G4SauterGavrilaAngularDistribution.cc

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// $Id$
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4SauterGavrilaAngularDistribution
//
// Author:     Vladimir Ivanchenko using Michel Maire algorithm
//             developed for Geant3
// 
// Creation date: 23 July 2012
//
//
// -------------------------------------------------------------------
//

#include "G4SauterGavrilaAngularDistribution.hh"
#include "G4PhysicalConstants.hh"
#include "Randomize.hh"

G4SauterGavrilaAngularDistribution::G4SauterGavrilaAngularDistribution()
  : G4VEmAngularDistribution("AngularGenSauterGavrila")
{}    

G4SauterGavrilaAngularDistribution::~G4SauterGavrilaAngularDistribution() 
{}

G4ThreeVector& 
G4SauterGavrilaAngularDistribution::SampleDirection(
       const G4DynamicParticle* dp, G4double, G4int, const G4Material*)
{
  G4double tau = dp->GetKineticEnergy()/electron_mass_c2;
  const G4double taulimit = 30.0;

  if (tau > taulimit) {
    fLocalDirection = dp->GetMomentumDirection(); 
    // Bugzilla 1120
    // SI on 05/09/2010 as suggested by JG 04/09/10 
  } else {
 
    G4double invgamma  = 1.0/(tau + 1.0);
    G4double beta      = std::sqrt(tau*(tau + 2.0))*invgamma;
    G4double b         = 0.5*tau*(tau*tau - 1.0);
    G4double invgamma2 = invgamma*invgamma;
   
    G4double rndm,term,greject,grejsup,costeta,sint2;
    if (tau < 1.) { grejsup = (1.+b-beta*b)/invgamma2; }
    else          { grejsup = (1.+b+beta*b)/invgamma2; }

    do { 
      rndm    = 1 - 2*G4UniformRand();
      costeta = (rndm + beta)/(rndm*beta + 1);
      term    = invgamma2/(1 + beta*rndm);
      sint2   = (1 - costeta)*(1 + costeta);
      greject = sint2*(1 + b*term)/(term*term);

    } while(greject < G4UniformRand()*grejsup);
       
    G4double sinteta = std::sqrt(sint2);
    G4double phi  = CLHEP::twopi*G4UniformRand(); 

    fLocalDirection.set(sinteta*std::cos(phi), sinteta*std::sin(phi), costeta);
    fLocalDirection.rotateUz(dp->GetMomentumDirection());
  }
  return fLocalDirection;
}

void G4SauterGavrilaAngularDistribution::PrintGeneratorInformation() const
{
  G4cout << "\n" << G4endl;
  G4cout << "Non-polarized photoelectric effect angular generator." << G4endl;
  G4cout << "The Sauter-Gavrila distribution for the K-shell is used."<<G4endl;
  G4cout << "Originally developed by M.Maire for Geant3" 
         << G4endl;
} 

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