Getting spectrum of Cs 137

Particles, Track, Event, Run and Biasing
1

Hello!.

I am currently struggling with Cs 137 spectrum. The best I could get is:
Cs137

Comparing it to the correct spectrum, I clearly can see the backscatter peak, the Compton edge and the photopeak, however I have never seen the Ba x-rays line at 32 keV. Maybe there is an unobvious trick how to model it?

Currently I have a detector and a small disc filled with Cs 137. I simulate gamma particles from this disc with initial energy of 662 keV and collect data from scintillator. For simulation I use G4ParticleGun and QBBC as physics list.

Please help! Thank you in advance!

_Geant4 Version:_11.1.1

2

may be other physics lisit have different spectrum? I am not sure.
I simulate the proton in phantom, different physics list have huge difference spectrum.

3

Thank you for your response!

As far as I know, QBBC is optimal in this case because it’s possibility to accurately work in energy regions of 20MeV and less, which is required. I’ve recently changed it to several others and have not seen any difference in results.

4

Hi,

Have you tried with the example rdecay01 that is provided by Geant4? You can find it here or under

$G4INSTALL/share/Geant4/examples/extended/radioactivedecay/rdecay01

If you still want to use the Builtin physics list, you may need to fine tune the options, like:

  G4VModularPhysicsList* physicsList = new FTFP_BERT;
  physicsList->RegisterPhysics( new G4RadioactiveDecayPhysics );
  
  const G4double meanLife = 1*picosecond;  
  G4NuclideTable::GetInstance()->SetMeanLifeThreshold(meanLife);  
  G4NuclideTable::GetInstance()->SetLevelTolerance(1.0*eV);

  // define flags for the atomic de-excitation module
  //
  G4EmParameters::Instance()->SetDefaults();
  G4EmParameters::Instance()->SetAugerCascade(true);
  G4EmParameters::Instance()->SetDeexcitationIgnoreCut(true);    

  // define flags for nuclear gamma de-excitation model
  //
  G4DeexPrecoParameters* deex = 
    G4NuclearLevelData::GetInstance()->GetParameters();
  deex->SetCorrelatedGamma(false);
  deex->SetStoreAllLevels(true);
  deex->SetInternalConversionFlag(true);	  
  deex->SetIsomerProduction(true);  
  deex->SetMaxLifeTime(meanLife);

  runManager->SetUserInitialization(physicsList);

This code comes from the example rdecay01.

Best,
Alvaro