source: trunk/source/processes/electromagnetic/standard/src/G4KleinNishinaCompton.cc @ 1340

Last change on this file since 1340 was 1337, checked in by garnier, 14 years ago

tag geant4.9.4 beta 1 + modifs locales
File size: 8.0 KB
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26// $Id: G4KleinNishinaCompton.cc,v 1.10 2009/05/15 17:12:33 vnivanch Exp $
27// GEANT4 tag $Name: geant4-09-04-beta-01 $
28//
29// -------------------------------------------------------------------
30//
31// GEANT4 Class file
32//
33//
34// File name:     G4KleinNishinaCompton
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// 27-03-06 Remove upper limit of cross section (V.Ivantchenko)
43//
44// Class Description:
45//
46// -------------------------------------------------------------------
47//
48//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
49//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
50
51#include "G4KleinNishinaCompton.hh"
52#include "G4Electron.hh"
53#include "G4Gamma.hh"
54#include "Randomize.hh"
55#include "G4DataVector.hh"
56#include "G4ParticleChangeForGamma.hh"
57
58//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
59
60using namespace std;
61
62G4KleinNishinaCompton::G4KleinNishinaCompton(const G4ParticleDefinition*,
63                                             const G4String& nam)
64  : G4VEmModel(nam)
65{
66  theGamma = G4Gamma::Gamma();
67  theElectron = G4Electron::Electron();
68  lowestGammaEnergy = 1.0*eV;
69}
70
71//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
72
73G4KleinNishinaCompton::~G4KleinNishinaCompton()
74{}
75
76//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
77
78void G4KleinNishinaCompton::Initialise(const G4ParticleDefinition*,
79                                       const G4DataVector&)
80{
81  fParticleChange = GetParticleChangeForGamma();
82}
83
84//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
85
86G4double G4KleinNishinaCompton::ComputeCrossSectionPerAtom(
87                                       const G4ParticleDefinition*,
88                                             G4double GammaEnergy,
89                                             G4double Z, G4double,
90                                             G4double, G4double)
91{
92  G4double CrossSection = 0.0 ;
93  if ( Z < 0.9999 )                 return CrossSection;
94  if ( GammaEnergy < 0.1*keV      ) return CrossSection;
95  //  if ( GammaEnergy > (100.*GeV/Z) ) return CrossSection;
96
97  static const G4double a = 20.0 , b = 230.0 , c = 440.0;
98 
99  static const G4double
100    d1= 2.7965e-1*barn, d2=-1.8300e-1*barn, d3= 6.7527   *barn, d4=-1.9798e+1*barn,
101    e1= 1.9756e-5*barn, e2=-1.0205e-2*barn, e3=-7.3913e-2*barn, e4= 2.7079e-2*barn,
102    f1=-3.9178e-7*barn, f2= 6.8241e-5*barn, f3= 6.0480e-5*barn, f4= 3.0274e-4*barn;
103     
104  G4double p1Z = Z*(d1 + e1*Z + f1*Z*Z), p2Z = Z*(d2 + e2*Z + f2*Z*Z),
105           p3Z = Z*(d3 + e3*Z + f3*Z*Z), p4Z = Z*(d4 + e4*Z + f4*Z*Z);
106
107  G4double T0  = 15.0*keV; 
108  if (Z < 1.5) T0 = 40.0*keV; 
109
110  G4double X   = max(GammaEnergy, T0) / electron_mass_c2;
111  CrossSection = p1Z*std::log(1.+2.*X)/X
112               + (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
113               
114  //  modification for low energy. (special case for Hydrogen)
115  if (GammaEnergy < T0) {
116    G4double dT0 = 1.*keV;
117    X = (T0+dT0) / electron_mass_c2 ;
118    G4double sigma = p1Z*log(1.+2*X)/X
119                    + (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
120    G4double   c1 = -T0*(sigma-CrossSection)/(CrossSection*dT0);             
121    G4double   c2 = 0.150; 
122    if (Z > 1.5) c2 = 0.375-0.0556*log(Z);
123    G4double    y = log(GammaEnergy/T0);
124    CrossSection *= exp(-y*(c1+c2*y));         
125  }
126  //  G4cout << "e= " << GammaEnergy << " Z= " << Z << " cross= " << CrossSection << G4endl;
127  return CrossSection;
128}
129
130//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
131
132void G4KleinNishinaCompton::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
133                                              const G4MaterialCutsCouple*,
134                                              const G4DynamicParticle* aDynamicGamma,
135                                              G4double,
136                                              G4double)
137{
138  // The scattered gamma energy is sampled according to Klein - Nishina formula.
139  // The random number techniques of Butcher & Messel are used
140  // (Nuc Phys 20(1960),15).
141  // Note : Effects due to binding of atomic electrons are negliged.
142 
143  G4double gamEnergy0 = aDynamicGamma->GetKineticEnergy();
144  G4double E0_m = gamEnergy0 / electron_mass_c2 ;
145
146  G4ThreeVector gamDirection0 = aDynamicGamma->GetMomentumDirection();
147
148  //
149  // sample the energy rate of the scattered gamma
150  //
151
152  G4double epsilon, epsilonsq, onecost, sint2, greject ;
153
154  G4double epsilon0   = 1./(1. + 2.*E0_m);
155  G4double epsilon0sq = epsilon0*epsilon0;
156  G4double alpha1     = - log(epsilon0);
157  G4double alpha2     = 0.5*(1.- epsilon0sq);
158
159  do {
160    if ( alpha1/(alpha1+alpha2) > G4UniformRand() ) {
161      epsilon   = exp(-alpha1*G4UniformRand());   // epsilon0**r
162      epsilonsq = epsilon*epsilon; 
163
164    } else {
165      epsilonsq = epsilon0sq + (1.- epsilon0sq)*G4UniformRand();
166      epsilon   = sqrt(epsilonsq);
167    };
168
169    onecost = (1.- epsilon)/(epsilon*E0_m);
170    sint2   = onecost*(2.-onecost);
171    greject = 1. - epsilon*sint2/(1.+ epsilonsq);
172
173  } while (greject < G4UniformRand());
174 
175  //
176  // scattered gamma angles. ( Z - axis along the parent gamma)
177  //
178
179  G4double cosTeta = 1. - onecost; 
180  G4double sinTeta = sqrt (sint2);
181  G4double Phi     = twopi * G4UniformRand();
182  G4double dirx = sinTeta*cos(Phi), diry = sinTeta*sin(Phi), dirz = cosTeta;
183
184  //
185  // update G4VParticleChange for the scattered gamma
186  //
187   
188  G4ThreeVector gamDirection1 ( dirx,diry,dirz );
189  gamDirection1.rotateUz(gamDirection0);
190  G4double gamEnergy1 = epsilon*gamEnergy0;
191  fParticleChange->SetProposedKineticEnergy(gamEnergy1);
192  if(gamEnergy1 > lowestGammaEnergy) {
193    fParticleChange->ProposeMomentumDirection(gamDirection1);
194  } else { 
195    fParticleChange->ProposeTrackStatus(fStopAndKill);
196    gamEnergy1 += fParticleChange->GetLocalEnergyDeposit();
197    fParticleChange->ProposeLocalEnergyDeposit(gamEnergy1);
198  }
199
200  //
201  // kinematic of the scattered electron
202  //
203
204  G4double eKinEnergy = gamEnergy0 - gamEnergy1;
205
206  if(eKinEnergy > DBL_MIN) {
207    G4ThreeVector eDirection = gamEnergy0*gamDirection0 - gamEnergy1*gamDirection1;
208    eDirection = eDirection.unit();
209
210    // create G4DynamicParticle object for the electron.
211    G4DynamicParticle* dp = new G4DynamicParticle(theElectron,eDirection,eKinEnergy);
212    fvect->push_back(dp);
213  }
214}
215
216//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
217
218
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