G4ModifiedTsai.cc

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// $Id$
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4ModifiedTsai
//
// Author:        Andreia Trindade (andreia@lip.pt)
//                Pedro Rodrigues  (psilva@lip.pt)
//                Luis Peralta     (luis@lip.pt)
// 
// Creation date: 21 March 2003
//
// Modifications: 
// 21 Mar 2003 A.Trindade First implementation acording with new design
// 24 Mar 2003 A.Trindade Fix in Tsai generator in order to prevent theta 
//                        generation above pi
// 13 Oct 2010  V.Ivanchenko  Moved to standard and improved comment
// 26.04.2011   V.Grichine    Clean-up of PolarAngle method 
//
// Class Description: 
//
// Bremsstrahlung Angular Distribution Generation 
// suggested by L.Urban (Geant3 manual (1993) Phys211)
// Derived from Tsai distribution (Rev Mod Phys 49,421(1977))
//
// Class Description: End 
//
// -------------------------------------------------------------------
//

#include "G4ModifiedTsai.hh"
#include "G4PhysicalConstants.hh"
#include "Randomize.hh"

G4ModifiedTsai::G4ModifiedTsai(const G4String&)
  : G4VEmAngularDistribution("AngularGenUrban")
{}    

G4ModifiedTsai::~G4ModifiedTsai() 
{}

G4ThreeVector& 
G4ModifiedTsai::SampleDirection(const G4DynamicParticle* dp,
                                G4double, G4int, const G4Material*)
{
  // Sample gamma angle (Z - axis along the parent particle).
  // Universal distribution suggested by L. Urban (Geant3 manual (1993) 
  // Phys211) derived from Tsai distribution (Rev Mod Phys 49,421(1977))

  G4double uMax = 2*(1. + dp->GetKineticEnergy()/electron_mass_c2);   

  const G4double a1     = 0.625;
  const G4double a2     = 1.875;
  const G4double border = 0.25;
  G4double u;

  do {
    u = - std::log(G4UniformRand()*G4UniformRand());

    if ( border > G4UniformRand() ) { u /= a1; }
    else                            { u /= a2; }
    
  } while(u > uMax);

  G4double cost = 1.0 - 2*u*u/(uMax*uMax);
  G4double sint = std::sqrt((1 - cost)*(1 + cost));
  G4double phi  = CLHEP::twopi*G4UniformRand(); 

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

  return fLocalDirection;
}

void G4ModifiedTsai::PrintGeneratorInformation() const
{
  G4cout << "\n" << G4endl;
  G4cout << "Bremsstrahlung Angular Generator is Modified Tsai" << G4endl;
  G4cout << "Distribution suggested by L.Urban (Geant3 manual (1993) Phys211)" 
         << G4endl;
  G4cout << "Derived from Tsai distribution (Rev Mod Phys 49,421(1977)) \n" 
         << G4endl;
} 

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