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Question absorbed dose for gamma 

Forum: Particles
Date: 05 Oct, 2011
From: Natalia <Natalia >

Hello, dear Geant4 users!

I need to calculate gap correction coefficient for X-ray calorimeter. That is the ratio between absorbed doses of gammas in the sensitive core of calorimeter with and without vacuum gap around the core. The calorimeter is carbon box with vacuum hole and sensitive carbon core inside it. The second geometry is the carbon box without hole. The thikness of carbon before sensitive core is the same in both cases. Energy of gammas is 1 MeV. Absorbed dose is calculated in SteppingAction.cc (based on TestEM11)in the following way:

 // In which volume point is licated
 G4StepPoint* point1 = aStep->GetPreStepPoint();
 G4TouchableHandle touch1 = point1->GetTouchableHandle();

 G4VPhysicalVolume* volume1 = touch1->GetVolume();
 G4String name = volume1->GetName();

   if (name == "Core")
   {
	   G4double cdep = aStep->GetTotalEnergyDeposit();
	    if (cdep <= 0.) return;
	   //absorbed energy in Core
	   G4double dosedep = cdep;   //Mev
	   eventAction->AddCoreEdep(cdep);
	   // Sum of absorbed energy in Core
	   histoManager->FillHisto(10, z, dosedep);
   }

The problem is that the result for gamma particles strongly depends on stepMax and statistics and seems incorrect. The difference of doses is about 20%. According to experimental data it should be about 0.2%. When I try to calculate the same for electrons, the ratio of doses is about 1.03 and this is more believable. I tried to use various physics lists, but the difference of doses for gamma is still too big.

What can I do wrong?

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