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Please see the license in the file LICENSE and URL above * // * for the full disclaimer and the limitation of liability. * // * * // * This code implementation is the result of the scientific and * // * technical work of the GEANT4 collaboration. * // * By using, copying, modifying or distributing the software (or * // * any work based on the software) you agree to acknowledge its * // * use in resulting scientific publications, and indicate your * // * acceptance of all terms of the Geant4 Software license. * // ******************************************************************** // // // ------------------------------------------------------------------- // // GEANT4 Class file // // // File name: G4eeToTwoGammaModel // // Author: Vladimir Ivanchenko on base of Michel Maire code // // Creation date: 02.08.2004 // // Modifications: // 08-04-05 Major optimisation of internal interfaces (V.Ivanchenko) // 18-04-05 Compute CrossSectionPerVolume (V.Ivanchenko) // 06-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma) // 29-06-06 Fix problem for zero energy incident positron (V.Ivanchenko) // 20-10-06 Add theGamma as a member (V.Ivanchenko) // // // Class Description: // // Implementation of e+ annihilation into 2 gamma // // The secondaries Gamma energies are sampled using the Heitler cross section. // // A modified version of the random number techniques of Butcher & Messel // is used (Nuc Phys 20(1960),15). // // GEANT4 internal units. // // Note 1: The initial electron is assumed free and at rest. // // Note 2: The annihilation processes producing one or more than two photons are // ignored, as negligible compared to the two photons process. // // ------------------------------------------------------------------- // //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... #include "G4eeToTwoGammaModel.hh" #include "G4PhysicalConstants.hh" #include "G4SystemOfUnits.hh" #include "G4TrackStatus.hh" #include "G4Electron.hh" #include "G4Positron.hh" #include "G4Gamma.hh" #include "Randomize.hh" #include "G4ParticleChangeForGamma.hh" #include "G4Log.hh" #include "G4Exp.hh" //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... using namespace std; G4eeToTwoGammaModel::G4eeToTwoGammaModel(const G4ParticleDefinition*, const G4String& nam) : G4VEmModel(nam), pi_rcl2(pi*classic_electr_radius*classic_electr_radius) { theGamma = G4Gamma::Gamma(); fParticleChange = nullptr; } //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... G4eeToTwoGammaModel::~G4eeToTwoGammaModel() {} //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.... void G4eeToTwoGammaModel::Initialise(const G4ParticleDefinition*, const G4DataVector&) { if(fParticleChange) { return; } fParticleChange = GetParticleChangeForGamma(); } //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... G4double G4eeToTwoGammaModel::ComputeCrossSectionPerElectron(G4double kineticEnergy) { // Calculates the cross section per electron of annihilation into two photons // from the Heilter formula. G4double ekin = std::max(eV,kineticEnergy); G4double tau = ekin/electron_mass_c2; G4double gam = tau + 1.0; G4double gamma2= gam*gam; G4double bg2 = tau * (tau+2.0); G4double bg = sqrt(bg2); G4double cross = pi_rcl2*((gamma2+4*gam+1.)*G4Log(gam+bg) - (gam+3.)*bg) / (bg2*(gam+1.)); return cross; } //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... G4double G4eeToTwoGammaModel::ComputeCrossSectionPerAtom( const G4ParticleDefinition*, G4double kineticEnergy, G4double Z, G4double, G4double, G4double) { // Calculates the cross section per atom of annihilation into two photons G4double cross = Z*ComputeCrossSectionPerElectron(kineticEnergy); return cross; } //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... G4double G4eeToTwoGammaModel::CrossSectionPerVolume( const G4Material* material, const G4ParticleDefinition*, G4double kineticEnergy, G4double, G4double) { // Calculates the cross section per volume of annihilation into two photons G4double eDensity = material->GetElectronDensity(); G4double cross = eDensity*ComputeCrossSectionPerElectron(kineticEnergy); return cross; } //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... // Polarisation of gamma according to M.H.L.Pryce and J.C.Ward, // Nature 4065 (1947) 435. void G4eeToTwoGammaModel::SampleSecondaries(vector* vdp, const G4MaterialCutsCouple*, const G4DynamicParticle* dp, G4double, G4double) { G4double posiKinEnergy = dp->GetKineticEnergy(); G4DynamicParticle *aGamma1, *aGamma2; CLHEP::HepRandomEngine* rndmEngine = G4Random::getTheEngine(); // Case at rest if(posiKinEnergy == 0.0) { G4double cost = 2.*rndmEngine->flat()-1.; G4double sint = sqrt((1. - cost)*(1. + cost)); G4double phi = twopi * rndmEngine->flat(); G4ThreeVector dir(sint*cos(phi), sint*sin(phi), cost); phi = twopi * rndmEngine->flat(); G4double cosphi = cos(phi); G4double sinphi = sin(phi); G4ThreeVector pol(cosphi, sinphi, 0.0); pol.rotateUz(dir); aGamma1 = new G4DynamicParticle(theGamma, dir, electron_mass_c2); aGamma1->SetPolarization(pol.x(),pol.y(),pol.z()); aGamma2 = new G4DynamicParticle(theGamma,-dir, electron_mass_c2); pol.set(-sinphi, cosphi, 0.0); pol.rotateUz(dir); aGamma2->SetPolarization(pol.x(),pol.y(),pol.z()); /* G4cout << "Annihilation at rest fly: e0= " << " dir= " << dir << G4endl; */ } else { G4ThreeVector posiDirection = dp->GetMomentumDirection(); G4double tau = posiKinEnergy/electron_mass_c2; G4double gam = tau + 1.0; G4double tau2 = tau + 2.0; G4double sqgrate = sqrt(tau/tau2)*0.5; G4double sqg2m1 = sqrt(tau*tau2); // limits of the energy sampling G4double epsilmin = 0.5 - sqgrate; G4double epsilmax = 0.5 + sqgrate; G4double epsilqot = epsilmax/epsilmin; // // sample the energy rate of the created gammas // G4double epsil, greject; do { epsil = epsilmin*G4Exp(G4Log(epsilqot)*rndmEngine->flat()); greject = 1. - epsil + (2.*gam*epsil-1.)/(epsil*tau2*tau2); // Loop checking, 03-Aug-2015, Vladimir Ivanchenko } while( greject < rndmEngine->flat()); // // scattered Gamma angles. ( Z - axis along the parent positron) // G4double cost = (epsil*tau2-1.)/(epsil*sqg2m1); if(std::abs(cost) > 1.0) { G4cout << "### G4eeToTwoGammaModel WARNING cost= " << cost << " positron Ekin(MeV)= " << posiKinEnergy << " gamma epsil= " << epsil << G4endl; if(cost > 1.0) cost = 1.0; else cost = -1.0; } G4double sint = sqrt((1.+cost)*(1.-cost)); G4double phi = twopi * rndmEngine->flat(); // // kinematic of the created pair // G4double totalEnergy = posiKinEnergy + 2.0*electron_mass_c2; G4double phot1Energy = epsil*totalEnergy; G4ThreeVector phot1Direction(sint*cos(phi), sint*sin(phi), cost); phot1Direction.rotateUz(posiDirection); aGamma1 = new G4DynamicParticle (theGamma,phot1Direction, phot1Energy); phi = twopi * rndmEngine->flat(); G4double cosphi = cos(phi); G4double sinphi = sin(phi); G4ThreeVector pol(cosphi, sinphi, 0.0); pol.rotateUz(phot1Direction); aGamma1->SetPolarization(pol.x(),pol.y(),pol.z()); G4double phot2Energy =(1.-epsil)*totalEnergy; G4double posiP= sqrt(posiKinEnergy*(posiKinEnergy+2.*electron_mass_c2)); G4ThreeVector dir = posiDirection*posiP - phot1Direction*phot1Energy; G4ThreeVector phot2Direction = dir.unit(); // create G4DynamicParticle object for the particle2 aGamma2 = new G4DynamicParticle (theGamma, phot2Direction, phot2Energy); //!!! likely problematic direction to be checked pol.set(-sinphi, cosphi, 0.0); pol.rotateUz(phot1Direction); cost = pol*phot2Direction; pol -= cost*phot2Direction; pol = pol.unit(); aGamma2->SetPolarization(pol.x(),pol.y(),pol.z()); /* G4cout << "Annihilation on fly: e0= " << posiKinEnergy << " m= " << electron_mass_c2 << " e1= " << phot1Energy << " e2= " << phot2Energy << " dir= " << dir << " -> " << phot1Direction << " " << phot2Direction << G4endl; */ } vdp->push_back(aGamma1); vdp->push_back(aGamma2); // kill primary positron fParticleChange->SetProposedKineticEnergy(0.0); fParticleChange->ProposeTrackStatus(fStopAndKill); } //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....