source: trunk/source/processes/electromagnetic/lowenergy/src/G4PenelopeAnnihilationModel.cc@ 992

Last change on this file since 992 was 991, checked in by garnier, 17 years ago

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[968]1//
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25//
26// $Id: G4PenelopeAnnihilationModel.cc,v 1.2 2008/12/04 14:09:36 pandola Exp $
[991]27// GEANT4 tag $Name: geant4-09-02 $
[968]28//
29// Author: Luciano Pandola
30//
31// History:
32// --------
33// 29 Oct 2008 L Pandola Migration from process to model
34//
35
36#include "G4PenelopeAnnihilationModel.hh"
37#include "G4ParticleDefinition.hh"
38#include "G4MaterialCutsCouple.hh"
39#include "G4ProductionCutsTable.hh"
40#include "G4DynamicParticle.hh"
41#include "G4Gamma.hh"
42
43//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
44
45
46G4PenelopeAnnihilationModel::G4PenelopeAnnihilationModel(const G4ParticleDefinition*,
47 const G4String& nam)
48 :G4VEmModel(nam),isInitialised(false)
49{
50 fIntrinsicLowEnergyLimit = 0.0*eV;
51 fIntrinsicHighEnergyLimit = 100.0*GeV;
52 SetLowEnergyLimit(fIntrinsicLowEnergyLimit);
53 SetHighEnergyLimit(fIntrinsicHighEnergyLimit);
54
55 //Calculate variable that will be used later on
56 fPielr2 = pi*classic_electr_radius*classic_electr_radius;
57
58 verboseLevel= 0;
59 // Verbosity scale:
60 // 0 = nothing
61 // 1 = warning for energy non-conservation
62 // 2 = details of energy budget
63 // 3 = calculation of cross sections, file openings, sampling of atoms
64 // 4 = entering in methods
65
66}
67
68//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
69
70G4PenelopeAnnihilationModel::~G4PenelopeAnnihilationModel()
71{;}
72
73//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
74
75void G4PenelopeAnnihilationModel::Initialise(const G4ParticleDefinition* particle,
76 const G4DataVector& cuts)
77{
78 if (verboseLevel > 3)
79 G4cout << "Calling G4PenelopeAnnihilationModel::Initialise()" << G4endl;
80
81 InitialiseElementSelectors(particle,cuts);
82 if (LowEnergyLimit() < fIntrinsicLowEnergyLimit)
83 {
84 G4cout << "G4PenelopeAnnihilationModel: low energy limit increased from " <<
85 LowEnergyLimit()/eV << " eV to " << fIntrinsicLowEnergyLimit/eV << " eV" << G4endl;
86 SetLowEnergyLimit(fIntrinsicLowEnergyLimit);
87 }
88 if (HighEnergyLimit() > fIntrinsicHighEnergyLimit)
89 {
90 G4cout << "G4PenelopeAnnihilationModel: high energy limit decreased from " <<
91 HighEnergyLimit()/GeV << " GeV to " << fIntrinsicHighEnergyLimit/GeV << " GeV" << G4endl;
92 SetHighEnergyLimit(fIntrinsicHighEnergyLimit);
93 }
94
95 G4cout << "Penelope Annihilation model is initialized " << G4endl
96 << "Energy range: "
97 << LowEnergyLimit() / keV << " keV - "
98 << HighEnergyLimit() / GeV << " GeV"
99 << G4endl;
100
101 if(isInitialised) return;
102
103 if(pParticleChange)
104 fParticleChange = reinterpret_cast<G4ParticleChangeForGamma*>(pParticleChange);
105 else
106 fParticleChange = new G4ParticleChangeForGamma();
107 isInitialised = true;
108}
109
110//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
111
112G4double G4PenelopeAnnihilationModel::ComputeCrossSectionPerAtom(
113 const G4ParticleDefinition*,
114 G4double energy,
115 G4double Z, G4double,
116 G4double, G4double)
117{
118 if (verboseLevel > 3)
119 G4cout << "Calling ComputeCrossSectionPerAtom() of G4PenelopeAnnihilationModel" <<
120 G4endl;
121
122 G4double cs = Z*ComputeCrossSectionPerElectron(energy);
123
124 if (verboseLevel > 2)
125 G4cout << "Annihilation cross Section at " << energy/keV << " keV for Z=" << Z <<
126 " = " << cs/barn << " barn" << G4endl;
127 return cs;
128}
129
130//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
131
132void G4PenelopeAnnihilationModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
133 const G4MaterialCutsCouple*,
134 const G4DynamicParticle* aDynamicPositron,
135 G4double,
136 G4double)
137{
138 //
139 // Penelope model to sample final state for positron annihilation.
140 // Target eletrons are assumed to be free and at rest. Binding effects enabling
141 // one-photon annihilation are neglected.
142 // For annihilation at rest, two back-to-back photons are emitted, having energy of 511 keV
143 // and isotropic angular distribution.
144 // For annihilation in flight, it is used the theory from
145 // W. Heitler, The quantum theory of radiation, Oxford University Press (1954)
146 // The two photons can have different energy. The efficiency of the sampling algorithm
147 // of the photon energy from the dSigma/dE distribution is practically 100% for
148 // positrons of kinetic energy < 10 keV. It reaches a minimum (about 80%) at energy
149 // of about 10 MeV.
150 // The angle theta is kinematically linked to the photon energy, to ensure momentum
151 // conservation. The angle phi is sampled isotropically for the first gamma.
152 //
153 if (verboseLevel > 3)
154 G4cout << "Calling SamplingSecondaries() of G4PenelopeAnnihilationModel" << G4endl;
155
156 G4double kineticEnergy = aDynamicPositron->GetKineticEnergy();
157
158 if (kineticEnergy == 0)
159 {
160 //Old AtRestDoIt
161 G4double cosTheta = -1.0+2.0*G4UniformRand();
162 G4double sinTheta = std::sqrt(1.0-cosTheta*cosTheta);
163 G4double phi = twopi*G4UniformRand();
164 G4ThreeVector direction (sinTheta*std::cos(phi),sinTheta*std::sin(phi),cosTheta);
165 G4DynamicParticle* firstGamma = new G4DynamicParticle (G4Gamma::Gamma(),
166 direction, electron_mass_c2);
167 G4DynamicParticle* secondGamma = new G4DynamicParticle (G4Gamma::Gamma(),
168 -direction, electron_mass_c2);
169
170 fvect->push_back(firstGamma);
171 fvect->push_back(secondGamma);
172 fParticleChange->SetProposedKineticEnergy(0.);
173 fParticleChange->ProposeTrackStatus(fStopAndKill);
174 return;
175 }
176
177 //This is the "PostStep" case (annihilation in flight)
178 G4ParticleMomentum positronDirection =
179 aDynamicPositron->GetMomentumDirection();
180 G4double gamma = 1.0 + std::max(kineticEnergy,1.0*eV)/electron_mass_c2;
181 G4double gamma21 = std::sqrt(gamma*gamma-1);
182 G4double ani = 1.0+gamma;
183 G4double chimin = 1.0/(ani+gamma21);
184 G4double rchi = (1.0-chimin)/chimin;
185 G4double gt0 = ani*ani-2.0;
186 G4double test=0.0;
187 G4double epsilon = 0;
188 do{
189 epsilon = chimin*std::pow(rchi,G4UniformRand());
190 G4double reject = ani*ani*(1.0-epsilon)+2.0*gamma-(1.0/epsilon);
191 test = G4UniformRand()*gt0-reject;
192 }while(test>0);
193
194 G4double totalAvailableEnergy = kineticEnergy + 2.0*electron_mass_c2;
195 G4double photon1Energy = epsilon*totalAvailableEnergy;
196 G4double photon2Energy = (1.0-epsilon)*totalAvailableEnergy;
197 G4double cosTheta1 = (ani-1.0/epsilon)/gamma21;
198 G4double cosTheta2 = (ani-1.0/(1.0-epsilon))/gamma21;
199
200 //G4double localEnergyDeposit = 0.;
201
202 G4double sinTheta1 = std::sqrt(1.-cosTheta1*cosTheta1);
203 G4double phi1 = twopi * G4UniformRand();
204 G4double dirx1 = sinTheta1 * std::cos(phi1);
205 G4double diry1 = sinTheta1 * std::sin(phi1);
206 G4double dirz1 = cosTheta1;
207
208 G4double sinTheta2 = std::sqrt(1.-cosTheta2*cosTheta2);
209 G4double phi2 = phi1+pi;
210 G4double dirx2 = sinTheta2 * std::cos(phi2);
211 G4double diry2 = sinTheta2 * std::sin(phi2);
212 G4double dirz2 = cosTheta2;
213
214 G4ThreeVector photon1Direction (dirx1,diry1,dirz1);
215 photon1Direction.rotateUz(positronDirection);
216 // create G4DynamicParticle object for the particle1
217 G4DynamicParticle* aParticle1= new G4DynamicParticle (G4Gamma::Gamma(),
218 photon1Direction,
219 photon1Energy);
220 fvect->push_back(aParticle1);
221
222 G4ThreeVector photon2Direction(dirx2,diry2,dirz2);
223 photon2Direction.rotateUz(positronDirection);
224 // create G4DynamicParticle object for the particle2
225 G4DynamicParticle* aParticle2= new G4DynamicParticle (G4Gamma::Gamma(),
226 photon2Direction,
227 photon2Energy);
228 fvect->push_back(aParticle2);
229 fParticleChange->SetProposedKineticEnergy(0.);
230 fParticleChange->ProposeTrackStatus(fStopAndKill);
231
232 if (verboseLevel > 1)
233 {
234 G4cout << "-----------------------------------------------------------" << G4endl;
235 G4cout << "Energy balance from G4PenelopeAnnihilation" << G4endl;
236 G4cout << "Kinetic positron energy: " << kineticEnergy/keV << " keV" << G4endl;
237 G4cout << "Total available energy: " << totalAvailableEnergy/keV << " keV " << G4endl;
238 G4cout << "-----------------------------------------------------------" << G4endl;
239 G4cout << "Photon energy 1: " << photon1Energy/keV << " keV" << G4endl;
240 G4cout << "Photon energy 2: " << photon2Energy/keV << " keV" << G4endl;
241 G4cout << "Total final state: " << (photon1Energy+photon2Energy)/keV <<
242 " keV" << G4endl;
243 G4cout << "-----------------------------------------------------------" << G4endl;
244 }
245 if (verboseLevel > 0)
246 {
247
248 G4double energyDiff = std::fabs(totalAvailableEnergy-photon1Energy-photon2Energy);
249 if (energyDiff > 0.05*keV)
250 G4cout << "Warning from G4PenelopeAnnihilation: problem with energy conservation: " <<
251 (photon1Energy+photon2Energy)/keV <<
252 " keV (final) vs. " <<
253 totalAvailableEnergy/keV << " keV (initial)" << G4endl;
254 }
255 return;
256}
257
258//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
259
260G4double G4PenelopeAnnihilationModel:: ComputeCrossSectionPerElectron(G4double energy)
261{
262 //
263 // Penelope model to calculate cross section for positron annihilation.
264 // The annihilation cross section per electron is calculated according
265 // to the Heitler formula
266 // W. Heitler, The quantum theory of radiation, Oxford University Press (1954)
267 // in the assumptions of electrons free and at rest.
268 //
269 G4double gamma = 1.0+std::max(energy,1.0*eV)/electron_mass_c2;
270 G4double gamma2 = gamma*gamma;
271 G4double f2 = gamma2-1.0;
272 G4double f1 = std::sqrt(f2);
273 G4double crossSection = fPielr2*((gamma2+4.0*gamma+1.0)*std::log(gamma+f1)/f2
274 - (gamma+3.0)/f1)/(gamma+1.0);
275 return crossSection;
276}
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