source: trunk/source/processes/electromagnetic/standard/src/G4MollerBhabhaModel.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: 13.5 KB
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[819]1//
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25//
[1007]26// $Id: G4MollerBhabhaModel.cc,v 1.30 2007/05/22 17:34:36 vnivanch Exp $
27// GEANT4 tag $Name: geant4-09-02 $
[819]28//
29// -------------------------------------------------------------------
30//
31// GEANT4 Class file
32//
33//
34// File name: G4MollerBhabhaModel
35//
36// Author: Vladimir Ivanchenko on base of Laszlo Urban code
37//
38// Creation date: 03.01.2002
39//
40// Modifications:
41//
42// 13-11-02 Minor fix - use normalised direction (V.Ivanchenko)
43// 04-12-02 Change G4DynamicParticle constructor in PostStepDoIt (V.Ivanchenko)
44// 23-12-02 Change interface in order to move to cut per region (V.Ivanchenko)
45// 27-01-03 Make models region aware (V.Ivanchenko)
46// 13-02-03 Add name (V.Ivanchenko)
47// 08-04-05 Major optimisation of internal interfaces (V.Ivantchenko)
48// 25-07-05 Add protection in calculation of recoil direction for the case
49// of complete energy transfer from e+ to e- (V.Ivanchenko)
50// 06-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma)
51// 15-05-06 Fix MinEnergyCut (V.Ivanchenko)
52//
53//
54// Class Description:
55//
56// Implementation of energy loss and delta-electron production by e+/e-
57//
58// -------------------------------------------------------------------
59//
60//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
61//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
62
63#include "G4MollerBhabhaModel.hh"
64#include "G4Electron.hh"
65#include "G4Positron.hh"
66#include "Randomize.hh"
67#include "G4ParticleChangeForLoss.hh"
68
69//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
70
71using namespace std;
72
73G4MollerBhabhaModel::G4MollerBhabhaModel(const G4ParticleDefinition* p,
74 const G4String& nam)
75 : G4VEmModel(nam),
[1007]76 particle(0),
77 isElectron(true),
78 twoln10(2.0*log(10.0)),
79 lowLimit(0.2*keV)
[819]80{
81 theElectron = G4Electron::Electron();
82 if(p) SetParticle(p);
83}
84
85//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
86
87G4MollerBhabhaModel::~G4MollerBhabhaModel()
88{}
89
90//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
91
[1007]92void G4MollerBhabhaModel::SetParticle(const G4ParticleDefinition* p)
93{
94 particle = p;
95 if(p != theElectron) isElectron = false;
96}
97
98//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
99
[819]100G4double G4MollerBhabhaModel::MinEnergyCut(const G4ParticleDefinition*,
101 const G4MaterialCutsCouple* couple)
102{
103 G4double electronDensity = couple->GetMaterial()->GetElectronDensity();
104 G4double Zeff = electronDensity/couple->GetMaterial()->GetTotNbOfAtomsPerVolume();
105 return 0.25*sqrt(Zeff)*keV;
106}
107
108//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
109
110void G4MollerBhabhaModel::Initialise(const G4ParticleDefinition* p,
111 const G4DataVector&)
112{
113 if(!particle) SetParticle(p);
[1007]114 if(pParticleChange)
[819]115 fParticleChange = reinterpret_cast<G4ParticleChangeForLoss*>
116 (pParticleChange);
[1007]117 else
[819]118 fParticleChange = new G4ParticleChangeForLoss();
119}
120
121//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
122
123G4double G4MollerBhabhaModel::ComputeCrossSectionPerElectron(
124 const G4ParticleDefinition* p,
125 G4double kineticEnergy,
126 G4double cutEnergy,
127 G4double maxEnergy)
128{
129 if(!particle) SetParticle(p);
130
131 G4double cross = 0.0;
132 G4double tmax = MaxSecondaryEnergy(p, kineticEnergy);
133 tmax = min(maxEnergy, tmax);
134
135 if(cutEnergy < tmax) {
136
137 G4double xmin = cutEnergy/kineticEnergy;
138 G4double xmax = tmax/kineticEnergy;
139 G4double gam = kineticEnergy/electron_mass_c2 + 1.0;
140 G4double gamma2= gam*gam;
141 G4double beta2 = 1.0 - 1.0/gamma2;
142
143 //Moller (e-e-) scattering
144 if (isElectron) {
145
146 G4double g = (2.0*gam - 1.0)/gamma2;
147 cross = ((xmax - xmin)*(1.0 - g + 1.0/(xmin*xmax)
148 + 1.0/((1.0-xmin)*(1.0 - xmax)))
149 - g*log( xmax*(1.0 - xmin)/(xmin*(1.0 - xmax)) ) ) / beta2;
150
151 //Bhabha (e+e-) scattering
152 } else {
153
154 G4double y = 1.0/(1.0 + gam);
155 G4double y2 = y*y;
156 G4double y12 = 1.0 - 2.0*y;
157 G4double b1 = 2.0 - y2;
158 G4double b2 = y12*(3.0 + y2);
159 G4double y122= y12*y12;
160 G4double b4 = y122*y12;
161 G4double b3 = b4 + y122;
162
163 cross = (xmax - xmin)*(1.0/(beta2*xmin*xmax) + b2
164 - 0.5*b3*(xmin + xmax)
165 + b4*(xmin*xmin + xmin*xmax + xmax*xmax)/3.0)
166 - b1*log(xmax/xmin);
167 }
168
169 cross *= twopi_mc2_rcl2/kineticEnergy;
170 }
171 return cross;
172}
173
174//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
175
176G4double G4MollerBhabhaModel::ComputeCrossSectionPerAtom(
177 const G4ParticleDefinition* p,
178 G4double kineticEnergy,
179 G4double Z, G4double,
180 G4double cutEnergy,
181 G4double maxEnergy)
182{
183 G4double cross = Z*ComputeCrossSectionPerElectron
184 (p,kineticEnergy,cutEnergy,maxEnergy);
185 return cross;
186}
187
188//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
189
190G4double G4MollerBhabhaModel::CrossSectionPerVolume(
191 const G4Material* material,
192 const G4ParticleDefinition* p,
193 G4double kineticEnergy,
194 G4double cutEnergy,
195 G4double maxEnergy)
196{
197 G4double eDensity = material->GetElectronDensity();
198 G4double cross = eDensity*ComputeCrossSectionPerElectron
199 (p,kineticEnergy,cutEnergy,maxEnergy);
200 return cross;
201}
202
203//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
204
205G4double G4MollerBhabhaModel::ComputeDEDXPerVolume(
206 const G4Material* material,
207 const G4ParticleDefinition* p,
208 G4double kineticEnergy,
209 G4double cutEnergy)
210{
211 if(!particle) SetParticle(p);
212 // calculate the dE/dx due to the ionization by Seltzer-Berger formula
213
214 G4double electronDensity = material->GetElectronDensity();
215 G4double Zeff = electronDensity/material->GetTotNbOfAtomsPerVolume();
216 G4double th = 0.25*sqrt(Zeff)*keV;
217 G4double tkin = kineticEnergy;
218 G4bool lowEnergy = false;
219 if (kineticEnergy < th) {
220 tkin = th;
221 lowEnergy = true;
222 }
223 G4double tau = tkin/electron_mass_c2;
224 G4double gam = tau + 1.0;
225 G4double gamma2= gam*gam;
226 G4double beta2 = 1. - 1./gamma2;
227 G4double bg2 = beta2*gamma2;
228
229 G4double eexc = material->GetIonisation()->GetMeanExcitationEnergy();
230 eexc /= electron_mass_c2;
231 G4double eexc2 = eexc*eexc;
232
233 G4double d = min(cutEnergy, MaxSecondaryEnergy(p, tkin))/electron_mass_c2;
234 G4double dedx;
235
236 // electron
237 if (isElectron) {
238
239 dedx = log(2.0*(tau + 2.0)/eexc2) - 1.0 - beta2
240 + log((tau-d)*d) + tau/(tau-d)
241 + (0.5*d*d + (2.0*tau + 1.)*log(1. - d/tau))/gamma2;
242
243 //positron
244 } else {
245
246 G4double d2 = d*d*0.5;
247 G4double d3 = d2*d/1.5;
248 G4double d4 = d3*d*3.75;
249 G4double y = 1.0/(1.0 + gam);
250 dedx = log(2.0*(tau + 2.0)/eexc2) + log(tau*d)
251 - beta2*(tau + 2.0*d - y*(3.0*d2
252 + y*(d - d3 + y*(d2 - tau*d3 + d4))))/tau;
253 }
254
255 //density correction
256 G4double cden = material->GetIonisation()->GetCdensity();
257 G4double mden = material->GetIonisation()->GetMdensity();
258 G4double aden = material->GetIonisation()->GetAdensity();
259 G4double x0den = material->GetIonisation()->GetX0density();
260 G4double x1den = material->GetIonisation()->GetX1density();
261 G4double x = log(bg2)/twoln10;
262
263 if (x >= x0den) {
264 dedx -= twoln10*x - cden;
265 if (x < x1den) dedx -= aden*pow(x1den-x, mden);
266 }
267
268 // now you can compute the total ionization loss
269 dedx *= twopi_mc2_rcl2*electronDensity/beta2;
270 if (dedx < 0.0) dedx = 0.0;
271
272 // lowenergy extrapolation
273
274 if (lowEnergy) {
275
276 if (kineticEnergy >= lowLimit) dedx *= sqrt(tkin/kineticEnergy);
277 else dedx *= sqrt(tkin*kineticEnergy)/lowLimit;
278
279 }
280 return dedx;
281}
282
283//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
284
285void G4MollerBhabhaModel::SampleSecondaries(std::vector<G4DynamicParticle*>* vdp,
286 const G4MaterialCutsCouple*,
287 const G4DynamicParticle* dp,
288 G4double tmin,
289 G4double maxEnergy)
290{
291 G4double tmax = std::min(maxEnergy, MaxSecondaryKinEnergy(dp));
292 if(tmin >= tmax) return;
293
294 G4double kineticEnergy = dp->GetKineticEnergy();
295 G4double energy = kineticEnergy + electron_mass_c2;
296 G4double totalMomentum = sqrt(kineticEnergy*(energy + electron_mass_c2));
297 G4double xmin = tmin/kineticEnergy;
298 G4double xmax = tmax/kineticEnergy;
299 G4double gam = energy/electron_mass_c2;
300 G4double gamma2 = gam*gam;
301 G4double beta2 = 1.0 - 1.0/gamma2;
302 G4double x, z, q, grej;
303
304 G4ThreeVector direction = dp->GetMomentumDirection();
305
306 //Moller (e-e-) scattering
307 if (isElectron) {
308
309 G4double g = (2.0*gam - 1.0)/gamma2;
310 G4double y = 1.0 - xmax;
311 grej = 1.0 - g*xmax + xmax*xmax*(1.0 - g + (1.0 - g*y)/(y*y));
312
313 do {
314 q = G4UniformRand();
315 x = xmin*xmax/(xmin*(1.0 - q) + xmax*q);
316 y = 1.0 - x;
317 z = 1.0 - g*x + x*x*(1.0 - g + (1.0 - g*y)/(y*y));
318 /*
319 if(z > grej) {
320 G4cout << "G4MollerBhabhaModel::SampleSecondary Warning! "
321 << "Majorant " << grej << " < "
322 << z << " for x= " << x
323 << " e-e- scattering"
324 << G4endl;
325 }
326 */
327 } while(grej * G4UniformRand() > z);
328
329 //Bhabha (e+e-) scattering
330 } else {
331
332 G4double y = 1.0/(1.0 + gam);
333 G4double y2 = y*y;
334 G4double y12 = 1.0 - 2.0*y;
335 G4double b1 = 2.0 - y2;
336 G4double b2 = y12*(3.0 + y2);
337 G4double y122= y12*y12;
338 G4double b4 = y122*y12;
339 G4double b3 = b4 + y122;
340
341 y = xmax*xmax;
342 grej = -xmin*b1;
343 grej += y*b2;
344 grej -= xmin*xmin*xmin*b3;
345 grej += y*y*b4;
346 grej *= beta2;
347 grej += 1.0;
348 do {
349 q = G4UniformRand();
350 x = xmin*xmax/(xmin*(1.0 - q) + xmax*q);
351 z = -x*b1;
352 y = x*x;
353 z += y*b2;
354 y *= x;
355 z -= y*b3;
356 y *= x;
357 z += y*b4;
358 z *= beta2;
359 z += 1.0;
360 /*
361 if(z > grej) {
362 G4cout << "G4MollerBhabhaModel::SampleSecondary Warning! "
363 << "Majorant " << grej << " < "
364 << z << " for x= " << x
365 << " e+e- scattering"
366 << G4endl;
367 }
368 */
369 } while(grej * G4UniformRand() > z);
370 }
371
372 G4double deltaKinEnergy = x * kineticEnergy;
373
374 G4double deltaMomentum =
375 sqrt(deltaKinEnergy * (deltaKinEnergy + 2.0*electron_mass_c2));
376 G4double cost = deltaKinEnergy * (energy + electron_mass_c2) /
377 (deltaMomentum * totalMomentum);
378 G4double sint = 1.0 - cost*cost;
379 if(sint > 0.0) sint = sqrt(sint);
380
381 G4double phi = twopi * G4UniformRand() ;
382
383 G4ThreeVector deltaDirection(sint*cos(phi),sint*sin(phi), cost) ;
384 deltaDirection.rotateUz(direction);
385
386 // primary change
387 kineticEnergy -= deltaKinEnergy;
388 fParticleChange->SetProposedKineticEnergy(kineticEnergy);
389
390 if(kineticEnergy > DBL_MIN) {
391 G4ThreeVector dir = totalMomentum*direction - deltaMomentum*deltaDirection;
392 direction = dir.unit();
393 fParticleChange->SetProposedMomentumDirection(direction);
394 }
395
396 // create G4DynamicParticle object for delta ray
397 G4DynamicParticle* delta = new G4DynamicParticle(theElectron,
398 deltaDirection,deltaKinEnergy);
399 vdp->push_back(delta);
400}
401
402//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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