Introduction to GEANT4

GEANT4 provides a variety of physics processes. These processes are decoupled from one another and you can select those which are relevant to your simulation. The processes are grouped in seven categories and their full list is available [http://geant4.cern.ch/support/proc_mod_catalog/processes/ here]:

In method ConstructProcess() define your physics processes:

If you want to build more realistic physics list you have to use the class <span style="color:#ff0000"> G4VModularPhysicsList </span>. For example, the photon from the example above can undergo compton scattering apart from conversion. In <span style="color:#ff0000"> G4VModularPhysicsList </span> you can group the physics processes into separate modules: EM physics, hadronic physics, optical physics etc.  

<span style="color:#800000"> class MyPhysicsList:public G4VModularPhysicsList {

<span style="color:#800000"> public:

<span style="color:#800000"> MyPhysicsList();

<span style="color:#800000"> ~MyPhysicsList();

<span style="color:#800000"> virtual void ConstructParticle();

<span style="color:#800000"> virtual void SetCuts();

<span style="color:#800000"> void AddPhysicsList(const G4String& name);

<span style="color:#800000"> virtual void ConstructProcess();

<span style="color:#800000"> private:

<span style="color:#800000"> G4String                            fEmName;

<span style="color:#800000"> G4VPhysicsConstructor*              fEmPhysicsList;

<span style="color:#800000"> MyPhysicsList::MyPhysicsList():G4ModularPhysicsList() { </span>

<span style="color:#800000"> defaultCutValue = 1.0*mm; </span>

<span style="color:#800000"> RegisterPhysics(new ElectronPhysics()); // All physics processes having to do with electrons </span>

where for example class ProtonPhysics() is defined as:

<span style="color:#800000"> class ProtonPhysics():public G4VPhysicsConstructor { </span>

<span style="color:#800000"> public: </span>

<span style="color:#800000"> ProtonPhysics(const G4String& name="proton"); </span>

<span style="color:#800000"> virtual ~ProtonPhysics(); </span>

Particle production thresholds are defined in method SetCuts():

 

 

<span style="color:#800000"> void MyModPhysList::SetCuts() </span>

 

<span style="color:#800000"> {SetCutsWithDefault();} </span>