Significant improvements have been made in the `G4GoudsmitSaundersonMscModel`

in **version Geant4.10.4.** that includes:

- implemented possible
**Mott-correction** as an option to the default, screened Rutherford DCS based GS angular distributions
- the
**corresponding corrections to the integrated quantities**, e.g. elastic, first and second transport cross sections, are also available
- a
**scattering power correction**, that accounts the otherwise neglected effects of small angular deflections associated to sub-threshold ionisations along the step (i.e. those contributing to the continuous energy losses), is also included

Note, that while these corrections are not activated in the default `G4GoudsmitSaundersonMscModel`

, **all of these are active** when the model is used in the `G4EmStandardPhysics_option4`

* EM constructor **from version Geant.10.4.**.

Furthermore, small corrections has been made in version Geant4.10.5. and exactly the same model (`G4GoudsmitSaundersonMscModel`

with all above corrections) is used **since Geant4.10.5.** in `G4EmStandardPhysics_option4`

, `G4EmLivermorePhysics`

, `G4EmPenelopePhysics`

and `G4EmPolarizedLivermorePhysics`

EM physics constructors.

Also note, that beyond the corrections mentioned above, the `G4GoudsmitSaundersonMscModel`

is used with its *error-free* stepping in all above mentioned physics constructors (since version *Geant4.10.4.*) that guaranties exact boundary crossing. All these, together with the so called *Longitudinal and Lateral Correlation*

Algorithm applied in the `G4GoudsmitSaundersonMscModel`

to determine the post-step particle position, results in highly accurate simulation of `e-/e+`

transport.

If you decide to use the most recent version of Geant4, i.e. **Geant4.10.7.**, you might compare the MSC based simulation results with those obtained by the new (in 10.7.) `G4eDPWACoulombScatteringModel`

single scattering model. This single scattering model is based on the most accurate available numerical differential Coulomb scattering cross sections (computed by using Dirac Partial Wave Analysis, using screening based on numerical electron densities computed from the Dirac-Fock model of the atom, applying exchange and correlation-polarization corrections on the top of the static-field approximation, including the finite nuclear size effects by using a Fermi charge distribution).

Therefore, if you want to obtain the most accurate e-/e+ angular distributions in your simulation by using an MSC model, I would suggest to try the `G4EmStandardPhysics_option4`

EM physics constructor and do not tune any of the MSC parameters. These will reproduce very well the angular distributions and results that you would obtain with the above mentioned, most accurate single scattering model.

However, if you want to study the effects of the different MSC corrections and MSC related simulation parameter values to the obtained angular distributions, then you need to study carefully the physics reference manual, release notes and make sure you fully understand the role of these parameters before setting them to a certain value.

Good luck!