For the following two cases the I-Values are substantially different while the composition and density are EXACTLY the same! Case 1: G4Material* Lucite = new G4Material("Lucite",density=1.19*g/cm3,numberOfElements=3); Lucite->AddElement(elH,0.080538); Lucite->AddElement(elC,0.599848); Lucite->AddElement(elO,0.319614); Results in I-value of 68.61 eV Case 2: G4Material* Lucite = G4NistManager::Instance()->FindOrBuildMaterial("G4_LUCITE"); Ncomp Name density(g/cm^3) I(eV) ChFormula ============================================================= 3 G4_LUCITE 1.19 74 1 0.080538 6 0.599848 8 0.319614 Results in I-value of 74 eV
Hello, When the NIST manager finds a potential value defined, it uses it (instead of the one obtained by chemical formula). For the case of "G4_LUCITE", the material is defined as follows, in G4NistMaterialBuilder : // LUCITE is equal to plustiglass AddMaterial("G4_LUCITE", 1.19, 0, 74., 3); AddElementByWeightFraction( 1, 0.080538); AddElementByWeightFraction( 6, 0.599848); AddElementByWeightFraction( 8, 0.319614); AddMaterial is a method of G4NistMaterialBuilder; in the present case, you can see that the 4-th argument, 74. , is forcing the ionisation potential. Underneath, what is does for a material with pointer "mat" is: mat->GetIonisation()->SetMeanExcitationEnergy(Ivalue); You can explicitly make this call to set the ionisation energy Ivalue. This feature is certainly a bit confusing (because of similar case you report), but allows to be more precise. Marc
