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None Force photoelectric over Compton 

Forum: Biasing and Scoring
Date: 01 Dec, 2015
From: Paola Ferrario <Paola Ferrario>

Hi! I'd like to bias my physics in order to have only photoelectric process for a gamma particle (no Compton or pair production), but keeping the correct absorption length of the material, meaning that I want to keep the correct probability of the gamma of not interacting at all in the detector and, if it interacts, of the position where it occurs. Following Chapter 3.7.4 of the geant4 documentation and examples/extended/biasing/GB01, I've built my biasing operator class, called OperatorChangeCrossSection (which I attach), I've added the following lines to the geometry volume affected:

    OperatorChangeCrossSection* biasOp = new OperatorChangeCrossSection("gamma","ForcePhotoelectric");

and I've added to my specific physics list (which I attach) the lines

 pmanager = G4Gamma::Definition()->GetProcessManager();
      G4BiasingHelper::ActivatePhysicsBiasing(pmanager, "phot");

I'm using both the G4EMStandardPhysics and my specific physics list, through the commands:

/PhysicsList/RegisterPhysics G4EmStandardPhysics_option4

/PhysicsList/RegisterPhysics NexusPhysics

Which value of the cross section factor should I use in the OperatorChangeCrossSection class to obtain what I want? If I use 1000, for instance, it seems to me that gammas undergo photoelectric process every time they enter the volume, and this is not what I want. O maybe I'm using the wrong operator for my purpose. Any help would be appreciated! Thank you



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