Gabriele Cosmo
251 lines
8.9 KiB
C++
251 lines
8.9 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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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. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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// $Id: G4eeToTwoGammaModel.cc,v 1.12 2006/10/20 08:59:50 vnivanch Exp $
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// GEANT4 tag $Name: geant4-08-02 $
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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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// 08-04-05 Major optimisation of internal interfaces (V.Ivanchenko)
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// 18-04-05 Compute CrossSectionPerVolume (V.Ivanchenko)
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// 06-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma)
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// 29-06-06 Fix problem for zero energy incident positron (V.Ivanchenko)
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// 20-10-06 Add theGamma as a member (V.Ivanchenko)
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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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pi_rcl2(pi*classic_electr_radius*classic_electr_radius)
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{
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theGamma = G4Gamma::Gamma();
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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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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::ComputeCrossSectionPerElectron(
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const G4ParticleDefinition*,
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G4double kineticEnergy,
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G4double, G4double)
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{
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// Calculates the cross section per electron of annihilation into two photons
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// from the Heilter formula.
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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*((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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G4double G4eeToTwoGammaModel::ComputeCrossSectionPerAtom(
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const G4ParticleDefinition* p,
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G4double kineticEnergy, G4double Z,
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G4double, G4double, G4double)
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{
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// Calculates the cross section per atom of annihilation into two photons
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G4double cross = Z*ComputeCrossSectionPerElectron(p,kineticEnergy);
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return cross;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4double G4eeToTwoGammaModel::CrossSectionPerVolume(
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const G4Material* material,
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const G4ParticleDefinition* p,
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G4double kineticEnergy,
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G4double, G4double)
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{
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// Calculates the cross section per volume of annihilation into two photons
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G4double eDensity = material->GetElectronDensity();
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G4double cross = eDensity*ComputeCrossSectionPerElectron(p,kineticEnergy);
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return cross;
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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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vector<G4DynamicParticle*>* vdp = new vector<G4DynamicParticle*>;
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G4double PositKinEnergy = dp->GetKineticEnergy();
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// Case at rest
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if(PositKinEnergy == 0.0) {
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G4double cost = 2.*G4UniformRand()-1.;
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G4double sint = sqrt((1. - cost)*(1. + cost));
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G4double phi = twopi * G4UniformRand();
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G4ThreeVector dir (sint*cos(phi), sint*sin(phi), cost);
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G4DynamicParticle* aGamma1 = new G4DynamicParticle(theGamma,
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dir, electron_mass_c2);
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G4DynamicParticle* aGamma2 = new G4DynamicParticle(theGamma,
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-dir, electron_mass_c2);
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vdp->push_back(aGamma1);
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vdp->push_back(aGamma2);
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} else {
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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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if(std::abs(cost) > 1.0) {
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G4cout << "### G4eeToTwoGammaModel WARNING cost= " << cost
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<< " positron Ekin(MeV)= " << PositKinEnergy
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<< " gamma epsil= " << epsil
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<< G4endl;
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if(cost > 1.0) cost = 1.0;
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else cost = -1.0;
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}
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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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G4ThreeVector Phot1Direction (dirx, diry, dirz);
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Phot1Direction.rotateUz(PositDirection);
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G4DynamicParticle* aGamma1 =
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new G4DynamicParticle (theGamma,Phot1Direction, Phot1Energy);
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vdp->push_back(aGamma1);
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G4double Phot2Energy =(1.-epsil)*TotalAvailableEnergy;
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G4double PositP= sqrt(PositKinEnergy*(PositKinEnergy+2.*electron_mass_c2));
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G4ThreeVector dir = PositDirection*PositP - Phot1Direction*Phot1Energy;
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G4ThreeVector Phot2Direction = dir.unit();
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// create G4DynamicParticle object for the particle2
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G4DynamicParticle* aGamma2=
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new G4DynamicParticle (theGamma,Phot2Direction, Phot2Energy);
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vdp->push_back(aGamma2);
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/*
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G4cout << "Annihilation in fly: e0= " << PositKinEnergy
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<< " m= " << electron_mass_c2
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<< " e1= " << Phot1Energy
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<< " e2= " << Phot2Energy << " dir= " << dir
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<< " -> " << Phot1Direction << " "
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<< Phot2Direction << G4endl;
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*/
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}
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return vdp;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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