source: trunk/source/processes/electromagnetic/lowenergy/src/G4PenelopeAnnihilationModel.cc @ 1347

Last change on this file since 1347 was 1347, checked in by garnier, 13 years ago

geant4 tag 9.4
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26// $Id: G4PenelopeAnnihilationModel.cc,v 1.4 2009/06/10 13:32:36 mantero Exp $
27// GEANT4 tag $Name: geant4-09-04-ref-00 $
28//
29// Author: Luciano Pandola
30//
31// History:
32// --------
33// 29 Oct 2008   L Pandola    Migration from process to model
34// 15 Apr 2009   V Ivanchenko Cleanup initialisation and generation of secondaries:
35//                  - apply internal high-energy limit only in constructor
36//                  - do not apply low-energy limit (default is 0)
37//                  - do not use G4ElementSelector
38
39#include "G4PenelopeAnnihilationModel.hh"
40#include "G4ParticleDefinition.hh"
41#include "G4MaterialCutsCouple.hh"
42#include "G4ProductionCutsTable.hh"
43#include "G4DynamicParticle.hh"
44#include "G4Gamma.hh"
45
46//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
47
48
49G4PenelopeAnnihilationModel::G4PenelopeAnnihilationModel(const G4ParticleDefinition*,
50                                             const G4String& nam)
51  :G4VEmModel(nam),isInitialised(false)
52{
53  fIntrinsicLowEnergyLimit = 0.0;
54  fIntrinsicHighEnergyLimit = 100.0*GeV;
55  //  SetLowEnergyLimit(fIntrinsicLowEnergyLimit);
56  SetHighEnergyLimit(fIntrinsicHighEnergyLimit);
57 
58  //Calculate variable that will be used later on
59  fPielr2 = pi*classic_electr_radius*classic_electr_radius;
60
61  verboseLevel= 0;
62  // Verbosity scale:
63  // 0 = nothing
64  // 1 = warning for energy non-conservation
65  // 2 = details of energy budget
66  // 3 = calculation of cross sections, file openings, sampling of atoms
67  // 4 = entering in methods
68
69}
70
71//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
72
73G4PenelopeAnnihilationModel::~G4PenelopeAnnihilationModel()
74{;}
75
76//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
77
78void G4PenelopeAnnihilationModel::Initialise(const G4ParticleDefinition*,
79                                             const G4DataVector&)
80{
81  if (verboseLevel > 3)
82    G4cout << "Calling G4PenelopeAnnihilationModel::Initialise()" << G4endl;
83
84  if(verboseLevel > 0) {
85    G4cout << "Penelope Annihilation model is initialized " << G4endl
86           << "Energy range: "
87           << LowEnergyLimit() / keV << " keV - "
88           << HighEnergyLimit() / GeV << " GeV"
89           << G4endl;
90  }
91
92  if(isInitialised) return;
93  fParticleChange = GetParticleChangeForGamma();
94  isInitialised = true; 
95}
96
97//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
98
99G4double G4PenelopeAnnihilationModel::ComputeCrossSectionPerAtom(
100                                       const G4ParticleDefinition*,
101                                             G4double energy,
102                                             G4double Z, G4double,
103                                             G4double, G4double)
104{
105  if (verboseLevel > 3)
106    G4cout << "Calling ComputeCrossSectionPerAtom() of G4PenelopeAnnihilationModel" << 
107      G4endl;
108
109  G4double cs = Z*ComputeCrossSectionPerElectron(energy);
110 
111  if (verboseLevel > 2)
112    G4cout << "Annihilation cross Section at " << energy/keV << " keV for Z=" << Z << 
113      " = " << cs/barn << " barn" << G4endl;
114  return cs;
115}
116
117//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
118
119void G4PenelopeAnnihilationModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
120                                              const G4MaterialCutsCouple*,
121                                              const G4DynamicParticle* aDynamicPositron,
122                                              G4double,
123                                              G4double)
124{
125  //
126  // Penelope model to sample final state for positron annihilation.
127  // Target eletrons are assumed to be free and at rest. Binding effects enabling
128  // one-photon annihilation are neglected.
129  // For annihilation at rest, two back-to-back photons are emitted, having energy of 511 keV
130  // and isotropic angular distribution.
131  // For annihilation in flight, it is used the theory from
132  //  W. Heitler, The quantum theory of radiation, Oxford University Press (1954)
133  // The two photons can have different energy. The efficiency of the sampling algorithm
134  // of the photon energy from the dSigma/dE distribution is practically 100% for
135  // positrons of kinetic energy < 10 keV. It reaches a minimum (about 80%) at energy
136  // of about 10 MeV.
137  // The angle theta is kinematically linked to the photon energy, to ensure momentum
138  // conservation. The angle phi is sampled isotropically for the first gamma.
139  //
140  if (verboseLevel > 3)
141    G4cout << "Calling SamplingSecondaries() of G4PenelopeAnnihilationModel" << G4endl;
142
143  G4double kineticEnergy = aDynamicPositron->GetKineticEnergy();
144
145  // kill primary
146  fParticleChange->SetProposedKineticEnergy(0.);
147  fParticleChange->ProposeTrackStatus(fStopAndKill);
148 
149  if (kineticEnergy == 0.0)
150    {
151      //Old AtRestDoIt
152      G4double cosTheta = -1.0+2.0*G4UniformRand();
153      G4double sinTheta = std::sqrt(1.0-cosTheta*cosTheta);
154      G4double phi = twopi*G4UniformRand();
155      G4ThreeVector direction (sinTheta*std::cos(phi),sinTheta*std::sin(phi),cosTheta);
156      G4DynamicParticle* firstGamma = new G4DynamicParticle (G4Gamma::Gamma(),
157                                                             direction, electron_mass_c2);
158      G4DynamicParticle* secondGamma = new G4DynamicParticle (G4Gamma::Gamma(),
159                                                              -direction, electron_mass_c2);
160 
161      fvect->push_back(firstGamma);
162      fvect->push_back(secondGamma);
163      return;
164    }
165
166  //This is the "PostStep" case (annihilation in flight)
167  G4ParticleMomentum positronDirection = 
168    aDynamicPositron->GetMomentumDirection();
169  G4double gamma = 1.0 + std::max(kineticEnergy,1.0*eV)/electron_mass_c2;
170  G4double gamma21 = std::sqrt(gamma*gamma-1);
171  G4double ani = 1.0+gamma;
172  G4double chimin = 1.0/(ani+gamma21);
173  G4double rchi = (1.0-chimin)/chimin;
174  G4double gt0 = ani*ani-2.0;
175  G4double test=0.0;
176  G4double epsilon = 0;
177  do{
178    epsilon = chimin*std::pow(rchi,G4UniformRand());
179    G4double reject = ani*ani*(1.0-epsilon)+2.0*gamma-(1.0/epsilon);
180    test = G4UniformRand()*gt0-reject;
181  }while(test>0);
182   
183  G4double totalAvailableEnergy = kineticEnergy + 2.0*electron_mass_c2;
184  G4double photon1Energy = epsilon*totalAvailableEnergy;
185  G4double photon2Energy = (1.0-epsilon)*totalAvailableEnergy;
186  G4double cosTheta1 = (ani-1.0/epsilon)/gamma21;
187  G4double cosTheta2 = (ani-1.0/(1.0-epsilon))/gamma21;
188 
189  //G4double localEnergyDeposit = 0.;
190
191  G4double sinTheta1 = std::sqrt(1.-cosTheta1*cosTheta1);
192  G4double phi1  = twopi * G4UniformRand();
193  G4double dirx1 = sinTheta1 * std::cos(phi1);
194  G4double diry1 = sinTheta1 * std::sin(phi1);
195  G4double dirz1 = cosTheta1;
196 
197  G4double sinTheta2 = std::sqrt(1.-cosTheta2*cosTheta2);
198  G4double phi2  = phi1+pi;
199  G4double dirx2 = sinTheta2 * std::cos(phi2);
200  G4double diry2 = sinTheta2 * std::sin(phi2);
201  G4double dirz2 = cosTheta2;
202 
203  G4ThreeVector photon1Direction (dirx1,diry1,dirz1);
204  photon1Direction.rotateUz(positronDirection);   
205  // create G4DynamicParticle object for the particle1 
206  G4DynamicParticle* aParticle1= new G4DynamicParticle (G4Gamma::Gamma(),
207                                                           photon1Direction, 
208                                                           photon1Energy);
209  fvect->push_back(aParticle1);
210 
211  G4ThreeVector photon2Direction(dirx2,diry2,dirz2);
212  photon2Direction.rotateUz(positronDirection); 
213     // create G4DynamicParticle object for the particle2
214  G4DynamicParticle* aParticle2= new G4DynamicParticle (G4Gamma::Gamma(),
215                                                           photon2Direction,
216                                                           photon2Energy);
217  fvect->push_back(aParticle2);
218
219  if (verboseLevel > 1)
220    {
221      G4cout << "-----------------------------------------------------------" << G4endl;
222      G4cout << "Energy balance from G4PenelopeAnnihilation" << G4endl;
223      G4cout << "Kinetic positron energy: " << kineticEnergy/keV << " keV" << G4endl;
224      G4cout << "Total available energy: " << totalAvailableEnergy/keV << " keV " << G4endl;
225      G4cout << "-----------------------------------------------------------" << G4endl;
226      G4cout << "Photon energy 1: " << photon1Energy/keV << " keV" << G4endl;
227      G4cout << "Photon energy 2: " << photon2Energy/keV << " keV" << G4endl;
228      G4cout << "Total final state: " << (photon1Energy+photon2Energy)/keV << 
229        " keV" << G4endl;
230      G4cout << "-----------------------------------------------------------" << G4endl;
231    }
232  if (verboseLevel > 0)
233    {     
234      G4double energyDiff = std::fabs(totalAvailableEnergy-photon1Energy-photon2Energy);
235      if (energyDiff > 0.05*keV)
236        G4cout << "Warning from G4PenelopeAnnihilation: problem with energy conservation: " << 
237          (photon1Energy+photon2Energy)/keV << 
238          " keV (final) vs. " << 
239          totalAvailableEnergy/keV << " keV (initial)" << G4endl;
240    }
241  return;
242}
243
244//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
245
246G4double G4PenelopeAnnihilationModel:: ComputeCrossSectionPerElectron(G4double energy)
247{
248  //
249  // Penelope model to calculate cross section for positron annihilation.
250  // The annihilation cross section per electron is calculated according
251  // to the Heitler formula
252  //  W. Heitler, The quantum theory of radiation, Oxford University Press (1954)
253  // in the assumptions of electrons free and at rest.
254  //
255  G4double gamma = 1.0+std::max(energy,1.0*eV)/electron_mass_c2;
256  G4double gamma2 = gamma*gamma;
257  G4double f2 = gamma2-1.0;
258  G4double f1 = std::sqrt(f2);
259  G4double crossSection = fPielr2*((gamma2+4.0*gamma+1.0)*std::log(gamma+f1)/f2
260                         - (gamma+3.0)/f1)/(gamma+1.0);
261  return crossSection;
262}
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