Neutron induced fission events

Hi, I’m working on neutron induced fission simulation, I used BIC_HP physics model. ( GEANT4 10.02 )
Geometry is very simple, I used Uranium-238 target, larger than beam size, thickness 0.5 umT, and neutron beam with various energy ( 10 ~ 40 MeV, mono energy )
I scored number of total fission event and I found total fission event suddenly drop over 19.9 MeV neutron energy.

I compared my result with ENDF data.(attached file).

GEANT4 cross section result was drawn in proportion to the number of total fission events. ( I matched 10 MeV results with ENDF data for normalization )
At energy range 10 ~ 19 MeV looks good but GEANT4 result suddenly drop at 19.9~20 MeV energy range.

Maybe something problem between 19.9 ~ 20 MeV energy range, If I didn’t mistake.
What can I try at this problem?
This is nFission process for my simulation.

Hadronic Processes for neutron
Process: nFission
Model: NeutronHPFission: 0 eV —> 20 MeV
Model: G4LFission: 19.9 MeV —> 2.88022e+295 J
Cr_sctns: NeutronHPFissionXS: 0 eV —> 20 MeV
Cr_sctns: GheishaFissionXS: 0 eV —> 100 TeV

Thanks in advance,


example Hadr03 with attached macro.
I do not see the phenomena you describe. At 19.9 MeV cross section is still 1.4 barn.
At 20 MeV too, but fission fragments are not generated ! ( an incoherence …)
Above 20 MeV, GheishaFission cross sections seem to be null.

moon.mac.txt (725 Bytes)
moon.out.txt (2.0 KB)

Above figure, I did mistake when I write neutron energy beside some point.
I mean, 19.1MeV -> 19.91MeV, 19.2MeV -> 19.92MeV …
sorry for confusion.

By the way, I did run Hadr03 example by reference to your opinion.
But result was same with my own code and fission fragments are generated below 20MeV also above 20 MeV, unlike your case … I didn’t change anything, just change neutron energy.

Thank you for reply, maire.

I scanned again 19.9 --> 20 MeV. Clearly Geant4 10.2 and 10.6 behave differently in this transition region …
More surprising is the problem of GheishaFission cross sections : nul or not ?
Maybe you can open a bug report.

Maybe I should test with 10.6 version.
I will check about GheishaFission cross sections.

thank you for your opinion, maire.