Geant4 User's Guide for Application Developers - Geant4 - CERN

Tracking and PhysicsOther base classes for processesSpecialized processes may be derived from seven additional virtual base classes which are themselves derivedfrom G4VProcess. Three of these classes are used for simple processes:G4VRestProcessProcesses using only the AtRestDoIt method.example: neutron captureG4VDiscreteProcessProcesses using only the PostStepDoIt method.example: compton scattering, hadron inelastic interactionThe other four classes are provided for rather complex processes:G4VContinuousDiscreteProcessProcesses using both AlongStepDoIt and PostStepDoIt methods.example: transportation, ionisation(energy loss and delta ray)G4VRestDiscreteProcessProcesses using both AtRestDoIt and PostStepDoIt methods.example: positron annihilation, decay (both in flight and at rest)G4VRestContinuousProcessProcesses using both AtRestDoIt and AlongStepDoIt methods.G4VRestContinuousDiscreteProcessProcesses using AtRestDoIt, AlongStepDoIt and PostStepDoIt methods.Particle changeG4VParticleChange and its descendants are used to store the final state information of the track, including secondarytracks, which has been generated by the DoIt methods. The instance of G4VParticleChange is the onlyobject whose information is updated by the physics processes, hence it is responsible for updating the step. Thestepping manager collects secondary tracks and only sends requests via particle change to update G4Step.G4VParticleChange is introduced as an abstract class. It has a minimal set of methods for updating G4Stepand handling secondaries. A physics process can therefore define its own particle change derived fromG4VParticleChange. Three pure virtual methods are provided,• virtual G4Step* UpdateStepForAtRest( G4Step* step),• virtual G4Step* UpdateStepForAlongStep( G4Step* step ) and• virtual G4Step* UpdateStepForPostStep( G4Step* step),which correspond to the three DoIt methods of G4VProcess. Each derived class should implement these methods.5.2.1. Electromagnetic InteractionsThis section summarizes the electromagnetic (EM) physics processes which are provided with Geant4. Extendedinformation are avalable at EM web pages. For details on the implementation of these processes please refer tothe Physics Reference Manual.5.2.1.1. "Standard" Electromagnetic ProcessesThe following is a summary of the standard electromagnetic processes available in Geant4.149