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G4MollerBhabhaModel.cc
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26 // $Id$
27 //
28 // -------------------------------------------------------------------
29 //
30 // GEANT4 Class file
31 //
32 //
33 // File name: G4MollerBhabhaModel
34 //
35 // Author: Vladimir Ivanchenko on base of Laszlo Urban code
36 //
37 // Creation date: 03.01.2002
38 //
39 // Modifications:
40 //
41 // 13-11-02 Minor fix - use normalised direction (V.Ivanchenko)
42 // 04-12-02 Change G4DynamicParticle constructor in PostStepDoIt (V.Ivanchenko)
43 // 23-12-02 Change interface in order to move to cut per region (V.Ivanchenko)
44 // 27-01-03 Make models region aware (V.Ivanchenko)
45 // 13-02-03 Add name (V.Ivanchenko)
46 // 08-04-05 Major optimisation of internal interfaces (V.Ivantchenko)
47 // 25-07-05 Add protection in calculation of recoil direction for the case
48 // of complete energy transfer from e+ to e- (V.Ivanchenko)
49 // 06-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma)
50 // 15-05-06 Fix MinEnergyCut (V.Ivanchenko)
51 //
52 //
53 // Class Description:
54 //
55 // Implementation of energy loss and delta-electron production by e+/e-
56 //
57 // -------------------------------------------------------------------
58 //
59 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
60 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
61 
62 #include "G4MollerBhabhaModel.hh"
63 #include "G4PhysicalConstants.hh"
64 #include "G4SystemOfUnits.hh"
65 #include "G4Electron.hh"
66 #include "G4Positron.hh"
67 #include "Randomize.hh"
68 #include "G4ParticleChangeForLoss.hh"
69 
70 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
71 
72 using namespace std;
73 
74 G4MollerBhabhaModel::G4MollerBhabhaModel(const G4ParticleDefinition* p,
75  const G4String& nam)
76  : G4VEmModel(nam),
77  particle(0),
78  isElectron(true),
79  twoln10(2.0*log(10.0)),
80  lowLimit(0.02*keV),
81  isInitialised(false)
82 {
83  theElectron = G4Electron::Electron();
84  if(p) { SetParticle(p); }
85  fParticleChange = 0;
86 }
87 
88 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
89 
90 G4MollerBhabhaModel::~G4MollerBhabhaModel()
91 {}
92 
93 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
94 
95 G4double G4MollerBhabhaModel::MaxSecondaryEnergy(const G4ParticleDefinition*,
96  G4double kinEnergy)
97 {
98  G4double tmax = kinEnergy;
99  if(isElectron) { tmax *= 0.5; }
100  return tmax;
101 }
102 
103 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
104 
105 void G4MollerBhabhaModel::Initialise(const G4ParticleDefinition* p,
106  const G4DataVector&)
107 {
108  if(!particle) { SetParticle(p); }
109 
110  if(isInitialised) { return; }
111 
112  isInitialised = true;
113  fParticleChange = GetParticleChangeForLoss();
114 }
115 
116 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
117 
118 G4double
119 G4MollerBhabhaModel::ComputeCrossSectionPerElectron(const G4ParticleDefinition* p,
120  G4double kineticEnergy,
121  G4double cutEnergy,
122  G4double maxEnergy)
123 {
124  if(!particle) { SetParticle(p); }
125 
126  G4double cross = 0.0;
127  G4double tmax = MaxSecondaryEnergy(p, kineticEnergy);
128  tmax = std::min(maxEnergy, tmax);
129 
130  if(cutEnergy < tmax) {
131 
132  G4double xmin = cutEnergy/kineticEnergy;
133  G4double xmax = tmax/kineticEnergy;
134  G4double tau = kineticEnergy/electron_mass_c2;
135  G4double gam = tau + 1.0;
136  G4double gamma2= gam*gam;
137  G4double beta2 = tau*(tau + 2)/gamma2;
138 
139  //Moller (e-e-) scattering
140  if (isElectron) {
141 
142  G4double gg = (2.0*gam - 1.0)/gamma2;
143  cross = ((xmax - xmin)*(1.0 - gg + 1.0/(xmin*xmax)
144  + 1.0/((1.0-xmin)*(1.0 - xmax)))
145  - gg*log( xmax*(1.0 - xmin)/(xmin*(1.0 - xmax)) ) ) / beta2;
146 
147  //Bhabha (e+e-) scattering
148  } else {
149 
150  G4double y = 1.0/(1.0 + gam);
151  G4double y2 = y*y;
152  G4double y12 = 1.0 - 2.0*y;
153  G4double b1 = 2.0 - y2;
154  G4double b2 = y12*(3.0 + y2);
155  G4double y122= y12*y12;
156  G4double b4 = y122*y12;
157  G4double b3 = b4 + y122;
158 
159  cross = (xmax - xmin)*(1.0/(beta2*xmin*xmax) + b2
160  - 0.5*b3*(xmin + xmax)
161  + b4*(xmin*xmin + xmin*xmax + xmax*xmax)/3.0)
162  - b1*log(xmax/xmin);
163  }
164 
165  cross *= twopi_mc2_rcl2/kineticEnergy;
166  }
167  return cross;
168 }
169 
170 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
171 
172 G4double G4MollerBhabhaModel::ComputeCrossSectionPerAtom(
173  const G4ParticleDefinition* p,
174  G4double kineticEnergy,
175  G4double Z, G4double,
176  G4double cutEnergy,
177  G4double maxEnergy)
178 {
179  return Z*ComputeCrossSectionPerElectron(p,kineticEnergy,cutEnergy,maxEnergy);
180 }
181 
182 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
183 
184 G4double G4MollerBhabhaModel::CrossSectionPerVolume(
185  const G4Material* material,
186  const G4ParticleDefinition* p,
187  G4double kinEnergy,
188  G4double cutEnergy,
189  G4double maxEnergy)
190 {
191  G4double eDensity = material->GetElectronDensity();
192  return eDensity*ComputeCrossSectionPerElectron(p,kinEnergy,cutEnergy,maxEnergy);
193  /*
194  G4double Zeff = eDensity/material->GetTotNbOfAtomsPerVolume();
195  G4double th = 0.25*sqrt(Zeff)*keV;
196  G4double cut;
197  if(isElectron) { cut = std::max(th*0.5, cutEnergy); }
198  else { cut = std::max(th, cutEnergy); }
199  G4double res = 0.0;
200  // below this threshold no bremsstrahlung
201  if (kinEnergy > th) {
202  res = eDensity*ComputeCrossSectionPerElectron(p,kinEnergy,cut,maxEnergy);
203  }
204  return res;
205  */
206 }
207 
208 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
209 
210 G4double G4MollerBhabhaModel::ComputeDEDXPerVolume(
211  const G4Material* material,
212  const G4ParticleDefinition* p,
213  G4double kineticEnergy,
214  G4double cut)
215 {
216  if(!particle) { SetParticle(p); }
217  // calculate the dE/dx due to the ionization by Seltzer-Berger formula
218  // checl low-energy limit
219  G4double electronDensity = material->GetElectronDensity();
220 
221  G4double Zeff = electronDensity/material->GetTotNbOfAtomsPerVolume();
222  G4double th = 0.25*sqrt(Zeff)*keV;
223  // G4double cut;
224  // if(isElectron) { cut = std::max(th*0.5, cutEnergy); }
225  // else { cut = std::max(th, cutEnergy); }
226  G4double tkin = kineticEnergy;
227  if (kineticEnergy < th) { tkin = th; }
228 
229  G4double tau = tkin/electron_mass_c2;
230  G4double gam = tau + 1.0;
231  G4double gamma2= gam*gam;
232  G4double bg2 = tau*(tau + 2);
233  G4double beta2 = bg2/gamma2;
234 
235  G4double eexc = material->GetIonisation()->GetMeanExcitationEnergy();
236  eexc /= electron_mass_c2;
237  G4double eexc2 = eexc*eexc;
238 
239  G4double d = std::min(cut, MaxSecondaryEnergy(p, tkin))/electron_mass_c2;
240  G4double dedx;
241 
242  // electron
243  if (isElectron) {
244 
245  dedx = log(2.0*(tau + 2.0)/eexc2) - 1.0 - beta2
246  + log((tau-d)*d) + tau/(tau-d)
247  + (0.5*d*d + (2.0*tau + 1.)*log(1. - d/tau))/gamma2;
248 
249  //positron
250  } else {
251 
252  G4double d2 = d*d*0.5;
253  G4double d3 = d2*d/1.5;
254  G4double d4 = d3*d*0.75;
255  G4double y = 1.0/(1.0 + gam);
256  dedx = log(2.0*(tau + 2.0)/eexc2) + log(tau*d)
257  - beta2*(tau + 2.0*d - y*(3.0*d2
258  + y*(d - d3 + y*(d2 - tau*d3 + d4))))/tau;
259  }
260 
261  //density correction
262  G4double x = log(bg2)/twoln10;
263  dedx -= material->GetIonisation()->DensityCorrection(x);
264 
265  // now you can compute the total ionization loss
266  dedx *= twopi_mc2_rcl2*electronDensity/beta2;
267  if (dedx < 0.0) { dedx = 0.0; }
268 
269  // lowenergy extrapolation
270 
271  if (kineticEnergy < th) {
272  x = kineticEnergy/th;
273  if(x > 0.25) { dedx /= sqrt(x); }
274  else { dedx *= 1.4*sqrt(x)/(0.1 + x); }
275  }
276  return dedx;
277 }
278 
279 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
280 
281 void G4MollerBhabhaModel::SampleSecondaries(std::vector<G4DynamicParticle*>* vdp,
282  const G4MaterialCutsCouple*,
283  const G4DynamicParticle* dp,
284  G4double cutEnergy,
285  G4double maxEnergy)
286 {
287  G4double kineticEnergy = dp->GetKineticEnergy();
288  //const G4Material* mat = couple->GetMaterial();
289  //G4double Zeff = mat->GetElectronDensity()/mat->GetTotNbOfAtomsPerVolume();
290  // G4double th = 0.25*sqrt(Zeff)*keV;
291  G4double tmax;
292  G4double tmin = cutEnergy;
293  if(isElectron) {
294  tmax = 0.5*kineticEnergy;
295  } else {
296  tmax = kineticEnergy;
297  }
298  if(maxEnergy < tmax) { tmax = maxEnergy; }
299  if(tmin >= tmax) { return; }
300 
301  G4double energy = kineticEnergy + electron_mass_c2;
302  G4double totalMomentum = sqrt(kineticEnergy*(energy + electron_mass_c2));
303  G4double xmin = tmin/kineticEnergy;
304  G4double xmax = tmax/kineticEnergy;
305  G4double gam = energy/electron_mass_c2;
306  G4double gamma2 = gam*gam;
307  G4double beta2 = 1.0 - 1.0/gamma2;
308  G4double x, z, q, grej;
309 
310  G4ThreeVector direction = dp->GetMomentumDirection();
311 
312  //Moller (e-e-) scattering
313  if (isElectron) {
314 
315  G4double gg = (2.0*gam - 1.0)/gamma2;
316  G4double y = 1.0 - xmax;
317  grej = 1.0 - gg*xmax + xmax*xmax*(1.0 - gg + (1.0 - gg*y)/(y*y));
318 
319  do {
320  q = G4UniformRand();
321  x = xmin*xmax/(xmin*(1.0 - q) + xmax*q);
322  y = 1.0 - x;
323  z = 1.0 - gg*x + x*x*(1.0 - gg + (1.0 - gg*y)/(y*y));
324  /*
325  if(z > grej) {
326  G4cout << "G4MollerBhabhaModel::SampleSecondary Warning! "
327  << "Majorant " << grej << " < "
328  << z << " for x= " << x
329  << " e-e- scattering"
330  << G4endl;
331  }
332  */
333  } while(grej * G4UniformRand() > z);
334 
335  //Bhabha (e+e-) scattering
336  } else {
337 
338  G4double y = 1.0/(1.0 + gam);
339  G4double y2 = y*y;
340  G4double y12 = 1.0 - 2.0*y;
341  G4double b1 = 2.0 - y2;
342  G4double b2 = y12*(3.0 + y2);
343  G4double y122= y12*y12;
344  G4double b4 = y122*y12;
345  G4double b3 = b4 + y122;
346 
347  y = xmax*xmax;
348  grej = 1.0 + (y*y*b4 - xmin*xmin*xmin*b3 + y*b2 - xmin*b1)*beta2;
349  do {
350  q = G4UniformRand();
351  x = xmin*xmax/(xmin*(1.0 - q) + xmax*q);
352  y = x*x;
353  z = 1.0 + (y*y*b4 - x*y*b3 + y*b2 - x*b1)*beta2;
354  /*
355  if(z > grej) {
356  G4cout << "G4MollerBhabhaModel::SampleSecondary Warning! "
357  << "Majorant " << grej << " < "
358  << z << " for x= " << x
359  << " e+e- scattering"
360  << G4endl;
361  }
362  */
363  } while(grej * G4UniformRand() > z);
364  }
365 
366  G4double deltaKinEnergy = x * kineticEnergy;
367 
368  G4double deltaMomentum =
369  sqrt(deltaKinEnergy * (deltaKinEnergy + 2.0*electron_mass_c2));
370  G4double cost = deltaKinEnergy * (energy + electron_mass_c2) /
371  (deltaMomentum * totalMomentum);
372  G4double sint = (1.0 - cost)*(1. + cost);
373  if(sint > 0.0) { sint = sqrt(sint); }
374  else { sint = 0.0; }
375 
376  G4double phi = twopi * G4UniformRand() ;
377 
378  G4ThreeVector deltaDirection(sint*cos(phi),sint*sin(phi), cost) ;
379  deltaDirection.rotateUz(direction);
380 
381  // primary change
382  kineticEnergy -= deltaKinEnergy;
383  fParticleChange->SetProposedKineticEnergy(kineticEnergy);
384 
385  G4ThreeVector dir = totalMomentum*direction - deltaMomentum*deltaDirection;
386  direction = dir.unit();
387  fParticleChange->SetProposedMomentumDirection(direction);
388 
389  // create G4DynamicParticle object for delta ray
390  G4DynamicParticle* delta = new G4DynamicParticle(theElectron,
391  deltaDirection,deltaKinEnergy);
392  vdp->push_back(delta);
393 }
394 
395 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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