source: trunk/source/processes/electromagnetic/lowenergy/src/G4LivermoreGammaConversionModel.cc @ 991

Last change on this file since 991 was 991, checked in by garnier, 15 years ago

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26// $Id: G4LivermoreGammaConversionModel.cc,v 1.1 2008/10/30 14:16:35 sincerti Exp $
27// GEANT4 tag $Name: geant4-09-02 $
28//
29
30#include "G4LivermoreGammaConversionModel.hh"
31
32//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
33
34using namespace std;
35
36//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
37
38G4LivermoreGammaConversionModel::G4LivermoreGammaConversionModel(const G4ParticleDefinition*,
39                                             const G4String& nam)
40:G4VEmModel(nam),smallEnergy(2.*MeV),isInitialised(false)
41{
42  lowEnergyLimit = 1.022000 * MeV;
43  highEnergyLimit = 100 * GeV;
44 
45  G4cout << "Livermore Gamma conversion is constructed " << G4endl
46         << "Energy range: "
47         << lowEnergyLimit / keV << " keV - "
48         << highEnergyLimit / GeV << " GeV"
49         << G4endl;
50         
51  verboseLevel= 0;
52  // Verbosity scale:
53  // 0 = nothing
54  // 1 = warning for energy non-conservation
55  // 2 = details of energy budget
56  // 3 = calculation of cross sections, file openings, sampling of atoms
57  // 4 = entering in methods
58
59}
60
61//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
62
63G4LivermoreGammaConversionModel::~G4LivermoreGammaConversionModel()
64{ 
65  delete meanFreePathTable;
66  delete crossSectionHandler;
67}
68
69//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
70
71void G4LivermoreGammaConversionModel::Initialise(const G4ParticleDefinition* particle,
72                                       const G4DataVector& cuts)
73{
74  if (verboseLevel > 3)
75    G4cout << "Calling G4LivermoreGammaConversionModel::Initialise()" << G4endl;
76
77  InitialiseElementSelectors(particle,cuts);
78
79  // Energy limits
80 
81  if (LowEnergyLimit() < lowEnergyLimit)
82  {
83    G4cout << "G4LivermoreGammaConversionModel: low energy limit increased from " << 
84        LowEnergyLimit()/eV << " eV to " << lowEnergyLimit << " eV" << G4endl;
85    SetLowEnergyLimit(lowEnergyLimit);
86  }
87
88  if (HighEnergyLimit() > highEnergyLimit)
89  {
90    G4cout << "G4LivermoreGammaConversionModel: high energy limit decreased from " << 
91        HighEnergyLimit()/GeV << " GeV to " << highEnergyLimit << " GeV" << G4endl;
92    SetHighEnergyLimit(highEnergyLimit);
93  }
94
95  // Read data tables for all materials
96 
97  crossSectionHandler = new G4CrossSectionHandler();
98  crossSectionHandler->Initialise(0,1.0220*MeV,100.*GeV,400);
99  G4String crossSectionFile = "pair/pp-cs-";
100  crossSectionHandler->LoadData(crossSectionFile);
101
102  meanFreePathTable = 0;
103  meanFreePathTable = crossSectionHandler->BuildMeanFreePathForMaterials();
104
105  //
106 
107  if (verboseLevel > 2) 
108    G4cout << "Loaded cross section files for PenelopeGammaConversion" << G4endl;
109
110  G4cout << "Livermore Gamma Conversion model is initialized " << G4endl
111         << "Energy range: "
112         << LowEnergyLimit() / MeV << " MeV - "
113         << HighEnergyLimit() / GeV << " GeV"
114         << G4endl;
115
116  if(isInitialised) return;
117
118  if(pParticleChange)
119    fParticleChange = reinterpret_cast<G4ParticleChangeForGamma*>(pParticleChange);
120  else
121    fParticleChange = new G4ParticleChangeForGamma();
122  isInitialised = true;}
123
124//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
125
126G4double G4LivermoreGammaConversionModel::ComputeCrossSectionPerAtom(
127                                       const G4ParticleDefinition*,
128                                             G4double GammaEnergy,
129                                             G4double Z, G4double,
130                                             G4double, G4double)
131{
132  if (verboseLevel > 3)
133    G4cout << "Calling ComputeCrossSectionPerAtom() of G4LivermoreGammaConversionModel" << G4endl;
134
135  G4double cs = crossSectionHandler->FindValue(G4int(Z), GammaEnergy);
136  return cs;
137}
138
139//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
140
141void G4LivermoreGammaConversionModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
142                                              const G4MaterialCutsCouple* couple,
143                                              const G4DynamicParticle* aDynamicGamma,
144                                              G4double,
145                                              G4double)
146{
147
148// The energies of the e+ e- secondaries are sampled using the Bethe - Heitler
149// cross sections with Coulomb correction. A modified version of the random
150// number techniques of Butcher & Messel is used (Nuc Phys 20(1960),15).
151
152// Note 1 : Effects due to the breakdown of the Born approximation at low
153// energy are ignored.
154// Note 2 : The differential cross section implicitly takes account of
155// pair creation in both nuclear and atomic electron fields. However triplet
156// prodution is not generated.
157
158  if (verboseLevel > 3)
159    G4cout << "Calling SampleSecondaries() of G4LivermoreGammaConversionModel" << G4endl;
160
161  G4double photonEnergy = aDynamicGamma->GetKineticEnergy();
162  G4ParticleMomentum photonDirection = aDynamicGamma->GetMomentumDirection();
163
164  G4double epsilon ;
165  G4double epsilon0 = electron_mass_c2 / photonEnergy ;
166
167  // Do it fast if photon energy < 2. MeV
168  if (photonEnergy < smallEnergy )
169    {
170      epsilon = epsilon0 + (0.5 - epsilon0) * G4UniformRand();
171    }
172  else
173    {
174      // Select randomly one element in the current material
175      const G4Element* element = crossSectionHandler->SelectRandomElement(couple,photonEnergy);
176
177      if (element == 0)
178        {
179          G4cout << "G4LivermoreGammaConversionModel::SampleSecondaries - element = 0" << G4endl;
180        }
181      G4IonisParamElm* ionisation = element->GetIonisation();
182       if (ionisation == 0)
183        {
184          G4cout << "G4LivermoreGammaConversionModel::SampleSecondaries - ionisation = 0" << G4endl;
185        }
186
187      // Extract Coulomb factor for this Element
188      G4double fZ = 8. * (ionisation->GetlogZ3());
189      if (photonEnergy > 50. * MeV) fZ += 8. * (element->GetfCoulomb());
190
191      // Limits of the screening variable
192      G4double screenFactor = 136. * epsilon0 / (element->GetIonisation()->GetZ3()) ;
193      G4double screenMax = std::exp ((42.24 - fZ)/8.368) - 0.952 ;
194      G4double screenMin = std::min(4.*screenFactor,screenMax) ;
195
196      // Limits of the energy sampling
197      G4double epsilon1 = 0.5 - 0.5 * std::sqrt(1. - screenMin / screenMax) ;
198      G4double epsilonMin = std::max(epsilon0,epsilon1);
199      G4double epsilonRange = 0.5 - epsilonMin ;
200
201      // Sample the energy rate of the created electron (or positron)
202      G4double screen;
203      G4double gReject ;
204
205      G4double f10 = ScreenFunction1(screenMin) - fZ;
206      G4double f20 = ScreenFunction2(screenMin) - fZ;
207      G4double normF1 = std::max(f10 * epsilonRange * epsilonRange,0.);
208      G4double normF2 = std::max(1.5 * f20,0.);
209
210      do {
211        if (normF1 / (normF1 + normF2) > G4UniformRand() )
212          {
213            epsilon = 0.5 - epsilonRange * std::pow(G4UniformRand(), 0.3333) ;
214            screen = screenFactor / (epsilon * (1. - epsilon));
215            gReject = (ScreenFunction1(screen) - fZ) / f10 ;
216          }
217        else
218          {
219            epsilon = epsilonMin + epsilonRange * G4UniformRand();
220            screen = screenFactor / (epsilon * (1 - epsilon));
221            gReject = (ScreenFunction2(screen) - fZ) / f20 ;
222          }
223      } while ( gReject < G4UniformRand() );
224
225    }   //  End of epsilon sampling
226
227  // Fix charges randomly
228
229  G4double electronTotEnergy;
230  G4double positronTotEnergy;
231
232  if (CLHEP::RandBit::shootBit())
233    {
234      electronTotEnergy = (1. - epsilon) * photonEnergy;
235      positronTotEnergy = epsilon * photonEnergy;
236    }
237  else
238    {
239      positronTotEnergy = (1. - epsilon) * photonEnergy;
240      electronTotEnergy = epsilon * photonEnergy;
241    }
242
243  // Scattered electron (positron) angles. ( Z - axis along the parent photon)
244  // Universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211),
245  // derived from Tsai distribution (Rev. Mod. Phys. 49, 421 (1977)
246
247  G4double u;
248  const G4double a1 = 0.625;
249  G4double a2 = 3. * a1;
250  //  G4double d = 27. ;
251
252  //  if (9. / (9. + d) > G4UniformRand())
253  if (0.25 > G4UniformRand())
254    {
255      u = - std::log(G4UniformRand() * G4UniformRand()) / a1 ;
256    }
257  else
258    {
259      u = - std::log(G4UniformRand() * G4UniformRand()) / a2 ;
260    }
261
262  G4double thetaEle = u*electron_mass_c2/electronTotEnergy;
263  G4double thetaPos = u*electron_mass_c2/positronTotEnergy;
264  G4double phi  = twopi * G4UniformRand();
265
266  G4double dxEle= std::sin(thetaEle)*std::cos(phi),dyEle= std::sin(thetaEle)*std::sin(phi),dzEle=std::cos(thetaEle);
267  G4double dxPos=-std::sin(thetaPos)*std::cos(phi),dyPos=-std::sin(thetaPos)*std::sin(phi),dzPos=std::cos(thetaPos);
268 
269 
270  // Kinematics of the created pair:
271  // the electron and positron are assumed to have a symetric angular
272  // distribution with respect to the Z axis along the parent photon
273 
274//  aParticleChange.SetNumberOfSecondaries(2) ;
275  G4double electronKineEnergy = std::max(0.,electronTotEnergy - electron_mass_c2) ;
276 
277// SI - The range test has been removed wrt original G4LowEnergyGammaconversion class
278
279  G4ThreeVector electronDirection (dxEle, dyEle, dzEle);
280  electronDirection.rotateUz(photonDirection);
281     
282  G4DynamicParticle* particle1 = new G4DynamicParticle (G4Electron::Electron(),
283                                                            electronDirection,
284                                                            electronKineEnergy);
285
286  // The e+ is always created (even with kinetic energy = 0) for further annihilation
287  G4double positronKineEnergy = std::max(0.,positronTotEnergy - electron_mass_c2) ;
288
289// SI - The range test has been removed wrt original G4LowEnergyGammaconversion class
290
291  G4ThreeVector positronDirection (dxPos, dyPos, dzPos);
292  positronDirection.rotateUz(photonDirection);   
293 
294  // Create G4DynamicParticle object for the particle2
295  G4DynamicParticle* particle2 = new G4DynamicParticle(G4Positron::Positron(),
296                                                       positronDirection, positronKineEnergy);
297  // Fill output vector
298  fvect->push_back(particle1);
299  fvect->push_back(particle2);
300
301  // kill incident photon
302  fParticleChange->SetProposedKineticEnergy(0.);
303  fParticleChange->ProposeTrackStatus(fStopAndKill);   
304
305}
306
307//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
308
309G4double G4LivermoreGammaConversionModel::ScreenFunction1(G4double screenVariable)
310{
311  // Compute the value of the screening function 3*phi1 - phi2
312
313  G4double value;
314 
315  if (screenVariable > 1.)
316    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
317  else
318    value = 42.392 - screenVariable * (7.796 - 1.961 * screenVariable);
319 
320  return value;
321} 
322
323//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
324
325G4double G4LivermoreGammaConversionModel::ScreenFunction2(G4double screenVariable)
326{
327  // Compute the value of the screening function 1.5*phi1 - 0.5*phi2
328 
329  G4double value;
330 
331  if (screenVariable > 1.)
332    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
333  else
334    value = 41.405 - screenVariable * (5.828 - 0.8945 * screenVariable);
335 
336  return value;
337} 
338
339//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
340
341G4double G4LivermoreGammaConversionModel::GetMeanFreePath(const G4Track& track, 
342                                                     G4double, // previousStepSize
343                                                     G4ForceCondition*)
344{
345  const G4DynamicParticle* photon = track.GetDynamicParticle();
346  G4double energy = photon->GetKineticEnergy();
347  const G4MaterialCutsCouple* couple = track.GetMaterialCutsCouple();
348  size_t materialIndex = couple->GetIndex();
349
350  G4double meanFreePath;
351  if (energy > highEnergyLimit) meanFreePath = meanFreePathTable->FindValue(highEnergyLimit,materialIndex);
352  else if (energy < lowEnergyLimit) meanFreePath = DBL_MAX;
353  else meanFreePath = meanFreePathTable->FindValue(energy,materialIndex);
354  return meanFreePath;
355}
356
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