source: trunk/source/processes/electromagnetic/standard/src/G4UniversalFluctuation.cc@ 1199

Last change on this file since 1199 was 1196, checked in by garnier, 16 years ago

update CVS release candidate geant4.9.3.01
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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-cand-01 $
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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