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 // ----------------------------------------------------------------------------
 //
 // GEANT4 Class header file
 //
 // File name:     G4GSMottCorrection
 //
 // Author:        Mihaly Novak
 //
 // Creation date: 23.08.2017
 //
 // Modifications:
 // 26.10.2025 M. Novak: added the related technical note as the proper reference.
 //
 // Class description:
 //   An object of this calss is used in the G4GoudsmitSaundersonTable when Mott-correction
 //   was required by the user in the G4GoudsmitSaundersonMscModel.
 //   The class is responsible to handle pre-computed Mott correction (rejection) functions
 //   obtained as a ratio of GS angular distributions computed based on the Screened-Rutherford
 //   DCS to GS angular distributions computed based on a more accurate corrected DCS_{cor}.
 //   The DCS used to compute the accurate Goudsmit-Saunderson angular distributions is [1]:
 //   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 [2]
 //    # 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 [3].
 //  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.
 //  [1] I.Kawrakow, E.Mainegra-Hing, D.W.O.Rogers, F.Tessier,B.R.B.Walters, NRCC
 //      Report PIRS-701 (2013)
 //  [2] N.F. Mott, Proc. Roy. Soc. (London) A 124 (1929) 425.
 //  [3] F.Salvat, A.Jablonski, C.J. Powell, CPC 165(2005) 157-190
 //
 // References:
 //   M. Novak: https://arxiv.org/abs/2410.13361
 //
 // -----------------------------------------------------------------------------
 
 #ifndef G4GSMottCorrection_h
 #define G4GSMottCorrection_h 1
 
 #include <CLHEP/Units/SystemOfUnits.h>
 
 #include "globals.hh"
 
 #include <vector>
 #include <string>
 #include <sstream>
 
 class G4Material;
 class G4Element;
 
 
 class G4GSMottCorrection {
 public:
   G4GSMottCorrection(G4bool iselectron=true);
 
  ~G4GSMottCorrection();
 
   void     Initialise();
 
   void     GetMottCorrectionFactors(G4double logekin, G4double beta2, G4int matindx,
                                     G4double &mcToScr, G4double &mcToQ1, G4double &mcToG2PerG1);
 
   G4double GetMottRejectionValue(G4double logekin, G4double G4beta2, G4double q1, G4double cost,
                                  G4int matindx, G4int &ekindx, G4int &deltindx);
 
   static G4int GetMaxZet() { return gMaxZet; }
 
 private:
   void InitMCDataPerElement();
 
   void InitMCDataPerMaterials();
 
   void LoadMCDataElement(const G4Element*);
 
   void ReadCompressedFile(const std::string& fname, std::istringstream &iss);
 
   void InitMCDataMaterial(const G4Material*);
   //
   // dat structures
   struct DataPerDelta {
     G4double         fSA;             // a,b,c,d spline interpolation parameters for the last \sin(0.5\theta) bin
     G4double         fSB;
     G4double         fSC;
     G4double         fSD;
     G4double        *fRejFuntion;     // rejection func. for a given E_{kin}, \delta, e^-/e^+ over the \sin(0.5\theta) grid
   };
 
   struct DataPerEkin {
     G4double         fMCScreening;    // correction factor to Moliere screening parameter
     G4double         fMCFirstMoment;  // correction factor to first moment
     G4double         fMCSecondMoment; // correction factor to second
     DataPerDelta   **fDataPerDelta;   // per delta value data structure for each delta values
   };
 
   // either per material or per Z
   struct DataPerMaterial {
     DataPerEkin  **fDataPerEkin;    // per kinetic energy data structure for each kinetic energy value
   };
   //
   void AllocateDataPerMaterial(DataPerMaterial*);
   void DeAllocateDataPerMaterial(DataPerMaterial*);
   void ClearMCDataPerElement();
   void ClearMCDataPerMaterial();
   //
   // data members:
   // - Mott correction data are computed over a :
   //  I.  Kinetic energy grid [both rejection functions and correction factors]:
   //      1. kinetic energy grid from 1[keV] - 100[keV] with log-spacing 16 points:
   //                 # linear interpolation on \ln[E_{kin}] will be used
   //      2. \beta^2 grid from E_{kin} = 100[keV](~0.300546) - \beta^2=0.9999(~50.5889MeV]) with linear spacing 16 points:
   //                 # linear interpolation on \beta^2 will be used
   //      3. the overall kinetic energy grid is from E_{kin}=1[keV] - E_{kin}<=\beta^2=0.9999(~50.5889MeV]) with 31 points
   //  II. Delta value grid [rejection functions at a given kinetic energy(also depends on \theta;Z,e-/e+)]:
   //      1. \delta=2 Q_{1SR} (\eta_{MCcor})/ [1-2 Q_{1SR} (\eta_{MCcor})] where Q_{1SR} is the first moment i.e.
   //         Q_{1SR}(\eta_{MCcor}) =s/\lambda_{el}G_{1SR}(\eta_{MCcor}) where s/\lambda_{el} is the mean number of elastic
   //         scattering along the path s and G_{1SR}(\eta_{MCcor}) is the first, Screened-Rutherford transport coefficient
   //         but computed by using the Mott-corrected Moliere screening parameter
   //      2. the delta value grid is from [0(1e-3) - 0.9] with linear spacing of 28 points:
   //                 # linear interpolation will be used on \delta
   // III. \sin(0.5\theta) grid[rejection function at a given kinetic energy - delta value pair (also depends on Z,e-/e+)]:
   //      1. 32 \sin(0.5\theta) pints between [0,1] with linear spacing: # linear interpolation on \sin(0.5\theta) will
   //         be used exept the last bin where spline is used (the corresponding 4 spline parameters are also stored)
 private:
   G4bool                     fIsElectron;
   static constexpr G4int     gNumEkin   = 31;                 // number of kinetic energy grid points for Mott correction
   static constexpr G4int     gNumBeta2  = 16;                 // \beta^2 values between [fMinBeta2-fMaxBeta2]
   static constexpr G4int     gNumDelta  = 28;                 // \delta values between [0(1.e-3)-0.9]
   static constexpr G4int     gNumAngle  = 32;                 //
   static constexpr G4int     gMaxZet    = 98;                 // max. Z for which Mott-correction data were computed (98)
   static constexpr G4double  gMinEkin   =   1.*CLHEP::keV;   // minimum kinetic energy value
   static constexpr G4double  gMidEkin   = 100.*CLHEP::keV;   // kinetic energy at the border of the E_{kin}-\beta^2 grids
   static constexpr G4double  gMaxBeta2  =   0.9999;           // maximum \beta^2 value
   static constexpr G4double  gMaxDelta  =   0.9;              // maximum \delta value (the minimum is 0(1.e-3))
   //
   G4double                   fMaxEkin;        // from max fMaxBeta2 = 0.9999 (~50.5889 [MeV])
   G4double                   fLogMinEkin;     // \ln[fMinEkin]
   G4double                   fInvLogDelEkin;  // 1/[\ln(fMidEkin/fMinEkin)/(fNumEkin-fNumBeta2)]
   G4double                   fMinBeta2;       // <= E_{kin}=100 [keV] (~0.300546)
   G4double                   fInvDelBeta2;    // 1/[(fMaxBeta2-fMinBeta2)/(fNumBeta2-1)]
   G4double                   fInvDelDelta;    // 1/[0.9/(fNumDelta-1)]
   G4double                   fInvDelAngle;    // 1/[(1-0)/fNumAngle-1]
   //
   static const std::string   gElemSymbols[];
   //
   std::vector<DataPerMaterial*>  fMCDataPerElement;   // size will be gMaxZet+1; won't be null only at used Z indices
   std::vector<DataPerMaterial*>  fMCDataPerMaterial;  // size will #materials; won't be null only at used mat. indices
 };
 
 #endif // G4GSMottCorrection_h

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