| Geant4 Cross Reference |
1 // 1
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25 //
26 // -------------------------------------------
27 ///
28 //
29 //
30 // -------------------------------------------
31 //
32 // Author: A. Forti
33 // Maria Grazia Pia (Maria.Grazia.Pia@
34 //
35 // History:
36 // --------
37 // 02/03/1999 A. Forti 1st implementation
38 // 14.03.2000 Veronique Lefebure;
39 // Change initialisation of lowestEnergyLimit
40 // Note that the hard coded value 1.022 should
41 // 2*electron_mass_c2 in order to agree with t
42 // 24.04.01 V.Ivanchenko remove RogueWave
43 // 27.07.01 F.Longo correct bug in energy dist
44 // 21.01.03 V.Ivanchenko Cut per region
45 // 25.03.03 F.Longo fix in angular distributio
46 // 24.04.03 V.Ivanchenko - Cut per region mfpt
47 //
48 // -------------------------------------------
49
50 #include "G4LowEnergyGammaConversion.hh"
51
52 #include "Randomize.hh"
53 #include "G4PhysicalConstants.hh"
54 #include "G4SystemOfUnits.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 "G4RDVCrossSectionHandler.hh"
68 #include "G4RDCrossSectionHandler.hh"
69 #include "G4RDVEMDataSet.hh"
70 #include "G4RDVDataSetAlgorithm.hh"
71 #include "G4RDLogLogInterpolation.hh"
72 #include "G4RDVRangeTest.hh"
73 #include "G4RDRangeTest.hh"
74 #include "G4MaterialCutsCouple.hh"
75
76 G4LowEnergyGammaConversion::G4LowEnergyGammaCo
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 > intrinsicHighEnergyLim
87 {
88 G4Exception("G4LowEnergyGammaConversion:
89 "OutOfRange", FatalException
90 "Energy limit outside intrin
91 }
92
93 // The following pointer is owned by G4DataH
94
95 crossSectionHandler = new G4RDCrossSectionHa
96 crossSectionHandler->Initialise(0,1.0220*MeV
97 meanFreePathTable = 0;
98 rangeTest = new G4RDRangeTest;
99
100 if (verboseLevel > 0)
101 {
102 G4cout << GetProcessName() << " is crea
103 << "Energy range: "
104 << lowEnergyLimit / MeV << " MeV - "
105 << highEnergyLimit / GeV << " GeV"
106 << G4endl;
107 }
108 }
109
110 G4LowEnergyGammaConversion::~G4LowEnergyGammaC
111 {
112 delete meanFreePathTable;
113 delete crossSectionHandler;
114 delete rangeTest;
115 }
116
117 void G4LowEnergyGammaConversion::BuildPhysicsT
118 {
119
120 crossSectionHandler->Clear();
121 G4String crossSectionFile = "pair/pp-cs-";
122 crossSectionHandler->LoadData(crossSectionFi
123
124 delete meanFreePathTable;
125 meanFreePathTable = crossSectionHandler->Bui
126 }
127
128 G4VParticleChange* G4LowEnergyGammaConversion:
129 const G4Step& aStep)
130 {
131 // The energies of the e+ e- secondaries are s
132 // cross sections with Coulomb correction. A m
133 // number techniques of Butcher & Messel is us
134
135 // Note 1 : Effects due to the breakdown of th
136 // energy are ignored.
137 // Note 2 : The differential cross section imp
138 // pair creation in both nuclear and atomic el
139 // prodution is not generated.
140
141 aParticleChange.Initialize(aTrack);
142
143 const G4MaterialCutsCouple* couple = aTrack.
144
145 const G4DynamicParticle* incidentPhoton = aT
146 G4double photonEnergy = incidentPhoton->GetK
147 G4ParticleMomentum photonDirection = inciden
148
149 G4double epsilon ;
150 G4double epsilon0 = electron_mass_c2 / photo
151
152 // Do it fast if photon energy < 2. MeV
153 if (photonEnergy < smallEnergy )
154 {
155 epsilon = epsilon0 + (0.5 - epsilon0) *
156 }
157 else
158 {
159 // Select randomly one element in the cu
160 const G4Element* element = crossSectionH
161
162 if (element == 0)
163 {
164 G4cout << "G4LowEnergyGammaConversion::Pos
165 }
166 G4IonisParamElm* ionisation = element->G
167 if (ionisation == 0)
168 {
169 G4cout << "G4LowEnergyGammaConversion::Pos
170 }
171
172 // Extract Coulomb factor for this Eleme
173 G4double fZ = 8. * (ionisation->GetlogZ3
174 if (photonEnergy > 50. * MeV) fZ += 8. *
175
176 // Limits of the screening variable
177 G4double screenFactor = 136. * epsilon0
178 G4double screenMax = std::exp ((42.24 -
179 G4double screenMin = std::min(4.*screenF
180
181 // Limits of the energy sampling
182 G4double epsilon1 = 0.5 - 0.5 * std::sqr
183 G4double epsilonMin = std::max(epsilon0,
184 G4double epsilonRange = 0.5 - epsilonMin
185
186 // Sample the energy rate of the created
187 G4double screen;
188 G4double gReject ;
189
190 G4double f10 = ScreenFunction1(screenMin
191 G4double f20 = ScreenFunction2(screenMin
192 G4double normF1 = std::max(f10 * epsilon
193 G4double normF2 = std::max(1.5 * f20,0.)
194
195 do {
196 if (normF1 / (normF1 + normF2) > G4UniformRa
197 {
198 epsilon = 0.5 - epsilonRange * std::pow(
199 screen = screenFactor / (epsilon * (1. -
200 gReject = (ScreenFunction1(screen) - fZ)
201 }
202 else
203 {
204 epsilon = epsilonMin + epsilonRange * G4
205 screen = screenFactor / (epsilon * (1 -
206 gReject = (ScreenFunction2(screen) - fZ)
207 }
208 } while ( gReject < G4UniformRand() );
209
210 } // End of epsilon sampling
211
212 // Fix charges randomly
213
214 G4double electronTotEnergy;
215 G4double positronTotEnergy;
216
217 if (CLHEP::RandBit::shootBit())
218 {
219 electronTotEnergy = (1. - epsilon) * pho
220 positronTotEnergy = epsilon * photonEner
221 }
222 else
223 {
224 positronTotEnergy = (1. - epsilon) * pho
225 electronTotEnergy = epsilon * photonEner
226 }
227
228 // Scattered electron (positron) angles. ( Z
229 // Universal distribution suggested by L. Ur
230 // derived from Tsai distribution (Rev. Mod.
231
232 G4double u;
233 const G4double a1 = 0.625;
234 G4double a2 = 3. * a1;
235 // G4double d = 27. ;
236
237 // if (9. / (9. + d) > G4UniformRand())
238 if (0.25 > G4UniformRand())
239 {
240 u = - std::log(G4UniformRand() * G4Unifo
241 }
242 else
243 {
244 u = - std::log(G4UniformRand() * G4Unifo
245 }
246
247 G4double thetaEle = u*electron_mass_c2/elect
248 G4double thetaPos = u*electron_mass_c2/posit
249 G4double phi = twopi * G4UniformRand();
250
251 G4double dxEle= std::sin(thetaEle)*std::cos(
252 G4double dxPos=-std::sin(thetaPos)*std::cos(
253
254
255 // Kinematics of the created pair:
256 // the electron and positron are assumed to
257 // distribution with respect to the Z axis a
258
259 G4double localEnergyDeposit = 0. ;
260
261 aParticleChange.SetNumberOfSecondaries(2) ;
262 G4double electronKineEnergy = std::max(0.,el
263
264 // Generate the electron only if with large
265
266 G4double safety = aStep.GetPostStepPoint()->
267
268 if (rangeTest->Escape(G4Electron::Electron()
269 {
270 G4ThreeVector electronDirection (dxEle,
271 electronDirection.rotateUz(photonDirecti
272
273 G4DynamicParticle* particle1 = new G4Dyn
274 electronDirection,
275 electronKineEnergy);
276 aParticleChange.AddSecondary(particle1)
277 }
278 else
279 {
280 localEnergyDeposit += electronKineEnergy
281 }
282
283 // The e+ is always created (even with kinet
284 G4double positronKineEnergy = std::max(0.,po
285
286 // Is the local energy deposit correct, if t
287 if (! (rangeTest->Escape(G4Positron::Positro
288 {
289 localEnergyDeposit += positronKineEnergy
290 positronKineEnergy = 0. ;
291 }
292
293 G4ThreeVector positronDirection (dxPos, dyPo
294 positronDirection.rotateUz(photonDirection);
295
296 // Create G4DynamicParticle object for the p
297 G4DynamicParticle* particle2 = new G4Dynamic
298 positronDirection, positron
299 aParticleChange.AddSecondary(particle2) ;
300
301 aParticleChange.ProposeLocalEnergyDeposit(lo
302
303 // Kill the incident photon
304 aParticleChange.ProposeMomentumDirection(0.,
305 aParticleChange.ProposeEnergy(0.) ;
306 aParticleChange.ProposeTrackStatus(fStopAndK
307
308 // Reset NbOfInteractionLengthLeft and retu
309 return G4VDiscreteProcess::PostStepDoIt(aTra
310 }
311
312 G4bool G4LowEnergyGammaConversion::IsApplicabl
313 {
314 return ( &particle == G4Gamma::Gamma() );
315 }
316
317 G4double G4LowEnergyGammaConversion::GetMeanFr
318 G4double, // previousStepSize
319 G4ForceCondition*)
320 {
321 const G4DynamicParticle* photon = track.GetD
322 G4double energy = photon->GetKineticEnergy()
323 const G4MaterialCutsCouple* couple = track.G
324 size_t materialIndex = couple->GetIndex();
325
326 G4double meanFreePath;
327 if (energy > highEnergyLimit) meanFreePath =
328 else if (energy < lowEnergyLimit) meanFreePa
329 else meanFreePath = meanFreePathTable->FindV
330 return meanFreePath;
331 }
332
333 G4double G4LowEnergyGammaConversion::ScreenFun
334 {
335 // Compute the value of the screening functi
336
337 G4double value;
338
339 if (screenVariable > 1.)
340 value = 42.24 - 8.368 * std::log(screenVar
341 else
342 value = 42.392 - screenVariable * (7.796 -
343
344 return value;
345 }
346
347 G4double G4LowEnergyGammaConversion::ScreenFun
348 {
349 // Compute the value of the screening functi
350
351 G4double value;
352
353 if (screenVariable > 1.)
354 value = 42.24 - 8.368 * std::log(screenVar
355 else
356 value = 41.405 - screenVariable * (5.828 -
357
358 return value;
359 }
360