G4UrbanMscModel.hh

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// $Id:   $
// GEANT4 tag $Name:  $
//
// -------------------------------------------------------------------
//
//
// GEANT4 Class header file
//
//
// File name:     G4UrbanMscModel
//
// Author:        Laszlo Urban
//
// Creation date: 19.02.2013
//
// Created from G4UrbanMscModel96 
//
// New parametrization for theta0
// Correction for very small step length
//
// Class Description:
//
// Implementation of the model of multiple scattering based on
// H.W.Lewis Phys Rev 78 (1950) 526 and L.Urban model

// -------------------------------------------------------------------
//

#ifndef G4UrbanMscModel_h
#define G4UrbanMscModel_h 1

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#include <CLHEP/Units/SystemOfUnits.h>

#include "G4VMscModel.hh"
#include "G4MscStepLimitType.hh"
#include "G4Log.hh"
#include "G4Exp.hh"

class G4ParticleChangeForMSC;
class G4SafetyHelper;
class G4LossTableManager;

static const G4double c_highland = 13.6*CLHEP::MeV ;

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class G4UrbanMscModel : public G4VMscModel
{

public:

  G4UrbanMscModel(const G4String& nam = "UrbanMsc");

  virtual ~G4UrbanMscModel();

  void Initialise(const G4ParticleDefinition*, const G4DataVector&);

  void StartTracking(G4Track*);

  G4double ComputeCrossSectionPerAtom(const G4ParticleDefinition* particle,
                                      G4double KineticEnergy,
                                      G4double AtomicNumber,
                                      G4double AtomicWeight=0., 
                                      G4double cut =0.,
                                      G4double emax=DBL_MAX);

  G4ThreeVector& SampleScattering(const G4ThreeVector&, G4double safety);

  G4double ComputeTruePathLengthLimit(const G4Track& track,
                                      G4double& currentMinimalStep);

  G4double ComputeGeomPathLength(G4double truePathLength);

  G4double ComputeTrueStepLength(G4double geomStepLength);

  inline G4double ComputeTheta0(G4double truePathLength, 
                                G4double KineticEnergy);

private:

  G4double SampleCosineTheta(G4double trueStepLength, G4double KineticEnergy);

  inline void SetParticle(const G4ParticleDefinition*);

  inline void UpdateCache();
  
  inline G4double SampleDisplacement();

  inline G4double SimpleScattering(G4double xmeanth, G4double x2meanth);

  inline G4double LatCorrelation();

  //  hide assignment operator
  G4UrbanMscModel & operator=(const  G4UrbanMscModel &right);
  G4UrbanMscModel(const  G4UrbanMscModel&);

  const G4ParticleDefinition* particle;
  G4ParticleChangeForMSC*     fParticleChange;

  const G4MaterialCutsCouple* couple;
  G4LossTableManager*         theManager;

  G4double mass;
  G4double charge,ChargeSquare;
  G4double masslimite,lambdalimit,fr;

  G4double taubig;
  G4double tausmall;
  G4double taulim;
  G4double currentTau;
  G4double tlimit;
  G4double tlimitmin;
  G4double tlimitminfix,tlimitminfix2;
  G4double tgeom;

  G4double geombig;
  G4double geommin;
  G4double geomlimit;
  G4double skindepth;
  G4double smallstep;

  G4double presafety;

  G4double lambda0;
  G4double lambdaeff;
  G4double tPathLength;
  G4double zPathLength;
  G4double par1,par2,par3;

  G4double stepmin;

  G4double currentKinEnergy;
  G4double currentRange; 
  G4double rangeinit;
  G4double currentRadLength;

  G4double theta0max,rellossmax;
  G4double third;

  G4int    currentMaterialIndex;

  G4double y;
  G4double Zold;
  G4double Zeff,Z2,Z23,lnZ;
  G4double coeffth1,coeffth2;
  G4double coeffc1,coeffc2,coeffc3,coeffc4;

  G4bool   firstStep;
  G4bool   inside;
  G4bool   insideskin;
};

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inline
void G4UrbanMscModel::SetParticle(const G4ParticleDefinition* p)
{
  if (p != particle) {
    particle = p;
    mass = p->GetPDGMass();
    charge = p->GetPDGCharge()/CLHEP::eplus;
    ChargeSquare = charge*charge;
  }
}

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inline
void G4UrbanMscModel::UpdateCache()                                   
{
    lnZ = G4Log(Zeff);
    // correction in theta0 formula
    G4double w = G4Exp(lnZ/6.);
    G4double facz = 0.990395+w*(-0.168386+w*0.093286) ;
    coeffth1 = facz*(1. - 8.7780e-2/Zeff);
    coeffth2 = facz*(4.0780e-2 + 1.7315e-4*Zeff);

    // tail parameters
    G4double Z13 = std::exp(lnZ/3.);
    coeffc1  = 2.3785    - Z13*(4.1981e-1 - Z13*6.3100e-2);
    coeffc2  = 4.7526e-1 + Z13*(1.7694    - Z13*3.3885e-1);
    coeffc3  = 2.3683e-1 - Z13*(1.8111    - Z13*3.2774e-1);
    coeffc4  = 1.7888e-2 + Z13*(1.9659e-2 - Z13*2.6664e-3);

    Z2   = Zeff*Zeff;
    Z23  = Z13*Z13;               
                                              
    Zold = Zeff;
}

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inline
G4double G4UrbanMscModel::ComputeTheta0(G4double trueStepLength,
                                        G4double KineticEnergy)
{
  // for all particles take the width of the central part
  //  from a  parametrization similar to the Highland formula
  // ( Highland formula: Particle Physics Booklet, July 2002, eq. 26.10)
  G4double invbetacp = sqrt((currentKinEnergy+mass)*(KineticEnergy+mass)/
                            (currentKinEnergy*(currentKinEnergy+2.*mass)*
                             KineticEnergy*(KineticEnergy+2.*mass)));
  y = trueStepLength/currentRadLength;
  G4double theta0 = c_highland*std::abs(charge)*sqrt(y)*invbetacp;
  y = G4Log(y);
  // correction factor from e- scattering data
  theta0 *= (coeffth1+coeffth2*y);
  return theta0;
}

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inline
G4double G4UrbanMscModel::SimpleScattering(G4double xmeanth, G4double x2meanth)
{
  // 'large angle scattering'
  // 2 model functions with correct xmean and x2mean
  G4double a = (2.*xmeanth+9.*x2meanth-3.)/(2.*xmeanth-3.*x2meanth+1.);
  G4double prob = (a+2.)*xmeanth/a;

  // sampling
  G4double cth = 1.;
  if(G4UniformRand() < prob) {
    cth = -1.+2.*G4Exp(G4Log(G4UniformRand())/(a+1.));
  } else {
    cth = -1.+2.*G4UniformRand();
  }
  return cth;
}

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inline
G4double G4UrbanMscModel::SampleDisplacement()
{
  G4double r = 0.0;
  if ((currentTau >= tausmall) && !insideskin) {
    G4double rmax = sqrt((tPathLength-zPathLength)*(tPathLength+zPathLength));
    r = rmax*G4Exp(G4Log(G4UniformRand())*third);
  }
  return r;
}

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inline
G4double G4UrbanMscModel::LatCorrelation()
{
  static const G4double kappa = 2.5;
  static const G4double kappami1 = 1.5;
  
  G4double latcorr = 0.;
  if((currentTau >= tausmall) && !insideskin)
  {
    if(currentTau < taulim)
      latcorr = lambdaeff*kappa*currentTau*currentTau*
                (1.-(kappa+1.)*currentTau*third)*third;
    else
    {
      G4double etau = 0.;
      if(currentTau < taubig) { etau = G4Exp(-currentTau); }
      latcorr = -kappa*currentTau;
      latcorr = G4Exp(latcorr)/kappami1;
      latcorr += 1.-kappa*etau/kappami1 ;
      latcorr *= 2.*lambdaeff*third;
    }
  }
  return latcorr;
}

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#endif