New material for Scintillator building

Geometry, Fields and Transportation
1

Hello Geant4 users!

I am pretty new to GEANT4 and Linux. I am currently building a polystyrene scintillator bar however I want to change the default polystyrene material density to 1.03 g/cm^3. I tried doing this in DetectorConstruction.cc below :


void DetectorConstruction::DefineMaterials()
{
	auto nistManager = G4NistManager::Instance();
	
    // keep this for now : 
    
     G4Material* scintMat = new G4Material ("plasticScint", 1.03*g/cm3, 1, kStateSolid); 
   scintMat->AddMaterial(G4NistManager::Instance()->FindOrBuildMaterial("G4_POLYSTYRENE"), 1.0);



// Air
	nistManager->FindOrBuildMaterial("G4_AIR");


	
 // ------------ Generate & Add Material Properties Table ------------
 
 G4double photonEnergy[] ={2.034 * eV, 2.068 * eV, 2.103 * eV, 2.139 * eV,
 2.177 * eV, 2.216 * eV, 2.256 * eV, 2.298 * eV,
 2.341 * eV, 2.386 * eV, 2.433 * eV, 2.481 * eV,
 2.532 * eV, 2.585 * eV, 2.640 * eV, 2.697 * eV,
 2.757 * eV, 2.820 * eV, 2.885 * eV, 2.954 * eV,
 3.026 * eV, 3.102 * eV, 3.181 * eV, 3.265 * eV,
 3.353 * eV, 3.446 * eV, 3.545 * eV, 3.649 * eV,
 3.760 * eV, 3.877 * eV, 4.002 * eV, 4.136 * eV};
 const G4int nEntries = sizeof (photonEnergy) / sizeof (G4double);
 //
 G4double refractiveIndex[] ={1.57 , 1.57 , 1.57 , 1.57 , 1.57 ,
 1.57 , 1.57 , 1.57 , 1.57 ,1.57 ,
 1.57 , 1.57 , 1.57 , 1.57 ,1.57 ,
 1.57 , 1.57 , 1.57 , 1.57  ,1.57 ,
 1.57 , 1.57 , 1.57 , 1.57 , 1.57 ,
 1.57 , 1.57 , 1.57 , 1.57 , 1.57 ,
 1.57 , 1.57 };
 G4MaterialPropertiesTable* myMPT1 = new G4MaterialPropertiesTable();
 myMPT1->AddProperty("RINDEX", photonEnergy, refractiveIndex, nEntries)->SetSpline(true);
 scintMat->SetMaterialPropertiesTable(myMPT1);
 
 scintMat->GetIonisation()->SetBirksConstant(0.126*mm/MeV);
}

Then in next field I build scintillator bar like this [I didn’t include world volume declaration here) :


 G4NistManager* nist = G4NistManager::Instance();
 G4bool checkOverlaps = true; 

 G4double ScintX = 5.*cm;
    G4double ScintY = 5.*cm;                      
    G4double ScintZ = 37.5*cm;                       // on each side adding to 75 cm total 
                         
    auto solidScint = new G4Box("Scint",ScintX, ScintY,ScintZ);
    auto logicScint = new G4LogicalVolume(solidScint, nist->FindOrBuildMaterial("plasticScint"), "Scint");        
               
    G4double Scint_pX = 0.0*cm;
    G4double Scint_pY = 0.0*cm;
    G4double Scint_pZ = 0.0*cm;

    auto physTube = new G4PVPlacement(0, G4ThreeVector(Scint_pX, Scint_pY, Scint_pZ), logicScint, "Scint", logicWorld, false, 0, checkOverlaps);

The code does run but I am not sure if the code worked or it used the default G4_POLYSTYRENE density of 1.06*g/cm3. I also want to know if there is a way to check the properties of volume placed such as density from visualization QT OpenGL screen.

Thank you for your time.

2

There should be text output, either in the terminal or the Qt text window, showing what materials are used. You might need to turn up the verbosity with
/run/verbose 2

3

Hi thank you for your feedback. I looked at terminal output and it does indeed show optical material (verbose is set to 2):

Checking overlaps for volume Scint (G4Box) ... OK!
Checking overlaps for volume Sensor (G4Box) ... OK!
World is registered to the default region.
physicsList->Construct() start.
G4OpticalPhysics:: Add Optical Physics Processes
### Birks coefficients used in run time
plasticScint     0.126 mm/MeV     0.012978 g/cm^2/MeV  massFactor=  101.167 effCharge= 0.027027
G4_POLYSTYRENE     0.07943 mm/MeV     0.00841958 g/cm^2/MeV  massFactor=  101.167 effCharge= 0.027027

It does show two different material (One I specified and default G4_POLYSTYRENE) is built. It seems that the 1st set of values i.e 0.126 mm/MeV is Birks constants which is then multiplied with density (which I specified 1.03*g/cm3). I am just unsure that as G4_POLYSTYRENE was also build whether in this line

scintMat->AddMaterial(G4NistManager::Instance() >FindOrBuildMaterial("G4_POLYSTYRENE"), 1.0);

The scintMat inherits properties defined in previous line or is it redefined by properties of G4_POLYSTYRENE ?

Thank you again for your time.

4

I don’t know. You may want to try building plasticScint from scratch (that is, without reference to G4_POLYSTYRENE). Then, presumably, the material won’t inherit anything from G4_POLYSTYRENE.

1 Like
5

Thank you for the advice and help, I will do that.