source: trunk/source/processes/electromagnetic/lowenergy/src/G4LivermoreGammaConversionModel.cc @ 1315

Last change on this file since 1315 was 1315, checked in by garnier, 14 years ago

update geant4-09-04-beta-cand-01 interfaces-V09-03-09 vis-V09-03-08
File size: 12.0 KB
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26// $Id: G4LivermoreGammaConversionModel.cc,v 1.8 2009/06/11 15:47:08 mantero Exp $
27// GEANT4 tag $Name: geant4-09-04-beta-cand-01 $
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 "G4LivermoreGammaConversionModel.hh"
43
44//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
45
46using namespace std;
47
48//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
49
50G4LivermoreGammaConversionModel::G4LivermoreGammaConversionModel(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 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
78G4LivermoreGammaConversionModel::~G4LivermoreGammaConversionModel()
79{ 
80  if (crossSectionHandler) delete crossSectionHandler;
81}
82
83//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
84
85void 
86G4LivermoreGammaConversionModel::Initialise(const G4ParticleDefinition*,
87                                            const G4DataVector&)
88{
89  if (verboseLevel > 3)
90    G4cout << "Calling G4LivermoreGammaConversionModel::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 = "pair/pp-cs-";
103  crossSectionHandler->LoadData(crossSectionFile);
104
105  //
106 
107  if (verboseLevel > 2) 
108    G4cout << "Loaded cross section files for PenelopeGammaConversion" << G4endl;
109
110  if (verboseLevel > 0) { 
111    G4cout << "Livermore Gamma Conversion model is initialized " << G4endl
112           << "Energy range: "
113           << LowEnergyLimit() / MeV << " MeV - "
114           << HighEnergyLimit() / GeV << " GeV"
115           << G4endl;
116  }
117
118  if(isInitialised) return;
119  fParticleChange = GetParticleChangeForGamma();
120  isInitialised = true;
121}
122
123//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
124
125G4double
126G4LivermoreGammaConversionModel::ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
127                                                            G4double GammaEnergy,
128                                                            G4double Z, G4double,
129                                                            G4double, G4double)
130{
131  if (verboseLevel > 3) {
132    G4cout << "Calling ComputeCrossSectionPerAtom() of G4LivermoreGammaConversionModel" 
133           << G4endl;
134  }
135  if (GammaEnergy < lowEnergyLimit || GammaEnergy > highEnergyLimit) return 0;
136
137  G4double cs = crossSectionHandler->FindValue(G4int(Z), GammaEnergy);
138  return cs;
139}
140
141//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
142
143void G4LivermoreGammaConversionModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
144                                              const G4MaterialCutsCouple* couple,
145                                              const G4DynamicParticle* aDynamicGamma,
146                                              G4double,
147                                              G4double)
148{
149
150// The energies of the e+ e- secondaries are sampled using the Bethe - Heitler
151// cross sections with Coulomb correction. A modified version of the random
152// number techniques of Butcher & Messel is used (Nuc Phys 20(1960),15).
153
154// Note 1 : Effects due to the breakdown of the Born approximation at low
155// energy are ignored.
156// Note 2 : The differential cross section implicitly takes account of
157// pair creation in both nuclear and atomic electron fields. However triplet
158// prodution is not generated.
159
160  if (verboseLevel > 3)
161    G4cout << "Calling SampleSecondaries() of G4LivermoreGammaConversionModel" << G4endl;
162
163  G4double photonEnergy = aDynamicGamma->GetKineticEnergy();
164  G4ParticleMomentum photonDirection = aDynamicGamma->GetMomentumDirection();
165
166  G4double epsilon ;
167  G4double epsilon0 = electron_mass_c2 / photonEnergy ;
168
169  // Do it fast if photon energy < 2. MeV
170  if (photonEnergy < smallEnergy )
171    {
172      epsilon = epsilon0 + (0.5 - epsilon0) * G4UniformRand();
173    }
174  else
175    {
176      // Select randomly one element in the current material
177      //const G4Element* element = crossSectionHandler->SelectRandomElement(couple,photonEnergy);
178      const G4ParticleDefinition* particle =  aDynamicGamma->GetDefinition();
179      const G4Element* element = SelectRandomAtom(couple,particle,photonEnergy);
180
181      if (element == 0)
182        {
183          G4cout << "G4LivermoreGammaConversionModel::SampleSecondaries - element = 0" 
184                 << G4endl;
185          return;
186        }
187      G4IonisParamElm* ionisation = element->GetIonisation();
188      if (ionisation == 0)
189        {
190          G4cout << "G4LivermoreGammaConversionModel::SampleSecondaries - ionisation = 0" 
191                 << G4endl;
192          return;
193        }
194
195      // Extract Coulomb factor for this Element
196      G4double fZ = 8. * (ionisation->GetlogZ3());
197      if (photonEnergy > 50. * MeV) fZ += 8. * (element->GetfCoulomb());
198
199      // Limits of the screening variable
200      G4double screenFactor = 136. * epsilon0 / (element->GetIonisation()->GetZ3()) ;
201      G4double screenMax = std::exp ((42.24 - fZ)/8.368) - 0.952 ;
202      G4double screenMin = std::min(4.*screenFactor,screenMax) ;
203
204      // Limits of the energy sampling
205      G4double epsilon1 = 0.5 - 0.5 * std::sqrt(1. - screenMin / screenMax) ;
206      G4double epsilonMin = std::max(epsilon0,epsilon1);
207      G4double epsilonRange = 0.5 - epsilonMin ;
208
209      // Sample the energy rate of the created electron (or positron)
210      G4double screen;
211      G4double gReject ;
212
213      G4double f10 = ScreenFunction1(screenMin) - fZ;
214      G4double f20 = ScreenFunction2(screenMin) - fZ;
215      G4double normF1 = std::max(f10 * epsilonRange * epsilonRange,0.);
216      G4double normF2 = std::max(1.5 * f20,0.);
217
218      do {
219        if (normF1 / (normF1 + normF2) > G4UniformRand() )
220          {
221            epsilon = 0.5 - epsilonRange * std::pow(G4UniformRand(), 0.3333) ;
222            screen = screenFactor / (epsilon * (1. - epsilon));
223            gReject = (ScreenFunction1(screen) - fZ) / f10 ;
224          }
225        else
226          {
227            epsilon = epsilonMin + epsilonRange * G4UniformRand();
228            screen = screenFactor / (epsilon * (1 - epsilon));
229            gReject = (ScreenFunction2(screen) - fZ) / f20 ;
230          }
231      } while ( gReject < G4UniformRand() );
232
233    }   //  End of epsilon sampling
234
235  // Fix charges randomly
236
237  G4double electronTotEnergy;
238  G4double positronTotEnergy;
239
240  if (CLHEP::RandBit::shootBit())
241    {
242      electronTotEnergy = (1. - epsilon) * photonEnergy;
243      positronTotEnergy = epsilon * photonEnergy;
244    }
245  else
246    {
247      positronTotEnergy = (1. - epsilon) * photonEnergy;
248      electronTotEnergy = epsilon * photonEnergy;
249    }
250
251  // Scattered electron (positron) angles. ( Z - axis along the parent photon)
252  // Universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211),
253  // derived from Tsai distribution (Rev. Mod. Phys. 49, 421 (1977)
254
255  G4double u;
256  const G4double a1 = 0.625;
257  G4double a2 = 3. * a1;
258  //  G4double d = 27. ;
259
260  //  if (9. / (9. + d) > G4UniformRand())
261  if (0.25 > G4UniformRand())
262    {
263      u = - std::log(G4UniformRand() * G4UniformRand()) / a1 ;
264    }
265  else
266    {
267      u = - std::log(G4UniformRand() * G4UniformRand()) / a2 ;
268    }
269
270  G4double thetaEle = u*electron_mass_c2/electronTotEnergy;
271  G4double thetaPos = u*electron_mass_c2/positronTotEnergy;
272  G4double phi  = twopi * G4UniformRand();
273
274  G4double dxEle= std::sin(thetaEle)*std::cos(phi),dyEle= std::sin(thetaEle)*std::sin(phi),dzEle=std::cos(thetaEle);
275  G4double dxPos=-std::sin(thetaPos)*std::cos(phi),dyPos=-std::sin(thetaPos)*std::sin(phi),dzPos=std::cos(thetaPos);
276 
277 
278  // Kinematics of the created pair:
279  // the electron and positron are assumed to have a symetric angular
280  // distribution with respect to the Z axis along the parent photon
281 
282  G4double electronKineEnergy = std::max(0.,electronTotEnergy - electron_mass_c2) ;
283 
284  // SI - The range test has been removed wrt original G4LowEnergyGammaconversion class
285
286  G4ThreeVector electronDirection (dxEle, dyEle, dzEle);
287  electronDirection.rotateUz(photonDirection);
288     
289  G4DynamicParticle* particle1 = new G4DynamicParticle (G4Electron::Electron(),
290                                                            electronDirection,
291                                                            electronKineEnergy);
292
293  // The e+ is always created (even with kinetic energy = 0) for further annihilation
294  G4double positronKineEnergy = std::max(0.,positronTotEnergy - electron_mass_c2) ;
295
296  // SI - The range test has been removed wrt original G4LowEnergyGammaconversion class
297
298  G4ThreeVector positronDirection (dxPos, dyPos, dzPos);
299  positronDirection.rotateUz(photonDirection);   
300 
301  // Create G4DynamicParticle object for the particle2
302  G4DynamicParticle* particle2 = new G4DynamicParticle(G4Positron::Positron(),
303                                                       positronDirection, positronKineEnergy);
304  // Fill output vector
305  fvect->push_back(particle1);
306  fvect->push_back(particle2);
307
308  // kill incident photon
309  fParticleChange->SetProposedKineticEnergy(0.);
310  fParticleChange->ProposeTrackStatus(fStopAndKill);   
311
312}
313
314//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
315
316G4double G4LivermoreGammaConversionModel::ScreenFunction1(G4double screenVariable)
317{
318  // Compute the value of the screening function 3*phi1 - phi2
319
320  G4double value;
321 
322  if (screenVariable > 1.)
323    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
324  else
325    value = 42.392 - screenVariable * (7.796 - 1.961 * screenVariable);
326 
327  return value;
328} 
329
330//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
331
332G4double G4LivermoreGammaConversionModel::ScreenFunction2(G4double screenVariable)
333{
334  // Compute the value of the screening function 1.5*phi1 - 0.5*phi2
335 
336  G4double value;
337 
338  if (screenVariable > 1.)
339    value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
340  else
341    value = 41.405 - screenVariable * (5.828 - 0.8945 * screenVariable);
342 
343  return value;
344} 
345
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