source: trunk/source/processes/electromagnetic/standard/src/G4BetheHeitlerModel.cc@ 1036

Last change on this file since 1036 was 1007, checked in by garnier, 17 years ago

update to geant4.9.2
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[819]1//
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25//
[961]26// $Id: G4BetheHeitlerModel.cc,v 1.12 2008/10/15 15:54:57 vnivanch Exp $
[1007]27// GEANT4 tag $Name: geant4-09-02 $
[819]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"
[961]63#include "G4LossTableManager.hh"
[819]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),
[961]73 nbins(10)
[819]74{
[961]75 fParticleChange = 0;
[819]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{
[961]96 if(!fParticleChange) {
97 if(pParticleChange) {
98 fParticleChange = reinterpret_cast<G4ParticleChangeForGamma*>(pParticleChange);
99 } else {
100 fParticleChange = new G4ParticleChangeForGamma();
101 }
102 }
[819]103
104 if(theCrossSectionTable) {
105 theCrossSectionTable->clearAndDestroy();
106 delete theCrossSectionTable;
107 }
108
109 const G4ElementTable* theElementTable = G4Element::GetElementTable();
110 size_t nvect = G4Element::GetNumberOfElements();
111 theCrossSectionTable = new G4PhysicsTable(nvect);
112 G4PhysicsLogVector* ptrVector;
113 G4double emin = LowEnergyLimit();
114 G4double emax = HighEnergyLimit();
[961]115 G4int n = nbins*G4int(log10(emax/emin));
116 G4bool spline = G4LossTableManager::Instance()->SplineFlag();
[819]117 G4double e, value;
118
119 for(size_t j=0; j<nvect ; j++) {
120
[961]121 ptrVector = new G4PhysicsLogVector(emin, emax, n);
122 ptrVector->SetSpline(spline);
[819]123 G4double Z = (*theElementTable)[j]->GetZ();
124 G4int iz = G4int(Z);
125 indexZ[iz] = j;
126
127 for(G4int i=0; i<nbins; i++) {
128 e = ptrVector->GetLowEdgeEnergy( i ) ;
129 value = ComputeCrossSectionPerAtom(theGamma, e, Z);
130 ptrVector->PutValue( i, value );
131 }
132
133 theCrossSectionTable->insert(ptrVector);
134 }
135}
136
137//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
138
139G4double G4BetheHeitlerModel::ComputeCrossSectionPerAtom(
140 const G4ParticleDefinition*,
141 G4double GammaEnergy, G4double Z,
142 G4double, G4double, G4double)
143// Calculates the microscopic cross section in GEANT4 internal units.
144// A parametrized formula from L. Urban is used to estimate
145// the total cross section.
146// It gives a good description of the data from 1.5 MeV to 100 GeV.
147// below 1.5 MeV: sigma=sigma(1.5MeV)*(GammaEnergy-2electronmass)
148// *(GammaEnergy-2electronmass)
149{
150 static const G4double GammaEnergyLimit = 1.5*MeV;
151 G4double CrossSection = 0.0 ;
152 if ( Z < 1. ) return CrossSection;
153 if ( GammaEnergy <= 2.0*electron_mass_c2 ) return CrossSection;
154
155 static const G4double
156 a0= 8.7842e+2*microbarn, a1=-1.9625e+3*microbarn, a2= 1.2949e+3*microbarn,
157 a3=-2.0028e+2*microbarn, a4= 1.2575e+1*microbarn, a5=-2.8333e-1*microbarn;
158
159 static const G4double
160 b0=-1.0342e+1*microbarn, b1= 1.7692e+1*microbarn, b2=-8.2381 *microbarn,
161 b3= 1.3063 *microbarn, b4=-9.0815e-2*microbarn, b5= 2.3586e-3*microbarn;
162
163 static const G4double
164 c0=-4.5263e+2*microbarn, c1= 1.1161e+3*microbarn, c2=-8.6749e+2*microbarn,
165 c3= 2.1773e+2*microbarn, c4=-2.0467e+1*microbarn, c5= 6.5372e-1*microbarn;
166
167 G4double GammaEnergySave = GammaEnergy;
168 if (GammaEnergy < GammaEnergyLimit) GammaEnergy = GammaEnergyLimit ;
169
170 G4double X=log(GammaEnergy/electron_mass_c2), X2=X*X, X3=X2*X, X4=X3*X, X5=X4*X;
171
172 G4double F1 = a0 + a1*X + a2*X2 + a3*X3 + a4*X4 + a5*X5,
173 F2 = b0 + b1*X + b2*X2 + b3*X3 + b4*X4 + b5*X5,
174 F3 = c0 + c1*X + c2*X2 + c3*X3 + c4*X4 + c5*X5;
175
176 CrossSection = (Z + 1.)*(F1*Z + F2*Z*Z + F3);
177
178 if (GammaEnergySave < GammaEnergyLimit) {
179
180 X = (GammaEnergySave - 2.*electron_mass_c2)
181 / (GammaEnergyLimit - 2.*electron_mass_c2);
182 CrossSection *= X*X;
183 }
184
185 if (CrossSection < 0.) CrossSection = 0.;
186 return CrossSection;
187}
188
189//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
190
191void G4BetheHeitlerModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
192 const G4MaterialCutsCouple* couple,
193 const G4DynamicParticle* aDynamicGamma,
194 G4double,
195 G4double)
196// The secondaries e+e- energies are sampled using the Bethe - Heitler
197// cross sections with Coulomb correction.
198// A modified version of the random number techniques of Butcher & Messel
199// is used (Nuc Phys 20(1960),15).
200//
201// GEANT4 internal units.
202//
203// Note 1 : Effects due to the breakdown of the Born approximation at
204// low energy are ignored.
205// Note 2 : The differential cross section implicitly takes account of
206// pair creation in both nuclear and atomic electron fields.
207// However triplet prodution is not generated.
208{
209 const G4Material* aMaterial = couple->GetMaterial();
210
211 G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
212 G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection();
213
214 G4double epsil ;
215 G4double epsil0 = electron_mass_c2/GammaEnergy ;
216 if(epsil0 > 1.0) return;
217
218 // do it fast if GammaEnergy < 2. MeV
219 static const G4double Egsmall=2.*MeV;
220
221 // select randomly one element constituing the material
222 const G4Element* anElement = SelectRandomAtom(aMaterial, theGamma, GammaEnergy);
223
224 if (GammaEnergy < Egsmall) {
225
226 epsil = epsil0 + (0.5-epsil0)*G4UniformRand();
227
228 } else {
229 // now comes the case with GammaEnergy >= 2. MeV
230
231 // Extract Coulomb factor for this Element
232 G4double FZ = 8.*(anElement->GetIonisation()->GetlogZ3());
233 if (GammaEnergy > 50.*MeV) FZ += 8.*(anElement->GetfCoulomb());
234
235 // limits of the screening variable
236 G4double screenfac = 136.*epsil0/(anElement->GetIonisation()->GetZ3());
237 G4double screenmax = exp ((42.24 - FZ)/8.368) - 0.952 ;
238 G4double screenmin = min(4.*screenfac,screenmax);
239
240 // limits of the energy sampling
241 G4double epsil1 = 0.5 - 0.5*sqrt(1. - screenmin/screenmax) ;
242 G4double epsilmin = max(epsil0,epsil1) , epsilrange = 0.5 - epsilmin;
243
244 //
245 // sample the energy rate of the created electron (or positron)
246 //
247 //G4double epsil, screenvar, greject ;
248 G4double screenvar, greject ;
249
250 G4double F10 = ScreenFunction1(screenmin) - FZ;
251 G4double F20 = ScreenFunction2(screenmin) - FZ;
252 G4double NormF1 = max(F10*epsilrange*epsilrange,0.);
253 G4double NormF2 = max(1.5*F20,0.);
254
255 do {
256 if ( NormF1/(NormF1+NormF2) > G4UniformRand() ) {
257 epsil = 0.5 - epsilrange*pow(G4UniformRand(), 0.333333);
258 screenvar = screenfac/(epsil*(1-epsil));
259 greject = (ScreenFunction1(screenvar) - FZ)/F10;
260
261 } else {
262 epsil = epsilmin + epsilrange*G4UniformRand();
263 screenvar = screenfac/(epsil*(1-epsil));
264 greject = (ScreenFunction2(screenvar) - FZ)/F20;
265 }
266
267 } while( greject < G4UniformRand() );
268
269 } // end of epsil sampling
270
271 //
272 // fixe charges randomly
273 //
274
275 G4double ElectTotEnergy, PositTotEnergy;
276 if (G4UniformRand() > 0.5) {
277
278 ElectTotEnergy = (1.-epsil)*GammaEnergy;
279 PositTotEnergy = epsil*GammaEnergy;
280
281 } else {
282
283 PositTotEnergy = (1.-epsil)*GammaEnergy;
284 ElectTotEnergy = epsil*GammaEnergy;
285 }
286
287 //
288 // scattered electron (positron) angles. ( Z - axis along the parent photon)
289 //
290 // universal distribution suggested by L. Urban
291 // (Geant3 manual (1993) Phys211),
292 // derived from Tsai distribution (Rev Mod Phys 49,421(1977))
293
294 G4double u;
295 const G4double a1 = 0.625 , a2 = 3.*a1 , d = 27. ;
296
297 if (9./(9.+d) >G4UniformRand()) u= - log(G4UniformRand()*G4UniformRand())/a1;
298 else u= - log(G4UniformRand()*G4UniformRand())/a2;
299
300 G4double TetEl = u*electron_mass_c2/ElectTotEnergy;
301 G4double TetPo = u*electron_mass_c2/PositTotEnergy;
302 G4double Phi = twopi * G4UniformRand();
303 G4double dxEl= sin(TetEl)*cos(Phi),dyEl= sin(TetEl)*sin(Phi),dzEl=cos(TetEl);
304 G4double dxPo=-sin(TetPo)*cos(Phi),dyPo=-sin(TetPo)*sin(Phi),dzPo=cos(TetPo);
305
306 //
307 // kinematic of the created pair
308 //
309 // the electron and positron are assumed to have a symetric
310 // angular distribution with respect to the Z axis along the parent photon.
311
312 G4double ElectKineEnergy = max(0.,ElectTotEnergy - electron_mass_c2);
313
314 G4ThreeVector ElectDirection (dxEl, dyEl, dzEl);
315 ElectDirection.rotateUz(GammaDirection);
316
317 // create G4DynamicParticle object for the particle1
318 G4DynamicParticle* aParticle1= new G4DynamicParticle(
319 theElectron,ElectDirection,ElectKineEnergy);
320
321 // the e+ is always created (even with Ekine=0) for further annihilation.
322
323 G4double PositKineEnergy = max(0.,PositTotEnergy - electron_mass_c2);
324
325 G4ThreeVector PositDirection (dxPo, dyPo, dzPo);
326 PositDirection.rotateUz(GammaDirection);
327
328 // create G4DynamicParticle object for the particle2
329 G4DynamicParticle* aParticle2= new G4DynamicParticle(
330 thePositron,PositDirection,PositKineEnergy);
331
332 // Fill output vector
333 fvect->push_back(aParticle1);
334 fvect->push_back(aParticle2);
335
336 // kill incident photon
337 fParticleChange->SetProposedKineticEnergy(0.);
338 fParticleChange->ProposeTrackStatus(fStopAndKill);
339}
340
341//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
342
343
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