source: trunk/source/processes/electromagnetic/standard/src/G4KleinNishinaCompton.cc@ 1036

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

update to geant4.9.2
File size: 8.1 KB
Line 
1//
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19// * technical work of the GEANT4 collaboration. *
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25//
26// $Id: G4KleinNishinaCompton.cc,v 1.9 2007/05/22 17:34:36 vnivanch Exp $
27// GEANT4 tag $Name: geant4-09-02 $
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 if(pParticleChange)
82 fParticleChange = reinterpret_cast<G4ParticleChangeForGamma*>(pParticleChange);
83 else
84 fParticleChange = new G4ParticleChangeForGamma();
85}
86
87//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
88
89G4double G4KleinNishinaCompton::ComputeCrossSectionPerAtom(
90 const G4ParticleDefinition*,
91 G4double GammaEnergy,
92 G4double Z, G4double,
93 G4double, G4double)
94{
95 G4double CrossSection = 0.0 ;
96 if ( Z < 0.9999 ) return CrossSection;
97 if ( GammaEnergy < 0.1*keV ) return CrossSection;
98 // if ( GammaEnergy > (100.*GeV/Z) ) return CrossSection;
99
100 static const G4double a = 20.0 , b = 230.0 , c = 440.0;
101
102 static const G4double
103 d1= 2.7965e-1*barn, d2=-1.8300e-1*barn, d3= 6.7527 *barn, d4=-1.9798e+1*barn,
104 e1= 1.9756e-5*barn, e2=-1.0205e-2*barn, e3=-7.3913e-2*barn, e4= 2.7079e-2*barn,
105 f1=-3.9178e-7*barn, f2= 6.8241e-5*barn, f3= 6.0480e-5*barn, f4= 3.0274e-4*barn;
106
107 G4double p1Z = Z*(d1 + e1*Z + f1*Z*Z), p2Z = Z*(d2 + e2*Z + f2*Z*Z),
108 p3Z = Z*(d3 + e3*Z + f3*Z*Z), p4Z = Z*(d4 + e4*Z + f4*Z*Z);
109
110 G4double T0 = 15.0*keV;
111 if (Z < 1.5) T0 = 40.0*keV;
112
113 G4double X = max(GammaEnergy, T0) / electron_mass_c2;
114 CrossSection = p1Z*std::log(1.+2.*X)/X
115 + (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
116
117 // modification for low energy. (special case for Hydrogen)
118 if (GammaEnergy < T0) {
119 G4double dT0 = 1.*keV;
120 X = (T0+dT0) / electron_mass_c2 ;
121 G4double sigma = p1Z*log(1.+2*X)/X
122 + (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
123 G4double c1 = -T0*(sigma-CrossSection)/(CrossSection*dT0);
124 G4double c2 = 0.150;
125 if (Z > 1.5) c2 = 0.375-0.0556*log(Z);
126 G4double y = log(GammaEnergy/T0);
127 CrossSection *= exp(-y*(c1+c2*y));
128 }
129 // G4cout << "e= " << GammaEnergy << " Z= " << Z << " cross= " << CrossSection << G4endl;
130 return CrossSection;
131}
132
133//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
134
135void G4KleinNishinaCompton::SampleSecondaries(std::vector<G4DynamicParticle*>* fvect,
136 const G4MaterialCutsCouple*,
137 const G4DynamicParticle* aDynamicGamma,
138 G4double,
139 G4double)
140{
141 // The scattered gamma energy is sampled according to Klein - Nishina formula.
142 // The random number techniques of Butcher & Messel are used
143 // (Nuc Phys 20(1960),15).
144 // Note : Effects due to binding of atomic electrons are negliged.
145
146 G4double gamEnergy0 = aDynamicGamma->GetKineticEnergy();
147 G4double E0_m = gamEnergy0 / electron_mass_c2 ;
148
149 G4ThreeVector gamDirection0 = aDynamicGamma->GetMomentumDirection();
150
151 //
152 // sample the energy rate of the scattered gamma
153 //
154
155 G4double epsilon, epsilonsq, onecost, sint2, greject ;
156
157 G4double epsilon0 = 1./(1. + 2.*E0_m);
158 G4double epsilon0sq = epsilon0*epsilon0;
159 G4double alpha1 = - log(epsilon0);
160 G4double alpha2 = 0.5*(1.- epsilon0sq);
161
162 do {
163 if ( alpha1/(alpha1+alpha2) > G4UniformRand() ) {
164 epsilon = exp(-alpha1*G4UniformRand()); // epsilon0**r
165 epsilonsq = epsilon*epsilon;
166
167 } else {
168 epsilonsq = epsilon0sq + (1.- epsilon0sq)*G4UniformRand();
169 epsilon = sqrt(epsilonsq);
170 };
171
172 onecost = (1.- epsilon)/(epsilon*E0_m);
173 sint2 = onecost*(2.-onecost);
174 greject = 1. - epsilon*sint2/(1.+ epsilonsq);
175
176 } while (greject < G4UniformRand());
177
178 //
179 // scattered gamma angles. ( Z - axis along the parent gamma)
180 //
181
182 G4double cosTeta = 1. - onecost;
183 G4double sinTeta = sqrt (sint2);
184 G4double Phi = twopi * G4UniformRand();
185 G4double dirx = sinTeta*cos(Phi), diry = sinTeta*sin(Phi), dirz = cosTeta;
186
187 //
188 // update G4VParticleChange for the scattered gamma
189 //
190
191 G4ThreeVector gamDirection1 ( dirx,diry,dirz );
192 gamDirection1.rotateUz(gamDirection0);
193 G4double gamEnergy1 = epsilon*gamEnergy0;
194 fParticleChange->SetProposedKineticEnergy(gamEnergy1);
195 if(gamEnergy1 > lowestGammaEnergy) {
196 fParticleChange->ProposeMomentumDirection(gamDirection1);
197 } else {
198 fParticleChange->ProposeTrackStatus(fStopAndKill);
199 gamEnergy1 += fParticleChange->GetLocalEnergyDeposit();
200 fParticleChange->ProposeLocalEnergyDeposit(gamEnergy1);
201 }
202
203 //
204 // kinematic of the scattered electron
205 //
206
207 G4double eKinEnergy = gamEnergy0 - gamEnergy1;
208
209 if(eKinEnergy > DBL_MIN) {
210 G4ThreeVector eDirection = gamEnergy0*gamDirection0 - gamEnergy1*gamDirection1;
211 eDirection = eDirection.unit();
212
213 // create G4DynamicParticle object for the electron.
214 G4DynamicParticle* dp = new G4DynamicParticle(theElectron,eDirection,eKinEnergy);
215 fvect->push_back(dp);
216 }
217}
218
219//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
220
221
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