Hello,
I am puzzled with the implementation of the screening parameter, A, in G4Wentzel model.
The expression for A is given in the Physics Reference Manual (PRM) e. g. between equations (58) and (59) over there. This expression corresponds to what is usually found in the literature. I am fine with that.
However, in the implemented G4Wentzel model a different expression is used which I don’t quite understand. Specifically at line 168 of G4WentzelOKandVIxSection.cc
. For particles other than electrons (comparing to line 169 below) there is an additional term: 1 + G4Exp(-j*j*0.001)
. For light target atoms (j=Z) this is approximately a factor of ~2 difference with the PRM.
What would be the origin of this additional term? I could not find any reference to it. The coefficient value (0.001
) looks empirical. Maybe it was added in order to better fit experimental data from Attwood et al., NIMB 251 (2006) ?