source: trunk/source/processes/electromagnetic/lowenergy/src/G4LowEnergyGammaConversion.cc@ 1057

Last change on this file since 1057 was 1055, checked in by garnier, 17 years ago

maj sur la beta de geant 4.9.3
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[819]1//
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18// * This code implementation is the result of the scientific and *
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26// --------------------------------------------------------------------
27///
[1055]28// $Id: G4LowEnergyGammaConversion.cc,v 1.37 2009/05/02 09:59:16 sincerti Exp $
29// GEANT4 tag $Name: geant4-09-03-beta-cand-01 $
[819]30//
31//
32// --------------------------------------------------------------
33//
34// Author: A. Forti
35// Maria Grazia Pia (Maria.Grazia.Pia@cern.ch)
36//
37// History:
38// --------
39// 02/03/1999 A. Forti 1st implementation
40// 14.03.2000 Veronique Lefebure;
41// Change initialisation of lowestEnergyLimit from 1.22 to 1.022.
42// Note that the hard coded value 1.022 should be used instead of
43// 2*electron_mass_c2 in order to agree with the value of the data bank EPDL97
44// 24.04.01 V.Ivanchenko remove RogueWave
45// 27.07.01 F.Longo correct bug in energy distribution
46// 21.01.03 V.Ivanchenko Cut per region
47// 25.03.03 F.Longo fix in angular distribution of e+/e-
48// 24.04.03 V.Ivanchenko - Cut per region mfpt
49//
50// --------------------------------------------------------------
51
52#include "G4LowEnergyGammaConversion.hh"
53
54#include "Randomize.hh"
55#include "G4ParticleDefinition.hh"
56#include "G4Track.hh"
57#include "G4Step.hh"
58#include "G4ForceCondition.hh"
59#include "G4Gamma.hh"
60#include "G4Electron.hh"
61#include "G4DynamicParticle.hh"
62#include "G4VParticleChange.hh"
63#include "G4ThreeVector.hh"
64#include "G4Positron.hh"
65#include "G4IonisParamElm.hh"
66#include "G4Material.hh"
67#include "G4VCrossSectionHandler.hh"
68#include "G4CrossSectionHandler.hh"
69#include "G4VEMDataSet.hh"
70#include "G4VDataSetAlgorithm.hh"
71#include "G4LogLogInterpolation.hh"
72#include "G4VRangeTest.hh"
73#include "G4RangeTest.hh"
74#include "G4MaterialCutsCouple.hh"
75
76G4LowEnergyGammaConversion::G4LowEnergyGammaConversion(const G4String& processName)
77 : G4VDiscreteProcess(processName),
78 lowEnergyLimit(1.022000*MeV),
79 highEnergyLimit(100*GeV),
80 intrinsicLowEnergyLimit(1.022000*MeV),
81 intrinsicHighEnergyLimit(100*GeV),
82 smallEnergy(2.*MeV)
83
84{
85 if (lowEnergyLimit < intrinsicLowEnergyLimit ||
86 highEnergyLimit > intrinsicHighEnergyLimit)
87 {
88 G4Exception("G4LowEnergyGammaConversion::G4LowEnergyGammaConversion - energy limit outside intrinsic process validity range");
89 }
90
91 // The following pointer is owned by G4DataHandler
92
93 crossSectionHandler = new G4CrossSectionHandler();
94 crossSectionHandler->Initialise(0,1.0220*MeV,100.*GeV,400);
95 meanFreePathTable = 0;
96 rangeTest = new G4RangeTest;
97
98 if (verboseLevel > 0)
99 {
100 G4cout << GetProcessName() << " is created " << G4endl
101 << "Energy range: "
102 << lowEnergyLimit / MeV << " MeV - "
103 << highEnergyLimit / GeV << " GeV"
104 << G4endl;
105 }
[1055]106
107 G4cout << G4endl;
108 G4cout << "*******************************************************************************" << G4endl;
109 G4cout << "*******************************************************************************" << G4endl;
110 G4cout << " The class G4LowEnergyGammaConversion is NOT SUPPORTED ANYMORE. " << G4endl;
111 G4cout << " It will be REMOVED with the next major release of Geant4. " << G4endl;
112 G4cout << " Please consult: https://twiki.cern.ch/twiki/bin/view/Geant4/LoweProcesses" << G4endl;
113 G4cout << "*******************************************************************************" << G4endl;
114 G4cout << "*******************************************************************************" << G4endl;
115 G4cout << G4endl;
[819]116}
117
118G4LowEnergyGammaConversion::~G4LowEnergyGammaConversion()
119{
120 delete meanFreePathTable;
121 delete crossSectionHandler;
122 delete rangeTest;
123}
124
125void G4LowEnergyGammaConversion::BuildPhysicsTable(const G4ParticleDefinition& )
126{
127
128 crossSectionHandler->Clear();
129 G4String crossSectionFile = "pair/pp-cs-";
130 crossSectionHandler->LoadData(crossSectionFile);
131
132 delete meanFreePathTable;
133 meanFreePathTable = crossSectionHandler->BuildMeanFreePathForMaterials();
134}
135
136G4VParticleChange* G4LowEnergyGammaConversion::PostStepDoIt(const G4Track& aTrack,
137 const G4Step& aStep)
138{
139// The energies of the e+ e- secondaries are sampled using the Bethe - Heitler
140// cross sections with Coulomb correction. A modified version of the random
141// number techniques of Butcher & Messel is used (Nuc Phys 20(1960),15).
142
143// Note 1 : Effects due to the breakdown of the Born approximation at low
144// energy are ignored.
145// Note 2 : The differential cross section implicitly takes account of
146// pair creation in both nuclear and atomic electron fields. However triplet
147// prodution is not generated.
148
149 aParticleChange.Initialize(aTrack);
150
151 const G4MaterialCutsCouple* couple = aTrack.GetMaterialCutsCouple();
152
153 const G4DynamicParticle* incidentPhoton = aTrack.GetDynamicParticle();
154 G4double photonEnergy = incidentPhoton->GetKineticEnergy();
155 G4ParticleMomentum photonDirection = incidentPhoton->GetMomentumDirection();
156
157 G4double epsilon ;
158 G4double epsilon0 = electron_mass_c2 / photonEnergy ;
159
160 // Do it fast if photon energy < 2. MeV
161 if (photonEnergy < smallEnergy )
162 {
163 epsilon = epsilon0 + (0.5 - epsilon0) * G4UniformRand();
164 }
165 else
166 {
167 // Select randomly one element in the current material
168 const G4Element* element = crossSectionHandler->SelectRandomElement(couple,photonEnergy);
169
170 if (element == 0)
171 {
172 G4cout << "G4LowEnergyGammaConversion::PostStepDoIt - element = 0" << G4endl;
173 }
174 G4IonisParamElm* ionisation = element->GetIonisation();
175 if (ionisation == 0)
176 {
177 G4cout << "G4LowEnergyGammaConversion::PostStepDoIt - ionisation = 0" << G4endl;
178 }
179
180 // Extract Coulomb factor for this Element
181 G4double fZ = 8. * (ionisation->GetlogZ3());
182 if (photonEnergy > 50. * MeV) fZ += 8. * (element->GetfCoulomb());
183
184 // Limits of the screening variable
185 G4double screenFactor = 136. * epsilon0 / (element->GetIonisation()->GetZ3()) ;
186 G4double screenMax = std::exp ((42.24 - fZ)/8.368) - 0.952 ;
187 G4double screenMin = std::min(4.*screenFactor,screenMax) ;
188
189 // Limits of the energy sampling
190 G4double epsilon1 = 0.5 - 0.5 * std::sqrt(1. - screenMin / screenMax) ;
191 G4double epsilonMin = std::max(epsilon0,epsilon1);
192 G4double epsilonRange = 0.5 - epsilonMin ;
193
194 // Sample the energy rate of the created electron (or positron)
195 G4double screen;
196 G4double gReject ;
197
198 G4double f10 = ScreenFunction1(screenMin) - fZ;
199 G4double f20 = ScreenFunction2(screenMin) - fZ;
200 G4double normF1 = std::max(f10 * epsilonRange * epsilonRange,0.);
201 G4double normF2 = std::max(1.5 * f20,0.);
202
203 do {
204 if (normF1 / (normF1 + normF2) > G4UniformRand() )
205 {
206 epsilon = 0.5 - epsilonRange * std::pow(G4UniformRand(), 0.3333) ;
207 screen = screenFactor / (epsilon * (1. - epsilon));
208 gReject = (ScreenFunction1(screen) - fZ) / f10 ;
209 }
210 else
211 {
212 epsilon = epsilonMin + epsilonRange * G4UniformRand();
213 screen = screenFactor / (epsilon * (1 - epsilon));
214 gReject = (ScreenFunction2(screen) - fZ) / f20 ;
215 }
216 } while ( gReject < G4UniformRand() );
217
218 } // End of epsilon sampling
219
220 // Fix charges randomly
221
222 G4double electronTotEnergy;
223 G4double positronTotEnergy;
224
225 if (CLHEP::RandBit::shootBit())
226 {
227 electronTotEnergy = (1. - epsilon) * photonEnergy;
228 positronTotEnergy = epsilon * photonEnergy;
229 }
230 else
231 {
232 positronTotEnergy = (1. - epsilon) * photonEnergy;
233 electronTotEnergy = epsilon * photonEnergy;
234 }
235
236 // Scattered electron (positron) angles. ( Z - axis along the parent photon)
237 // Universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211),
238 // derived from Tsai distribution (Rev. Mod. Phys. 49, 421 (1977)
239
240 G4double u;
241 const G4double a1 = 0.625;
242 G4double a2 = 3. * a1;
243 // G4double d = 27. ;
244
245 // if (9. / (9. + d) > G4UniformRand())
246 if (0.25 > G4UniformRand())
247 {
248 u = - std::log(G4UniformRand() * G4UniformRand()) / a1 ;
249 }
250 else
251 {
252 u = - std::log(G4UniformRand() * G4UniformRand()) / a2 ;
253 }
254
255 G4double thetaEle = u*electron_mass_c2/electronTotEnergy;
256 G4double thetaPos = u*electron_mass_c2/positronTotEnergy;
257 G4double phi = twopi * G4UniformRand();
258
259 G4double dxEle= std::sin(thetaEle)*std::cos(phi),dyEle= std::sin(thetaEle)*std::sin(phi),dzEle=std::cos(thetaEle);
260 G4double dxPos=-std::sin(thetaPos)*std::cos(phi),dyPos=-std::sin(thetaPos)*std::sin(phi),dzPos=std::cos(thetaPos);
261
262
263 // Kinematics of the created pair:
264 // the electron and positron are assumed to have a symetric angular
265 // distribution with respect to the Z axis along the parent photon
266
267 G4double localEnergyDeposit = 0. ;
268
269 aParticleChange.SetNumberOfSecondaries(2) ;
270 G4double electronKineEnergy = std::max(0.,electronTotEnergy - electron_mass_c2) ;
271
272 // Generate the electron only if with large enough range w.r.t. cuts and safety
273
274 G4double safety = aStep.GetPostStepPoint()->GetSafety();
275
276 if (rangeTest->Escape(G4Electron::Electron(),couple,electronKineEnergy,safety))
277 {
278 G4ThreeVector electronDirection (dxEle, dyEle, dzEle);
279 electronDirection.rotateUz(photonDirection);
280
281 G4DynamicParticle* particle1 = new G4DynamicParticle (G4Electron::Electron(),
282 electronDirection,
283 electronKineEnergy);
284 aParticleChange.AddSecondary(particle1) ;
285 }
286 else
287 {
288 localEnergyDeposit += electronKineEnergy ;
289 }
290
291 // The e+ is always created (even with kinetic energy = 0) for further annihilation
292 G4double positronKineEnergy = std::max(0.,positronTotEnergy - electron_mass_c2) ;
293
294 // Is the local energy deposit correct, if the positron is always created?
295 if (! (rangeTest->Escape(G4Positron::Positron(),couple,positronKineEnergy,safety)))
296 {
297 localEnergyDeposit += positronKineEnergy ;
298 positronKineEnergy = 0. ;
299 }
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 aParticleChange.AddSecondary(particle2) ;
308
309 aParticleChange.ProposeLocalEnergyDeposit(localEnergyDeposit) ;
310
311 // Kill the incident photon
312 aParticleChange.ProposeMomentumDirection(0.,0.,0.) ;
313 aParticleChange.ProposeEnergy(0.) ;
314 aParticleChange.ProposeTrackStatus(fStopAndKill) ;
315
316 // Reset NbOfInteractionLengthLeft and return aParticleChange
317 return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
318}
319
320G4bool G4LowEnergyGammaConversion::IsApplicable(const G4ParticleDefinition& particle)
321{
322 return ( &particle == G4Gamma::Gamma() );
323}
324
325G4double G4LowEnergyGammaConversion::GetMeanFreePath(const G4Track& track,
326 G4double, // previousStepSize
327 G4ForceCondition*)
328{
329 const G4DynamicParticle* photon = track.GetDynamicParticle();
330 G4double energy = photon->GetKineticEnergy();
331 const G4MaterialCutsCouple* couple = track.GetMaterialCutsCouple();
332 size_t materialIndex = couple->GetIndex();
333
334 G4double meanFreePath;
335 if (energy > highEnergyLimit) meanFreePath = meanFreePathTable->FindValue(highEnergyLimit,materialIndex);
336 else if (energy < lowEnergyLimit) meanFreePath = DBL_MAX;
337 else meanFreePath = meanFreePathTable->FindValue(energy,materialIndex);
338 return meanFreePath;
339}
340
341G4double G4LowEnergyGammaConversion::ScreenFunction1(G4double screenVariable)
342{
343 // Compute the value of the screening function 3*phi1 - phi2
344
345 G4double value;
346
347 if (screenVariable > 1.)
348 value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
349 else
350 value = 42.392 - screenVariable * (7.796 - 1.961 * screenVariable);
351
352 return value;
353}
354
355G4double G4LowEnergyGammaConversion::ScreenFunction2(G4double screenVariable)
356{
357 // Compute the value of the screening function 1.5*phi1 - 0.5*phi2
358
359 G4double value;
360
361 if (screenVariable > 1.)
362 value = 42.24 - 8.368 * std::log(screenVariable + 0.952);
363 else
364 value = 41.405 - screenVariable * (5.828 - 0.8945 * screenVariable);
365
366 return value;
367}
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