Geant4 Version: 11.3.2
Operating System: Ubuntu 24.04 LTS (Noble Numbat)
Compiler/Version: g++ (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
CMake Version: 3.28.3
Hi 
I’m trying to understand how the transportation process is working and how to extract the correct info from PreStep and PostStep points.
My current implementation to save hit information in the detector is this one:
// Called every time a step occurs in a volume associated with this sensitive detector
G4bool ActiveAreaSD::ProcessHits(G4Step *step, G4TouchableHistory *)
{
// Get basic pointers
const G4Track *track = step->GetTrack();
const G4StepPoint *preStep = step->GetPreStepPoint();
const G4StepPoint *postStep = step->GetPostStepPoint();
const G4TouchableHandle touchablePreStep = preStep->GetTouchableHandle();
// Energy deposit in this step
G4double Edep = step->GetTotalEnergyDeposit();
if (Edep == 0)
return true;
// Event ID
G4int eventID = G4RunManager::GetRunManager()->GetCurrentEvent()->GetEventID();
// Create new hit
auto hit = new MyHit();
G4bool isActive = fLayerMap[touchablePreStep->GetVolume()->GetLogicalVolume()->GetName()];
if (isActive)
hit->SetIsActiveArea(1);
else
hit->SetIsActiveArea(0);
// Store spatial info
hit->SetPreStepPos(preStep->GetPosition());
hit->SetPostStepPos(postStep->GetPosition());
if (preStep->GetStepStatus() == fGeomBoundary)
hit->SetIsPreStepPointOnBoundary(1);
else
hit->SetIsPreStepPointOnBoundary(0);
if (postStep->GetStepStatus() == fGeomBoundary)
hit->SetIsPostStepPointOnBoundary(1);
else
hit->SetIsPostStepPointOnBoundary(0);
G4ThreeVector mom = track->GetMomentum();
hit->SetMomentum(mom);
hit->SetEdep(Edep);
// Time
hit->SetTime(preStep->GetGlobalTime());
// Volume and geometry info
hit->SetVolumeName(touchablePreStep->GetVolume()->GetName());
// Optional: layer ID if using copy numbers
hit->SetCopyNumber(touchablePreStep->GetCopyNumber());
// Particle info
const G4ParticleDefinition *particleDef = track->GetParticleDefinition();
hit->SetName(particleDef->GetParticleName());
// hit->SetPDGCode(particleDef->GetPDGEncoding());
hit->SetMass(particleDef->GetPDGMass());
hit->SetCharge(particleDef->GetPDGCharge());
// Track info
hit->SetTrackID(track->GetTrackID());
hit->SetParentTrackID(track->GetParentID());
hit->SetEventID(eventID);
hit->SetEnergy(track->GetKineticEnergy());
// hit->SetTotalEnergy(track->GetTotalEnergy());
// Process
if (postStep->GetProcessDefinedStep())
hit->SetProcess(postStep->GetProcessDefinedStep()->GetProcessName());
else
hit->SetProcess("unknown");
// Optional: material names
hit->SetPreStepMaterialName(preStep->GetMaterial()->GetName());
hit->SetPostStepMaterialName(postStep->GetMaterial()->GetName());
// Add to collection
fHitsCollection->insert(hit);
return true;
}
Basically, all the information I’m extracting is:
| Field | Type | Description |
|---|---|---|
IsActiveArea |
G4int |
Whether the hit occurred in an active area (1) or passive (0). |
PreStepPos |
G4ThreeVector |
Position at the start of the step (global coordinates). |
PostStepPos |
G4ThreeVector |
Position at the end of the step (global coordinates). |
IsPreStepPointOnBoundary |
G4int |
1 if the pre-step point is at a geometry boundary, else 0. |
IsPostStepPointOnBoundary |
G4int |
1 if the post-step point is at a geometry boundary, else 0. |
Momentum |
G4ThreeVector |
Momentum of the particle at the current step. |
Edep |
G4double |
Total energy deposited during the step (step->GetTotalEnergyDeposit()). |
Time |
G4double |
Global time of the hit (preStep->GetGlobalTime(), in ns). |
VolumeName |
G4String |
Name of the volume where the hit occurred. |
CopyNumber |
G4int |
Volume copy number (used for repeated structures or layers). |
Name |
G4String |
Name of the particle (e.g., "alpha", "proton", "neutron"). |
Mass |
G4double |
Mass of the particle (in MeV/c²). |
Charge |
G4double |
Electric charge of the particle (in e units). |
TrackID |
G4int |
Unique ID of the track. |
ParentTrackID |
G4int |
ID of the parent track (if secondary particle). |
EventID |
G4int |
Event number (from G4RunManager). |
Energy |
G4double |
Kinetic energy of the particle at the hit (in MeV). |
Process |
G4String |
Name of the process that ended the step (e.g., "hIoni", "alphaInelastic"). |
PreStepMaterialName |
G4String |
Name of the material at the pre-step point. |
PostStepMaterialName |
G4String |
Name of the material at the post-step point. |
I don’t understand how I may have some hits where the E deposited is != 0 and the PostStep point process is equal to “Transportation”, (I was imagining transportation just as a process with E deposited == 0)
Especially if I try to plot spectra of energy for each specific process, what I see is that this “Transportation” leads to an extra counting, see spectra2.pdf:
spectra2.pdf (17.8 KB)
- x-axis: E deposited MeV
- y-axis: Counts
While if I’m excluding from the counting all the hits where the post-step point is on a geometrical boundary (e.g. on the boundary between two layers in the detector), this Transportation contribution in terms of energy is zero:
spectra1.pdf (17.2 KB)
- x-axis: E deposited MeV
- y-axis: Counts
I’m wondering if I’m interpreting this information correctly, and if I can safely exclude these boundary points from the count of the deposited energy.
Thanks a lot in advance,
Michael