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Question highly un reasonable positron penetration depth in Fe. (LowEnergy, Penelope and default) 

Forum: Physics List
Date: 28 Jul, 2008
From: Or Chen <Or Chen>

Hey,

I'm working on a PAS (Positron Annihilation Spectroscopy) simulation,

In the experimental system's most basic structure, positrons leave the source at about ~200*keV, loose about 10*keV ant the source's house and then loose energy in the Iron and annihilate at around thermal energy.

From what I understand, the Penelope model is best for my geometrical setup and energy ranges.

As a first and basic validation of my simulation I looked at the penetration depth of the positron in the Iron.

Using both Penelope, LowEnergy and the Default model I got about 20 micron, when I know that a reasonable result should be around the 100 micron.

(give or take 30 is still fine)

Obviously, this is a major problem...

Another related thing that I noticed is that in many of the examples, all particles are using the LowEenergy or Penelope model, and the positron is the only one who uses the default model, why is that?

Here is my physics list:

(I would appreciate it if you could take a look at it and tell me what I should change in order to get a reasonable result according to my energy ranges and setup)

void PhysicsList::ConstructProcess()
{	
	AddTransportation();

	theParticleIterator->reset();
	while( (*theParticleIterator)() ){
		G4ParticleDefinition* particle = theParticleIterator->value();
		G4ProcessManager* pmanager = particle->GetProcessManager();
		G4String particleName = particle->GetParticleName();

		if (particleName == "gamma") {
			// gamma         
			pmanager->AddDiscreteProcess(new G4PenelopePhotoElectric);
			pmanager->AddDiscreteProcess(new G4PenelopeCompton);
			pmanager->AddDiscreteProcess(new G4PenelopeGammaConversion);
			pmanager->AddDiscreteProcess(new G4PenelopeRayleigh);
		} else if (particleName == "e-") {
			//electron
			pmanager->AddProcess(new G4MultipleScattering,     -1, 1, 1);
			pmanager->AddProcess(new G4PenelopeIonisation,     -1, 2, 2);
			pmanager->AddProcess(new G4PenelopeBremsstrahlung, -1,-1, 3);
		} else if (particleName == "e+") {
			//positron
			pmanager->AddProcess(new G4MultipleScattering,     -1, 1, 2);
			pmanager->AddProcess(new G4PenelopeIonisation,     -1, 2, 3);
			pmanager->AddProcess(new G4PenelopeBremsstrahlung, -1,-1, 4);  
			G4VProcess* penelopeAnnihilation = new G4PenelopeAnnihilation;
			pmanager->AddProcess(penelopeAnnihilation);
			pmanager ->SetProcessOrderingToFirst(penelopeAnnihilation, idxAtRest);
			pmanager ->SetProcessOrderingToFirst(penelopeAnnihilation, idxPostStep);
		} else if ((!particle->IsShortLived()) &&
			(particle->GetPDGCharge() != 0.0) && 
			(particle->GetParticleName() != "chargedgeantino")) {
			//all others charged particles except geantino
			pmanager->AddProcess(new G4MultipleScattering, -1, 1, 1);
			pmanager->AddProcess(new G4hIonisation,        -1, 2, 2);
		}
	}

	G4Decay* theDecayProcess = new G4Decay();
	theParticleIterator->reset();
	while( (*theParticleIterator)() )
	{
		G4ParticleDefinition* particle = theParticleIterator->value();
		G4ProcessManager* pmanager = particle->GetProcessManager();
		if (theDecayProcess->IsApplicable(*particle)) 
		{ 
			pmanager ->AddProcess(theDecayProcess);
			// set ordering for PostStepDoIt and AtRestDoIt
			pmanager ->SetProcessOrdering(theDecayProcess, idxPostStep);
			pmanager ->SetProcessOrdering(theDecayProcess, idxAtRest);
		}
	}
}

Thanks' Or Chen.

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1 None: Re: highly un reasonable positron penetration depth in Fe. (LowEnergy, Penelope and default)   (michel maire - 29 Jul, 2008)
(_ Disagree: Re: highly un reasonable positron penetration depth in Fe. (LowEnergy, Penelope and default)   (Or Chen - 29 Jul, 2008)
1 None: Re: highly un reasonable positron penetration depth in Fe. (LowEnergy, Penelope and default)   (Or Chen - 29 Jul, 2008)
2 None: Re: highly un reasonable positron penetration depth in Fe. (LowEnergy, Penelope and default)   (michel maire - 30 Jul, 2008)
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