source: trunk/source/processes/electromagnetic/lowenergy/src/G4LivermoreNuclearGammaConversionModel.cc @ 1353

Last change on this file since 1353 was 1350, checked in by garnier, 14 years ago

update to last version 4.9.4
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26// $Id: G4LivermoreNuclearGammaConversionModel.cc,v 1.1 2010/11/10 17:09:16 flongo Exp $
27// GEANT4 tag $Name: geant4-09-04-ref-00 $
28//
29//
30// Author: Sebastien Inserti
31//         30 October 2008
32//
33// History:
34// --------
35// 12 Apr 2009   V Ivanchenko Cleanup initialisation and generation of secondaries:
36//                  - apply internal high-energy limit only in constructor
37//                  - do not apply low-energy limit (default is 0)
38//                  - use CLHEP electron mass for low-enegry limit
39//                  - remove MeanFreePath method and table
40
41
42#include "G4LivermoreNuclearGammaConversionModel.hh"
43
44//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
45
46using namespace std;
47
48//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
49
50G4LivermoreNuclearGammaConversionModel::G4LivermoreNuclearGammaConversionModel(const G4ParticleDefinition*,
51                                                                 const G4String& nam)
52  :G4VEmModel(nam),smallEnergy(2.*MeV),isInitialised(false),
53   crossSectionHandler(0),meanFreePathTable(0)
54{
55  lowEnergyLimit = 2.0*electron_mass_c2;
56  highEnergyLimit = 100 * GeV;
57  SetHighEnergyLimit(highEnergyLimit);
58         
59  verboseLevel= 0;
60  // Verbosity scale:
61  // 0 = nothing
62  // 1 = warning for energy non-conservation
63  // 2 = details of energy budget
64  // 3 = calculation of cross sections, file openings, sampling of atoms
65  // 4 = entering in methods
66
67  if(verboseLevel > 0) {
68    G4cout << "Livermore Nuclear Gamma conversion is constructed " << G4endl
69           << "Energy range: "
70           << lowEnergyLimit / MeV << " MeV - "
71           << highEnergyLimit / GeV << " GeV"
72           << G4endl;
73  }
74}
75
76//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
77
78G4LivermoreNuclearGammaConversionModel::~G4LivermoreNuclearGammaConversionModel()
79{ 
80  if (crossSectionHandler) delete crossSectionHandler;
81}
82
83//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
84
85void 
86G4LivermoreNuclearGammaConversionModel::Initialise(const G4ParticleDefinition*,
87                                            const G4DataVector&)
88{
89  if (verboseLevel > 3)
90    G4cout << "Calling G4LivermoreNuclearGammaConversionModel::Initialise()" << G4endl;
91
92  if (crossSectionHandler)
93  {
94    crossSectionHandler->Clear();
95    delete crossSectionHandler;
96  }
97
98  // Read data tables for all materials
99 
100  crossSectionHandler = new G4CrossSectionHandler();
101  crossSectionHandler->Initialise(0,lowEnergyLimit,100.*GeV,400);
102  G4String crossSectionFile = "pairdata/pp-pair-cs-"; // here only pair in nuclear field cs should be used
103  crossSectionHandler->LoadData(crossSectionFile);
104
105  //
106 
107  if (verboseLevel > 0) {
108    G4cout << "Loaded cross section files for Livermore GammaConversion" << G4endl;
109    G4cout << "To obtain the total cross section this should be used only " << G4endl
110           << "in connection with G4ElectronGammaConversion " << G4endl;
111  }
112
113  if (verboseLevel > 0) { 
114    G4cout << "Livermore Nuclear Gamma Conversion model is initialized " << G4endl
115           << "Energy range: "
116           << LowEnergyLimit() / MeV << " MeV - "
117           << HighEnergyLimit() / GeV << " GeV"
118           << G4endl;
119  }
120
121  if(isInitialised) return;
122  fParticleChange = GetParticleChangeForGamma();
123  isInitialised = true;
124}
125
126//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
127
128G4double
129G4LivermoreNuclearGammaConversionModel::ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
130                                                            G4double GammaEnergy,
131                                                            G4double Z, G4double,
132                                                            G4double, G4double)
133{
134  if (verboseLevel > 3) {
135    G4cout << "Calling ComputeCrossSectionPerAtom() of G4LivermoreNuclearGammaConversionModel" 
136           << G4endl;
137  }
138  if (GammaEnergy < lowEnergyLimit || GammaEnergy > highEnergyLimit) return 0;
139
140  G4double cs = crossSectionHandler->FindValue(G4int(Z), GammaEnergy);
141  return cs;
142}
143
144//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
145
146void G4LivermoreNuclearGammaConversionModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
147                                              const G4MaterialCutsCouple* couple,
148                                              const G4DynamicParticle* aDynamicGamma,
149                                              G4double,
150                                              G4double)
151{
152
153// The energies of the e+ e- secondaries are sampled using the Bethe - Heitler
154// cross sections with Coulomb correction. A modified version of the random
155// number techniques of Butcher & Messel is used (Nuc Phys 20(1960),15).
156
157// Note 1 : Effects due to the breakdown of the Born approximation at low
158// energy are ignored.
159// Note 2 : The differential cross section implicitly takes account of
160// pair creation in both nuclear and atomic electron fields. However triplet
161// prodution is not generated.
162
163  if (verboseLevel > 3)
164    G4cout << "Calling SampleSecondaries() of G4LivermoreNuclearGammaConversionModel" << G4endl;
165
166  G4double photonEnergy = aDynamicGamma->GetKineticEnergy();
167  G4ParticleMomentum photonDirection = aDynamicGamma->GetMomentumDirection();
168
169  G4double epsilon ;
170  G4double epsilon0 = electron_mass_c2 / photonEnergy ;
171
172  // Do it fast if photon energy < 2. MeV
173  if (photonEnergy < smallEnergy )
174    {
175      epsilon = epsilon0 + (0.5 - epsilon0) * G4UniformRand();
176    }
177  else
178    {
179      // Select randomly one element in the current material
180      //const G4Element* element = crossSectionHandler->SelectRandomElement(couple,photonEnergy);
181      const G4ParticleDefinition* particle =  aDynamicGamma->GetDefinition();
182      const G4Element* element = SelectRandomAtom(couple,particle,photonEnergy);
183
184      if (element == 0)
185        {
186          G4cout << "G4LivermoreNuclearGammaConversionModel::SampleSecondaries - element = 0" 
187                 << G4endl;
188          return;
189        }
190      G4IonisParamElm* ionisation = element->GetIonisation();
191      if (ionisation == 0)
192        {
193          G4cout << "G4LivermoreNuclearGammaConversionModel::SampleSecondaries - ionisation = 0" 
194                 << G4endl;
195          return;
196        }
197
198      // Extract Coulomb factor for this Element
199      G4double fZ = 8. * (ionisation->GetlogZ3());
200      if (photonEnergy > 50. * MeV) fZ += 8. * (element->GetfCoulomb());
201
202      // Limits of the screening variable
203      G4double screenFactor = 136. * epsilon0 / (element->GetIonisation()->GetZ3()) ;
204      G4double screenMax = std::exp ((42.24 - fZ)/8.368) - 0.952 ;
205      G4double screenMin = std::min(4.*screenFactor,screenMax) ;
206
207      // Limits of the energy sampling
208      G4double epsilon1 = 0.5 - 0.5 * std::sqrt(1. - screenMin / screenMax) ;
209      G4double epsilonMin = std::max(epsilon0,epsilon1);
210      G4double epsilonRange = 0.5 - epsilonMin ;
211
212      // Sample the energy rate of the created electron (or positron)
213      G4double screen;
214      G4double gReject ;
215
216      G4double f10 = ScreenFunction1(screenMin) - fZ;
217      G4double f20 = ScreenFunction2(screenMin) - fZ;
218      G4double normF1 = std::max(f10 * epsilonRange * epsilonRange,0.);
219      G4double normF2 = std::max(1.5 * f20,0.);
220
221      do {
222        if (normF1 / (normF1 + normF2) > G4UniformRand() )
223          {
224            epsilon = 0.5 - epsilonRange * std::pow(G4UniformRand(), 0.3333) ;
225            screen = screenFactor / (epsilon * (1. - epsilon));
226            gReject = (ScreenFunction1(screen) - fZ) / f10 ;
227          }
228        else
229          {
230            epsilon = epsilonMin + epsilonRange * G4UniformRand();
231            screen = screenFactor / (epsilon * (1 - epsilon));
232            gReject = (ScreenFunction2(screen) - fZ) / f20 ;
233          }
234      } while ( gReject < G4UniformRand() );
235
236    }   //  End of epsilon sampling
237
238  // Fix charges randomly
239
240  G4double electronTotEnergy;
241  G4double positronTotEnergy;
242
243  if (CLHEP::RandBit::shootBit())
244    {
245      electronTotEnergy = (1. - epsilon) * photonEnergy;
246      positronTotEnergy = epsilon * photonEnergy;
247    }
248  else
249    {
250      positronTotEnergy = (1. - epsilon) * photonEnergy;
251      electronTotEnergy = epsilon * photonEnergy;
252    }
253
254  // Scattered electron (positron) angles. ( Z - axis along the parent photon)
255  // Universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211),
256  // derived from Tsai distribution (Rev. Mod. Phys. 49, 421 (1977)
257
258  G4double u;
259  const G4double a1 = 0.625;
260  G4double a2 = 3. * a1;
261  //  G4double d = 27. ;
262
263  //  if (9. / (9. + d) > G4UniformRand())
264  if (0.25 > G4UniformRand())
265    {
266      u = - std::log(G4UniformRand() * G4UniformRand()) / a1 ;
267    }
268  else
269    {
270      u = - std::log(G4UniformRand() * G4UniformRand()) / a2 ;
271    }
272
273  G4double thetaEle = u*electron_mass_c2/electronTotEnergy;
274  G4double thetaPos = u*electron_mass_c2/positronTotEnergy;
275  G4double phi  = twopi * G4UniformRand();
276
277  G4double dxEle= std::sin(thetaEle)*std::cos(phi),dyEle= std::sin(thetaEle)*std::sin(phi),dzEle=std::cos(thetaEle);
278  G4double dxPos=-std::sin(thetaPos)*std::cos(phi),dyPos=-std::sin(thetaPos)*std::sin(phi),dzPos=std::cos(thetaPos);
279 
280 
281  // Kinematics of the created pair:
282  // the electron and positron are assumed to have a symetric angular
283  // distribution with respect to the Z axis along the parent photon
284 
285  G4double electronKineEnergy = std::max(0.,electronTotEnergy - electron_mass_c2) ;
286 
287  // SI - The range test has been removed wrt original G4LowEnergyGammaconversion class
288
289  G4ThreeVector electronDirection (dxEle, dyEle, dzEle);
290  electronDirection.rotateUz(photonDirection);
291     
292  G4DynamicParticle* particle1 = new G4DynamicParticle (G4Electron::Electron(),
293                                                            electronDirection,
294                                                            electronKineEnergy);
295
296  // The e+ is always created (even with kinetic energy = 0) for further annihilation
297  G4double positronKineEnergy = std::max(0.,positronTotEnergy - electron_mass_c2) ;
298
299  // SI - The range test has been removed wrt original G4LowEnergyGammaconversion class
300
301  G4ThreeVector positronDirection (dxPos, dyPos, dzPos);
302  positronDirection.rotateUz(photonDirection);   
303 
304  // Create G4DynamicParticle object for the particle2
305  G4DynamicParticle* particle2 = new G4DynamicParticle(G4Positron::Positron(),
306                                                       positronDirection, positronKineEnergy);
307  // Fill output vector
308
309  fvect->push_back(particle1);
310  fvect->push_back(particle2);
311
312  // kill incident photon
313  fParticleChange->SetProposedKineticEnergy(0.);
314  fParticleChange->ProposeTrackStatus(fStopAndKill);   
315
316}
317
318//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
319
320G4double G4LivermoreNuclearGammaConversionModel::ScreenFunction1(G4double screenVariable)
321{
322  // Compute the value of the screening function 3*phi1 - phi2
323
324  G4double value;
325 
326  if (screenVariable > 1.)
327    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
328  else
329    value = 42.392 - screenVariable * (7.796 - 1.961 * screenVariable);
330 
331  return value;
332} 
333
334//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
335
336G4double G4LivermoreNuclearGammaConversionModel::ScreenFunction2(G4double screenVariable)
337{
338  // Compute the value of the screening function 1.5*phi1 - 0.5*phi2
339 
340  G4double value;
341 
342  if (screenVariable > 1.)
343    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
344  else
345    value = 41.405 - screenVariable * (5.828 - 0.8945 * screenVariable);
346 
347  return value;
348} 
349
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