Import Geant4 7.0.0 source tree
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Gabriele Cosmo
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//
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// ********************************************************************
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// * DISCLAIMER *
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// * *
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// * The following disclaimer summarizes all the specific disclaimers *
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// * of contributors to this software. The specific disclaimers,which *
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// * govern, are listed with their locations in: *
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// * http://cern.ch/geant4/license *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. *
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// * *
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// * This code implementation is the intellectual property of the *
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// * GEANT4 collaboration. *
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// * By copying, distributing or modifying the Program (or any work *
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// * based on the Program) you indicate your acceptance of this *
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// * statement, and all its terms. *
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// ********************************************************************
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//
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// $Id: G4eeToTwoGammaModel.cc,v 1.4 2004/12/01 19:37:15 vnivanch Exp $
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// GEANT4 tag $Name: geant4-07-00-cand-03 $
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//
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// -------------------------------------------------------------------
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//
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// GEANT4 Class file
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//
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//
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// File name: G4eeToTwoGammaModel
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//
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// Author: Vladimir Ivanchenko on base of Michel Maire code
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//
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// Creation date: 02.08.2004
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//
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// Modifications:
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//
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//
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// Class Description:
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//
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// Implementation of e+ annihilation into 2 gamma
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//
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// The secondaries Gamma energies are sampled using the Heitler cross section.
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//
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// A modified version of the random number techniques of Butcher & Messel
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// is used (Nuc Phys 20(1960),15).
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//
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// GEANT4 internal units.
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//
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// Note 1: The initial electron is assumed free and at rest.
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//
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// Note 2: The annihilation processes producing one or more than two photons are
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// ignored, as negligible compared to the two photons process.
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//
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// -------------------------------------------------------------------
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//
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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#include "G4eeToTwoGammaModel.hh"
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#include "G4Electron.hh"
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#include "G4Positron.hh"
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#include "G4Gamma.hh"
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#include "Randomize.hh"
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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using namespace std;
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G4eeToTwoGammaModel::G4eeToTwoGammaModel(const G4ParticleDefinition*,
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const G4String& nam)
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: G4VEmModel(nam),
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highKinEnergy(10.*TeV),
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lowKinEnergy(0.1*keV),
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pi_rcl2(pi*classic_electr_radius*classic_electr_radius)
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{
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4eeToTwoGammaModel::~G4eeToTwoGammaModel()
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{}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4eeToTwoGammaModel::HighEnergyLimit(const G4ParticleDefinition*)
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{
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return highKinEnergy;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4eeToTwoGammaModel::LowEnergyLimit(const G4ParticleDefinition*)
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{
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return lowKinEnergy;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4eeToTwoGammaModel::MinEnergyCut(const G4ParticleDefinition*,
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const G4MaterialCutsCouple*)
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{
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return 0.0;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4bool G4eeToTwoGammaModel::IsInCharge(const G4ParticleDefinition* p)
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{
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return (p == G4Positron::Positron());
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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void G4eeToTwoGammaModel::Initialise(const G4ParticleDefinition*,
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const G4DataVector&)
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{}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4eeToTwoGammaModel::ComputeDEDX(const G4MaterialCutsCouple*,
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const G4ParticleDefinition*,
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G4double,
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G4double)
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{
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return 0.0;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4eeToTwoGammaModel::CrossSection(const G4MaterialCutsCouple* couple,
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const G4ParticleDefinition*,
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G4double kineticEnergy,
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G4double,
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G4double)
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{
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// Calculates the cross section per atom of annihilation into two photons
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// from the Heilter formula.
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const G4Material* material = couple->GetMaterial();
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G4double eDensity = material->GetElectronDensity();
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G4double tau = kineticEnergy/electron_mass_c2;
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G4double gam = tau + 1.0;
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G4double gamma2= gam*gam;
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G4double bg2 = tau * (tau+2.0);
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G4double bg = sqrt(bg2);
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G4double cross = pi_rcl2*eDensity*((gamma2+4*gam+1.)*log(gam+bg) - (gam+3.)*bg)
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/ (bg2*(gam+1.));
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return cross;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4DynamicParticle* G4eeToTwoGammaModel::SampleSecondary(
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const G4MaterialCutsCouple*,
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const G4DynamicParticle*,
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G4double,
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G4double)
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{
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return 0;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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vector<G4DynamicParticle*>* G4eeToTwoGammaModel::SampleSecondaries(
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const G4MaterialCutsCouple*,
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const G4DynamicParticle* dp,
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G4double,
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G4double)
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{
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G4double PositKinEnergy = dp->GetKineticEnergy();
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G4ThreeVector PositDirection = dp->GetMomentumDirection();
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G4double tau = PositKinEnergy/electron_mass_c2;
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G4double gam = tau + 1.0;
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G4double tau2 = tau + 2.0;
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G4double sqgrate = sqrt(tau/tau2)*0.5;
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G4double sqg2m1 = sqrt(tau*tau2);
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// limits of the energy sampling
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G4double epsilmin = 0.5 - sqgrate;
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G4double epsilmax = 0.5 + sqgrate;
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G4double epsilqot = epsilmax/epsilmin;
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//
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// sample the energy rate of the created gammas
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//
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G4double epsil, greject;
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do {
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epsil = epsilmin*pow(epsilqot,G4UniformRand());
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greject = 1. - epsil + (2.*gam*epsil-1.)/(epsil*tau2*tau2);
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} while( greject < G4UniformRand() );
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//
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// scattered Gamma angles. ( Z - axis along the parent positron)
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//
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G4double cost = (epsil*tau2-1.)/(epsil*sqg2m1);
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G4double sint = sqrt((1.+cost)*(1.-cost));
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G4double phi = twopi * G4UniformRand();
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G4double dirx = sint*cos(phi) , diry = sint*sin(phi) , dirz = cost;
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//
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// kinematic of the created pair
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//
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G4double TotalAvailableEnergy = PositKinEnergy + 2.0*electron_mass_c2;
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G4double Phot1Energy = epsil*TotalAvailableEnergy;
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vector<G4DynamicParticle*>* vdp = new vector<G4DynamicParticle*>;
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G4ThreeVector Phot1Direction (dirx, diry, dirz);
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Phot1Direction.rotateUz(PositDirection);
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G4DynamicParticle* aParticle1 = new G4DynamicParticle (G4Gamma::Gamma(),
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Phot1Direction, Phot1Energy);
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vdp->push_back(aParticle1);
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G4double Phot2Energy =(1.-epsil)*TotalAvailableEnergy;
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G4double Eratio= Phot1Energy/Phot2Energy;
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G4double PositP= sqrt(PositKinEnergy*(PositKinEnergy+2.*electron_mass_c2));
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G4ThreeVector Phot2Direction (-dirx*Eratio, -diry*Eratio,
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(PositP-dirz*Phot1Energy)/Phot2Energy);
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Phot2Direction.unit();
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Phot2Direction.rotateUz(PositDirection);
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// create G4DynamicParticle object for the particle2
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G4DynamicParticle* aParticle2= new G4DynamicParticle (G4Gamma::Gamma(),
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Phot2Direction, Phot2Energy);
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vdp->push_back(aParticle2);
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return vdp;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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