source: trunk/source/processes/electromagnetic/standard/src/G4UniversalFluctuation.cc @ 961

Last change on this file since 961 was 961, checked in by garnier, 15 years ago

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25//
26// $Id: G4UniversalFluctuation.cc,v 1.17 2009/02/19 11:26:01 vnivanch Exp $
27// GEANT4 tag $Name: geant4-09-02-ref-02 $
28//
29// -------------------------------------------------------------------
30//
31// GEANT4 Class file
32//
33//
34// File name:     G4UniversalFluctuation
35//
36// Author:        Vladimir Ivanchenko
37//
38// Creation date: 03.01.2002
39//
40// Modifications:
41//
42// 28-12-02 add method Dispersion (V.Ivanchenko)
43// 07-02-03 change signature (V.Ivanchenko)
44// 13-02-03 Add name (V.Ivanchenko)
45// 16-10-03 Changed interface to Initialisation (V.Ivanchenko)
46// 07-11-03 Fix problem of rounding of double in G4UniversalFluctuations
47// 06-02-04 Add control on big sigma > 2*meanLoss (V.Ivanchenko)
48// 26-04-04 Comment out the case of very small step (V.Ivanchenko)
49// 07-02-05 define problim = 5.e-3 (mma)
50// 03-05-05 conditions of Gaussian fluctuation changed (bugfix)
51//          + smearing for very small loss (L.Urban)
52// 03-10-05 energy dependent rate -> cut dependence of the
53//          distribution is much weaker (L.Urban)
54// 17-10-05 correction for very small loss (L.Urban)
55// 20-03-07 'GLANDZ' part rewritten completely, no 'very small loss'
56//          regime any more (L.Urban)
57// 03-04-07 correction to get better width of eloss distr.(L.Urban)
58// 13-07-07 add protection for very small step or low-density material (VI)
59//         
60
61//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
62//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
63
64#include "G4UniversalFluctuation.hh"
65#include "Randomize.hh"
66#include "G4Poisson.hh"
67#include "G4Step.hh"
68#include "G4Material.hh"
69#include "G4DynamicParticle.hh"
70#include "G4ParticleDefinition.hh"
71
72//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
73
74using namespace std;
75
76G4UniversalFluctuation::G4UniversalFluctuation(const G4String& nam)
77 :G4VEmFluctuationModel(nam),
78  particle(0),
79  minNumberInteractionsBohr(10.0),
80  theBohrBeta2(50.0*keV/proton_mass_c2),
81  minLoss(10.*eV),
82  nmaxCont1(4.),
83  nmaxCont2(16.)
84{
85  lastMaterial = 0;
86  facwidth     = 1.000/keV;
87  oldloss = 0.;
88  samestep = 0.;
89}
90
91//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
92
93G4UniversalFluctuation::~G4UniversalFluctuation()
94{}
95
96//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
97
98void G4UniversalFluctuation::InitialiseMe(const G4ParticleDefinition* part)
99{
100  particle       = part;
101  particleMass   = part->GetPDGMass();
102  G4double q     = part->GetPDGCharge()/eplus;
103  chargeSquare   = q*q;
104}
105
106//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
107
108G4double G4UniversalFluctuation::SampleFluctuations(const G4Material* material,
109                                                    const G4DynamicParticle* dp,
110                                                    G4double& tmax,
111                                                    G4double& length,
112                                                    G4double& meanLoss)
113{
114// Calculate actual loss from the mean loss.
115// The model used to get the fluctuations is essentially the same
116// as in Glandz in Geant3 (Cern program library W5013, phys332).
117// L. Urban et al. NIM A362, p.416 (1995) and Geant4 Physics Reference Manual
118
119  // shortcut for very very small loss (out of validity of the model)
120  //
121  if (meanLoss < minLoss)
122  { 
123    oldloss = meanLoss;
124    return meanLoss;
125  }
126
127  if(!particle) InitialiseMe(dp->GetDefinition());
128
129  G4double tau   = dp->GetKineticEnergy()/particleMass;
130  G4double gam   = tau + 1.0;
131  G4double gam2  = gam*gam;
132  G4double beta2 = tau*(tau + 2.0)/gam2;
133
134  G4double loss(0.), siga(0.);
135 
136  // Gaussian regime
137  // for heavy particles only and conditions
138  // for Gauusian fluct. has been changed
139  //
140  if ((particleMass > electron_mass_c2) &&
141      (meanLoss >= minNumberInteractionsBohr*tmax))
142  {
143    G4double massrate = electron_mass_c2/particleMass ;
144    G4double tmaxkine = 2.*electron_mass_c2*beta2*gam2/
145                        (1.+massrate*(2.*gam+massrate)) ;
146    if (tmaxkine <= 2.*tmax)   
147    {
148      electronDensity = material->GetElectronDensity();
149      siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
150                                * electronDensity * chargeSquare;
151      siga = sqrt(siga);
152      G4double twomeanLoss = meanLoss + meanLoss;
153      if (twomeanLoss < siga) {
154        G4double x;
155        do {
156          loss = twomeanLoss*G4UniformRand();
157          x = (loss - meanLoss)/siga;
158        } while (1.0 - 0.5*x*x < G4UniformRand());
159      } else {
160        do {
161          loss = G4RandGauss::shoot(meanLoss,siga);
162        } while (loss < 0. || loss > twomeanLoss);
163      }
164      return loss;
165    }
166  }
167
168  // Glandz regime : initialisation
169  //
170  if (material != lastMaterial) {
171    f1Fluct      = material->GetIonisation()->GetF1fluct();
172    f2Fluct      = material->GetIonisation()->GetF2fluct();
173    e1Fluct      = material->GetIonisation()->GetEnergy1fluct();
174    e2Fluct      = material->GetIonisation()->GetEnergy2fluct();
175    e1LogFluct   = material->GetIonisation()->GetLogEnergy1fluct();
176    e2LogFluct   = material->GetIonisation()->GetLogEnergy2fluct();
177    ipotFluct    = material->GetIonisation()->GetMeanExcitationEnergy();
178    ipotLogFluct = material->GetIonisation()->GetLogMeanExcEnergy();
179    e0 = material->GetIonisation()->GetEnergy0fluct();
180    lastMaterial = material;
181  }
182
183  // very small step or low-density material
184  if(tmax <= e0) return meanLoss;
185
186  G4double a1 = 0. , a2 = 0., a3 = 0. ;
187
188  // correction to get better width even using stepmax
189  if(abs(meanLoss- oldloss) < 1.*eV)
190    samestep += 1;
191  else
192    samestep = 1.;
193  oldloss = meanLoss;
194  G4double width = 1.+samestep*facwidth*meanLoss;
195  if(width > 4.50) width = 4.50;
196  e1 = width*e1Fluct;
197  e2 = width*e2Fluct;
198
199  // cut and material dependent rate
200  G4double rate = 1.0;
201  if(tmax > ipotFluct) {
202    G4double w2 = log(2.*electron_mass_c2*beta2*gam2)-beta2;
203
204    if(w2 > ipotLogFluct && w2 > e2LogFluct) {
205
206      rate = 0.03+0.23*log(log(tmax/ipotFluct));
207      G4double C = meanLoss*(1.-rate)/(w2-ipotLogFluct);
208      a1 = C*f1Fluct*(w2-e1LogFluct)/e1;
209      a2 = C*f2Fluct*(w2-e2LogFluct)/e2;
210    }
211  }
212
213  G4double w1 = tmax/e0;
214  if(tmax > e0) 
215    a3 = rate*meanLoss*(tmax-e0)/(e0*tmax*log(w1));
216
217  //'nearly' Gaussian fluctuation if a1>nmaxCont2&&a2>nmaxCont2&&a3>nmaxCont2 
218  G4double emean = 0.;
219  G4double sig2e = 0., sige = 0.;
220  G4double p1 = 0., p2 = 0., p3 = 0.;
221 
222  // excitation of type 1
223  if(a1 > nmaxCont2)
224  {
225    emean += a1*e1;
226    sig2e += a1*e1*e1;
227  }
228  else if(a1 > 0.)
229  {
230    p1 = G4double(G4Poisson(a1));
231    loss += p1*e1;
232    if(p1 > 0.) 
233      loss += (1.-2.*G4UniformRand())*e1;
234  }
235
236  // excitation of type 2
237  if(a2 > nmaxCont2)
238  {
239    emean += a2*e2;
240    sig2e += a2*e2*e2;
241  }
242  else if(a2 > 0.)
243  {
244    p2 = G4double(G4Poisson(a2));
245    loss += p2*e2;
246    if(p2 > 0.) 
247      loss += (1.-2.*G4UniformRand())*e2;
248  }
249
250  // ionisation
251  G4double lossc = 0.;
252  if(a3 > 0.)
253  {
254    p3 = a3;
255    G4double alfa = 1.;
256    if(a3 > nmaxCont2)
257    {
258       alfa            = w1*(nmaxCont2+a3)/(w1*nmaxCont2+a3);
259       G4double alfa1  = alfa*log(alfa)/(alfa-1.);
260       G4double namean = a3*w1*(alfa-1.)/((w1-1.)*alfa);
261       emean          += namean*e0*alfa1;
262       sig2e          += e0*e0*namean*(alfa-alfa1*alfa1);
263       p3              = a3-namean;
264    }
265
266    G4double w2 = alfa*e0;
267    G4double w  = (tmax-w2)/tmax;
268    G4int nb = G4Poisson(p3);
269    if(nb > 0)
270      for (G4int k=0; k<nb; k++) lossc += w2/(1.-w*G4UniformRand());
271  }
272
273  if(emean > 0.)
274  {
275    sige   = sqrt(sig2e);
276    loss += max(0.,G4RandGauss::shoot(emean,sige));
277  }
278
279  loss += lossc;
280
281  return loss;
282
283}
284
285//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
286
287
288G4double G4UniversalFluctuation::Dispersion(
289                          const G4Material* material,
290                          const G4DynamicParticle* dp,
291                                G4double& tmax,
292                                G4double& length)
293{
294  if(!particle) InitialiseMe(dp->GetDefinition());
295
296  electronDensity = material->GetElectronDensity();
297
298  G4double gam   = (dp->GetKineticEnergy())/particleMass + 1.0;
299  G4double beta2 = 1.0 - 1.0/(gam*gam);
300
301  G4double siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
302                 * electronDensity * chargeSquare;
303
304  return siga;
305}
306
307//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
308
309void 
310G4UniversalFluctuation::SetParticleAndCharge(const G4ParticleDefinition* part,
311                                             G4double q2)
312{
313  if(part != particle) {
314    particle       = part;
315    particleMass   = part->GetPDGMass();
316  }
317  chargeSquare = q2;
318}
319
320//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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