Gabriele Cosmo
200 lines
7.3 KiB
C++
200 lines
7.3 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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//
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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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// 18-01-20 Introduce thermal model of annihilation at rest (J.Allison)
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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 if atomic PDF
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// is not defined
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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 "G4PhysicalConstants.hh"
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#include "G4SystemOfUnits.hh"
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#include "G4TrackStatus.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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#include "G4RandomDirection.hh"
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#include "G4ParticleChangeForGamma.hh"
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#include "G4EmParameters.hh"
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#include "G4Log.hh"
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#include "G4Exp.hh"
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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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(CLHEP::pi*CLHEP::classic_electr_radius*CLHEP::classic_electr_radius)
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{
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theGamma = G4Gamma::Gamma();
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fParticleChange = nullptr;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4eeToTwoGammaModel::~G4eeToTwoGammaModel() = default;
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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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if (nullptr != fParticleChange) { return; }
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fParticleChange = GetParticleChangeForGamma();
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4double
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G4eeToTwoGammaModel::ComputeCrossSectionPerElectron(G4double kineticEnergy)
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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 ekin = std::max(CLHEP::eV, kineticEnergy);
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G4double tau = ekin/CLHEP::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 = std::sqrt(bg2);
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G4double cross = pi_rcl2*((gamma2+4*gam+1.)*G4Log(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*,
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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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return Z*ComputeCrossSectionPerElectron(kineticEnergy);
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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*,
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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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return material->GetElectronDensity()*ComputeCrossSectionPerElectron(kineticEnergy);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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// Polarisation of gamma according to M.H.L.Pryce and J.C.Ward,
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// Nature 4065 (1947) 435.
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void G4eeToTwoGammaModel::SampleSecondaries(std::vector<G4DynamicParticle*>* vdp,
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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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// kill primary positron
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fParticleChange->SetProposedKineticEnergy(0.0);
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fParticleChange->ProposeTrackStatus(fStopAndKill);
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// Case at rest not considered anymore inside this model
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G4LorentzVector lv(dp->GetMomentum(),
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dp->GetKineticEnergy() + 2*CLHEP::electron_mass_c2);
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G4double eGammaCMS = 0.5 * lv.mag();
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G4ThreeVector dir1 = G4RandomDirection();
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G4double phi = CLHEP::twopi * G4UniformRand();
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G4double cosphi = std::cos(phi);
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G4double sinphi = std::sin(phi);
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G4ThreeVector pol1(cosphi, sinphi, 0.0);
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pol1.rotateUz(dir1);
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G4LorentzVector lv1(eGammaCMS*dir1, eGammaCMS);
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G4ThreeVector pol2(-sinphi, cosphi, 0.0);
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pol2.rotateUz(dir1);
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// transformation to lab system
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lv1.boost(lv.boostVector());
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lv -= lv1;
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//!!! boost of polarisation vector is not yet implemented
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// use constructors optimal for massless particle
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auto aGamma1 = new G4DynamicParticle(G4Gamma::Gamma(), lv1.vect());
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aGamma1->SetPolarization(pol1);
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auto aGamma2 = new G4DynamicParticle(G4Gamma::Gamma(), lv.vect());
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aGamma2->SetPolarization(pol2);
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vdp->push_back(aGamma1);
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vdp->push_back(aGamma2);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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