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 // ----------------------------------------------------------------------------
 //
 // GEANT4 Class header file
 //
 // File name:     G4GoudsmitSaundersonMscModel
 //
 // Author:        Mihaly Novak / (Omrane Kadri)
 //
 // Creation date: 20.02.2009
 //
 // Modifications:
 // 04.03.2009 V.Ivanchenko cleanup and format according to Geant4 EM style
 // 12.05.2010 O.Kadri: adding Qn1 and Qn12 as private doubles
 // 18.05.2015 M. Novak provide PLERIMINARYY version of updated class.
 //            All algorithms of the class were revised and updated, new methods added.
 //            A new version of Kawrakow-Bielajew Goudsmit-Saunderson MSC model
 //            based on the screened Rutherford DCS for elastic scattering of
 //            electrons/positrons has been introduced[1,2]. The corresponding MSC
 //            angular distributions over a 2D parameter grid have been recomputed
 //            and the CDFs are now stored in a variable transformed (smooth) form[2,3]
 //            together with the corresponding rational interpolation parameters.
 //            These angular distributions are handled by the new
 //            G4GoudsmitSaundersonTable class that is responsible to sample if
 //            it was no, single, few or multiple scattering case and delivers the
 //            angular deflection (i.e. cos(theta) and sin(theta)).
 //            Two screening options are provided:
 //             - if fgIsUsePWATotalXsecData=TRUE i.e. SetOptionPWAScreening(TRUE)
 //               was called before initialisation: screening parameter value A is
 //               determined such that the first transport coefficient G1(A)
 //               computed according to the screened Rutherford DCS for elastic
 //               scattering will reproduce the one computed from the PWA elastic
 //               and first transport mean free paths[4].
 //             - if fgIsUsePWATotalXsecData=FALSE i.e. default value or
 //               SetOptionPWAScreening(FALSE) was called before initialisation:
 //               screening parameter value A is computed according to Moliere's
 //               formula (by using material dependent parameters \chi_cc2 and b_c
 //               precomputed for each material used at initialization in
 //               G4GoudsmitSaundersonTable) [3]
 //            Elastic and first trasport mean free paths are used consistently.
 //            The new version is self-consistent, several times faster, more
 //            robust and accurate compared to the earlier version.
 //            Spin effects as well as a more accurate energy loss correction and
 //            computations of Lewis moments will be implemented later on.
 //            [1] A.F.Bielajew, NIMB 111 (1996) 195-208
 //            [2] I.Kawrakow, A.F.Bielajew, NIMB 134(1998) 325-336
 //            [3] I.Kawrakow, E.Mainegra-Hing, D.W.O.Rogers, F.Tessier,B.R.B.Walters,
 //                NRCC Report PIRS-701 (2013)
 //            [4] F.Salvat, A.Jablonski, C.J. Powell, CPC 165(2005) 157-190
 // 02.09.2015 M. Novak: first version of new step limit is provided.
 //            fUseSafetyPlus corresponds to Urban fUseSafety (default)
 //            fUseDistanceToBoundary corresponds to Urban fUseDistanceToBoundary
 //            fUseSafety  corresponds to EGSnrc error-free stepping algorithm
 //            Range factor can be significantly higher at each case than in Urban.
 // 23.08.2017 M. Novak: added corrections to account spin effects (Mott-correction).
 //            It can be activated by setting the fIsMottCorrection flag to be true
 //            before initialization using the SetOptionMottCorrection() public method.
 //            The fMottCorrection member is responsible to handle pre-computed Mott
 //            correction (rejection) functions obtained by numerically computing
 //            Goudsmit-Saunderson agnular distributions based on a DCS accounting spin
 //            effects and screening corrections. The DCS used to compute the accurate
 //            GS angular distributions is: DCS_{cor} = DCS_{SR}x[ DCS_{R}/DCS_{Mott}] where :
 //               # DCS_{SR} is the relativistic Screened-Rutherford DCS (first Born approximate
 //                 solution of the Klein-Gordon i.e. relativistic Schrodinger equation =>
 //                 scattering of spinless e- on exponentially screened Coulomb potential)
 //                 note: the default (without using Mott-correction) GS angular distributions
 //                 are based on this DCS_{SR} with Moliere's screening parameter!
 //               # DCS_{R} is the Rutherford DCS which is the same as above but without
 //                 screening
 //               # DCS_{Mott} is the Mott DCS i.e. solution of the Dirac equation with a bare
 //                 Coulomb potential i.e. scattering of particles with spin (e- or e+) on a
 //                 point-like unscreened Coulomb potential
 //               # moreover, the screening parameter of the DCS_{cor} was determined such that
 //                 the DCS_{cor} with this corrected screening parameter reproduce the first
 //                 transport cross sections obtained from the corresponding most accurate DCS
 //                 (i.e. from elsepa [4])
 //            Unlike the default GS, the Mott-corrected angular distributions are particle type
 //            (different for e- and e+ <= the DCS_{Mott} and the screening correction) and target
 //            (Z and material) dependent.
 // 02.02.2018 M. Novak: implemented CrossSectionPerVolume interface method (used only for testing)
 // 26.10.2025 M. Novak: the model has only its accurate stepping and boundary crossing algorithms
 //            left as the only option that ensures the expected precision, especially when activating
 //            its Mott correction option (that also activates the screeing and scattering power
 //            corrections). The model has been used for describing e-/e+ MSC (below 100 MeV kinetic)
 //            energy in the option4, Penelope and Livermore EM physics constructors since Geant4 10.6.
 //
 //
 // Class description:
 //   Kawrakow-Bielajew Goudsmit-Saunderson MSC model based on the screened Rutherford DCS
 //   for elastic scattering of e-/e+. Option, to include Mott correction, is also available
 //   that also activates the screening and scattering power corrections leading to the most
 //   precise settings of the model. With the accurate electron stepping and boundary crossing
 //   algorithm the model provides very precise e-/e+ simulation and tracking independently
 //   from the target material and geometrical configurations similarly to EGSnrc. All details
 //   are available in the corresponding technical note (M. Novak: https://arxiv.org/abs/2410.13361).
 //
 // References:
 //   M. Novak: https://arxiv.org/abs/2410.13361
 //
 // -----------------------------------------------------------------------------
 
 #ifndef G4GoudsmitSaundersonMscModel_h
 #define G4GoudsmitSaundersonMscModel_h 1
 
 #include <CLHEP/Units/SystemOfUnits.h>
 
 #include "G4VMscModel.hh"
 #include "G4PhysicsTable.hh"
 #include "G4MaterialCutsCouple.hh"
 #include "globals.hh"
 
 
 class G4DataVector;
 class G4ParticleChangeForMSC;
 class G4LossTableManager;
 class G4GoudsmitSaundersonTable;
 class G4GSPWACorrections;
 
 class G4GoudsmitSaundersonMscModel : public G4VMscModel
 {
 public:
 
   G4GoudsmitSaundersonMscModel(const G4String& nam = "GoudsmitSaunderson");
 
   ~G4GoudsmitSaundersonMscModel() override;
 
   void Initialise(const G4ParticleDefinition*, const G4DataVector&) override;
 
   void InitialiseLocal(const G4ParticleDefinition* p, G4VEmModel* masterModel) override;
 
   G4ThreeVector& SampleScattering(const G4ThreeVector&, G4double safety) override;
 
   G4double ComputeTruePathLengthLimit(const G4Track& track, G4double& currentMinimalStep) override;
 
   G4double ComputeGeomPathLength(G4double truePathLength) override;
 
   G4double ComputeTrueStepLength(G4double geomStepLength) override;
 
   // method to compute first transport cross section per Volume (i.e. macroscropic first transport cross section; this
   // method is used only for testing and not during a normal simulation)
   G4double CrossSectionPerVolume(const G4Material*, const G4ParticleDefinition*, G4double kineticEnergy, G4double cutEnergy = 0.0, G4double maxEnergy = DBL_MAX) override;
 
   void     StartTracking(G4Track*) override;
 
   void     SampleMSC();
 
   G4double GetTransportMeanFreePath(const G4ParticleDefinition*, G4double);
 
   void SetOptionPWACorrection(G4bool opt)    { fIsUsePWACorrection = opt; }
 
   G4bool GetOptionPWACorrection() const      { return fIsUsePWACorrection; }
 
   void   SetOptionMottCorrection(G4bool opt) { fIsUseMottCorrection = opt; }
 
   G4bool GetOptionMottCorrection() const     { return fIsUseMottCorrection; }
 
   void   SetOptionOptimisation(G4bool opt) { fIsUseOptimisation = opt; }
 
   G4bool GetOptionOptimisation() const     { return fIsUseOptimisation; }
 
   G4GoudsmitSaundersonTable* GetGSTable()          { return fGSTable; }
 
   G4GSPWACorrections*        GetPWACorrection()    { return fPWACorrection; }
 
   //  hide assignment operator
   G4GoudsmitSaundersonMscModel & operator=(const  G4GoudsmitSaundersonMscModel &right) = delete;
   G4GoudsmitSaundersonMscModel(const  G4GoudsmitSaundersonMscModel&) = delete;
 
 private:
   inline void     SetParticle(const G4ParticleDefinition* p);
 
   inline G4double GetLambda(G4double);
 
   G4double GetTransportMeanFreePathOnly(const G4ParticleDefinition*,G4double);
 
 private:
 
   G4double currentKinEnergy;
   G4double currentRange;
   G4double presafety;
   G4int    currentMaterialIndex;
   //
   const G4ParticleDefinition* particle;
   G4ParticleChangeForMSC*     fParticleChange;
   const G4MaterialCutsCouple* currentCouple;
 
   G4GoudsmitSaundersonTable*  fGSTable;
   G4GSPWACorrections*         fPWACorrection;
 
   G4bool   fIsUsePWACorrection;
   G4bool   fIsUseMottCorrection;
   G4bool   fIsUseOptimisation;
   //
   G4double fLambda0; // elastic mean free path
   G4double fLambda1; // first transport mean free path
   G4double fScrA;    // screening parameter
   G4double fG1;      // first transport coef.
   // in case of Mott-correction
   G4double fMCtoScrA;
   G4double fMCtoQ1;
   G4double fMCtoG2PerG1;
   //
   G4double fTheTrueStepLenght;
   G4double fTheZPathLenght;
   //
   G4ThreeVector fTheDisplacementVector;
   G4ThreeVector fTheNewDirection;
   //
   G4bool fIsEndedUpOnBoundary;
   G4bool fIsMultipleScattering;
   G4bool fIsSingleScattering;
   G4bool fIsNoScatteringInMSC;
   G4bool fIsSimplified;
 };
 
 ////////////////////////////////////////////////////////////////////////////////
 inline
 void G4GoudsmitSaundersonMscModel::SetParticle(const G4ParticleDefinition* p)
 {
   if (p != particle) {
     particle = p;
   }
 }
 
 #endif

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