source: trunk/source/processes/electromagnetic/standard/src/G4UniversalFluctuation.cc @ 1340

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25//
26// $Id: G4UniversalFluctuation.cc,v 1.28 2010/10/26 10:06:12 vnivanch Exp $
27// GEANT4 tag $Name: emstand-V09-03-24 $
28//
29// -------------------------------------------------------------------
30//
31// GEANT4 Class file
32//
33//
34// File name:     G4UniversalFluctuation
35//
36// Author:        Laszlo Urban
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// 14-06-10 fixed tail distribution - do not use uniform function (L.Urban)
62// 08-08-10 width correction algorithm has bee modified -->
63//          better results for thin targets (L.Urban)
64//
65
66//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
67//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
68
69#include "G4UniversalFluctuation.hh"
70#include "Randomize.hh"
71#include "G4Poisson.hh"
72#include "G4Step.hh"
73#include "G4Material.hh"
74#include "G4DynamicParticle.hh"
75#include "G4ParticleDefinition.hh"
76
77//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
78
79using namespace std;
80
81G4UniversalFluctuation::G4UniversalFluctuation(const G4String& nam)
82 :G4VEmFluctuationModel(nam),
83  particle(0),
84  minNumberInteractionsBohr(10.0),
85  theBohrBeta2(50.0*keV/proton_mass_c2),
86  minLoss(10.*eV),
87  nmaxCont(16.),
88  rate(0.55),
89  fw(4.)
90{
91  lastMaterial = 0;
92
93  particleMass = chargeSquare = ipotFluct = electronDensity = f1Fluct = f2Fluct
94    = e1Fluct = e2Fluct = e1LogFluct = e2LogFluct = ipotLogFluct = e0 = esmall
95    = e1 = e2 = 0;
96}
97
98//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
99
100G4UniversalFluctuation::~G4UniversalFluctuation()
101{}
102
103//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
104
105void G4UniversalFluctuation::InitialiseMe(const G4ParticleDefinition* part)
106{
107  particle       = part;
108  particleMass   = part->GetPDGMass();
109  G4double q     = part->GetPDGCharge()/eplus;
110  chargeSquare   = q*q;
111}
112
113//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
114
115G4double G4UniversalFluctuation::SampleFluctuations(const G4Material* material,
116                                                    const G4DynamicParticle* dp,
117                                                    G4double& tmax,
118                                                    G4double& length,
119                                                    G4double& meanLoss)
120{
121// Calculate actual loss from the mean loss.
122// The model used to get the fluctuations is essentially the same
123// as in Glandz in Geant3 (Cern program library W5013, phys332).
124// L. Urban et al. NIM A362, p.416 (1995) and Geant4 Physics Reference Manual
125
126  // shortcut for very very small loss (out of validity of the model)
127  //
128  if (meanLoss < minLoss) { return meanLoss; }
129
130  if(!particle) { InitialiseMe(dp->GetDefinition()); }
131
132  G4double tau   = dp->GetKineticEnergy()/particleMass;
133  G4double gam   = tau + 1.0;
134  G4double gam2  = gam*gam;
135  G4double beta2 = tau*(tau + 2.0)/gam2;
136
137  G4double loss(0.), siga(0.);
138 
139  // Gaussian regime
140  // for heavy particles only and conditions
141  // for Gauusian fluct. has been changed
142  //
143  if ((particleMass > electron_mass_c2) &&
144      (meanLoss >= minNumberInteractionsBohr*tmax))
145  {
146    G4double massrate = electron_mass_c2/particleMass ;
147    G4double tmaxkine = 2.*electron_mass_c2*beta2*gam2/
148                        (1.+massrate*(2.*gam+massrate)) ;
149    if (tmaxkine <= 2.*tmax)   
150    {
151      electronDensity = material->GetElectronDensity();
152      siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
153                                * electronDensity * chargeSquare;
154      siga = sqrt(siga);
155      G4double twomeanLoss = meanLoss + meanLoss;
156      if (twomeanLoss < siga) {
157        G4double x;
158        do {
159          loss = twomeanLoss*G4UniformRand();
160          x = (loss - meanLoss)/siga;
161        } while (1.0 - 0.5*x*x < G4UniformRand());
162      } else {
163        do {
164          loss = G4RandGauss::shoot(meanLoss,siga);
165        } while (loss < 0. || loss > twomeanLoss);
166      }
167      return loss;
168    }
169  }
170
171  // Glandz regime : initialisation
172  //
173  if (material != lastMaterial) {
174    f1Fluct      = material->GetIonisation()->GetF1fluct();
175    f2Fluct      = material->GetIonisation()->GetF2fluct();
176    e1Fluct      = material->GetIonisation()->GetEnergy1fluct();
177    e2Fluct      = material->GetIonisation()->GetEnergy2fluct();
178    e1LogFluct   = material->GetIonisation()->GetLogEnergy1fluct();
179    e2LogFluct   = material->GetIonisation()->GetLogEnergy2fluct();
180    ipotFluct    = material->GetIonisation()->GetMeanExcitationEnergy();
181    ipotLogFluct = material->GetIonisation()->GetLogMeanExcEnergy();
182    e0 = material->GetIonisation()->GetEnergy0fluct();
183    esmall = 0.5*sqrt(e0*ipotFluct); 
184    lastMaterial = material;
185   
186  }
187
188  // very small step or low-density material
189  if(tmax <= e0) return meanLoss;
190
191  G4double a1 = 0. , a2 = 0., a3 = 0. ;
192
193  if(tmax > ipotFluct) {
194    G4double w2 = log(2.*electron_mass_c2*beta2*gam2)-beta2;
195
196    if(w2 > ipotLogFluct && w2 > e2LogFluct && tmax> ipotFluct)  {
197      G4double C = meanLoss*(1.-rate)/(w2-ipotLogFluct);
198      a1 = C*f1Fluct*(w2-e1LogFluct)/e1Fluct;
199      a2 = C*f2Fluct*(w2-e2LogFluct)/e2Fluct;
200         
201
202  if(a1 < nmaxCont) 
203  { 
204    //small energy loss
205    G4double sa1 = sqrt(a1);
206    if(G4UniformRand() < exp(-sa1))
207      {
208       e1 = esmall;
209       a1 = meanLoss*(1.-rate)/e1;
210       a2 = 0.;
211       e2 = e2Fluct;
212      } 
213      else
214      {
215       a1 = sa1 ;   
216       e1 = sa1*e1Fluct;
217       e2 = e2Fluct;
218      }
219    }
220    else
221    {
222      //not small energy loss
223      //correction to get better fwhm value
224      a1 /= fw;
225      e1 = fw*e1Fluct;
226      e2 = e2Fluct;
227    }
228  }   
229 }
230
231  G4double w1 = tmax/e0;
232  if(tmax > e0) 
233    a3 = rate*meanLoss*(tmax-e0)/(e0*tmax*log(w1));
234
235  //'nearly' Gaussian fluctuation if a1>nmaxCont&&a2>nmaxCont&&a3>nmaxCont 
236  G4double emean = 0.;
237  G4double sig2e = 0., sige = 0.;
238  G4double p1 = 0., p2 = 0., p3 = 0.;
239 
240  // excitation of type 1
241  if(a1 > nmaxCont)
242  {
243    emean += a1*e1;
244    sig2e += a1*e1*e1;
245  }
246  else if(a1 > 0.)
247  {
248    p1 = G4double(G4Poisson(a1));
249    loss += p1*e1;
250    if(p1 > 0.) 
251      loss += (1.-2.*G4UniformRand())*e1;
252  }
253
254  // excitation of type 2
255  if(a2 > nmaxCont)
256  {
257    emean += a2*e2;
258    sig2e += a2*e2*e2;
259  }
260  else if(a2 > 0.)
261  {
262    p2 = G4double(G4Poisson(a2));
263    loss += p2*e2;
264    if(p2 > 0.) 
265      loss += (1.-2.*G4UniformRand())*e2;
266  }
267
268  // ionisation
269  G4double lossc = 0.;
270  if(a3 > 0.)
271  {
272    p3 = a3;
273    G4double alfa = 1.;
274    if(a3 > nmaxCont)
275    {
276       alfa            = w1*(nmaxCont+a3)/(w1*nmaxCont+a3);
277       G4double alfa1  = alfa*log(alfa)/(alfa-1.);
278       G4double namean = a3*w1*(alfa-1.)/((w1-1.)*alfa);
279       emean          += namean*e0*alfa1;
280       sig2e          += e0*e0*namean*(alfa-alfa1*alfa1);
281       p3              = a3-namean;
282    }
283
284    G4double w2 = alfa*e0;
285    G4double w  = (tmax-w2)/tmax;
286    G4int nb = G4Poisson(p3);
287    if(nb > 0)
288      for (G4int k=0; k<nb; k++) lossc += w2/(1.-w*G4UniformRand());
289  }
290
291  if(emean > 0.)
292  {
293    sige   = sqrt(sig2e);
294    loss += max(0.,G4RandGauss::shoot(emean,sige));
295  }
296
297  loss += lossc;
298
299  return loss;
300
301}
302
303//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
304
305
306G4double G4UniversalFluctuation::Dispersion(
307                          const G4Material* material,
308                          const G4DynamicParticle* dp,
309                                G4double& tmax,
310                                G4double& length)
311{
312  if(!particle) InitialiseMe(dp->GetDefinition());
313
314  electronDensity = material->GetElectronDensity();
315
316  G4double gam   = (dp->GetKineticEnergy())/particleMass + 1.0;
317  G4double beta2 = 1.0 - 1.0/(gam*gam);
318
319  G4double siga  = (1.0/beta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
320                 * electronDensity * chargeSquare;
321
322  return siga;
323}
324
325//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
326
327void 
328G4UniversalFluctuation::SetParticleAndCharge(const G4ParticleDefinition* part,
329                                             G4double q2)
330{
331  if(part != particle) {
332    particle       = part;
333    particleMass   = part->GetPDGMass();
334  }
335  chargeSquare = q2;
336}
337
338//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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