source: trunk/source/processes/electromagnetic/standard/src/G4BetheHeitlerModel.cc@ 1201

Last change on this file since 1201 was 1196, checked in by garnier, 16 years ago

update CVS release candidate geant4.9.3.01
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24// ********************************************************************
25//
26// $Id: G4BetheHeitlerModel.cc,v 1.13 2009/04/09 18:41:18 vnivanch Exp $
27// GEANT4 tag $Name: geant4-09-03-cand-01 $
28//
29// -------------------------------------------------------------------
30//
31// GEANT4 Class file
32//
33//
34// File name: G4BetheHeitlerModel
35//
36// Author: Vladimir Ivanchenko on base of Michel Maire code
37//
38// Creation date: 15.03.2005
39//
40// Modifications:
41// 18-04-05 Use G4ParticleChangeForGamma (V.Ivantchenko)
42// 24-06-05 Increase number of bins to 200 (V.Ivantchenko)
43// 16-11-05 replace shootBit() by G4UniformRand() mma
44// 04-12-05 SetProposedKineticEnergy(0.) for the killed photon (mma)
45// 20-02-20 SelectRandomElement is called for any initial gamma energy
46// in order to have selected element for polarized model (VI)
47//
48// Class Description:
49//
50// -------------------------------------------------------------------
51//
52//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
53//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
54
55#include "G4BetheHeitlerModel.hh"
56#include "G4Electron.hh"
57#include "G4Positron.hh"
58#include "G4Gamma.hh"
59#include "Randomize.hh"
60#include "G4DataVector.hh"
61#include "G4PhysicsLogVector.hh"
62#include "G4ParticleChangeForGamma.hh"
63#include "G4LossTableManager.hh"
64
65//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
66
67using namespace std;
68
69G4BetheHeitlerModel::G4BetheHeitlerModel(const G4ParticleDefinition*,
70 const G4String& nam)
71 : G4VEmModel(nam),
72 theCrossSectionTable(0),
73 nbins(10)
74{
75 fParticleChange = 0;
76 theGamma = G4Gamma::Gamma();
77 thePositron = G4Positron::Positron();
78 theElectron = G4Electron::Electron();
79}
80
81//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
82
83G4BetheHeitlerModel::~G4BetheHeitlerModel()
84{
85 if(theCrossSectionTable) {
86 theCrossSectionTable->clearAndDestroy();
87 delete theCrossSectionTable;
88 }
89}
90
91//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
92
93void G4BetheHeitlerModel::Initialise(const G4ParticleDefinition*,
94 const G4DataVector&)
95{
96 if(!fParticleChange) fParticleChange = GetParticleChangeForGamma();
97
98 if(theCrossSectionTable) {
99 theCrossSectionTable->clearAndDestroy();
100 delete theCrossSectionTable;
101 }
102
103 const G4ElementTable* theElementTable = G4Element::GetElementTable();
104 size_t nvect = G4Element::GetNumberOfElements();
105 theCrossSectionTable = new G4PhysicsTable(nvect);
106 G4PhysicsLogVector* ptrVector;
107 G4double emin = LowEnergyLimit();
108 G4double emax = HighEnergyLimit();
109 G4int n = nbins*G4int(log10(emax/emin));
110 G4bool spline = G4LossTableManager::Instance()->SplineFlag();
111 G4double e, value;
112
113 for(size_t j=0; j<nvect ; j++) {
114
115 ptrVector = new G4PhysicsLogVector(emin, emax, n);
116 ptrVector->SetSpline(spline);
117 G4double Z = (*theElementTable)[j]->GetZ();
118 G4int iz = G4int(Z);
119 indexZ[iz] = j;
120
121 for(G4int i=0; i<nbins; i++) {
122 e = ptrVector->GetLowEdgeEnergy( i ) ;
123 value = ComputeCrossSectionPerAtom(theGamma, e, Z);
124 ptrVector->PutValue( i, value );
125 }
126
127 theCrossSectionTable->insert(ptrVector);
128 }
129}
130
131//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
132
133G4double G4BetheHeitlerModel::ComputeCrossSectionPerAtom(
134 const G4ParticleDefinition*,
135 G4double GammaEnergy, G4double Z,
136 G4double, G4double, G4double)
137// Calculates the microscopic cross section in GEANT4 internal units.
138// A parametrized formula from L. Urban is used to estimate
139// the total cross section.
140// It gives a good description of the data from 1.5 MeV to 100 GeV.
141// below 1.5 MeV: sigma=sigma(1.5MeV)*(GammaEnergy-2electronmass)
142// *(GammaEnergy-2electronmass)
143{
144 static const G4double GammaEnergyLimit = 1.5*MeV;
145 G4double CrossSection = 0.0 ;
146 if ( Z < 1. ) return CrossSection;
147 if ( GammaEnergy <= 2.0*electron_mass_c2 ) return CrossSection;
148
149 static const G4double
150 a0= 8.7842e+2*microbarn, a1=-1.9625e+3*microbarn, a2= 1.2949e+3*microbarn,
151 a3=-2.0028e+2*microbarn, a4= 1.2575e+1*microbarn, a5=-2.8333e-1*microbarn;
152
153 static const G4double
154 b0=-1.0342e+1*microbarn, b1= 1.7692e+1*microbarn, b2=-8.2381 *microbarn,
155 b3= 1.3063 *microbarn, b4=-9.0815e-2*microbarn, b5= 2.3586e-3*microbarn;
156
157 static const G4double
158 c0=-4.5263e+2*microbarn, c1= 1.1161e+3*microbarn, c2=-8.6749e+2*microbarn,
159 c3= 2.1773e+2*microbarn, c4=-2.0467e+1*microbarn, c5= 6.5372e-1*microbarn;
160
161 G4double GammaEnergySave = GammaEnergy;
162 if (GammaEnergy < GammaEnergyLimit) GammaEnergy = GammaEnergyLimit ;
163
164 G4double X=log(GammaEnergy/electron_mass_c2), X2=X*X, X3=X2*X, X4=X3*X, X5=X4*X;
165
166 G4double F1 = a0 + a1*X + a2*X2 + a3*X3 + a4*X4 + a5*X5,
167 F2 = b0 + b1*X + b2*X2 + b3*X3 + b4*X4 + b5*X5,
168 F3 = c0 + c1*X + c2*X2 + c3*X3 + c4*X4 + c5*X5;
169
170 CrossSection = (Z + 1.)*(F1*Z + F2*Z*Z + F3);
171
172 if (GammaEnergySave < GammaEnergyLimit) {
173
174 X = (GammaEnergySave - 2.*electron_mass_c2)
175 / (GammaEnergyLimit - 2.*electron_mass_c2);
176 CrossSection *= X*X;
177 }
178
179 if (CrossSection < 0.) CrossSection = 0.;
180 return CrossSection;
181}
182
183//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
184
185void G4BetheHeitlerModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
186 const G4MaterialCutsCouple* couple,
187 const G4DynamicParticle* aDynamicGamma,
188 G4double,
189 G4double)
190// The secondaries e+e- energies are sampled using the Bethe - Heitler
191// cross sections with Coulomb correction.
192// A modified version of the random number techniques of Butcher & Messel
193// is used (Nuc Phys 20(1960),15).
194//
195// GEANT4 internal units.
196//
197// Note 1 : Effects due to the breakdown of the Born approximation at
198// low energy are ignored.
199// Note 2 : The differential cross section implicitly takes account of
200// pair creation in both nuclear and atomic electron fields.
201// However triplet prodution is not generated.
202{
203 const G4Material* aMaterial = couple->GetMaterial();
204
205 G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
206 G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection();
207
208 G4double epsil ;
209 G4double epsil0 = electron_mass_c2/GammaEnergy ;
210 if(epsil0 > 1.0) return;
211
212 // do it fast if GammaEnergy < 2. MeV
213 static const G4double Egsmall=2.*MeV;
214
215 // select randomly one element constituing the material
216 const G4Element* anElement = SelectRandomAtom(aMaterial, theGamma, GammaEnergy);
217
218 if (GammaEnergy < Egsmall) {
219
220 epsil = epsil0 + (0.5-epsil0)*G4UniformRand();
221
222 } else {
223 // now comes the case with GammaEnergy >= 2. MeV
224
225 // Extract Coulomb factor for this Element
226 G4double FZ = 8.*(anElement->GetIonisation()->GetlogZ3());
227 if (GammaEnergy > 50.*MeV) FZ += 8.*(anElement->GetfCoulomb());
228
229 // limits of the screening variable
230 G4double screenfac = 136.*epsil0/(anElement->GetIonisation()->GetZ3());
231 G4double screenmax = exp ((42.24 - FZ)/8.368) - 0.952 ;
232 G4double screenmin = min(4.*screenfac,screenmax);
233
234 // limits of the energy sampling
235 G4double epsil1 = 0.5 - 0.5*sqrt(1. - screenmin/screenmax) ;
236 G4double epsilmin = max(epsil0,epsil1) , epsilrange = 0.5 - epsilmin;
237
238 //
239 // sample the energy rate of the created electron (or positron)
240 //
241 //G4double epsil, screenvar, greject ;
242 G4double screenvar, greject ;
243
244 G4double F10 = ScreenFunction1(screenmin) - FZ;
245 G4double F20 = ScreenFunction2(screenmin) - FZ;
246 G4double NormF1 = max(F10*epsilrange*epsilrange,0.);
247 G4double NormF2 = max(1.5*F20,0.);
248
249 do {
250 if ( NormF1/(NormF1+NormF2) > G4UniformRand() ) {
251 epsil = 0.5 - epsilrange*pow(G4UniformRand(), 0.333333);
252 screenvar = screenfac/(epsil*(1-epsil));
253 greject = (ScreenFunction1(screenvar) - FZ)/F10;
254
255 } else {
256 epsil = epsilmin + epsilrange*G4UniformRand();
257 screenvar = screenfac/(epsil*(1-epsil));
258 greject = (ScreenFunction2(screenvar) - FZ)/F20;
259 }
260
261 } while( greject < G4UniformRand() );
262
263 } // end of epsil sampling
264
265 //
266 // fixe charges randomly
267 //
268
269 G4double ElectTotEnergy, PositTotEnergy;
270 if (G4UniformRand() > 0.5) {
271
272 ElectTotEnergy = (1.-epsil)*GammaEnergy;
273 PositTotEnergy = epsil*GammaEnergy;
274
275 } else {
276
277 PositTotEnergy = (1.-epsil)*GammaEnergy;
278 ElectTotEnergy = epsil*GammaEnergy;
279 }
280
281 //
282 // scattered electron (positron) angles. ( Z - axis along the parent photon)
283 //
284 // universal distribution suggested by L. Urban
285 // (Geant3 manual (1993) Phys211),
286 // derived from Tsai distribution (Rev Mod Phys 49,421(1977))
287
288 G4double u;
289 const G4double a1 = 0.625 , a2 = 3.*a1 , d = 27. ;
290
291 if (9./(9.+d) >G4UniformRand()) u= - log(G4UniformRand()*G4UniformRand())/a1;
292 else u= - log(G4UniformRand()*G4UniformRand())/a2;
293
294 G4double TetEl = u*electron_mass_c2/ElectTotEnergy;
295 G4double TetPo = u*electron_mass_c2/PositTotEnergy;
296 G4double Phi = twopi * G4UniformRand();
297 G4double dxEl= sin(TetEl)*cos(Phi),dyEl= sin(TetEl)*sin(Phi),dzEl=cos(TetEl);
298 G4double dxPo=-sin(TetPo)*cos(Phi),dyPo=-sin(TetPo)*sin(Phi),dzPo=cos(TetPo);
299
300 //
301 // kinematic of the created pair
302 //
303 // the electron and positron are assumed to have a symetric
304 // angular distribution with respect to the Z axis along the parent photon.
305
306 G4double ElectKineEnergy = max(0.,ElectTotEnergy - electron_mass_c2);
307
308 G4ThreeVector ElectDirection (dxEl, dyEl, dzEl);
309 ElectDirection.rotateUz(GammaDirection);
310
311 // create G4DynamicParticle object for the particle1
312 G4DynamicParticle* aParticle1= new G4DynamicParticle(
313 theElectron,ElectDirection,ElectKineEnergy);
314
315 // the e+ is always created (even with Ekine=0) for further annihilation.
316
317 G4double PositKineEnergy = max(0.,PositTotEnergy - electron_mass_c2);
318
319 G4ThreeVector PositDirection (dxPo, dyPo, dzPo);
320 PositDirection.rotateUz(GammaDirection);
321
322 // create G4DynamicParticle object for the particle2
323 G4DynamicParticle* aParticle2= new G4DynamicParticle(
324 thePositron,PositDirection,PositKineEnergy);
325
326 // Fill output vector
327 fvect->push_back(aParticle1);
328 fvect->push_back(aParticle2);
329
330 // kill incident photon
331 fParticleChange->SetProposedKineticEnergy(0.);
332 fParticleChange->ProposeTrackStatus(fStopAndKill);
333}
334
335//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
336
337
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