Hi all,

In upgrading from Geant4 10.3.p01 to 10.3.p02, I noticed a change in the spectrum of gamma rays produced by neutron capture on gadolinium. The spectrum of individual gamma ray energies appears to be shifted to higher energies and the total gamma ray energy has a long tail above the Q-value. Plots demonstrating both of these effects are attached.

Both 10.3.p01 and 10.3.p02 are using the G4NDL 4.5 data library. I have checked this behavior using 10.3.p03 and 10.5 as well and have confirmed that both produce results similar to 10.3.p02.

Below I show a print out of the processes registered to neutrons for both 10.3.p01 and 10.3.p02.

It’s unclear what’s caused this change. I checked the patch notes, but didn’t see anything that seemed like it would explain this behavior.

Any guidance on how to proceed would be appreciated. For now, I am sticking to 10.3.p01 because the new behavior seems like a bug.

```
---------------------------------------------------
Hadronic Processes for neutron
Process: hadElastic
Model: hElasticCHIPS: 19.5 MeV ---> 100 TeV
Model: NeutronHPElastic: 4 eV ---> 20 MeV
Model: NeutronHPThermalScattering: 0 eV ---> 4 eV
Cr_sctns: NeutronHPThermalScatteringData: 0 eV ---> 4 eV
Cr_sctns: NeutronHPElasticXS: 0 eV ---> 20 MeV
Cr_sctns: G4NeutronElasticXS: 0 eV ---> 100 TeV
Cr_sctns: GheishaElastic: 0 eV ---> 100 TeV
Process: neutronInelastic
Model: FTFP: 4 GeV ---> 100 TeV
Model: BertiniCascade: 19.9 MeV ---> 5 GeV
Model: NeutronHPInelastic: 0 eV ---> 20 MeV
Cr_sctns: NeutronHPInelasticXS: 0 eV ---> 20 MeV
Cr_sctns: JENDLHEInelasticCrossSection: 0 eV ---> 100 TeV
Cr_sctns: Barashenkov-Glauber: 0 eV ---> 100 TeV
Cr_sctns: NeutronHPInelasticXS: 0 eV ---> 20 MeV
Cr_sctns: Barashenkov-Glauber: 0 eV ---> 100 TeV
Cr_sctns: GheishaInelastic: 0 eV ---> 100 TeV
Process: nCapture
Model: NeutronHPCapture: 0 eV ---> 20 MeV
Model: nRadCapture: 19.9 MeV ---> 100 TeV
Cr_sctns: NeutronHPCaptureXS: 0 eV ---> 20 MeV
Cr_sctns: G4NeutronCaptureXS: 0 eV ---> 100 TeV
Cr_sctns: NeutronHPCaptureXS: 0 eV ---> 20 MeV
Cr_sctns: GheishaCaptureXS: 0 eV ---> 100 TeV
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
---------------------------------------------------
```

individualGammaEnergy.pdf (14.9 KB) totalGammaEnergy.pdf (15.4 KB)