Problem 2474

Summary: Incorrect value of the mean excitation energy (I) of carbon (G4_C)
Product: Geant4 Reporter: Marcin Pietrzak <marcinptrzk>
Component: materialsAssignee: Vladimir.Ivantchenko
Status: RESOLVED FIXED    
Severity: normal CC: Vladimir.Ivantchenko
Priority: P4    
Version: other   
Hardware: All   
OS: All   

Description Marcin Pietrzak 2022-03-08 18:48:02 CET 
According to NIST, it should be equal to 78 eV (https://physics.nist.gov/PhysRefData/XrayMassCoef/tab1.html), but in Geant4, it is equal to 81 eV. This value is present in both the documentation (https://geant4-userdoc.web.cern.ch/UsersGuides/ForApplicationDeveloper/html/Appendix/materialNames.html) and the code (G4NistMaterialBuilder.cc).

Values for all other elements are the same. Only carbon has different values.
Comment 1 Vladimir.Ivantchenko 2022-03-09 18:16:19 CET 
Marc,

please, assign it to me. Carbon is a difficult material, because may exist in many forms why the current choice made and not NIST data directly are used we have to investigate.

VI
Comment 2 Vladimir.Ivantchenko 2022-04-08 18:47:37 CEST 
Hello Marcin,

Thanks for reporting on this problem. These numbers are taken from PSTAR and ASTAR material DB:

 https://physics.nist.gov/cgi-bin/Star 

There is a contradiction with NIST XRAY element data for carbon

in the element data: rho=1.7  I = 78
in PSTAR and ASTAR:  rho=2    I = 81

Inside Geant4 density effect data we have I=78, so likely we should change 81 to 78 but what to choose as the default for carbon density for me not clear.

The fix will be available in the next public release of Geant4.

VI
Comment 3 Vladimir.Ivantchenko 2022-04-17 13:54:00 CEST 
Hello,

mean ionisation potential for G4_C is changed. The fix will be available in the next public release and in the next patch to Geant4 11.0.

VI