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// $Id: G4ModifiedTsai.cc,v 1.1 2010/10/14 15:17:48 vnivanch Exp $
// GEANT4 tag $Name: emstand-V09-03-24 $
//
// -------------------------------------------------------------------
//
// 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
//
// 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 "Randomize.hh"

G4ModifiedTsai::G4ModifiedTsai(const G4String&)
  : G4VBremAngularDistribution("AngularGenUrban")
{}    

G4ModifiedTsai::~G4ModifiedTsai() 
{}

G4double G4ModifiedTsai::PolarAngle(const G4double initial_energy,
				    const G4double, // final_energy
				    const G4int ) // Z
{
  // 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 totalEnergy = initial_energy + electron_mass_c2;   

  const G4double a1 = 0.625, a2 = 3.*a1, d = 27.;
  G4double u, theta = 0;

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

    if (9./(9.+d) > G4UniformRand()) { u /= a1; }
    else                             { u /= a2; }
    
    theta = u*electron_mass_c2/totalEnergy;
  } while(u*electron_mass_c2 > totalEnergy*pi);

  return theta;
}

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;
}