Geometry and physic characteristics

Particles, Track, Event, Run and Biasing
1

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_Geant4 Version: 10.7
_Operating System: Ubuntu WSL
_Compiler/Version: -
_CMake Version: 3.23.0

Evaluating TID in a 3 layers PCB for space LEO missions, I’m finding an error on the computation of the mass of the object.

OUT

Layer 1
Total energy accumulated: 9.38297e-12 eV
Density (kg/m³) di Ground: 2699
Mass Ground: 1.34767e+22 kg (2.1592 g )
Dose (TID): 6.96238e-34 Gy
Fluence totale: 12.757 particles/cm^2 (unità scorer)
Volume (mm^3) di Ground: 800
Mass calculated (kg): 1.34767e+22

[…] with a mass calculated proportional to e+22

here part of the code (RunAction.cc)

void RunAction::EndOfRunAction(const G4Run*)
{
std::vector volumeNames = { “Patch”, “Dielectric”, “Ground” };

for (size_t i = 0; i < volumeNames.size(); ++i) {
    G4LogicalVolume* logicVolume = GetLogicalVolumeByName(volumeNames[i]);
    if (!logicVolume) {
        G4cerr << "Volume logico " << volumeNames[i] << " non trovato!" << G4endl;
        continue;
    }

    double volume = logicVolume->GetSolid()->GetCubicVolume();
    double volume_m3 = volume * mm3; // da mm³ a m³
    double density = logicVolume->GetMaterial()->GetDensity();
    //double density_m3 = density * 0.0000000001;

    double mass = volume_m3 * density;
    
    if (mass <= 0) {
        G4cerr << "Massa del volume" << volumeNames[i] << "non valida!" << G4endl;
        continue;
    }

    double edep_J = fTotalEdep[i] * eV;  // Converti da eV a Joule
    double dose = edep_J / mass;

    G4cout << "\n>>> Layer " << (i + 1) << " (" << volumeNames[i] << "):" << G4endl;
    G4cout << "    Energia totale depositata: " << G4BestUnit(fTotalEdep[i], "Energy") << G4endl;
    G4cout << "Densità (kg/m³) di " << volumeNames[i] << ": " << density / (kg / m3) << G4endl;
    G4cout << "Mass " << volumeNames[i] << ": " << mass << " kg (" << G4BestUnit(mass, "Mass")<<")" << G4endl;
    G4cout << "Dose (TID): " << G4BestUnit(dose, "Dose") << G4endl;
    G4cout << "Fluence totale: " << fTotalFluence[i] << " particles/cm^2 (unità scorer)" << G4endl;
    G4cout << "Volume (mm^3) di " << volumeNames[i] << ": " << volume << G4endl;
    G4cout << "Densità (kg/m^3) di " << volumeNames[i] << ": " << density / (kg / m3) << G4endl;
    //G4cout << "Massa calcolata (kg): " << mass << G4endl;
}

}

any suggestions?

2

It looks like you’re using Geant4 units backwards. When you call a function like G4VSolid::GetCubicVolume(), it already has units assigned to it:

G4double volume = lv->GetSolid()->GetCubicVolume();
G4cout << " volume is " << volume/mm3 << " cubic mm, or "
       << volume/m3 << " cubic m" << G4endl;

Notice that what you do is divide out the units for printing. The quantity (variable) itself stays the same.

If you want to compute mass = volume*density, just do that. No other units:

double volume = lv->GetSolid()->GetCubicVolume();
double density = lv->GetMaterial()->GetDensity();
double mass = volume*density;
G4cout << " mass is " << mass/kg << " kg" << G4endl;
3

Many thanks, I’m going to try and I’ll let you know.