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

Last change on this file was 1350, checked in by garnier, 15 years ago

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25//
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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