source: trunk/source/processes/electromagnetic/lowenergy/src/G4Penelope08GammaConversionModel.cc @ 1347

Last change on this file since 1347 was 1347, checked in by garnier, 13 years ago

geant4 tag 9.4
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26// $Id: G4Penelope08GammaConversionModel.cc,v 1.4 2010/07/28 07:09:16 pandola Exp $
27// GEANT4 tag $Name: geant4-09-04-ref-00 $
28//
29// Author: Luciano Pandola
30//
31// History:
32// --------
33// 13 Jan 2010   L Pandola    First implementation (updated to Penelope08)
34//
35
36#include "G4Penelope08GammaConversionModel.hh"
37#include "G4ParticleDefinition.hh"
38#include "G4MaterialCutsCouple.hh"
39#include "G4ProductionCutsTable.hh"
40#include "G4DynamicParticle.hh"
41#include "G4Element.hh"
42#include "G4Gamma.hh"
43#include "G4Electron.hh"
44#include "G4Positron.hh"
45#include "G4PhysicsFreeVector.hh"
46
47//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
48
49
50G4Penelope08GammaConversionModel::G4Penelope08GammaConversionModel(const G4ParticleDefinition*,
51                                             const G4String& nam)
52  :G4VEmModel(nam),logAtomicCrossSection(0),fEffectiveCharge(0),fMaterialInvScreeningRadius(0),
53   fScreeningFunction(0),isInitialised(false)
54{
55  fIntrinsicLowEnergyLimit = 2.0*electron_mass_c2;
56  fIntrinsicHighEnergyLimit = 100.0*GeV;
57  fSmallEnergy = 1.1*MeV;
58  InitializeScreeningRadii();
59
60  //  SetLowEnergyLimit(fIntrinsicLowEnergyLimit);
61  SetHighEnergyLimit(fIntrinsicHighEnergyLimit);
62  //
63  verboseLevel= 0;
64  // Verbosity scale:
65  // 0 = nothing
66  // 1 = warning for energy non-conservation
67  // 2 = details of energy budget
68  // 3 = calculation of cross sections, file openings, sampling of atoms
69  // 4 = entering in methods
70}
71
72//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
73
74G4Penelope08GammaConversionModel::~G4Penelope08GammaConversionModel()
75{
76  std::map <const G4int,G4PhysicsFreeVector*>::iterator i;
77  if (logAtomicCrossSection)
78    {
79      for (i=logAtomicCrossSection->begin();i != logAtomicCrossSection->end();i++)
80        if (i->second) delete i->second;
81      delete logAtomicCrossSection;
82    }
83  if (fEffectiveCharge)
84    delete fEffectiveCharge;
85  if (fMaterialInvScreeningRadius)
86    delete fMaterialInvScreeningRadius;
87  if (fScreeningFunction)
88    delete fScreeningFunction;
89}
90
91
92//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
93
94void G4Penelope08GammaConversionModel::Initialise(const G4ParticleDefinition*,
95                                                const G4DataVector&)
96{
97  if (verboseLevel > 3)
98    G4cout << "Calling  G4Penelope08GammaConversionModel::Initialise()" << G4endl;
99
100  // logAtomicCrossSection is created only once, since it is  never cleared
101  if (!logAtomicCrossSection)
102    logAtomicCrossSection =  new std::map<const G4int,G4PhysicsFreeVector*>;
103
104  //delete old material data...
105  if (fEffectiveCharge)
106    {
107      delete fEffectiveCharge;
108      fEffectiveCharge = 0;
109    }
110  if (fMaterialInvScreeningRadius)
111    {
112      delete fMaterialInvScreeningRadius;
113      fMaterialInvScreeningRadius = 0;
114    }
115  if (fScreeningFunction)
116    {
117      delete fScreeningFunction;
118      fScreeningFunction = 0;
119    }     
120  //and create new ones
121  fEffectiveCharge = new std::map<const G4Material*,G4double>;
122  fMaterialInvScreeningRadius = new std::map<const G4Material*,G4double>;
123  fScreeningFunction = new std::map<const G4Material*,std::pair<G4double,G4double> >;
124
125  if (verboseLevel > 0) { 
126    G4cout << "Penelope Gamma Conversion model is initialized " << G4endl
127           << "Energy range: "
128           << LowEnergyLimit() / MeV << " MeV - "
129           << HighEnergyLimit() / GeV << " GeV"
130           << G4endl;
131  }
132
133  if(isInitialised) return;
134  fParticleChange = GetParticleChangeForGamma();
135  isInitialised = true;
136}
137
138//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
139
140G4double G4Penelope08GammaConversionModel::ComputeCrossSectionPerAtom(
141                                       const G4ParticleDefinition*,
142                                             G4double energy,
143                                             G4double Z, G4double,
144                                             G4double, G4double)
145{
146  //
147  // Penelope model.
148  // Cross section (including triplet production) read from database and managed
149  // through the G4CrossSectionHandler utility. Cross section data are from
150  // M.J. Berger and J.H. Hubbel (XCOM), Report NBSIR 887-3598
151  //
152 
153  if (energy < fIntrinsicLowEnergyLimit)
154    return 0;
155
156  G4int iZ = (G4int) Z;
157
158 //read data files
159  if (!logAtomicCrossSection->count(iZ))
160    ReadDataFile(iZ);
161  //now it should be ok
162  if (!logAtomicCrossSection->count(iZ))
163     {
164       G4cout << "Problem in G4Penelope08GammaConversion::ComputeCrossSectionPerAtom"
165              << G4endl;
166       G4Exception();
167     }
168
169  G4double cs = 0;
170  G4double logene = std::log(energy);
171  G4PhysicsFreeVector* theVec = logAtomicCrossSection->find(iZ)->second;
172
173  G4double logXS = theVec->Value(logene);
174  cs = std::exp(logXS);
175
176  if (verboseLevel > 2)
177    G4cout << "Gamma conversion cross section at " << energy/MeV << " MeV for Z=" << Z << 
178      " = " << cs/barn << " barn" << G4endl;
179  return cs;
180}
181
182//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
183
184void 
185G4Penelope08GammaConversionModel::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
186                                                  const G4MaterialCutsCouple* couple,
187                                                  const G4DynamicParticle* aDynamicGamma,
188                                                  G4double,
189                                                  G4double)
190{
191  //
192  // Penelope model.
193  // Final state is sampled according to the Bethe-Heitler model with Coulomb
194  // corrections, according to the semi-empirical model of
195  //  J. Baro' et al., Radiat. Phys. Chem. 44 (1994) 531.
196  //
197  // The model uses the high energy Coulomb correction from
198  //  H. Davies et al., Phys. Rev. 93 (1954) 788
199  // and atomic screening radii tabulated from
200  //  J.H. Hubbel et al., J. Phys. Chem. Ref. Data 9 (1980) 1023
201  // for Z= 1 to 92.
202  //
203  if (verboseLevel > 3)
204    G4cout << "Calling SamplingSecondaries() of G4Penelope08GammaConversionModel" << G4endl;
205
206  G4double photonEnergy = aDynamicGamma->GetKineticEnergy();
207
208  // Always kill primary
209  fParticleChange->ProposeTrackStatus(fStopAndKill);
210  fParticleChange->SetProposedKineticEnergy(0.);
211
212  if (photonEnergy <= fIntrinsicLowEnergyLimit)
213    {
214      fParticleChange->ProposeLocalEnergyDeposit(photonEnergy);
215      return ;
216    }
217
218  G4ParticleMomentum photonDirection = aDynamicGamma->GetMomentumDirection();
219  const G4Material* mat = couple->GetMaterial();
220
221  //check if material data are available
222  if (!fEffectiveCharge->count(mat))
223    InitializeScreeningFunctions(mat); 
224  if (!fEffectiveCharge->count(mat))
225    {
226      G4cout << "Problem in G4Penelope08GammaConversion::SampleSecondaries()" << G4endl;
227      G4cout << "Unable to allocate the EffectiveCharge data" << G4endl;
228      G4Exception();
229    }
230
231  // eps is the fraction of the photon energy assigned to e- (including rest mass)
232  G4double eps = 0;
233  G4double eki = electron_mass_c2/photonEnergy;
234
235  //Do it fast for photon energy < 1.1 MeV (close to threshold)
236  if (photonEnergy < fSmallEnergy)
237    eps = eki + (1.0-2.0*eki)*G4UniformRand();
238  else
239    {
240      //Complete calculation
241      G4double effC = fEffectiveCharge->find(mat)->second;
242      G4double alz = effC*fine_structure_const;
243      G4double T = std::sqrt(2.0*eki);
244      G4double F00=(-1.774-1.210e1*alz+1.118e1*alz*alz)*T
245         +(8.523+7.326e1*alz-4.441e1*alz*alz)*T*T
246         -(1.352e1+1.211e2*alz-9.641e1*alz*alz)*T*T*T
247        +(8.946+6.205e1*alz-6.341e1*alz*alz)*T*T*T*T;
248     
249      G4double F0b = fScreeningFunction->find(mat)->second.second;
250      G4double g0 = F0b + F00;
251      G4double invRad = fMaterialInvScreeningRadius->find(mat)->second;
252      G4double bmin = 4.0*eki/invRad;
253      std::pair<G4double,G4double> scree =  GetScreeningFunctions(bmin);
254      G4double g1 = scree.first;
255      G4double g2 = scree.second;
256      G4double g1min = g1+g0;
257      G4double g2min = g2+g0;
258      G4double xr = 0.5-eki;
259      G4double a1 = 2.*g1min*xr*xr/3.;     
260      G4double p1 = a1/(a1+g2min);
261
262      G4bool loopAgain = false;
263      //Random sampling of eps
264      do{
265        loopAgain = false;
266        if (G4UniformRand() <= p1)
267          {
268            G4double  ru2m1 = 2.0*G4UniformRand()-1.0;
269            if (ru2m1 < 0)
270              eps = 0.5-xr*std::pow(std::abs(ru2m1),1./3.);
271            else
272              eps = 0.5+xr*std::pow(ru2m1,1./3.);
273            G4double B = eki/(invRad*eps*(1.0-eps));
274            scree =  GetScreeningFunctions(B);
275            g1 = scree.first;
276            g1 = std::max(g1+g0,0.);
277            if (G4UniformRand()*g1min > g1) 
278              loopAgain = true;
279          }
280        else
281          {
282            eps = eki+2.0*xr*G4UniformRand();
283            G4double B = eki/(invRad*eps*(1.0-eps));
284            scree =  GetScreeningFunctions(B);
285            g2 = scree.second;
286            g2 = std::max(g2+g0,0.);
287            if (G4UniformRand()*g2min > g2)
288              loopAgain = true;
289          }     
290      }while(loopAgain);
291     
292    }
293  if (verboseLevel > 4)
294    G4cout << "Sampled eps = " << eps << G4endl;
295
296  G4double electronTotEnergy = eps*photonEnergy;
297  G4double positronTotEnergy = (1.0-eps)*photonEnergy;
298 
299  // Scattered electron (positron) angles. ( Z - axis along the parent photon)
300
301  //electron kinematics
302  G4double electronKineEnergy = std::max(0.,electronTotEnergy - electron_mass_c2) ; 
303  G4double costheta_el = G4UniformRand()*2.0-1.0;
304  G4double kk = std::sqrt(electronKineEnergy*(electronKineEnergy+2.*electron_mass_c2));
305  costheta_el = (costheta_el*electronTotEnergy+kk)/(electronTotEnergy+costheta_el*kk);
306  G4double phi_el  = twopi * G4UniformRand() ;
307  G4double dirX_el = std::sqrt(1.-costheta_el*costheta_el) * std::cos(phi_el);
308  G4double dirY_el = std::sqrt(1.-costheta_el*costheta_el) * std::sin(phi_el);
309  G4double dirZ_el = costheta_el;
310
311  //positron kinematics
312  G4double positronKineEnergy = std::max(0.,positronTotEnergy - electron_mass_c2) ;
313  G4double costheta_po = G4UniformRand()*2.0-1.0;
314  kk = std::sqrt(positronKineEnergy*(positronKineEnergy+2.*electron_mass_c2));
315  costheta_po = (costheta_po*positronTotEnergy+kk)/(positronTotEnergy+costheta_po*kk);
316  G4double phi_po  = twopi * G4UniformRand() ;
317  G4double dirX_po = std::sqrt(1.-costheta_po*costheta_po) * std::cos(phi_po);
318  G4double dirY_po = std::sqrt(1.-costheta_po*costheta_po) * std::sin(phi_po);
319  G4double dirZ_po = costheta_po;
320
321  // Kinematics of the created pair:
322  // the electron and positron are assumed to have a symetric angular
323  // distribution with respect to the Z axis along the parent photon
324  G4double localEnergyDeposit = 0. ;
325 
326  if (electronKineEnergy > 0.0)
327    {
328      G4ThreeVector electronDirection ( dirX_el, dirY_el, dirZ_el);
329      electronDirection.rotateUz(photonDirection);
330      G4DynamicParticle* electron = new G4DynamicParticle (G4Electron::Electron(),
331                                                           electronDirection,
332                                                           electronKineEnergy);
333      fvect->push_back(electron);
334    }
335  else
336    {
337      localEnergyDeposit += electronKineEnergy;
338      electronKineEnergy = 0;
339    }
340
341  //Generate the positron. Real particle in any case, because it will annihilate. If below
342  //threshold, produce it at rest
343  if (positronKineEnergy < 0.0)
344    {
345      localEnergyDeposit += positronKineEnergy;
346      positronKineEnergy = 0; //produce it at rest
347    }
348  G4ThreeVector positronDirection(dirX_po,dirY_po,dirZ_po);
349  positronDirection.rotateUz(photonDirection);
350  G4DynamicParticle* positron = new G4DynamicParticle(G4Positron::Positron(),
351                                                      positronDirection, positronKineEnergy);
352  fvect->push_back(positron);
353
354  //Add rest of energy to the local energy deposit
355  fParticleChange->ProposeLocalEnergyDeposit(localEnergyDeposit);
356 
357  if (verboseLevel > 1)
358    {
359      G4cout << "-----------------------------------------------------------" << G4endl;
360      G4cout << "Energy balance from G4Penelope08GammaConversion" << G4endl;
361      G4cout << "Incoming photon energy: " << photonEnergy/keV << " keV" << G4endl;
362      G4cout << "-----------------------------------------------------------" << G4endl;
363      if (electronKineEnergy)
364        G4cout << "Electron (explicitely produced) " << electronKineEnergy/keV << " keV" 
365               << G4endl;
366      if (positronKineEnergy)
367        G4cout << "Positron (not at rest) " << positronKineEnergy/keV << " keV" << G4endl;
368      G4cout << "Rest masses of e+/- " << 2.0*electron_mass_c2/keV << " keV" << G4endl;
369      if (localEnergyDeposit)
370        G4cout << "Local energy deposit " << localEnergyDeposit/keV << " keV" << G4endl;
371      G4cout << "Total final state: " << (electronKineEnergy+positronKineEnergy+
372                                          localEnergyDeposit+2.0*electron_mass_c2)/keV <<
373        " keV" << G4endl;
374      G4cout << "-----------------------------------------------------------" << G4endl;
375    }
376 if (verboseLevel > 0)
377    {
378      G4double energyDiff = std::fabs(electronKineEnergy+positronKineEnergy+
379                                      localEnergyDeposit+2.0*electron_mass_c2-photonEnergy);
380      if (energyDiff > 0.05*keV)
381        G4cout << "Warning from G4Penelope08GammaConversion: problem with energy conservation: " 
382               << (electronKineEnergy+positronKineEnergy+
383                   localEnergyDeposit+2.0*electron_mass_c2)/keV
384               << " keV (final) vs. " << photonEnergy/keV << " keV (initial)" << G4endl;
385    } 
386}
387
388//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
389
390void G4Penelope08GammaConversionModel::ReadDataFile(const G4int Z)
391{
392 if (verboseLevel > 2)
393    {
394      G4cout << "G4Penelope08GammaConversionModel::ReadDataFile()" << G4endl;
395      G4cout << "Going to read Gamma Conversion data files for Z=" << Z << G4endl;
396    }
397 
398  char* path = getenv("G4LEDATA");
399  if (!path)
400    {
401      G4String excep = 
402        "G4Penelope08GammaConversionModel - G4LEDATA environment variable not set!";
403      G4Exception(excep);
404    }
405 
406  /*
407    Read the cross section file
408  */
409  std::ostringstream ost;
410  if (Z>9)
411    ost << path << "/penelope/pairproduction/pdgpp" << Z << ".p08";
412  else
413    ost << path << "/penelope/pairproduction/pdgpp0" << Z << ".p08";
414  std::ifstream file(ost.str().c_str());
415  if (!file.is_open())
416    {
417      G4String excep = "G4Penelope08GammaConversionModel - data file " + 
418        G4String(ost.str()) + " not found!";
419      G4Exception(excep);
420    }
421
422  //I have to know in advance how many points are in the data list
423  //to initialize the G4PhysicsFreeVector()
424  size_t ndata=0;
425  G4String line;
426  while( getline(file, line) )
427    ndata++;
428  ndata -= 1; //remove one header line
429  //G4cout << "Found: " << ndata << " lines" << G4endl;
430
431  file.clear();
432  file.close();
433  file.open(ost.str().c_str());
434  G4int readZ =0;
435  file >> readZ; 
436
437  if (verboseLevel > 3)
438    G4cout << "Element Z=" << Z << G4endl;
439
440  //check the right file is opened.
441  if (readZ != Z)
442    {
443      G4cout << "G4Penelope08GammaConversionModel::ReadDataFile()" << G4endl;
444      G4cout << "Corrupted data file for Z=" << Z << G4endl;
445      G4Exception();
446    }
447
448  G4PhysicsFreeVector* theVec = new G4PhysicsFreeVector(ndata);
449  G4double ene=0,xs=0;
450  for (size_t i=0;i<ndata;i++)
451    {
452      file >> ene >> xs;
453      //dimensional quantities
454      ene *= eV;
455      xs *= barn;
456      if (xs < 1e-40*cm2) //protection against log(0)
457        xs = 1e-40*cm2;
458      theVec->PutValue(i,std::log(ene),std::log(xs));     
459    }
460  file.close();
461
462  if (!logAtomicCrossSection)
463    {
464      G4cout << "G4Penelope08RayleighModel::ReadDataFile()" << G4endl;
465      G4cout << "Problem with allocation of logAtomicCrossSection data table " << G4endl;
466      G4Exception();
467    }
468  logAtomicCrossSection->insert(std::make_pair(Z,theVec));
469
470  return;
471
472}
473
474//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
475
476void G4Penelope08GammaConversionModel::InitializeScreeningRadii()
477{
478  G4double temp[99] = {1.2281e+02,7.3167e+01,6.9228e+01,6.7301e+01,6.4696e+01,
479                       6.1228e+01,5.7524e+01,5.4033e+01,5.0787e+01,4.7851e+01,4.6373e+01,
480                       4.5401e+01,4.4503e+01,4.3815e+01,4.3074e+01,4.2321e+01,4.1586e+01,
481                       4.0953e+01,4.0524e+01,4.0256e+01,3.9756e+01,3.9144e+01,3.8462e+01,
482                       3.7778e+01,3.7174e+01,3.6663e+01,3.5986e+01,3.5317e+01,3.4688e+01,
483                       3.4197e+01,3.3786e+01,3.3422e+01,3.3068e+01,3.2740e+01,3.2438e+01,
484                       3.2143e+01,3.1884e+01,3.1622e+01,3.1438e+01,3.1142e+01,3.0950e+01,
485                       3.0758e+01,3.0561e+01,3.0285e+01,3.0097e+01,2.9832e+01,2.9581e+01,
486                       2.9411e+01,2.9247e+01,2.9085e+01,2.8930e+01,2.8721e+01,2.8580e+01,
487                       2.8442e+01,2.8312e+01,2.8139e+01,2.7973e+01,2.7819e+01,2.7675e+01,
488                       2.7496e+01,2.7285e+01,2.7093e+01,2.6911e+01,2.6705e+01,2.6516e+01,
489                       2.6304e+01,2.6108e+01,2.5929e+01,2.5730e+01,2.5577e+01,2.5403e+01,
490                       2.5245e+01,2.5100e+01,2.4941e+01,2.4790e+01,2.4655e+01,2.4506e+01,
491                       2.4391e+01,2.4262e+01,2.4145e+01,2.4039e+01,2.3922e+01,2.3813e+01,
492                       2.3712e+01,2.3621e+01,2.3523e+01,2.3430e+01,2.3331e+01,2.3238e+01,
493                       2.3139e+01,2.3048e+01,2.2967e+01,2.2833e+01,2.2694e+01,2.2624e+01,
494                       2.2545e+01,2.2446e+01,2.2358e+01,2.2264e+01};
495
496  //copy temporary vector in class data member
497  for (G4int i=0;i<99;i++)
498    fAtomicScreeningRadius[i] = temp[i];
499}
500
501//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
502
503void G4Penelope08GammaConversionModel::InitializeScreeningFunctions(const G4Material* material)
504{
505  // This is subroutine GPPa0 of Penelope
506  //
507  // 1) calculate the effective Z for the purpose
508  //
509  G4double zeff = 0;
510  G4int intZ = 0;
511  G4int nElements = material->GetNumberOfElements();
512  const G4ElementVector* elementVector = material->GetElementVector();
513
514  //avoid calculations if only one building element!
515  if (nElements == 1)
516    {
517      zeff = (*elementVector)[0]->GetZ();
518      intZ = (G4int) zeff;
519    }
520  else // many elements...let's do the calculation
521    {
522      const G4double* fractionVector = material->GetVecNbOfAtomsPerVolume();
523     
524      G4double atot = 0;
525      for (G4int i=0;i<nElements;i++)
526        {
527          G4double Zelement = (*elementVector)[i]->GetZ();
528          G4double Aelement = (*elementVector)[i]->GetA();
529          atot += Aelement*fractionVector[i];
530          zeff += Zelement*Aelement*fractionVector[i]; //average with the number of nuclei
531        }
532      atot /= material->GetTotNbOfAtomsPerVolume();
533      zeff /= (material->GetTotNbOfAtomsPerVolume()*atot);
534     
535      intZ = (G4int) (zeff+0.25);
536      if (intZ <= 0)
537        intZ = 1;
538      if (intZ > 99)
539        intZ = 99;
540    }
541
542  if (fEffectiveCharge)
543    fEffectiveCharge->insert(std::make_pair(material,zeff));
544
545  //
546  // 2) Calculate Coulomb Correction
547  //
548  G4double alz = fine_structure_const*zeff;
549  G4double alzSquared = alz*alz;
550  G4double fc =  alzSquared*(0.202059-alzSquared*
551                             (0.03693-alzSquared*
552                              (0.00835-alzSquared*(0.00201-alzSquared*
553                                                   (0.00049-alzSquared*
554                                                    (0.00012-alzSquared*0.00003)))))
555                             +1.0/(alzSquared+1.0));
556  //
557  // 3) Screening functions and low-energy corrections
558  //
559  G4double matRadius = 2.0/ fAtomicScreeningRadius[intZ-1];
560  if (fMaterialInvScreeningRadius)
561    fMaterialInvScreeningRadius->insert(std::make_pair(material,matRadius));
562
563  std::pair<G4double,G4double> myPair(0,0);
564  G4double f0a = 4.0*std::log(fAtomicScreeningRadius[intZ-1]);
565  G4double f0b = f0a - 4.0*fc;
566  myPair.first = f0a;
567  myPair.second = f0b;
568
569  if (fScreeningFunction)
570    fScreeningFunction->insert(std::make_pair(material,myPair));
571
572  if (verboseLevel > 2)
573    {
574      G4cout << "Average Z for material " << material->GetName() << " = " << 
575        zeff << G4endl;
576      G4cout << "Effective radius for material " << material->GetName() << " = " << 
577        fAtomicScreeningRadius[intZ-1] << " m_e*c/hbar --> BCB = " << 
578        matRadius << G4endl;
579      G4cout << "Screening parameters F0 for material " << material->GetName() << " = " << 
580        f0a << "," << f0b << G4endl;
581    }
582  return;
583}
584
585//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
586
587std::pair<G4double,G4double> 
588G4Penelope08GammaConversionModel::GetScreeningFunctions(G4double B)
589{
590  // This is subroutine SCHIFF of Penelope
591  //
592  // Screening Functions F1(B) and F2(B) in the Bethe-Heitler differential cross
593  // section for pair production
594  //
595  std::pair<G4double,G4double> result(0.,0.);
596  G4double BSquared = B*B;
597  G4double f1 = 2.0-2.0*std::log(1.0+BSquared);
598  G4double f2 = f1 - 6.66666666e-1; // (-2/3)
599  if (B < 1.0e-10)
600    f1 = f1-twopi*B;
601  else
602    {
603      G4double a0 = 4.0*B*std::atan(1./B);
604      f1 = f1 - a0;
605      f2 += 2.0*BSquared*(4.0-a0-3.0*std::log((1.0+BSquared)/BSquared));
606    }
607  G4double g1 = 0.5*(3.0*f1-f2);
608  G4double g2 = 0.25*(3.0*f1+f2);
609
610  result.first = g1;
611  result.second = g2;
612
613  return result;
614}
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