230Th spontaneous fission

Physics Processes, Models and Cross Sections
1

Hello,

I’m interested into the decay products of the 230Th spontaneous fission.
I’m using the following code to access it:

G4DecayTable* radTable = isotope->GetDecayTable();

for (int ii = 0; ii < radTable->entries(); ++ii)
    {
G4double branching_ratio = radTable->GetDecayChannel(ii)->GetBR();

        G4cout<<"BR = "<< branching_ratio<<"  "<< radTable->GetDecayChannel(ii)->GetKinematicsName ()<<G4endl;

        if(radTable->GetDecayChannel(ii)->GetKinematicsName() == "SF decay"){
            ((G4SFDecay*)radTable->GetDecayChannel(ii))->DumpNuclearInfo ();

            for (int jj = 0; jj < radTable->GetDecayChannel(ii)->GetNumberOfDaughters() && Pam == NULL; jj++)
        {

              G4ParticleDefinition* daughter_meta = radTable->GetDecayChannel(ii)->GetDaughter(jj);

              G4cout<<"  - "<< daughter_meta->GetParticleName()<<G4endl;
}
        }

This returns:

BR = 4e-14  SF decay
 G4SFDecay for parent nucleus Th230
 decays to neutrons and gammas, with branching ratio 4e-14% and Q value 1e-09
  - Th230

Which is definitively not the fission products.

Is it possible to access to the products ?
Thanks,

Quentin

2

No. The spontaneous fission model in Geant4 incorporates four parameterized distributions: neutron multiplicity, neutron energy, gamma multiplicity, and gamma energy. The fission products are not generated, nor is there code in the model to do so.

3

Thanks for the clarification. If the fission products are not generated, are the gammas from the fission products generated ?

4

The G4 gamma spectrum used in G4 SF is an “inclusive”, “prompt” fit. The Physics Reference Manual should have more detail. What I’ve assumed (we have a Cf-252 source we’re modelling) is that the spectrum includes whatever prompt gammas would come off the compound fission fragments, just as the neutrons are a mix of “direct” neutrons from the fission, and evaporation neutrons from the compound fragments.

What’s missing are the ground state fission fragments, and then all of the decay products of those. Because you won’t conserve four-momentum anyway if you’re drawing randomly from the neutron and gamma spectrum, I could imagine implementing code yourself to pick one random mass from the bilobed fragment distribution, and combining that with the neutron multiplicity to get the other fragment. Then you have to pick a Z value consistent with the masses. Either emplant those to G4Ions as additional at-rest seconaries, or try throwing a kinetic energy to assign them as back-to-back secondaries.

It’s not impossible, but it’s not going to be formally correct (in terms of conserving four momentum). You can’t really get it right on an event-by-event basis without doing a detailed model of the fissioning process.

5

Thanks for the clarification, that was helpful.