source: trunk/source/processes/electromagnetic/standard/src/G4UniversalFluctuation.cc @ 1315

Last change on this file since 1315 was 1228, checked in by garnier, 14 years ago

update geant4.9.3 tag
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25//
26// $Id: G4UniversalFluctuation.cc,v 1.22 2009/03/20 18:11:23 urban Exp $
27// GEANT4 tag $Name: geant4-09-03 $
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// 19-03-09 new width correction (does not depend on previous steps) (L.Urban)         
60// 20-03-09 modification in the width correction (L.Urban)
61//
62
63//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
64//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
65
66#include "G4UniversalFluctuation.hh"
67#include "Randomize.hh"
68#include "G4Poisson.hh"
69#include "G4Step.hh"
70#include "G4Material.hh"
71#include "G4DynamicParticle.hh"
72#include "G4ParticleDefinition.hh"
73
74//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
75
76using namespace std;
77
78G4UniversalFluctuation::G4UniversalFluctuation(const G4String& nam)
79 :G4VEmFluctuationModel(nam),
80  particle(0),
81  minNumberInteractionsBohr(10.0),
82  theBohrBeta2(50.0*keV/proton_mass_c2),
83  minLoss(10.*eV),
84  nmaxCont1(4.),
85  nmaxCont2(16.)
86{
87  lastMaterial = 0;
88}
89
90//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
91
92G4UniversalFluctuation::~G4UniversalFluctuation()
93{}
94
95//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
96
97void G4UniversalFluctuation::InitialiseMe(const G4ParticleDefinition* part)
98{
99  particle       = part;
100  particleMass   = part->GetPDGMass();
101  G4double q     = part->GetPDGCharge()/eplus;
102  chargeSquare   = q*q;
103}
104
105//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
106
107G4double G4UniversalFluctuation::SampleFluctuations(const G4Material* material,
108                                                    const G4DynamicParticle* dp,
109                                                    G4double& tmax,
110                                                    G4double& length,
111                                                    G4double& meanLoss)
112{
113// Calculate actual loss from the mean loss.
114// The model used to get the fluctuations is essentially the same
115// as in Glandz in Geant3 (Cern program library W5013, phys332).
116// L. Urban et al. NIM A362, p.416 (1995) and Geant4 Physics Reference Manual
117
118  // shortcut for very very small loss (out of validity of the model)
119  //
120  if (meanLoss < minLoss)
121    return meanLoss;
122
123  if(!particle) InitialiseMe(dp->GetDefinition());
124
125  G4double tau   = dp->GetKineticEnergy()/particleMass;
126  G4double gam   = tau + 1.0;
127  G4double gam2  = gam*gam;
128  G4double beta2 = tau*(tau + 2.0)/gam2;
129
130  G4double loss(0.), siga(0.);
131 
132  // Gaussian regime
133  // for heavy particles only and conditions
134  // for Gauusian fluct. has been changed
135  //
136  if ((particleMass > electron_mass_c2) &&
137      (meanLoss >= minNumberInteractionsBohr*tmax))
138  {
139    G4double massrate = electron_mass_c2/particleMass ;
140    G4double tmaxkine = 2.*electron_mass_c2*beta2*gam2/
141                        (1.+massrate*(2.*gam+massrate)) ;
142    if (tmaxkine <= 2.*tmax)   
143    {
144      electronDensity = material->GetElectronDensity();
145      siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
146                                * electronDensity * chargeSquare;
147      siga = sqrt(siga);
148      G4double twomeanLoss = meanLoss + meanLoss;
149      if (twomeanLoss < siga) {
150        G4double x;
151        do {
152          loss = twomeanLoss*G4UniformRand();
153          x = (loss - meanLoss)/siga;
154        } while (1.0 - 0.5*x*x < G4UniformRand());
155      } else {
156        do {
157          loss = G4RandGauss::shoot(meanLoss,siga);
158        } while (loss < 0. || loss > twomeanLoss);
159      }
160      return loss;
161    }
162  }
163
164  // Glandz regime : initialisation
165  //
166  if (material != lastMaterial) {
167    f1Fluct      = material->GetIonisation()->GetF1fluct();
168    f2Fluct      = material->GetIonisation()->GetF2fluct();
169    e1Fluct      = material->GetIonisation()->GetEnergy1fluct();
170    e2Fluct      = material->GetIonisation()->GetEnergy2fluct();
171    e1LogFluct   = material->GetIonisation()->GetLogEnergy1fluct();
172    e2LogFluct   = material->GetIonisation()->GetLogEnergy2fluct();
173    ipotFluct    = material->GetIonisation()->GetMeanExcitationEnergy();
174    ipotLogFluct = material->GetIonisation()->GetLogMeanExcEnergy();
175    e0 = material->GetIonisation()->GetEnergy0fluct();
176    lastMaterial = material;
177 
178    // modification of some model parameters
179    // (this part should go to materials later)
180    G4double p = 1.40;
181    f2Fluct *= p;
182    f1Fluct = 1.-f2Fluct;
183    G4double q = 1.00;
184    e2Fluct *= q;
185    e2LogFluct = log(e2Fluct);
186    e1LogFluct = (ipotLogFluct-f2Fluct*e2LogFluct)/f1Fluct;
187    e1Fluct = exp(e1LogFluct);
188  }
189
190  // very small step or low-density material
191  if(tmax <= e0) return meanLoss;
192
193  G4double a1 = 0. , a2 = 0., a3 = 0. ;
194
195  // cut and material dependent rate
196  G4double rate = 1.0;
197  if(tmax > ipotFluct) {
198    G4double w2 = log(2.*electron_mass_c2*beta2*gam2)-beta2;
199
200    if(w2 > ipotLogFluct && w2 > e2LogFluct) {
201
202      rate = 0.03+0.23*log(log(tmax/ipotFluct));
203      G4double C = meanLoss*(1.-rate)/(w2-ipotLogFluct);
204      a1 = C*f1Fluct*(w2-e1LogFluct)/e1Fluct;
205      a2 = C*f2Fluct*(w2-e2LogFluct)/e2Fluct;
206      // correction in order to get better FWHM values
207      // ( scale parameters a1 and e1)
208      G4double width = 1.;
209      if(meanLoss > 10.*e1Fluct)
210      {
211        width = 3.1623/sqrt(meanLoss/e1Fluct);
212        if(width < a2/a1)
213        width = a2/a1;
214      } 
215      a1 *= width;
216      e1 = e1Fluct/width;
217      e2 = e2Fluct;
218    }
219  }
220
221  G4double w1 = tmax/e0;
222  if(tmax > e0) 
223    a3 = rate*meanLoss*(tmax-e0)/(e0*tmax*log(w1));
224
225  //'nearly' Gaussian fluctuation if a1>nmaxCont2&&a2>nmaxCont2&&a3>nmaxCont2 
226  G4double emean = 0.;
227  G4double sig2e = 0., sige = 0.;
228  G4double p1 = 0., p2 = 0., p3 = 0.;
229 
230  // excitation of type 1
231  if(a1 > nmaxCont2)
232  {
233    emean += a1*e1;
234    sig2e += a1*e1*e1;
235  }
236  else if(a1 > 0.)
237  {
238    p1 = G4double(G4Poisson(a1));
239    loss += p1*e1;
240    if(p1 > 0.) 
241      loss += (1.-2.*G4UniformRand())*e1;
242  }
243
244  // excitation of type 2
245  if(a2 > nmaxCont2)
246  {
247    emean += a2*e2;
248    sig2e += a2*e2*e2;
249  }
250  else if(a2 > 0.)
251  {
252    p2 = G4double(G4Poisson(a2));
253    loss += p2*e2;
254    if(p2 > 0.) 
255      loss += (1.-2.*G4UniformRand())*e2;
256  }
257
258  // ionisation
259  G4double lossc = 0.;
260  if(a3 > 0.)
261  {
262    p3 = a3;
263    G4double alfa = 1.;
264    if(a3 > nmaxCont2)
265    {
266       alfa            = w1*(nmaxCont2+a3)/(w1*nmaxCont2+a3);
267       G4double alfa1  = alfa*log(alfa)/(alfa-1.);
268       G4double namean = a3*w1*(alfa-1.)/((w1-1.)*alfa);
269       emean          += namean*e0*alfa1;
270       sig2e          += e0*e0*namean*(alfa-alfa1*alfa1);
271       p3              = a3-namean;
272    }
273
274    G4double w2 = alfa*e0;
275    G4double w  = (tmax-w2)/tmax;
276    G4int nb = G4Poisson(p3);
277    if(nb > 0)
278      for (G4int k=0; k<nb; k++) lossc += w2/(1.-w*G4UniformRand());
279  }
280
281  if(emean > 0.)
282  {
283    sige   = sqrt(sig2e);
284    loss += max(0.,G4RandGauss::shoot(emean,sige));
285  }
286
287  loss += lossc;
288
289  return loss;
290
291}
292
293//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
294
295
296G4double G4UniversalFluctuation::Dispersion(
297                          const G4Material* material,
298                          const G4DynamicParticle* dp,
299                                G4double& tmax,
300                                G4double& length)
301{
302  if(!particle) InitialiseMe(dp->GetDefinition());
303
304  electronDensity = material->GetElectronDensity();
305
306  G4double gam   = (dp->GetKineticEnergy())/particleMass + 1.0;
307  G4double beta2 = 1.0 - 1.0/(gam*gam);
308
309  G4double siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
310                 * electronDensity * chargeSquare;
311
312  return siga;
313}
314
315//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
316
317void 
318G4UniversalFluctuation::SetParticleAndCharge(const G4ParticleDefinition* part,
319                                             G4double q2)
320{
321  if(part != particle) {
322    particle       = part;
323    particleMass   = part->GetPDGMass();
324  }
325  chargeSquare = q2;
326}
327
328//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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