source: trunk/source/processes/electromagnetic/standard/src/G4eeToTwoGammaModel.cc@ 1005

Last change on this file since 1005 was 991, checked in by garnier, 17 years ago

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[819]1//
2// ********************************************************************
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4// * *
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14// * regarding this software system or assume any liability for its *
15// * use. Please see the license in the file LICENSE and URL above *
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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 *
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24// ********************************************************************
25//
26// $Id: G4eeToTwoGammaModel.cc,v 1.14 2007/05/23 08:47:35 vnivanch Exp $
[991]27// GEANT4 tag $Name: geant4-09-02 $
[819]28//
29// -------------------------------------------------------------------
30//
31// GEANT4 Class file
32//
33//
34// File name: G4eeToTwoGammaModel
35//
36// Author: Vladimir Ivanchenko on base of Michel Maire code
37//
38// Creation date: 02.08.2004
39//
40// Modifications:
41// 08-04-05 Major optimisation of internal interfaces (V.Ivanchenko)
42// 18-04-05 Compute CrossSectionPerVolume (V.Ivanchenko)
43// 06-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma)
44// 29-06-06 Fix problem for zero energy incident positron (V.Ivanchenko)
45// 20-10-06 Add theGamma as a member (V.Ivanchenko)
46//
47//
48// Class Description:
49//
50// Implementation of e+ annihilation into 2 gamma
51//
52// The secondaries Gamma energies are sampled using the Heitler cross section.
53//
54// A modified version of the random number techniques of Butcher & Messel
55// is used (Nuc Phys 20(1960),15).
56//
57// GEANT4 internal units.
58//
59// Note 1: The initial electron is assumed free and at rest.
60//
61// Note 2: The annihilation processes producing one or more than two photons are
62// ignored, as negligible compared to the two photons process.
63
64
65
66//
67// -------------------------------------------------------------------
68//
69//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
70//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
71
72#include "G4eeToTwoGammaModel.hh"
73#include "G4TrackStatus.hh"
74#include "G4Electron.hh"
75#include "G4Positron.hh"
76#include "G4Gamma.hh"
77#include "Randomize.hh"
78#include "G4ParticleChangeForGamma.hh"
79
80//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
81
82using namespace std;
83
84G4eeToTwoGammaModel::G4eeToTwoGammaModel(const G4ParticleDefinition*,
85 const G4String& nam)
86 : G4VEmModel(nam),
87 pi_rcl2(pi*classic_electr_radius*classic_electr_radius),
88 isInitialised(false)
89{
90 theGamma = G4Gamma::Gamma();
91}
92
93//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
94
95G4eeToTwoGammaModel::~G4eeToTwoGammaModel()
96{}
97
98//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
99
100void G4eeToTwoGammaModel::Initialise(const G4ParticleDefinition*,
101 const G4DataVector&)
102{
103 if(isInitialised) return;
104
105 if(pParticleChange)
106 fParticleChange =
107 reinterpret_cast<G4ParticleChangeForGamma*>(pParticleChange);
108 else
109 fParticleChange = new G4ParticleChangeForGamma();
110
111 isInitialised = true;
112}
113
114//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
115
116G4double G4eeToTwoGammaModel::ComputeCrossSectionPerElectron(
117 const G4ParticleDefinition*,
118 G4double kineticEnergy,
119 G4double, G4double)
120{
121 // Calculates the cross section per electron of annihilation into two photons
122 // from the Heilter formula.
123
124 G4double tau = kineticEnergy/electron_mass_c2;
125 G4double gam = tau + 1.0;
126 G4double gamma2= gam*gam;
127 G4double bg2 = tau * (tau+2.0);
128 G4double bg = sqrt(bg2);
129
130 G4double cross = pi_rcl2*((gamma2+4*gam+1.)*log(gam+bg) - (gam+3.)*bg)
131 / (bg2*(gam+1.));
132 return cross;
133}
134
135//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
136
137G4double G4eeToTwoGammaModel::ComputeCrossSectionPerAtom(
138 const G4ParticleDefinition* p,
139 G4double kineticEnergy, G4double Z,
140 G4double, G4double, G4double)
141{
142 // Calculates the cross section per atom of annihilation into two photons
143
144 G4double cross = Z*ComputeCrossSectionPerElectron(p,kineticEnergy);
145 return cross;
146}
147
148//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
149
150G4double G4eeToTwoGammaModel::CrossSectionPerVolume(
151 const G4Material* material,
152 const G4ParticleDefinition* p,
153 G4double kineticEnergy,
154 G4double, G4double)
155{
156 // Calculates the cross section per volume of annihilation into two photons
157
158 G4double eDensity = material->GetElectronDensity();
159 G4double cross = eDensity*ComputeCrossSectionPerElectron(p,kineticEnergy);
160 return cross;
161}
162
163//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
164
165void G4eeToTwoGammaModel::SampleSecondaries(vector<G4DynamicParticle*>* vdp,
166 const G4MaterialCutsCouple*,
167 const G4DynamicParticle* dp,
168 G4double,
169 G4double)
170{
171 G4double PositKinEnergy = dp->GetKineticEnergy();
172
173 // Case at rest
174 if(PositKinEnergy == 0.0) {
175 G4double cost = 2.*G4UniformRand()-1.;
176 G4double sint = sqrt((1. - cost)*(1. + cost));
177 G4double phi = twopi * G4UniformRand();
178 G4ThreeVector dir (sint*cos(phi), sint*sin(phi), cost);
179 G4DynamicParticle* aGamma1 = new G4DynamicParticle(theGamma,
180 dir, electron_mass_c2);
181 G4DynamicParticle* aGamma2 = new G4DynamicParticle(theGamma,
182 -dir, electron_mass_c2);
183 vdp->push_back(aGamma1);
184 vdp->push_back(aGamma2);
185
186 } else {
187
188 G4ThreeVector PositDirection = dp->GetMomentumDirection();
189
190 G4double tau = PositKinEnergy/electron_mass_c2;
191 G4double gam = tau + 1.0;
192 G4double tau2 = tau + 2.0;
193 G4double sqgrate = sqrt(tau/tau2)*0.5;
194 G4double sqg2m1 = sqrt(tau*tau2);
195
196 // limits of the energy sampling
197 G4double epsilmin = 0.5 - sqgrate;
198 G4double epsilmax = 0.5 + sqgrate;
199 G4double epsilqot = epsilmax/epsilmin;
200
201 //
202 // sample the energy rate of the created gammas
203 //
204 G4double epsil, greject;
205
206 do {
207 epsil = epsilmin*pow(epsilqot,G4UniformRand());
208 greject = 1. - epsil + (2.*gam*epsil-1.)/(epsil*tau2*tau2);
209 } while( greject < G4UniformRand() );
210
211 //
212 // scattered Gamma angles. ( Z - axis along the parent positron)
213 //
214
215 G4double cost = (epsil*tau2-1.)/(epsil*sqg2m1);
216 if(std::abs(cost) > 1.0) {
217 G4cout << "### G4eeToTwoGammaModel WARNING cost= " << cost
218 << " positron Ekin(MeV)= " << PositKinEnergy
219 << " gamma epsil= " << epsil
220 << G4endl;
221 if(cost > 1.0) cost = 1.0;
222 else cost = -1.0;
223 }
224 G4double sint = sqrt((1.+cost)*(1.-cost));
225 G4double phi = twopi * G4UniformRand();
226
227 G4double dirx = sint*cos(phi) , diry = sint*sin(phi) , dirz = cost;
228
229 //
230 // kinematic of the created pair
231 //
232
233 G4double TotalAvailableEnergy = PositKinEnergy + 2.0*electron_mass_c2;
234 G4double Phot1Energy = epsil*TotalAvailableEnergy;
235
236 G4ThreeVector Phot1Direction (dirx, diry, dirz);
237 Phot1Direction.rotateUz(PositDirection);
238 G4DynamicParticle* aGamma1 =
239 new G4DynamicParticle (theGamma,Phot1Direction, Phot1Energy);
240 vdp->push_back(aGamma1);
241
242 G4double Phot2Energy =(1.-epsil)*TotalAvailableEnergy;
243 G4double PositP= sqrt(PositKinEnergy*(PositKinEnergy+2.*electron_mass_c2));
244 G4ThreeVector dir = PositDirection*PositP - Phot1Direction*Phot1Energy;
245 G4ThreeVector Phot2Direction = dir.unit();
246
247 // create G4DynamicParticle object for the particle2
248 G4DynamicParticle* aGamma2=
249 new G4DynamicParticle (theGamma,Phot2Direction, Phot2Energy);
250 vdp->push_back(aGamma2);
251 /*
252 G4cout << "Annihilation in fly: e0= " << PositKinEnergy
253 << " m= " << electron_mass_c2
254 << " e1= " << Phot1Energy
255 << " e2= " << Phot2Energy << " dir= " << dir
256 << " -> " << Phot1Direction << " "
257 << Phot2Direction << G4endl;
258 */
259 }
260 fParticleChange->SetProposedKineticEnergy(0.);
261 fParticleChange->ProposeTrackStatus(fStopAndKill);
262}
263
264//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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