Is there a possible bug in photonNuclear process (LENDorBERTModel) or G4HadronicProcess?

Physics Processes, Models and Cross Sections
1

I’m running a simple simulation based on Geant4’s exampleB4a to detect photoneutrons from targets illuminated by gamma rays < 20 MeV. The geometry is simple with a monoenergetic general particle source of gammas, a block target of solid nitrogen-14 (density 2g/cc) at a distance embedded in an air half space and a detector. Data is collected when a gamma ray intersects the detector volume. I use gtools Root analysis tools to store various properties of the emitted neutron. I am running Geant4 10.5 patch 01 on an i7 PC with 16GB RAM and 64bit Linux (Fedora 30).

I am using ShieldingLEND physics list and there appears to be some problem with it. With an incident gamma ray energy of 11.668 MeV, almost every event generates errors of the form (the energy E(initial - final) below changes from event to event but the error is the same):

…
G4WT1 >
-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : had012
issued by : G4HadronicProcess:CheckResult()
Warning: Bad energy non-conservation detected, will re-sample the interaction
Process / Model: photonNuclear / LENDorBERTModel
Primary: gamma (22), E= 11.668, target nucleus (7, 14)
E(initial - final) = -12108.5 MeV.

*** This is just a warning message. ***
-------- WWWW -------- G4Exception-END --------- WWWW -------
…

With an incident gamma ray energy of 16.107 MeV, I get the same types of errors, e.g.,:

G4WT2 >
-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : had012
issued by : G4HadronicProcess:CheckResult()
Warning: Bad energy non-conservation detected, will re-sample the interaction
Process / Model: photonNuclear / LENDorBERTModel
Primary: gamma (22), E= 16.107, target nucleus (7, 15)
E(initial - final) = -2787.09 MeV.

*** This is just a warning message. ***
-------- WWWW -------- G4Exception-END --------- WWWW -------

Also, at 16.107 MeV I infrequently (~1 per 2 billion events) get a segmentation fault. When I run the code with the gdb debugger on the seg fault, I get the following:

Thread 4 “exampleB4a” received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffede63700 (LWP 31599)]
0x00007ffff2a09d6c in G4HadronicProcess::CheckResult(G4HadProjectile const&, G4Nucleus const&, G4HadFinalState*) ()
from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4processes.so
Missing separate debuginfos, use: dnf debuginfo-install bzip2-libs-1.0.6-29.fc30.x86_64 expat-2.2.6-2.fc30.x86_64 freetype-2.9.1-7.fc30.x86_64 glib2-2.60.4-1.fc30.x86_64 glibc-2.29-15.fc30.x86_64 graphite2-1.3.10-7.fc30.x86_64 harfbuzz-2.3.1-1.fc30.x86_64 libICE-1.0.9-15.fc30.x86_64 libSM-1.2.3-2.fc30.x86_64 libX11-1.6.7-1.fc30.x86_64 libXau-1.0.9-1.fc30.x86_64 libXext-1.3.3-11.fc30.x86_64 libXmu-1.1.2-13.fc30.x86_64 libXt-1.1.5-11.20190424gitba4ec9376.fc30.x86_64 libgcc-9.1.1-1.fc30.x86_64 libgcrypt-1.8.4-3.fc30.x86_64 libglvnd-glx-1.1.0-4.gitf92208b.fc30.x86_64 libgpg-error-1.33-2.fc30.x86_64 libicu-63.2-2.fc30.x86_64 libpng-1.6.36-1.fc30.x86_64 libstdc+±9.1.1-1.fc30.x86_64 libuuid-2.33.2-1.fc30.x86_64 libxcb-1.13.1-2.fc30.x86_64 lz4-libs-1.8.3-2.fc30.x86_64 mesa-libGLU-9.0.0-17.fc30.x86_64 pcre2-utf16-10.33-4.fc30.x86_64 qt5-qtbase-5.12.1-7.fc30.x86_64 qt5-qtbase-gui-5.12.1-7.fc30.x86_64 xz-libs-5.2.4-5.fc30.x86_64 zlib-1.2.11-15.fc30.x86_64
(gdb) backtrace
#0 0x00007ffff2a09d6c in G4HadronicProcess::CheckResult(G4HadProjectile const&, G4Nucleus const&, G4HadFinalState*) ()
from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4processes.so
#1 0x00007ffff2a0c127 in G4HadronicProcess::PostStepDoIt(G4Track const&, G4Step const&) () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4processes.so
#2 0x00007ffff62b04de in G4SteppingManager::InvokePSDIP(unsigned long) () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4tracking.so
#3 0x00007ffff62b0c1b in G4SteppingManager::InvokePostStepDoItProcs() () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4tracking.so
#4 0x00007ffff62addc4 in G4SteppingManager::Stepping() () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4tracking.so
#5 0x00007ffff62b92fc in G4TrackingManager::ProcessOneTrack(G4Track*) () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4tracking.so
#6 0x00007ffff62f8a46 in G4EventManager::DoProcessing(G4Event*) () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4event.so
#7 0x00007ffff63a123c in G4WorkerRunManager::DoEventLoop(int, char const*, int) () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4run.so
#8 0x00007ffff639550e in G4RunManager::BeamOn(int, char const*, int) () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4run.so
#9 0x00007ffff63a29bc in G4WorkerRunManager::DoWork() () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4run.so
#10 0x00007ffff63abeca in G4MTRunManagerKernel::StartThread(G4WorkerThread*) () from /home/jmcfee/geant4/geant4.10.5.p01-install/lib64/libG4run.so
#11 0x00007ffff1306474 in ?? () from /lib64/libstdc++.so.6
#12 0x00007ffff10b55a2 in start_thread () from /lib64/libpthread.so.0
#13 0x00007ffff0fe2303 in clone () from /lib64/libc.so.6

So it seems that G4HadronicProcess::CheckResult(G4HadProjectile const&, G4Nucleus const&, G4HadFinalState*) () is causing a segmentation fault.

Is there a bug in photonNuclear LENDorBERTModel or G4HadronicProcess?

As always, any help is gratefully appreciated. Thanks.

2

Hello,

you may try out Physics Lists QGSP_BIC_HP or QBBC or Shielding. ShieldingLEND is less validated. Warning is showing a big non-concervation that is not good but should not crash an application. The crash likely due to LEND model.

VI

3

Hi,
Thank you for your reply. I will try some of the other lists you suggest to compare results. I have also submitted a bug report to Bugzilla/Geant4.
John

4

Respected Dr. McFee,

I would be grateful If you can please update this post with the solution of the bug and how it is resolved, when it is done.

Thanks very much!
Sanchit Sharma

5

Hello! Any news abous fixing this bug?

6

Hi.
Dennis Hebert Wright has been working diligently on this bug and related ones and seems near to having a solution. When the solution is verified, it will be posted. I am not sure when this will be, but hopefully soon.

7

You can track the progress on this here:
https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2174

8

This bug (2174) has now been fixed by Dennis.

9

I should note that there remains a related bug which yields an unphysical-looking step-function-like photoneutron spectrum for a number of nuclei for gamma rays in the 7-20 MeV energy range. I reported it in the forum a while ago. It is assigned problem 2197 in bugzilla and is not yet resolved.

10

Will the solution be available in the next patch?
And I have another question: will it be possible to use LENDorBERTModel for energies above 20 MeV? For instance if i set:

G4LENDorBERTModel* lend = new G4LENDorBERTModel(G4Gamma::Gamma());
lend->SetMaxEnergy(30MeV);
process->RegisterMe(lend);
G4LENDCombinedCrossSection lendXS = new G4LENDCombinedCrossSection(G4Gamma::Gamma());
process->AddDataSet(lendXS);

Because actually there are data for cross sections in LEND library for energies above 20 MeV, and when I try to get the value of cross section for Au196 (see attached image), I get some, but before segmentation fault (core dump) for 23.3 MeV incident gamma, and ofcourse there are a lot of exception like it was mentiond above.

Au196LEND
Au196LEND1525×933 43.9 KB