Hello.

I counted experimentally the various isotopes produced by neutron irradiation of iron (natural isotopic composition) at a reactor, and I would like to compare the data with a Geant4 simulation.

I do know the energy spectrum of the incident neutrons and I reproduced it in Geant4 using the G4GeneralParticleSource class.

The first thing that I did was to compare the ratio of the number of 54Mn isotopes created with the number of 59Fe isotopes produced. I found that the ratio of 54Mn/59Fe calculated by Geant4 is orders of magnitudes higher than the one observed experimentally.

59Fe is produced by neutron capture on 58Fe, whereas 54Mn is produced by (n,p) on 54Fe. This latter process is named â€ścharge exchangeâ€ť in Geant4.

I looked at the cross section for neutron capture on Fe in Geant4 (using G4HadronicProcessStore::GetCaptureCrossSectionPerAtom() ) and found it consistent with the radiative neutron capture cross section in ENDF.

I then looked at the charge exchange cross section on Fe used in Geant4 (using G4HadronicProcessStore::GetChargeExchangeCrossSectionPerAtom() ) and found values that are extremely high, much higher than the ENDF Fe(N,P) cross section.

I am attaching the plots of the charge exchange cross section from G4. The corresponding N,P cross section from ENDF can be retrieved from ENDF: Evaluated Nuclear Data File (new users can only embed one item in their posts!).

Please let me know if I am missing something. This is the list of processes and xsections enabled for neutrons in my Physics List.

```
Hadronic Processes for neutron
```

Process: hadElastic

Model: hElasticCHIPS: 19.5 MeV â€”> 100 TeV

Model: NeutronHPElastic: 4 eV â€”> 20 MeV

Model: NeutronHPThermalScattering: 0 eV â€”> 4 eV

Cr_sctns: NeutronHPThermalScatteringData: 0 eV â€”> 4 eV

```
Cr_sctns: NeutronHPElasticXS: 0 eV ---> 20 MeV
Cr_sctns: G4NeutronElasticXS: 0 eV ---> 100 TeV
```

Process: chargeExchange

Model: Charge Exchange: 0 eV â€”> 100 TeV

Cr_sctns: G4NeutronElasticXS: 0 eV â€”> 100 TeV

Process: neutronInelastic

Model: FTFP: 3 GeV â€”> 100 TeV

Model: BertiniCascade: 19.9 MeV â€”> 6 GeV

Model: NeutronHPInelastic: 0 eV â€”> 20 MeV

Cr_sctns: NeutronHPInelasticXS: 0 eV â€”> 20 MeV

```
Cr_sctns: JENDLHEInelasticCrossSection: 0 eV ---> 100 TeV
Cr_sctns: G4NeutronInelasticXS: 0 eV ---> 100 TeV
```

Process: nCapture

Model: NeutronHPCapture: 0 eV â€”> 20 MeV

Model: nRadCapture: 19.9 MeV â€”> 100 TeV

Cr_sctns: NeutronHPCaptureXS: 0 eV â€”> 20 MeV

```
Cr_sctns: G4NeutronCaptureXS: 0 eV ---> 100 TeV
```

Process: nFission

Model: NeutronHPFission: 0 eV â€”> 20 MeV

Model: G4LFission: 19.9 MeV â€”> 100 TeV

Cr_sctns: NeutronHPFissionXS: 0 eV â€”> 20 MeV

```
Cr_sctns: ZeroXS: 0 eV ---> 100 TeV
```

Thank you,

Elena