G4DipBustGenerator.cc

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//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4DipBustGenerator
//
// Author:  Vladimir Grichine
//
// Creation date: 17 May 2011
//
// Modifications:
//
// 17.07.2018  optimisations, using G4Pow in SampleCosTheta() method  M.Novak
//
// Class Description:
//
// Bremsstrahlung Angular Distribution Generation
// suggested  the dipole approximation in the rest frame of electron
// busted in the laboratory frame.
//
// Class Description: End
//
// -------------------------------------------------------------------
//
 
#include "G4DipBustGenerator.hh"
#include "Randomize.hh"
// #include "G4Log.hh"
// #include "G4Exp.hh"
#include "G4Pow.hh"
#include <CLHEP/Units/PhysicalConstants.h>
 
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G4DipBustGenerator::G4DipBustGenerator(const G4String&)
  : G4VEmAngularDistribution("DipBustGen")
{}
 
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G4DipBustGenerator::~G4DipBustGenerator() = default;
 
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G4double G4DipBustGenerator::SampleCosTheta(const G4double kinEnergy)
{
  const G4double c        = 4. - 8.*G4UniformRand();
  const G4double delta    = 0.5*(std::sqrt(c*c+4.) + std::abs(c));
  const G4double signc    = (c < 0.) ? -1.0 : 1.0;
  // const G4double cofA = -signc*G4Exp(G4Log(delta)/3.0);
  const G4double cofA     = -signc*G4Pow::GetInstance()->A13(delta);
  const G4double cosTheta = std::min(1.,std::max(-1.,cofA - 1./cofA));
  const G4double tau      = kinEnergy/CLHEP::electron_mass_c2;
  const G4double beta     = std::sqrt(tau*(tau + 2.))/(tau + 1.);
 
  return (cosTheta + beta)/(1. + cosTheta*beta);
}
 
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G4ThreeVector&
G4DipBustGenerator::SampleDirection(const G4DynamicParticle* dp, G4double,
                                     G4int, const G4Material*)
{
  const G4double cosTheta = SampleCosTheta(dp->GetKineticEnergy());
 
  const G4double sinTheta = std::sqrt((1. - cosTheta)*(1. + cosTheta));
  const G4double phi      = CLHEP::twopi*G4UniformRand();
 
  fLocalDirection.set(sinTheta*std::cos(phi), sinTheta*std::sin(phi),cosTheta);
  fLocalDirection.rotateUz(dp->GetMomentumDirection());
 
  return fLocalDirection;
}
 
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G4double G4DipBustGenerator::PolarAngle(G4double eTkin,
                                                   G4double, // final_energy
                                                   G4int ) // Z
{
  const G4double cosTheta = SampleCosTheta(eTkin);
  G4double theta = std::acos(cosTheta);
  theta = std::min(std::max(theta, 0.), CLHEP::pi);
  return theta;
}
 
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void G4DipBustGenerator::SamplePairDirections(const G4DynamicParticle* dp,
                                                         G4double elecKinEnergy,
                                                         G4double posiKinEnergy,
                                                         G4ThreeVector& dirElectron,
                                                         G4ThreeVector& dirPositron,
                                                         G4int, const G4Material*)
{
  const G4double phi  = CLHEP::twopi * G4UniformRand();
  const G4double sinp = std::sin(phi);
  const G4double cosp = std::cos(phi);
 
  G4double cost = SampleCosTheta(elecKinEnergy);
  G4double sint = std::sqrt((1. - cost)*(1. + cost));
 
  dirElectron.set(sint*cosp, sint*sinp, cost);
  dirElectron.rotateUz(dp->GetMomentumDirection());
 
  cost = SampleCosTheta(posiKinEnergy);
  sint = std::sqrt((1. - cost)*(1. + cost));
 
  dirPositron.set(-sint*cosp, -sint*sinp, cost);
  dirPositron.rotateUz(dp->GetMomentumDirection());
}
 
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void G4DipBustGenerator::PrintGeneratorInformation() const
{
  G4cout << "\n" << G4endl;
  G4cout << "Angular Generator based on classical formula from" << G4endl;
  G4cout << "J.D. Jackson, Classical Electrodynamics, Wiley, New York 1975"
     << G4endl;
}
 
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