G4Generator2BS.cc

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// $Id$
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4Generator2BS
//
// Author:        Andreia Trindade (andreia@lip.pt)
//                Pedro Rodrigues  (psilva@lip.pt)
//                Luis Peralta     (luis@lip.pt)
//
// Creation date: 2 June 2003
//
// Modifications: 
// 02 Jun 2003               First implementation acording with new design
// 05 Nov 2003  MGP          Fixed std namespace
// 17 Nov 2003  MGP          Fixed compilation problem on Windows                  
// 12 Oct 2010  V.Ivanchenko Moved RejectionFunction inline, use G4Pow to speadup
// 09 May 2011  L.Pandola    Initialize private members, to avoid Coverity warning
//
// Class Description: 
//
// Concrete base class for Bremsstrahlung Angular Distribution Generation 
// 2BS Distribution
//
// Class Description: End 
//
// -------------------------------------------------------------------
//

#include "G4Generator2BS.hh"
#include "Randomize.hh"   
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4Pow.hh"   

G4Generator2BS::G4Generator2BS(const G4String&)
  : G4VEmAngularDistribution("AngularGen2BS"),fz(1),ratio(1),
    ratio1(1),ratio2(1),delta(0)
{
  g4pow = G4Pow::GetInstance();
  nwarn = 0;
}

G4Generator2BS::~G4Generator2BS() 
{}

G4ThreeVector& G4Generator2BS::SampleDirection(const G4DynamicParticle* dp,
                                               G4double final_energy,
                                               G4int Z,
                                               const G4Material*)
{

  // Adapted from "Improved bremsstrahlung photon angular sampling in the EGS4 code system"
  // by Alex F. Bielajew, Rahde Mohan anc Chen-Shou Chui, PIRS-0203
  // Ionizing Radiation Standards
  // Institute for National Measurement Standards 
  // National Research Council of Canada
  // Departement of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York

  G4double energy = dp->GetTotalEnergy();
  ratio = final_energy/energy;
  ratio1 = (1 + ratio)*(1 + ratio);
  ratio2 = 1 + ratio*ratio;

  G4double gamma = energy/electron_mass_c2;
  G4double beta  = std::sqrt((gamma - 1)*(gamma + 1))/gamma;

  //G4double Zeff = std::sqrt(static_cast<G4double>(Z) * (static_cast<G4double>(Z) + 1.0));
  //z = (0.00008116224*(std::pow(Zeff,0.3333333)));

  // VI speadup
  fz = 0.00008116224*g4pow->Z13(Z)*g4pow->Z13(Z+1);

  // majoranta
  G4double ymax = 2*beta*(1 + beta)*gamma*gamma;
  G4double gMax = RejectionFunction(0.0);
  gMax = std::max(gMax,RejectionFunction(ymax));

  G4double y, gfun;

  do{
    G4double q = G4UniformRand();
    y = q*ymax/(1 + ymax*(1 - q));
    gfun = RejectionFunction(y);

    // violation point
    if(gfun > gMax && nwarn >= 20) {
      ++nwarn;
      G4cout << "### WARNING in G4Generator2BS: Etot(MeV)= " << energy/MeV 
             << "  Egamma(MeV)" << (energy - final_energy)/MeV
             << " gMax= " << gMax << "  < " << gfun
             << "  results are not reliable!" 
             << G4endl;
      if(20 == nwarn) { 
        G4cout << "   WARNING in G4Generator2BS is closed" << G4endl; 
      }
    }

  } while(G4UniformRand()*gMax > gfun || y > ymax);

  
  G4double cost = 1 - 2*y/ymax;
  G4double sint = std::sqrt((1 - cost)*(1 + cost));
  G4double phi  = twopi*G4UniformRand(); 

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

  return fLocalDirection;
}

void G4Generator2BS::PrintGeneratorInformation() const
{
  G4cout << "\n" << G4endl;
  G4cout << "Bremsstrahlung Angular Generator is 2BS Generator "
         << "from 2BS Koch & Motz distribution (Rev Mod Phys 31(4), 920 (1959))" << G4endl;
  G4cout << "Sampling algorithm adapted from PIRS-0203" << G4endl;
  G4cout << "\n" << G4endl;
} 

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