Extend Mott coefficients to include positrons and higher Z elements

[amandalund]

As @sethrj pointed out in #1392, the coefficients used to calculate the ratio of the Mott to Rutherford cross sections are provided in Boschini et al (2013) for 1 <= Z <= 118 for electrons and positrons. Geant4 includes that data in G4MottData.hh, but only for electrons and only for Z up to 92; this is what we were previously doing as well. This PR extends the data to include coefficients for higher Z elements and positrons.

[sethrj]

LGTM! Where did you get these numbers in tabulated form?? I also noticed in the Boschini paper a casual remark about the previous papers having typographical errors... and finally, do we know whether Geant4 uses these? Looking at the "single scattering" physics list on master I see

  if(param->UseMottCorrection()) {
    ss = new G4eDPWACoulombScatteringModel();
  } else {
    ss = new G4eCoulombScatteringModel(false);
  }

[amandalund]

I pulled the tables from here. It looks like Geant4 is also using the values from Boschini, not Lijian: they reference a 2011 Boschini paper in G4MottData.hh and that the coefficients were recalculated using the same procedure as in Lijian. And yeah, I also noticed when looking into #1391 that Geant4 by default uses that other model in the single Coulomb scattering physics list, which I don't think uses these?

[sethrj]

Sounds good. I was more wondering if you OCR/copy-pasted/manually transcribed them, or whether you found a database that the authors made available. Thanks!

[amandalund]

Yeah I didn't see any database, so copy-pasted + some python parsing/reformatting.

[sethrj]

Cool thanks! Hopefully Celeritas can be a resource in the future for anyone who needs to use those coefficients in the future...