WIP: get Z/A of current material from Geant4.

Simulation/DetSimDedx/src/BetheBlochEquationDedxSimTool.cpp

 #include "BetheBlochEquationDedxSimTool.h"
 #include "G4Step.hh"
+#include "G4SystemOfUnits.hh"
 
 // https://folk.uib.no/ruv004/
 DECLARE_COMPONENT(BetheBlochEquationDedxSimTool)
@@ -10,6 +11,14 @@ double BetheBlochEquationDedxSimTool::dedx(const G4Step* aStep)
     G4Track* gTrack = aStep->GetTrack() ;
     G4int z = gTrack->GetDefinition()->GetPDGCharge();
     if (z == 0) return 0;
+
+    G4Material* material = gTrack->GetMaterial();
+    G4double material_density = material->GetDensity() / (CLHEP::g/CLHEP::cm3); // conert from G4 unit.
+    G4double material_Z = material->GetZ();
+    G4double material_A = material->GetA();
+
+    m_I = material_Z*10;  // Approximate
+
     G4double M = gTrack->GetDefinition()->GetPDGMass();//MeV
     M = pow(10,6)*M; //to eV
     G4double gammabeta=aStep->GetPreStepPoint()->GetBeta() * aStep->GetPreStepPoint()->GetGamma();
@@ -17,10 +26,10 @@ double BetheBlochEquationDedxSimTool::dedx(const G4Step* aStep)
     float beta = gammabeta/sqrt(1.0+pow(gammabeta,2));
     float gamma = gammabeta/beta;
     float Tmax = 2*m_me*pow(gammabeta,2)/(1+(2*gamma*m_me/M)+pow(m_me/M,2));
-    float dedx = m_K*pow(z,2)*m_material_Z*(0.5*log(2*m_me*pow(gammabeta,2)*Tmax/pow(m_I,2))-pow(beta,2))/(m_material_A*pow(beta,2));    
+    float dedx = m_K*pow(z,2)*material_Z*(0.5*log(2*m_me*pow(gammabeta,2)*Tmax/pow(m_I,2))-pow(beta,2))/(material_A*pow(beta,2));    
     dedx = dedx*m_scale;// the material density can be absorbed in scale 
     dedx = dedx*(1+((*m_distribution)(m_generator)));
-    return dedx*m_material_density; // MeV / cm 
+    return dedx*material_density; // MeV / cm 
 }
 
 StatusCode BetheBlochEquationDedxSimTool::initialize()
@@ -28,12 +37,11 @@ StatusCode BetheBlochEquationDedxSimTool::initialize()
     m_distribution = new std::normal_distribution<double>(0, m_resolution);
     m_me = 0.511*pow(10,6);//0.511 MeV to eV
     m_K = 0.307075;//const
-    m_I = m_material_Z*10;  // Approximate
+
 
     info() << "Initialize BetheBlochEquationDedxSimTool with following parameters" << endmsg;
     info() << "-> m_me: " << m_me << endmsg;
     info() << "-> m_K: " << m_K << endmsg;
-    info() << "-> m_I: " << m_I << endmsg;
 
     return StatusCode::SUCCESS;
 }