source: trunk/source/processes/electromagnetic/highenergy/src/G4GammaConversionToMuons.cc @ 836

Last change on this file since 836 was 819, checked in by garnier, 16 years ago

import all except CVS
File size: 14.9 KB
Line 
1//
2// ********************************************************************
3// * License and Disclaimer                                           *
4// *                                                                  *
5// * The  Geant4 software  is  copyright of the Copyright Holders  of *
6// * the Geant4 Collaboration.  It is provided  under  the terms  and *
7// * conditions of the Geant4 Software License,  included in the file *
8// * LICENSE and available at  http://cern.ch/geant4/license .  These *
9// * include a list of copyright holders.                             *
10// *                                                                  *
11// * Neither the authors of this software system, nor their employing *
12// * institutes,nor the agencies providing financial support for this *
13// * work  make  any representation or  warranty, express or implied, *
14// * regarding  this  software system or assume any liability for its *
15// * use.  Please see the license in the file  LICENSE  and URL above *
16// * for the full disclaimer and the limitation of liability.         *
17// *                                                                  *
18// * This  code  implementation is the result of  the  scientific and *
19// * technical work of the GEANT4 collaboration.                      *
20// * By using,  copying,  modifying or  distributing the software (or *
21// * any work based  on the software)  you  agree  to acknowledge its *
22// * use  in  resulting  scientific  publications,  and indicate your *
23// * acceptance of all terms of the Geant4 Software license.          *
24// ********************************************************************
25//
26//
27// $Id: G4GammaConversionToMuons.cc,v 1.4 2006/06/29 19:32:40 gunter Exp $
28// GEANT4 tag $Name: geant4-09-01-patch-02 $
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
55//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
56
57// destructor
58
59G4GammaConversionToMuons::~G4GammaConversionToMuons() // (empty) destructor
60{ }
61
62//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
63
64G4bool G4GammaConversionToMuons::IsApplicable(
65                                        const G4ParticleDefinition& particle)
66{
67   return ( &particle == G4Gamma::Gamma() );
68}
69
70//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
71
72void G4GammaConversionToMuons::BuildPhysicsTable(const G4ParticleDefinition&)
73// Build cross section and mean free path tables
74{  //here no tables, just calling PrintInfoDefinition
75   PrintInfoDefinition();
76}
77
78//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
79
80G4double G4GammaConversionToMuons::GetMeanFreePath(const G4Track& aTrack,
81                                              G4double, G4ForceCondition*)
82
83// returns the photon mean free path in GEANT4 internal units
84// (MeanFreePath is a private member of the class)
85
86{
87   const G4DynamicParticle* aDynamicGamma = aTrack.GetDynamicParticle();
88   G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
89   G4Material* aMaterial = aTrack.GetMaterial();
90
91   if (GammaEnergy <  LowestEnergyLimit)
92     MeanFreePath = DBL_MAX;
93   else
94     MeanFreePath = ComputeMeanFreePath(GammaEnergy,aMaterial);
95
96   return MeanFreePath;
97}
98
99//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
100
101G4double G4GammaConversionToMuons::ComputeMeanFreePath(G4double GammaEnergy,
102                                                       G4Material* aMaterial)
103
104// computes and returns the photon mean free path in GEANT4 internal units
105{
106  const G4ElementVector* theElementVector = aMaterial->GetElementVector();
107  const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
108
109  G4double SIGMA = 0 ;
110
111  for ( size_t i=0 ; i < aMaterial->GetNumberOfElements() ; i++ )
112  {
113    G4double AtomicZ = (*theElementVector)[i]->GetZ();
114    G4double AtomicA = (*theElementVector)[i]->GetA()/(g/mole);
115    SIGMA += NbOfAtomsPerVolume[i] *
116      ComputeCrossSectionPerAtom(GammaEnergy,AtomicZ,AtomicA);
117  }
118  return SIGMA > DBL_MIN ? 1./SIGMA : DBL_MAX;
119}
120
121//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
122
123G4double G4GammaConversionToMuons::GetCrossSectionPerAtom(
124                                   const G4DynamicParticle* aDynamicGamma,
125                                         G4Element*         anElement)
126
127// gives the total cross section per atom in GEANT4 internal units
128{
129   G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
130   G4double AtomicZ = anElement->GetZ();
131   G4double AtomicA = anElement->GetA()/(g/mole);
132   G4double crossSection =
133        ComputeCrossSectionPerAtom(GammaEnergy,AtomicZ,AtomicA);
134   return crossSection;
135}
136
137//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
138
139G4double G4GammaConversionToMuons::ComputeCrossSectionPerAtom(
140                         G4double Egam, G4double Z, G4double A)
141                         
142// Calculates the microscopic cross section in GEANT4 internal units.
143// Total cross section parametrisation from H.Burkhardt
144// It gives a good description at any energy (from 0 to 10**21 eV)
145{ static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
146  static const G4double Mele=electron_mass_c2;
147  static const G4double Rc=elm_coupling/Mmuon; // classical particle radius
148  static const G4double sqrte=sqrt(exp(1.));
149  static const G4double PowSat=-0.88;
150
151  static G4double CrossSection = 0.0 ;
152
153  if ( A < 1. ) return 0;
154  if ( Egam < 4*Mmuon ) return 0 ; // below threshold return 0
155
156  static G4double EgamLast=0,Zlast=0,PowThres,Ecor,B,Dn,Zthird,Winfty,WMedAppr,
157      Wsatur,sigfac;
158 
159  if(Zlast==Z && Egam==EgamLast) return CrossSection; // already calculated
160  EgamLast=Egam;
161 
162  if(Zlast!=Z) // new element
163  { Zlast=Z;
164    if(Z==1) // special case of Hydrogen
165    { B=202.4;
166      Dn=1.49;
167    }
168    else
169    { B=183.;
170      Dn=1.54*pow(A,0.27);
171    }
172    Zthird=pow(Z,-1./3.); // Z**(-1/3)
173    Winfty=B*Zthird*Mmuon/(Dn*Mele);
174    WMedAppr=1./(4.*Dn*sqrte*Mmuon);
175    Wsatur=Winfty/WMedAppr;
176    sigfac=4.*fine_structure_const*Z*Z*Rc*Rc;
177    PowThres=1.479+0.00799*Dn;
178    Ecor=-18.+4347./(B*Zthird);
179  }
180  G4double CorFuc=1.+.04*log(1.+Ecor/Egam);
181  G4double Eg=pow(1.-4.*Mmuon/Egam,PowThres)*pow( pow(Wsatur,PowSat)+
182              pow(Egam,PowSat),1./PowSat); // threshold and saturation
183  CrossSection=7./9.*sigfac*log(1.+WMedAppr*CorFuc*Eg);
184  CrossSection*=CrossSecFactor; // increase the CrossSection by  (by default 1)
185  return CrossSection;
186}
187
188//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
189
190void G4GammaConversionToMuons::SetCrossSecFactor(G4double fac)
191// Set the factor to artificially increase the cross section
192{ CrossSecFactor=fac;
193  G4cout << "The cross section for GammaConversionToMuons is artificially "
194         << "increased by the CrossSecFactor=" << CrossSecFactor << G4endl;
195}
196
197//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
198
199G4VParticleChange* G4GammaConversionToMuons::PostStepDoIt(
200                                                        const G4Track& aTrack,
201                                                        const G4Step&  aStep)
202//
203// generation of gamma->mu+mu-
204//
205{
206  aParticleChange.Initialize(aTrack);
207  G4Material* aMaterial = aTrack.GetMaterial();
208
209  static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
210  static const G4double Mele=electron_mass_c2;
211  static const G4double sqrte=sqrt(exp(1.));
212
213  // current Gamma energy and direction, return if energy too low
214  const G4DynamicParticle *aDynamicGamma = aTrack.GetDynamicParticle();
215  G4double Egam = aDynamicGamma->GetKineticEnergy();
216  if (Egam < 4*Mmuon) return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
217  G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection();
218
219  // select randomly one element constituting the material
220  const G4Element& anElement = *SelectRandomAtom(aDynamicGamma, aMaterial);
221  G4double Z = anElement.GetZ();
222  G4double A = anElement.GetA()/(g/mole);
223
224  static G4double Zlast=0,B,Dn,Zthird,Winfty,A027,C1Num2,C2Term2;
225  if(Zlast!=Z) // the element has changed
226  { Zlast=Z;
227    if(Z==1) // special case of Hydrogen
228    { B=202.4;
229      Dn=1.49;
230    }
231    else
232    { B=183.;
233      Dn=1.54*pow(A,0.27);
234    }
235    Zthird=pow(Z,-1./3.); // Z**(-1/3)
236    Winfty=B*Zthird*Mmuon/(Dn*Mele);
237    A027=pow(A,0.27);
238    G4double C1Num=0.35*A027;
239    C1Num2=C1Num*C1Num;
240    C2Term2=Mele/(183.*Zthird*Mmuon);
241  }
242
243  G4double GammaMuonInv=Mmuon/Egam;
244  G4double sqrtx=sqrt(.25-GammaMuonInv);
245  G4double xmax=.5+sqrtx;
246  G4double xmin=.5-sqrtx;
247
248  // generate xPlus according to the differential cross section by rejection
249  G4double Ds2=(Dn*sqrte-2.);
250  G4double sBZ=sqrte*B*Zthird/Mele;
251  G4double LogWmaxInv=1./log(Winfty*(1.+2.*Ds2*GammaMuonInv)
252                             /(1.+2.*sBZ*Mmuon*GammaMuonInv));
253  G4double xPlus,xMinus,xPM,result,W;
254  do
255  { xPlus=xmin+G4UniformRand()*(xmax-xmin);
256    xMinus=1.-xPlus;
257    xPM=xPlus*xMinus;
258    G4double del=Mmuon*Mmuon/(2.*Egam*xPM);
259    W=Winfty*(1.+Ds2*del/Mmuon)/(1.+sBZ*del);
260    if(W<1.) W=1.; // to avoid negative cross section at xmin
261    G4double xxp=1.-4./3.*xPM; // the main xPlus dependence
262    result=xxp*log(W)*LogWmaxInv;
263    if(result>1.)
264    { G4cout << "error in dSigxPlusGen, result=" << result << " is >1" << '\n';
265      exit(10);
266    }
267  }
268  while (G4UniformRand() > result);
269
270  // now generate the angular variables via the auxilary variables t,psi,rho
271  G4double t;
272  G4double psi;
273  G4double rho;
274
275  G4double thetaPlus,thetaMinus,phiHalf; // final angular variables
276
277  do      // t, psi, rho generation start  (while angle < pi)
278  {
279    //generate t by the rejection method
280    G4double C1=C1Num2* GammaMuonInv/xPM;
281    G4double f1_max=(1.-xPM) / (1.+C1);
282    G4double f1; // the probability density
283    do
284    { t=G4UniformRand();
285      f1=(1.-2.*xPM+4.*xPM*t*(1.-t)) / (1.+C1/(t*t));
286      if(f1<0 || f1> f1_max) // should never happend
287      { G4cout << "outside allowed range f1=" << f1 << G4endl;
288        exit(1);
289      }
290    }
291    while ( G4UniformRand()*f1_max > f1);
292    // generate psi by the rejection method
293    G4double f2_max=1.-2.*xPM*(1.-4.*t*(1.-t));
294
295    // long version
296    G4double f2;
297    do
298    { psi=2.*pi*G4UniformRand();
299      f2=1.-2.*xPM+4.*xPM*t*(1.-t)*(1.+cos(2.*psi));
300      if(f2<0 || f2> f2_max) // should never happend
301      { G4cout << "outside allowed range f2=" << f2 << G4endl;
302        exit(1);
303      }
304    }
305    while ( G4UniformRand()*f2_max > f2);
306
307    // generate rho by direct transformation
308    G4double C2Term1=GammaMuonInv/(2.*xPM*t);
309    G4double C2=4./sqrt(xPM)*pow(C2Term1*C2Term1+C2Term2*C2Term2,2.);
310    G4double rhomax=1.9/A027*(1./t-1.);
311    G4double beta=log( (C2+pow(rhomax,4.))/C2 );
312    rho=pow(C2 *( exp(beta*G4UniformRand())-1. ) ,0.25);
313
314    //now get from t and psi the kinematical variables
315    G4double u=sqrt(1./t-1.);
316    G4double xiHalf=0.5*rho*cos(psi);
317    phiHalf=0.5*rho/u*sin(psi);
318
319    thetaPlus =GammaMuonInv*(u+xiHalf)/xPlus;
320    thetaMinus=GammaMuonInv*(u-xiHalf)/xMinus;
321
322  } while ( std::abs(thetaPlus)>pi || std::abs(thetaMinus) >pi);
323
324  // now construct the vectors
325  // azimuthal symmetry, take phi0 at random between 0 and 2 pi
326  G4double phi0=2.*pi*G4UniformRand(); 
327  G4double EPlus=xPlus*Egam;
328  G4double EMinus=xMinus*Egam;
329
330  // mu+ mu- directions for gamma in z-direction
331  G4ThreeVector MuPlusDirection  ( sin(thetaPlus) *cos(phi0+phiHalf),
332                   sin(thetaPlus)  *sin(phi0+phiHalf), cos(thetaPlus) );
333  G4ThreeVector MuMinusDirection (-sin(thetaMinus)*cos(phi0-phiHalf),
334                  -sin(thetaMinus) *sin(phi0-phiHalf), cos(thetaMinus) );
335  // rotate to actual gamma direction
336  MuPlusDirection.rotateUz(GammaDirection);
337  MuMinusDirection.rotateUz(GammaDirection);
338  aParticleChange.SetNumberOfSecondaries(2);
339  // create G4DynamicParticle object for the particle1
340  G4DynamicParticle* aParticle1= new G4DynamicParticle(
341                           G4MuonPlus::MuonPlus(),MuPlusDirection,EPlus-Mmuon);
342  aParticleChange.AddSecondary(aParticle1);
343  // create G4DynamicParticle object for the particle2
344  G4DynamicParticle* aParticle2= new G4DynamicParticle(
345                       G4MuonMinus::MuonMinus(),MuMinusDirection,EMinus-Mmuon);
346  aParticleChange.AddSecondary(aParticle2);
347  //
348  // Kill the incident photon
349  //
350  aParticleChange.ProposeMomentumDirection( 0., 0., 0. ) ;
351  aParticleChange.ProposeEnergy( 0. ) ;
352  aParticleChange.ProposeTrackStatus( fStopAndKill ) ;
353  //  Reset NbOfInteractionLengthLeft and return aParticleChange
354  return G4VDiscreteProcess::PostStepDoIt( aTrack, aStep );
355}
356
357//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
358
359G4Element* G4GammaConversionToMuons::SelectRandomAtom(
360                                        const G4DynamicParticle* aDynamicGamma,
361                                              G4Material* aMaterial)
362{
363  // select randomly 1 element within the material, invoked by PostStepDoIt
364
365  const G4int NumberOfElements            = aMaterial->GetNumberOfElements();
366  const G4ElementVector* theElementVector = aMaterial->GetElementVector();
367  if (NumberOfElements == 1) return (*theElementVector)[0];
368
369  const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
370
371  G4double PartialSumSigma = 0. ;
372  G4double rval = G4UniformRand()/MeanFreePath;
373
374
375  for ( G4int i=0 ; i < NumberOfElements ; i++ )
376      { PartialSumSigma += NbOfAtomsPerVolume[i] *
377                 GetCrossSectionPerAtom(aDynamicGamma, (*theElementVector)[i]);
378        if (rval <= PartialSumSigma) return ((*theElementVector)[i]);
379      }
380  G4cout << " WARNING !!! - The Material '"<< aMaterial->GetName()
381       << "' has no elements, NULL pointer returned." << G4endl;
382  return NULL;
383}
384
385//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
386
387void G4GammaConversionToMuons::PrintInfoDefinition()
388{
389  G4String comments ="gamma->mu+mu- Bethe Heitler process.\n";
390  G4cout << G4endl << GetProcessName() << ":  " << comments
391         << "        good cross section parametrization from "
392         << G4BestUnit(LowestEnergyLimit,"Energy")
393         << " to " << HighestEnergyLimit/GeV << " GeV for all Z." << G4endl;
394}
395
396//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
Note: See TracBrowser for help on using the repository browser.