Geant4 Photon Processes

This package contains a set of processes involving photons (Breit-Wheeler, elastic photon-photon scattering, Compton-scattering) allowing photon collision experiments to be modelled within the Geant4 framework.

Installing

Before installing the package, make sure you have the following libraries installed:

• Geant4 (required, tested with v11.1.1)
• HDF5 (required)
• CMake (required)
• Eigen3 (required)
• libgp https://github.com/mblum/libgp (optional)

Once the dependencies are installed, start by downloading the package

git clone https://github.com/robbiewatt1/Photon-Processes

Now create a build directory for the package (this should be outside the package source directory) and configure the build with cmake:

mkdir PhotonProcess_Build
cd PhotonProcess_Build
cmake ../Photon-Processes/ -DBUILD_GP=ON -DCMAKE_INSTALL_PREFIX=<install-location>

-DBUILD_GP=ON is optional, allowing a Gaussian process to be used to speed up the interaction probability calculation. Next, compile and install the package:

make install -j

Finally, run the following bash script to make sure the cross-section data tables can be found:

. <install-location>/bin/Photon-Process.sh

Using the package

All the processes in the package inherit from the base class G4VDiscreteProcess. Therefore, they can be added to the physics list in the standard way. The following is an example of how to add the Breit-Wheeler process, with a black body radiation field at 300eV:

BlackBody* field = new BlackBody(0.0003, 0.00003, 0.006 , 100, 100);
BreitWheeler* m_breitWheeler = new BreitWheeler(field);
G4ProcessManager* pmanagerG = G4Gamma::Gamma()->GetProcessManager();
 pmanagerG->AddProcess(m_breitWheeler, -1, -1, 1);

See G4EmStandardPhysics.cc for an example of how to add processes to the physics list. We also need to set the radiation volume in the DetectorConstruction class. This is achieved by defining a radiation material with the "Radiation" property set to 1:

G4Material* radiation = nist->FindOrBuildMaterial("G4_Galactic");
G4MaterialPropertiesTable* radiationTable  = new G4MaterialPropertiesTable();
radiationTable->AddConstProperty("Radiation",  1.0);
radiation->SetMaterialPropertiesTable(radTable);

The radiation material can now be registered with an instance of G4LogicalVolume