G4DipBustGenerator.cc

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// $Id$
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4DipBustGenerator
//
// Author:  Vladimir Grichine     
// 
// Creation date: 17 May 2011
//
// Modifications: 
// 
//
// 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 "G4PhysicalConstants.hh"
#include "Randomize.hh"

G4DipBustGenerator::G4DipBustGenerator(const G4String&)
  : G4VEmAngularDistribution("DipBustGen")
{}    

G4DipBustGenerator::~G4DipBustGenerator() 
{}

G4ThreeVector& 
G4DipBustGenerator::SampleDirection(const G4DynamicParticle* dp,
                                    G4double, G4int, const G4Material*)
{
  G4double c, cosTheta, delta, cofA, signc = 1., a, power = 1./3.;

  G4double eTkin = dp->GetKineticEnergy();

  c = 4. - 8.*G4UniformRand();
  a = c;
 
  if( c < 0. )
  {
    signc = -1.;
    a     = -c;
  }
  delta  = std::sqrt(a*a+4.);
  delta += a;
  delta *= 0.5; 

  cofA = -signc*std::pow(delta, power);

  cosTheta = cofA - 1./cofA;

  G4double tau = eTkin/electron_mass_c2;
  G4double beta = std::sqrt(tau*(tau + 2.))/(tau + 1.);

  cosTheta = (cosTheta + beta)/(1 + cosTheta*beta);

  G4double sinTheta = std::sqrt((1 - cosTheta)*(1 + cosTheta));
  G4double phi  = twopi*G4UniformRand(); 

  fLocalDirection.set(sinTheta*std::cos(phi), sinTheta*std::sin(phi),cosTheta);
  fLocalDirection.rotateUz(dp->GetMomentumDirection());

  return fLocalDirection;

}

G4double G4DipBustGenerator::PolarAngle(const G4double eTkin,
                                    const G4double, // final_energy
                                    const G4int ) // Z
{
  G4double c, cosTheta, delta, cofA, signc = 1., a, power = 1./3.;
  G4double gamma, beta, theta;

  c = 4. - 8.*G4UniformRand();
  a = c;
 
  if( c < 0. )
  {
    signc = -1.;
    a     = -c;
  }
  delta  = std::sqrt(a*a+4.);
  delta += a;
  delta *= 0.5; 

  cofA = -signc*std::pow(delta, power);

  cosTheta = cofA - 1./cofA;

  gamma = 1. + eTkin/electron_mass_c2;
  beta = std::sqrt(1. - 1./gamma/gamma);

  cosTheta = (cosTheta + beta)/(1 + cosTheta*beta);

  theta = std::acos(cosTheta);

  if( theta < 0. )  theta = 0.;
  if( theta > pi )  theta = pi;
  // G4cout <<"theta = "<<theta<<"; ";

  return theta;
}

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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