Two different G4_WATER mean excitation energy values?

Geant4 Version: 11.1.3
Operating System: Linux
Compiler/Version: GCC 11.4
CMake Version: 3.22.1

Dear G4 users and developers,

I noticed that there are two different G4_WATER mean excitation energy values in the source code.

One is in “G4NistMaterialBuilder.cc”, line 737, in function “G4NistMaterialBuilder::NistSimpleMaterials”, and the value is 78.0.

The other one is in “G4IonisParamMat.cc”, line 632, in function “G4IonisParamMat::FindMeanExcitationEnergy”, and the value is 75.0. The materials covered in this functions are all compounds. But the chemical formula is still “H_2O”, same as the one in NistSimpleMaterials.

Does anyone by any chance noticed this and know why they have different values?

Best,
Jun

Hello,

correct question. The answer: if G4_WATER is used the mean ionisation potential I=78 eV.

In more details:

  1. if a material from G4 NIST DB, then I is taken from NIST DB
  2. alternatively if a chemical formula is defined, then I is taken fron the list the table attached to the table of chemical formulas
  3. alternatively I is computed using atomic composition of the material
  4. user always may override by a custom value

VI

Thank you Civanch for your reply.
Best,
Jun