G4UrbanMscModel.hh

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// -------------------------------------------------------------------
//
//
// 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;
 
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class G4UrbanMscModel : public G4VMscModel
{
 
public:
 
  explicit G4UrbanMscModel(const G4String& nam = "UrbanMsc");
 
  ~G4UrbanMscModel() override;
 
  void Initialise(const G4ParticleDefinition*, 
          const G4DataVector&) override;
 
  void StartTracking(G4Track*) override;
 
  G4double 
  ComputeCrossSectionPerAtom(const G4ParticleDefinition* particle,
                 G4double KineticEnergy,
                 G4double AtomicNumber,
                 G4double AtomicWeight=0., 
                 G4double cut =0.,
                 G4double emax=DBL_MAX) 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;
 
  G4double ComputeTheta0(G4double truePathLength, G4double KineticEnergy);
 
  //  hide assignment operator
  G4UrbanMscModel & operator=(const  G4UrbanMscModel &right) = delete;
  G4UrbanMscModel(const  G4UrbanMscModel&) = delete;
 
private:
 
  G4double SampleCosineTheta(G4double trueStepLength, G4double KineticEnergy);
 
  void SampleDisplacement(G4double sinTheta, G4double phi);
 
  void SampleDisplacementNew(G4double sinTheta, G4double phi);
 
  void InitialiseModelCache();
 
  inline void SetParticle(const G4ParticleDefinition*);
 
  inline G4double Randomizetlimit();
  
  inline G4double SimpleScattering(G4double xmeanth, G4double x2meanth);
 
  inline G4double ComputeStepmin();
 
  inline G4double ComputeTlimitmin();
 
  CLHEP::HepRandomEngine*     rndmEngineMod;
 
  const G4ParticleDefinition* particle;
  const G4ParticleDefinition* positron;
  G4ParticleChangeForMSC*     fParticleChange;
 
  const G4MaterialCutsCouple* couple;
  G4LossTableManager*         theManager;
 
  G4double mass;
  G4double charge,ChargeSquare;
  G4double masslimite,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 currentLogKinEnergy;
  G4double currentRange; 
  G4double rangeinit;
  G4double currentRadLength;
 
  G4double rangecut;
  G4double drr,finalr;
 
  G4double tlow;
  G4double invmev;
 
  struct mscData {
    G4double ecut, Zeff, Z23, sqrtZ;
    G4double coeffth1, coeffth2;
    G4double coeffc1, coeffc2, coeffc3, coeffc4;
    G4double stepmina, stepminb;
    G4double doverra, doverrb;
  };
  static std::vector<mscData*> msc;
 
  // index of G4MaterialCutsCouple
  G4int    idx;
 
  G4bool   firstStep;
  G4bool   insideskin;
 
  G4bool   latDisplasmentbackup;
  G4bool   dispAlg96;
 
};
 
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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 G4double G4UrbanMscModel::Randomizetlimit()
{
  G4double res = tlimitmin;
  if(tlimit > tlimitmin)
  {
    res = G4RandGauss::shoot(rndmEngineMod,tlimit,0.1*(tlimit-tlimitmin));
    res = std::max(res, tlimitmin);
  }
  return res;
}
 
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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 rdm = rndmEngineMod->flat();
  G4double cth = (rndmEngineMod->flat() < prob)
    ? -1.+2.*G4Exp(G4Log(rdm)/(a+1.)) : -1.+2.*rdm;
  return cth;
}
 
inline G4double G4UrbanMscModel::ComputeStepmin()
{
  // define stepmin using estimation of the ratio 
  // of lambda_elastic/lambda_transport
  G4double rat = currentKinEnergy*invmev;
  return lambda0*1.e-3/(2.e-3+rat*(msc[idx]->stepmina+msc[idx]->stepminb*rat));
}
 
inline G4double G4UrbanMscModel::ComputeTlimitmin()
{
  G4double x = (particle == positron) ? 
    0.7*msc[idx]->sqrtZ*stepmin : 0.87*msc[idx]->Z23*stepmin;
  if(currentKinEnergy < tlow) { x *= 0.5*(1.+currentKinEnergy/tlow); }
  return std::max(x, tlimitminfix);
}
 
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#endif