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25 //
26 //
27 // Author: D.H. Wright
28 // Date: 1 May 2012
29 //
30 // Description: model for electron and positron interaction with nuclei
31 // using the equivalent photon spectrum. A real gamma is
32 // produced from the virtual photon spectrum and is then
33 // interacted hadronically by the Bertini cascade at low
34 // energies. At high energies the gamma is treated as a
35 // pi0 and interacted with the nucleus using the FTFP model.
36 // The electro- and photo-nuclear cross sections of
37 // M. Kossov are used to generate the virtual photon
38 // spectrum.
39 //
40
41 #include "G4ElectroVDNuclearModel.hh"
42
43 #include "G4PhysicalConstants.hh"
44 #include "G4SystemOfUnits.hh"
45
46 #include "G4ElectroNuclearCrossSection.hh"
47 #include "G4PhotoNuclearCrossSection.hh"
48 #include "G4CrossSectionDataSetRegistry.hh"
49
50 #include "G4CascadeInterface.hh"
51 #include "G4TheoFSGenerator.hh"
52 #include "G4GeneratorPrecompoundInterface.hh"
53 #include "G4ExcitationHandler.hh"
54 #include "G4PreCompoundModel.hh"
55 #include "G4LundStringFragmentation.hh"
56 #include "G4ExcitedStringDecay.hh"
57 #include "G4FTFModel.hh"
58
59 #include "G4HadFinalState.hh"
60 #include "G4HadronicInteractionRegistry.hh"
61 #include "G4PhysicsModelCatalog.hh"
62
63 #include "G4ElectroNuclearCrossSection.hh"
64 #include "G4PhotoNuclearCrossSection.hh"
65 #include "G4GammaNuclearXS.hh"
66
67
68 G4ElectroVDNuclearModel::G4ElectroVDNuclearModel()
69 : G4HadronicInteraction("G4ElectroVDNuclearModel"),
70 leptonKE(0.0), photonEnergy(0.0), photonQ2(0.0), secID(-1)
71 {
72 SetMinEnergy(0.0);
73 SetMaxEnergy(1*PeV);
74
75 electroXS =
76 (G4ElectroNuclearCrossSection*)G4CrossSectionDataSetRegistry::Instance()->
77 GetCrossSectionDataSet(G4ElectroNuclearCrossSection::Default_Name());
78 if ( electroXS == nullptr ) {
79 electroXS = new G4ElectroNuclearCrossSection;
80 }
81
82 gammaXS =
83 (G4PhotoNuclearCrossSection*)G4CrossSectionDataSetRegistry::Instance()->
84 GetCrossSectionDataSet(G4PhotoNuclearCrossSection::Default_Name());
85 if ( gammaXS == nullptr ) {
86 gammaXS =
87 (G4GammaNuclearXS*)G4CrossSectionDataSetRegistry::Instance()->
88 GetCrossSectionDataSet(G4GammaNuclearXS::Default_Name());
89 if ( gammaXS == nullptr ) {
90 gammaXS = new G4PhotoNuclearCrossSection;
91 }
92 }
93
94 // reuse existing pre-compound model
95 G4GeneratorPrecompoundInterface* precoInterface
96 = new G4GeneratorPrecompoundInterface();
97 G4HadronicInteraction* p =
98 G4HadronicInteractionRegistry::Instance()->FindModel("PRECO");
99 G4VPreCompoundModel* pre = static_cast<G4VPreCompoundModel*>(p);
100 if(!pre) { pre = new G4PreCompoundModel(); }
101 precoInterface->SetDeExcitation(pre);
102
103 // string model
104 ftfp = new G4TheoFSGenerator();
105 ftfp->SetTransport(precoInterface);
106 theFragmentation = new G4LundStringFragmentation();
107 theStringDecay = new G4ExcitedStringDecay(theFragmentation);
108 G4FTFModel* theStringModel = new G4FTFModel();
109 theStringModel->SetFragmentationModel(theStringDecay);
110 ftfp->SetHighEnergyGenerator(theStringModel);
111
112 // Build Bertini model
113 bert = new G4CascadeInterface();
114
115 // Creator model ID
116 secID = G4PhysicsModelCatalog::GetModelID( "model_" + GetModelName() );
117 }
118
119 G4ElectroVDNuclearModel::~G4ElectroVDNuclearModel()
120 {
121 delete theFragmentation;
122 delete theStringDecay;
123 }
124
125 void G4ElectroVDNuclearModel::ModelDescription(std::ostream& outFile) const
126 {
127 outFile << "G4ElectroVDNuclearModel handles the inelastic scattering\n"
128 << "of e- and e+ from nuclei using the equivalent photon\n"
129 << "approximation in which the incoming lepton generates a\n"
130 << "virtual photon at the electromagnetic vertex, and the\n"
131 << "virtual photon is converted to a real photon. At low\n"
132 << "energies, the photon interacts directly with the nucleus\n"
133 << "using the Bertini cascade. At high energies the photon\n"
134 << "is converted to a pi0 which interacts using the FTFP\n"
135 << "model. The electro- and gamma-nuclear cross sections of\n"
136 << "M. Kossov are used to generate the virtual photon spectrum\n";
137 }
138
139
140 G4HadFinalState*
141 G4ElectroVDNuclearModel::ApplyYourself(const G4HadProjectile& aTrack,
142 G4Nucleus& targetNucleus)
143 {
144 // Set up default particle change (just returns initial state)
145 theParticleChange.Clear();
146 theParticleChange.SetStatusChange(isAlive);
147 leptonKE = aTrack.GetKineticEnergy();
148 theParticleChange.SetEnergyChange(leptonKE);
149 theParticleChange.SetMomentumChange(aTrack.Get4Momentum().vect().unit() );
150
151 // Set up sanity checks for real photon production
152 G4DynamicParticle lepton(aTrack.GetDefinition(), aTrack.Get4Momentum() );
153
154 // Need to call GetElementCrossSection before calling GetEquivalentPhotonEnergy.
155 const G4Material* mat = aTrack.GetMaterial();
156 G4int targZ = targetNucleus.GetZ_asInt();
157 electroXS->GetElementCrossSection(&lepton, targZ, mat);
158
159 photonEnergy = electroXS->GetEquivalentPhotonEnergy();
160 // Photon energy cannot exceed lepton energy
161 if (photonEnergy < leptonKE) {
162 photonQ2 = electroXS->GetEquivalentPhotonQ2(photonEnergy);
163 G4double dM = G4Proton::Proton()->GetPDGMass() + G4Neutron::Neutron()->GetPDGMass();
164 // Photon
165 if (photonEnergy > photonQ2/dM) {
166 // Produce recoil lepton and transferred photon
167 G4DynamicParticle* transferredPhoton = CalculateEMVertex(aTrack, targetNucleus);
168 // Interact gamma with nucleus
169 if (transferredPhoton) CalculateHadronicVertex(transferredPhoton, targetNucleus);
170 }
171 }
172 return &theParticleChange;
173 }
174
175
176 G4DynamicParticle*
177 G4ElectroVDNuclearModel::CalculateEMVertex(const G4HadProjectile& aTrack,
178 G4Nucleus& targetNucleus)
179 {
180 G4DynamicParticle photon(G4Gamma::Gamma(), photonEnergy,
181 G4ThreeVector(0.,0.,1.) );
182
183 // Get gamma cross section at Q**2 = 0 (real gamma)
184 G4int targZ = targetNucleus.GetZ_asInt();
185 const G4Material* mat = aTrack.GetMaterial();
186 G4double sigNu =
187 gammaXS->GetElementCrossSection(&photon, targZ, mat);
188
189 // Change real gamma energy to equivalent energy and get cross section at that energy
190 G4double dM = G4Proton::Proton()->GetPDGMass() + G4Neutron::Neutron()->GetPDGMass();
191 photon.SetKineticEnergy(photonEnergy - photonQ2/dM);
192 G4double sigK =
193 gammaXS->GetElementCrossSection(&photon, targZ, mat);
194 G4double rndFraction = electroXS->GetVirtualFactor(photonEnergy, photonQ2);
195
196 // No gamma produced, return null ptr
197 if (sigNu*G4UniformRand() > sigK*rndFraction) return 0;
198
199 // Scatter the lepton
200 G4double mProj = aTrack.GetDefinition()->GetPDGMass();
201 G4double mProj2 = mProj*mProj;
202 G4double iniE = leptonKE + mProj; // Total energy of incident lepton
203 G4double finE = iniE - photonEnergy; // Total energy of scattered lepton
204 theParticleChange.SetEnergyChange(finE-mProj);
205 G4double iniP = std::sqrt(iniE*iniE-mProj2); // Incident lepton momentum
206 G4double finP = std::sqrt(finE*finE-mProj2); // Scattered lepton momentum
207 G4double cost = (iniE*finE - mProj2 - photonQ2/2.)/iniP/finP; // cos(theta) from Q**2
208 if (cost > 1.) cost= 1.;
209 if (cost < -1.) cost=-1.;
210 G4double sint = std::sqrt(1.-cost*cost);
211
212 G4ThreeVector dir = aTrack.Get4Momentum().vect().unit();
213 G4ThreeVector ortx = dir.orthogonal().unit(); // Ortho-normal to scattering plane
214 G4ThreeVector orty = dir.cross(ortx); // Third unit vector
215 G4double phi = twopi*G4UniformRand();
216 G4double sinx = sint*std::sin(phi);
217 G4double siny = sint*std::cos(phi);
218 G4ThreeVector findir = cost*dir+sinx*ortx+siny*orty;
219 theParticleChange.SetMomentumChange(findir); // change lepton direction
220
221 // Create a gamma with momentum equal to momentum transfer
222 G4ThreeVector photonMomentum = iniP*dir - finP*findir;
223 G4DynamicParticle* gamma = new G4DynamicParticle(G4Gamma::Gamma(),
224 photonEnergy, photonMomentum);
225 return gamma;
226 }
227
228
229 void
230 G4ElectroVDNuclearModel::CalculateHadronicVertex(G4DynamicParticle* incident,
231 G4Nucleus& target)
232 {
233 G4HadFinalState* hfs = 0;
234 G4double gammaE = incident->GetTotalEnergy();
235
236 if (gammaE < 10*GeV) {
237 G4HadProjectile projectile(*incident);
238 hfs = bert->ApplyYourself(projectile, target);
239 } else {
240 // At high energies convert incident gamma to a pion
241 G4double piMass = G4PionZero::PionZero()->GetPDGMass();
242 G4double piMom = std::sqrt(gammaE*gammaE - piMass*piMass);
243 G4ThreeVector piMomentum(incident->GetMomentumDirection() );
244 piMomentum *= piMom;
245 G4DynamicParticle theHadron(G4PionZero::PionZero(), piMomentum);
246 G4HadProjectile projectile(theHadron);
247 hfs = ftfp->ApplyYourself(projectile, target);
248 }
249
250 delete incident;
251
252 // Assign the creator model ID to the secondaries
253 for ( size_t i = 0; i < hfs->GetNumberOfSecondaries(); ++i ) {
254 hfs->GetSecondary( i )->SetCreatorModelID( secID );
255 }
256
257 // Copy secondaries from sub-model to model
258 theParticleChange.AddSecondaries(hfs);
259 }
260
261