Add electron/positron Single (Coulomb) Scattering Model

[whokion]

Add electron/positron Single (Coulomb) Scattering Model

[sethrj]

For G4NucleiProperties I think we should extend the MaterialParams to have nuclides as well as elements; the nuclide data would include binding energies imported from Geant4 via GeantImporter and associated classes.

[whokion]

That would be great as G4NucleiProperties will be used in many other places (in hadronic physics models including photo- and eletro-nuclear interactions). So, should we open another issue for extending MaterialParams to cover G4NucleiProperties and related classes?

[sethrj]

I think that the Nuclide upgrade would make a good first pull request: it's small enough and self contained. Then after that, based on a quick review of the Geant4 classes, I'd refactor the G4WentzelOKandVIxSection, G4eCoulombScatteringModel, and G4CoulombScattering into several classes:

• CoulombScatteringData and a corresponding Model class to manage the data
• CoulombScatteringView which would take a material and energy and have the helper functions like calc_nuclear_xs, calc_electron_xs
• I don't think it need to calculate cross sections on the fly , but if it does make a CoulombScatteringXsCalculator forG4eCoulombScatteringModel::ComputeCrossSectionPerAtom
• G4WentzelOKandVIxSection::SampleSingleScattering becomes a Distribution that samples polar angle
• G4eCoulombScatteringModel::SampleSecondaries becomes an Interactor
• Create the Process and add the interfaces to move the data from GeantImporter

And since a lot of these are tied to the WentzelOKandVI model which is abbreviated wokvi maybe some of these classes should have a Wokvi or WOI prefix instead of CoulombScattering?

[whokion]

Yes, we do not need to implement G4eCoulombScatteringModel::ComputeCrossSectionPerAtom as the lambda table for the CoulombScattering process will be imported from Geant4 (and do not need G4WentzelOKandVIxSection::ComputeTransportCrossSectionPerAtom either), but excerpt only relevant parts of G4WentzelOKandVIxSection that need for an Interactor associated with the model. So, can @stognini help for extending MaterialParams while Hayden reviews other relevant classes and start to implement them as parallel?

[hhollenb]

Add G4ScreeningMottCrossSections

[sethrj]

Starting point for material data:

//---------------------------------------------------------------------------//
/*!
 * Fundamental, invariant properties of a nuclide.
 */
struct NuclideRecord
{
    AtomicNumber atomic_number;  //!< Z number
    AtomicNumber atomic_mass;  //!< A number (TODO: fix type?)
    units::AmuMass atomic_mass;  //!< Isotope-weighted average atomic mass
};

//---------------------------------------------------------------------------//
/*!
 * Fractional element component of a material.
 *
 * This represents, e.g., the fraction of hydrogen in water.
 */
struct ElNuclideComponent
{
    NuclideId nuclide;  //!< Index in MaterialParams elements
    real_type fraction;  //!< Fraction of number density
};

//---------------------------------------------------------------------------//
/*!
 * Fundamental, invariant properties of an element.
 *
 * Add elemental properties as needed if they apply to more than one physics
 * model. (When nuclear physics is implemented, add isotopes.)
 *
 * Note that more than one "element def" can exist for a single atomic number:
 * there might be different enrichments of an element in the problem.
 */
struct ElementRecord
{
    AtomicNumber atomic_number;  //!< Z number
    units::AmuMass atomic_mass;  //!< Isotope-weighted average atomic mass
    ItemRange<ElNuclideComponent> nuclides;  //!< Nuclide components