Can we know which atom the deposited energy is deposited on

Physics Processes, Models and Cross Sections
3

@lvll98 I presume you’re asking about the target “atom type”, not position? Unfortunately, I don’t believe that’s available in a generic way. If the interaction was hadronic, then G4Isotope* G4HadronicProcess::GetTargetIsotope() or G4Nucleus* G4HadronicProcess::GetTargetNucleus() can get you this information.

Use code along the lines of (note the null pointer checks at each step)

  G4StepPoint* post = theStep->GetPostStepPoint();
  const G4VProcess* proc = (post ? post->GetProcessDefinedStep() : 0);
  const G4HadronicProcess* had = dynamic_cast<G4HadronicProcess*>(proc);

  G4Isotope* target = (had ? had->GetTargetIsotope() : 0);
  if (target) {
    G4cout << theStep->GetTrack()->GetParticleDefinition()->GetParticleName()
           << " interacted with " << target->GetName() << G4endl;
  }