source: trunk/source/processes/electromagnetic/highenergy/src/G4GammaConversionToMuons.cc @ 1315

Last change on this file since 1315 was 1228, checked in by garnier, 14 years ago

update geant4.9.3 tag
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27// $Id: G4GammaConversionToMuons.cc,v 1.7 2008/10/16 14:29:48 vnivanch Exp $
28// GEANT4 tag $Name: geant4-09-03 $
29//
30//         ------------ G4GammaConversionToMuons physics process ------
31//         by H.Burkhardt, S. Kelner and R. Kokoulin, April 2002
32//
33//
34// 07-08-02: missprint in OR condition in DoIt : f1<0 || f1>f1_max ..etc ...
35// 25-10-04: migrade to new interfaces of ParticleChange (vi)
36// ---------------------------------------------------------------------------
37
38#include "G4GammaConversionToMuons.hh"
39#include "G4EnergyLossTables.hh"
40#include "G4UnitsTable.hh"
41#include "G4MuonPlus.hh"
42#include "G4MuonMinus.hh"
43
44//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
45
46using namespace std;
47
48G4GammaConversionToMuons::G4GammaConversionToMuons(const G4String& processName,
49    G4ProcessType type):G4VDiscreteProcess (processName, type),
50    LowestEnergyLimit (4*G4MuonPlus::MuonPlus()->GetPDGMass()), // 4*Mmuon
51    HighestEnergyLimit(1e21*eV), // ok to 1e21eV=1e12GeV, then LPM suppression
52    CrossSecFactor(1.)
53{ 
54  SetProcessSubType(15);
55}
56
57//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
58
59// destructor
60
61G4GammaConversionToMuons::~G4GammaConversionToMuons() // (empty) destructor
62{ }
63
64//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
65
66G4bool G4GammaConversionToMuons::IsApplicable(
67                                        const G4ParticleDefinition& particle)
68{
69   return ( &particle == G4Gamma::Gamma() );
70}
71
72//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
73
74void G4GammaConversionToMuons::BuildPhysicsTable(const G4ParticleDefinition&)
75// Build cross section and mean free path tables
76{  //here no tables, just calling PrintInfoDefinition
77   PrintInfoDefinition();
78}
79
80//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
81
82G4double G4GammaConversionToMuons::GetMeanFreePath(const G4Track& aTrack,
83                                              G4double, G4ForceCondition*)
84
85// returns the photon mean free path in GEANT4 internal units
86// (MeanFreePath is a private member of the class)
87
88{
89   const G4DynamicParticle* aDynamicGamma = aTrack.GetDynamicParticle();
90   G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
91   G4Material* aMaterial = aTrack.GetMaterial();
92
93   if (GammaEnergy <  LowestEnergyLimit)
94     MeanFreePath = DBL_MAX;
95   else
96     MeanFreePath = ComputeMeanFreePath(GammaEnergy,aMaterial);
97
98   return MeanFreePath;
99}
100
101//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
102
103G4double G4GammaConversionToMuons::ComputeMeanFreePath(G4double GammaEnergy,
104                                                       G4Material* aMaterial)
105
106// computes and returns the photon mean free path in GEANT4 internal units
107{
108  const G4ElementVector* theElementVector = aMaterial->GetElementVector();
109  const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
110
111  G4double SIGMA = 0 ;
112
113  for ( size_t i=0 ; i < aMaterial->GetNumberOfElements() ; i++ )
114  {
115    G4double AtomicZ = (*theElementVector)[i]->GetZ();
116    G4double AtomicA = (*theElementVector)[i]->GetA()/(g/mole);
117    SIGMA += NbOfAtomsPerVolume[i] *
118      ComputeCrossSectionPerAtom(GammaEnergy,AtomicZ,AtomicA);
119  }
120  return SIGMA > DBL_MIN ? 1./SIGMA : DBL_MAX;
121}
122
123//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
124
125G4double G4GammaConversionToMuons::GetCrossSectionPerAtom(
126                                   const G4DynamicParticle* aDynamicGamma,
127                                         G4Element*         anElement)
128
129// gives the total cross section per atom in GEANT4 internal units
130{
131   G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
132   G4double AtomicZ = anElement->GetZ();
133   G4double AtomicA = anElement->GetA()/(g/mole);
134   G4double crossSection =
135        ComputeCrossSectionPerAtom(GammaEnergy,AtomicZ,AtomicA);
136   return crossSection;
137}
138
139//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
140
141G4double G4GammaConversionToMuons::ComputeCrossSectionPerAtom(
142                         G4double Egam, G4double Z, G4double A)
143                         
144// Calculates the microscopic cross section in GEANT4 internal units.
145// Total cross section parametrisation from H.Burkhardt
146// It gives a good description at any energy (from 0 to 10**21 eV)
147{ static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
148  static const G4double Mele=electron_mass_c2;
149  static const G4double Rc=elm_coupling/Mmuon; // classical particle radius
150  static const G4double sqrte=sqrt(exp(1.));
151  static const G4double PowSat=-0.88;
152
153  static G4double CrossSection = 0.0 ;
154
155  if ( A < 1. ) return 0;
156  if ( Egam < 4*Mmuon ) return 0 ; // below threshold return 0
157
158  static G4double EgamLast=0,Zlast=0,PowThres,Ecor,B,Dn,Zthird,Winfty,WMedAppr,
159      Wsatur,sigfac;
160 
161  if(Zlast==Z && Egam==EgamLast) return CrossSection; // already calculated
162  EgamLast=Egam;
163 
164  if(Zlast!=Z) // new element
165  { Zlast=Z;
166    if(Z==1) // special case of Hydrogen
167    { B=202.4;
168      Dn=1.49;
169    }
170    else
171    { B=183.;
172      Dn=1.54*pow(A,0.27);
173    }
174    Zthird=pow(Z,-1./3.); // Z**(-1/3)
175    Winfty=B*Zthird*Mmuon/(Dn*Mele);
176    WMedAppr=1./(4.*Dn*sqrte*Mmuon);
177    Wsatur=Winfty/WMedAppr;
178    sigfac=4.*fine_structure_const*Z*Z*Rc*Rc;
179    PowThres=1.479+0.00799*Dn;
180    Ecor=-18.+4347./(B*Zthird);
181  }
182  G4double CorFuc=1.+.04*log(1.+Ecor/Egam);
183  G4double Eg=pow(1.-4.*Mmuon/Egam,PowThres)*pow( pow(Wsatur,PowSat)+
184              pow(Egam,PowSat),1./PowSat); // threshold and saturation
185  CrossSection=7./9.*sigfac*log(1.+WMedAppr*CorFuc*Eg);
186  CrossSection*=CrossSecFactor; // increase the CrossSection by  (by default 1)
187  return CrossSection;
188}
189
190//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
191
192void G4GammaConversionToMuons::SetCrossSecFactor(G4double fac)
193// Set the factor to artificially increase the cross section
194{ CrossSecFactor=fac;
195  G4cout << "The cross section for GammaConversionToMuons is artificially "
196         << "increased by the CrossSecFactor=" << CrossSecFactor << G4endl;
197}
198
199//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
200
201G4VParticleChange* G4GammaConversionToMuons::PostStepDoIt(
202                                                        const G4Track& aTrack,
203                                                        const G4Step&  aStep)
204//
205// generation of gamma->mu+mu-
206//
207{
208  aParticleChange.Initialize(aTrack);
209  G4Material* aMaterial = aTrack.GetMaterial();
210
211  static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
212  static const G4double Mele=electron_mass_c2;
213  static const G4double sqrte=sqrt(exp(1.));
214
215  // current Gamma energy and direction, return if energy too low
216  const G4DynamicParticle *aDynamicGamma = aTrack.GetDynamicParticle();
217  G4double Egam = aDynamicGamma->GetKineticEnergy();
218  if (Egam < 4*Mmuon) return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
219  G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection();
220
221  // select randomly one element constituting the material
222  const G4Element& anElement = *SelectRandomAtom(aDynamicGamma, aMaterial);
223  G4double Z = anElement.GetZ();
224  G4double A = anElement.GetA()/(g/mole);
225
226  static G4double Zlast=0,B,Dn,Zthird,Winfty,A027,C1Num2,C2Term2;
227  if(Zlast!=Z) // the element has changed
228  { Zlast=Z;
229    if(Z==1) // special case of Hydrogen
230    { B=202.4;
231      Dn=1.49;
232    }
233    else
234    { B=183.;
235      Dn=1.54*pow(A,0.27);
236    }
237    Zthird=pow(Z,-1./3.); // Z**(-1/3)
238    Winfty=B*Zthird*Mmuon/(Dn*Mele);
239    A027=pow(A,0.27);
240    G4double C1Num=0.35*A027;
241    C1Num2=C1Num*C1Num;
242    C2Term2=Mele/(183.*Zthird*Mmuon);
243  }
244
245  G4double GammaMuonInv=Mmuon/Egam;
246  G4double sqrtx=sqrt(.25-GammaMuonInv);
247  G4double xmax=.5+sqrtx;
248  G4double xmin=.5-sqrtx;
249
250  // generate xPlus according to the differential cross section by rejection
251  G4double Ds2=(Dn*sqrte-2.);
252  G4double sBZ=sqrte*B*Zthird/Mele;
253  G4double LogWmaxInv=1./log(Winfty*(1.+2.*Ds2*GammaMuonInv)
254                             /(1.+2.*sBZ*Mmuon*GammaMuonInv));
255  G4double xPlus,xMinus,xPM,result,W;
256  do
257  { xPlus=xmin+G4UniformRand()*(xmax-xmin);
258    xMinus=1.-xPlus;
259    xPM=xPlus*xMinus;
260    G4double del=Mmuon*Mmuon/(2.*Egam*xPM);
261    W=Winfty*(1.+Ds2*del/Mmuon)/(1.+sBZ*del);
262    if(W<1.) W=1.; // to avoid negative cross section at xmin
263    G4double xxp=1.-4./3.*xPM; // the main xPlus dependence
264    result=xxp*log(W)*LogWmaxInv;
265    if(result>1.) {
266      G4cout << "G4GammaConversionToMuons::PostStepDoIt WARNING:"
267             << " in dSigxPlusGen, result=" << result << " > 1" << G4endl;
268    }
269  }
270  while (G4UniformRand() > result);
271
272  // now generate the angular variables via the auxilary variables t,psi,rho
273  G4double t;
274  G4double psi;
275  G4double rho;
276
277  G4double thetaPlus,thetaMinus,phiHalf; // final angular variables
278
279  do      // t, psi, rho generation start  (while angle < pi)
280  {
281    //generate t by the rejection method
282    G4double C1=C1Num2* GammaMuonInv/xPM;
283    G4double f1_max=(1.-xPM) / (1.+C1);
284    G4double f1; // the probability density
285    do
286    { t=G4UniformRand();
287      f1=(1.-2.*xPM+4.*xPM*t*(1.-t)) / (1.+C1/(t*t));
288      if(f1<0 || f1> f1_max) // should never happend
289        {
290          G4cout << "G4GammaConversionToMuons::PostStepDoIt WARNING:"
291                 << "outside allowed range f1=" << f1 << " is set to zero"
292                 << G4endl;
293          f1 = 0.0;
294        }
295    }
296    while ( G4UniformRand()*f1_max > f1);
297    // generate psi by the rejection method
298    G4double f2_max=1.-2.*xPM*(1.-4.*t*(1.-t));
299
300    // long version
301    G4double f2;
302    do
303    { psi=2.*pi*G4UniformRand();
304      f2=1.-2.*xPM+4.*xPM*t*(1.-t)*(1.+cos(2.*psi));
305      if(f2<0 || f2> f2_max) // should never happend
306        {
307          G4cout << "G4GammaConversionToMuons::PostStepDoIt WARNING:"
308                 << "outside allowed range f2=" << f2 << " is set to zero"
309                 << G4endl;
310          f2 = 0.0;
311        }
312    }
313    while ( G4UniformRand()*f2_max > f2);
314
315    // generate rho by direct transformation
316    G4double C2Term1=GammaMuonInv/(2.*xPM*t);
317    G4double C2=4./sqrt(xPM)*pow(C2Term1*C2Term1+C2Term2*C2Term2,2.);
318    G4double rhomax=1.9/A027*(1./t-1.);
319    G4double beta=log( (C2+pow(rhomax,4.))/C2 );
320    rho=pow(C2 *( exp(beta*G4UniformRand())-1. ) ,0.25);
321
322    //now get from t and psi the kinematical variables
323    G4double u=sqrt(1./t-1.);
324    G4double xiHalf=0.5*rho*cos(psi);
325    phiHalf=0.5*rho/u*sin(psi);
326
327    thetaPlus =GammaMuonInv*(u+xiHalf)/xPlus;
328    thetaMinus=GammaMuonInv*(u-xiHalf)/xMinus;
329
330  } while ( std::abs(thetaPlus)>pi || std::abs(thetaMinus) >pi);
331
332  // now construct the vectors
333  // azimuthal symmetry, take phi0 at random between 0 and 2 pi
334  G4double phi0=2.*pi*G4UniformRand(); 
335  G4double EPlus=xPlus*Egam;
336  G4double EMinus=xMinus*Egam;
337
338  // mu+ mu- directions for gamma in z-direction
339  G4ThreeVector MuPlusDirection  ( sin(thetaPlus) *cos(phi0+phiHalf),
340                   sin(thetaPlus)  *sin(phi0+phiHalf), cos(thetaPlus) );
341  G4ThreeVector MuMinusDirection (-sin(thetaMinus)*cos(phi0-phiHalf),
342                  -sin(thetaMinus) *sin(phi0-phiHalf), cos(thetaMinus) );
343  // rotate to actual gamma direction
344  MuPlusDirection.rotateUz(GammaDirection);
345  MuMinusDirection.rotateUz(GammaDirection);
346  aParticleChange.SetNumberOfSecondaries(2);
347  // create G4DynamicParticle object for the particle1
348  G4DynamicParticle* aParticle1= new G4DynamicParticle(
349                           G4MuonPlus::MuonPlus(),MuPlusDirection,EPlus-Mmuon);
350  aParticleChange.AddSecondary(aParticle1);
351  // create G4DynamicParticle object for the particle2
352  G4DynamicParticle* aParticle2= new G4DynamicParticle(
353                       G4MuonMinus::MuonMinus(),MuMinusDirection,EMinus-Mmuon);
354  aParticleChange.AddSecondary(aParticle2);
355  //
356  // Kill the incident photon
357  //
358  aParticleChange.ProposeMomentumDirection( 0., 0., 0. ) ;
359  aParticleChange.ProposeEnergy( 0. ) ;
360  aParticleChange.ProposeTrackStatus( fStopAndKill ) ;
361  //  Reset NbOfInteractionLengthLeft and return aParticleChange
362  return G4VDiscreteProcess::PostStepDoIt( aTrack, aStep );
363}
364
365//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
366
367G4Element* G4GammaConversionToMuons::SelectRandomAtom(
368                                        const G4DynamicParticle* aDynamicGamma,
369                                              G4Material* aMaterial)
370{
371  // select randomly 1 element within the material, invoked by PostStepDoIt
372
373  const G4int NumberOfElements            = aMaterial->GetNumberOfElements();
374  const G4ElementVector* theElementVector = aMaterial->GetElementVector();
375  if (NumberOfElements == 1) return (*theElementVector)[0];
376
377  const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
378
379  G4double PartialSumSigma = 0. ;
380  G4double rval = G4UniformRand()/MeanFreePath;
381
382
383  for ( G4int i=0 ; i < NumberOfElements ; i++ )
384      { PartialSumSigma += NbOfAtomsPerVolume[i] *
385                 GetCrossSectionPerAtom(aDynamicGamma, (*theElementVector)[i]);
386        if (rval <= PartialSumSigma) return ((*theElementVector)[i]);
387      }
388  G4cout << " WARNING !!! - The Material '"<< aMaterial->GetName()
389       << "' has no elements, NULL pointer returned." << G4endl;
390  return NULL;
391}
392
393//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
394
395void G4GammaConversionToMuons::PrintInfoDefinition()
396{
397  G4String comments ="gamma->mu+mu- Bethe Heitler process, SubType= ";
398  G4cout << G4endl << GetProcessName() << ":  " << comments
399         << GetProcessSubType() << G4endl;
400  G4cout << "        good cross section parametrization from "
401         << G4BestUnit(LowestEnergyLimit,"Energy")
402         << " to " << HighestEnergyLimit/GeV << " GeV for all Z." << G4endl;
403}
404
405//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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