Uranium enrichment issues

[Andrew_Parker]

Hi,

I am try to replicate some experimental measurements of uranium dioxide fuel pellets in GEANT4. The pellets are 4.46% enriched. I have run my model using the general particle source function specifiying the number of particles to run for each isotope on their relative weight and specific activity.

Comparing the experimental and simulated data it appears that the U-238 decay-chain peak at 1001 keV is greater than that observed experimentally. This suggests that the simulation is wrong. This could be because my calculation for the number of particles to run for each isotope is incorrect, or that the gaussian broadening algorithm i am applying to the raw geant4 data is incorrect.

Any help would be very welcome.

[civanch]

Hello,

Gamma emission nuclear de-excitation in Geant4 is data driven. There is a probability that data for these lines are not accurate. It is important to mention what version of Geant4 and what Physics List are used.

VI

[CharlesJ]

Hello,
I’m trying to simulate U3O8 with a certain enrichment level of U235 (for a gamma spectra study). I’ve activated G4RadioactiveDecayPhysics() and G4DecayPhysics() , but I can’t observe the 1001 keV peak of U238. When I enable G4IonPhysics() , the peak appears, but other peaks at higher energies also show up. I feel like enabling G4IonPhysics() is distorting the simulation.
Can you help me please? Thanks a lot,

[mkelsey]

1. Did you use /process/had/rdm/nucleusLimits to restrict decays to just U-235?
2. In your source configuration, do you specify both U-235 and U-238 ions?

Geant4 does not treat materials as active; they will never decay. If you want to see the U-238 gammas, you have to specify it in your source.

[CharlesJ]

Thanks a lot:

1. No, I don’t apply any cuts on the nucleus limits.

2. I am generating both ions. Below is an example:

   G4double ionCharge = 0. * eplus;
   G4double excitEnergy = 0 * keV;

   G4int A = 238 //or 235
   G4int Z = 92;

   G4ParticleDefinition* ion = G4IonTable::GetIonTable()->GetIon(Z, A, excitEnergy);
   fParticleGun->SetParticleDefinition(ion).

   The 1001 keV peak appears only when G4IonPhysics() is activated. However, I feel that G4IonPhysics() is not relevant for studying a gamma source without external excitation.

[mkelsey]

If you don’t apply cuts on which nuclei decay, then in every event you’re going to get the whole decay chain (U-238 all the way to lead, for example). If you don’t have timing cuts in your analysis code, then you are very likely seeing gammas from other daughters.

I don’t have a good answer for whether or no you “should need” G4IonPhysics or not. The canonical answer is always, “use one of the reference physics lists.”

[CharlesJ]

Thank you for your answer!

Today, I switched to the latest version of Geant4 (11.2). I reused the same physics settings that I had activated in the previous version (10.5), but my gamma spectrum is fundamentally different. The characteristic peaks of U-235 have disappeared, and my spectrum is now dominated by a continuum of low-energy photons. Thank you for your help!