last updated:** [September 29, 2026, 5:37pm UTC](https://geant4-forum.web.cern.ch/t/coupling-realistic-pulsed-beam-temporal-structures-micro-macro-pulses-with-moleculardna-for-dna-damage-scoring-and-rbe-estimation/15380 "2026-09-29T17:37:54Z")
Hello Geant4-DNA community, I am a PhD student working on proton FLASH radiobiology using a laboratory cyclotron that delivers ultra-high dose rate beams with a complex temporal structure (micro-pulses on the ns scale a… --- ## [Simulating 40 GeV/c π⁻ + C interactions in Geant4](https://geant4-forum.web.cern.ch/t/simulating-40-gev-c-c-interactions-in-geant4/15383)
**Author:** [@Maratbek-Shodmonov](https://geant4-forum.web.cern.ch/u/Maratbek-Shodmonov)\ **Replies:** 1\ **Last updated:** [September 29, 2026, 3:58pm UTC](https://geant4-forum.web.cern.ch/t/simulating-40-gev-c-c-interactions-in-geant4/15383 "2026-09-29T15:58:43Z")
Hello everyone, I would like to simulate the interaction of a negative pion (π⁻) with a carbon target (π⁻ + C) at a momentum of 40 GeV/c using Geant4. Could you please advise whether Geant4 can reliably simulate this t… --- ## [molecularDNA 11.4.2: higher DNA damage using the molecularDNA example in Geant4](https://geant4-forum.web.cern.ch/t/moleculardna-11-4-2-higher-dna-damage-using-the-moleculardna-example-in-geant4/15367)
**Author:** [@Jonathan\_Setiawan](https://geant4-forum.web.cern.ch/u/Jonathan_Setiawan)\ **Replies:** 1\ **Last updated:** [September 28, 2026, 2:00pm UTC](https://geant4-forum.web.cern.ch/t/moleculardna-11-4-2-higher-dna-damage-using-the-moleculardna-example-in-geant4/15367 "2026-09-28T14:00:50Z")
Hello, I am investigating proton-induced DNA damage using the molecularDNA example in Geant4 11.4.2. I am trying to understand a discrepancy between the current public implementation and the proton result reported by Sh… --- ## [Geant4 license clarification or standardization](https://geant4-forum.web.cern.ch/t/geant4-license-clarification-or-standardization/15278)
**Author:** [@ferhue](https://geant4-forum.web.cern.ch/u/ferhue)\ **Replies:** 2\ **Last updated:** [September 25, 2026, 5:19pm UTC](https://geant4-forum.web.cern.ch/t/geant4-license-clarification-or-standardization/15278 "2026-09-25T17:19:10Z")
The fact that the Geant4 collaboration chose not to use any of the over 300 standard licenses ( SPDX License List | Software Package Data Exchange (SPDX)) and created yet-another-custom-one is leading to quite some issue… --- ## [Polarized Bremsstrahlung model doesn't seem to activate](https://geant4-forum.web.cern.ch/t/polarized-bremsstrahlung-model-doesnt-seem-to-activate/15365)
**Author:** [@Tommi\_Koskinen](https://geant4-forum.web.cern.ch/u/Tommi_Koskinen)\ **Replies:** 2\ **Last updated:** [September 23, 2026, 7:52am UTC](https://geant4-forum.web.cern.ch/t/polarized-bremsstrahlung-model-doesnt-seem-to-activate/15365 "2026-09-23T07:52:34Z")
Geant4 Version: 11.4.2 Operating System: Windows 11 Pro Compiler/Version: Visual Studio Community 2026, 18.10.0 CMake Version: 4.4.3 Issue: I’m directing 160 keV electrons towards a tungsten block to produce Bremss… --- ## [Question regarding the lambdaFactor in G4HadronicProcess](https://geant4-forum.web.cern.ch/t/question-regarding-the-lambdafactor-in-g4hadronicprocess/15332)
**Author:** [@MathieuBoissier](https://geant4-forum.web.cern.ch/u/MathieuBoissier)\ **Replies:** 3\ **Last updated:** [September 21, 2026, 1:23pm UTC](https://geant4-forum.web.cern.ch/t/question-regarding-the-lambdafactor-in-g4hadronicprocess/15332 "2026-09-21T13:23:42Z")
Geant4 Version:11.4.2 Operating System:Ubuntu22.04 Hello everyone, While simulating deuteron-induced reactions in thin targets to generate neutrons, I noticed a strange behavior in the neutron energy spectrum. After s… --- ## [E-beam current simulation in X-ray tube](https://geant4-forum.web.cern.ch/t/e-beam-current-simulation-in-x-ray-tube/15361)
**Author:** [@Geant4Fan](https://geant4-forum.web.cern.ch/u/Geant4Fan)\ **Replies:** 6\ **Last updated:** [September 21, 2026, 3:38am UTC](https://geant4-forum.web.cern.ch/t/e-beam-current-simulation-in-x-ray-tube/15361 "2026-09-21T03:38:09Z")
Hi guys, I have a question to verify I am doing right. I have a model of an X-ray tube and want to know the dose for 1mA beam current. I am running 1e9 electrons which takes 6 hours to complete. If I ran 1E16 electrons, … --- ## [/run/printProgress effectively leaks memory](https://geant4-forum.web.cern.ch/t/run-printprogress-effectively-leaks-memory/15340)
**Author:** [@wsetterb](https://geant4-forum.web.cern.ch/u/wsetterb)\ **Replies:** 5\ **Last updated:** [September 18, 2026, 4:43pm UTC](https://geant4-forum.web.cern.ch/t/run-printprogress-effectively-leaks-memory/15340 "2026-09-18T16:43:07Z")
Punchline: Running a simulation with /run/printProgress 1000, 100k events per run, very short time per event (~milliseconds), and a few hundred runs in a row leads to massive memory consumption and can crash the program … --- ## [ParticleHP does not produce any residual isotopes in Hadr03 from inelastic interactions](https://geant4-forum.web.cern.ch/t/particlehp-does-not-produce-any-residual-isotopes-in-hadr03-from-inelastic-interactions/15358)
**Author:** [@MNeuberger](https://geant4-forum.web.cern.ch/u/MNeuberger)\ **Replies:** 3\ **Last updated:** [September 16, 2026, 4:46pm UTC](https://geant4-forum.web.cern.ch/t/particlehp-does-not-produce-any-residual-isotopes-in-hadr03-from-inelastic-interactions/15358 "2026-09-16T16:46:13Z")
At the risk of potentially asking something already covered several times (\[2597\], \[2715\]), I observed that ParticleHP does not producing any residual isotopes after inelastic interactions. I ran Hadr03 starting 20000 p… --- ## [Region specific DNA physics for protons](https://geant4-forum.web.cern.ch/t/region-specific-dna-physics-for-protons/15353)
**Author:** [@afish58](https://geant4-forum.web.cern.ch/u/afish58)\ **Replies:** 11\ **Last updated:** [September 15, 2026, 3:21am UTC](https://geant4-forum.web.cern.ch/t/region-specific-dna-physics-for-protons/15353 "2026-09-15T03:21:03Z")
\_Geant4 Version:\_11.4.2 Hi all, I’m trying to write a physics list to use DNA-processes in specific regions similar to the AuNP example. examples/extended/medical/dna/AuNP AuNP provided a working example for the elec… [Next page](https://geant4-forum.web.cern.ch/latest.md?page=1)