source: trunk/source/processes/electromagnetic/highenergy/src/G4mplIonisationModel.cc @ 1340

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26// $Id: G4mplIonisationModel.cc,v 1.8 2010/10/26 15:40:03 vnivanch Exp $
27// GEANT4 tag $Name: emhighenergy-V09-03-02 $
28//
29// -------------------------------------------------------------------
30//
31// GEANT4 Class header file
32//
33//
34// File name:     G4mplIonisationModel
35//
36// Author:        Vladimir Ivanchenko
37//
38// Creation date: 06.09.2005
39//
40// Modifications:
41// 12.08.2007 Changing low energy approximation and extrapolation.
42//            Small bug fixing and refactoring (M. Vladymyrov)
43// 13.11.2007 Use low-energy asymptotic from [3] (V.Ivanchenko)
44//
45//
46// -------------------------------------------------------------------
47// References
48// [1] Steven P. Ahlen: Energy loss of relativistic heavy ionizing particles,
49//     S.P. Ahlen, Rev. Mod. Phys 52(1980), p121
50// [2] K.A. Milton arXiv:hep-ex/0602040
51// [3] S.P. Ahlen and K. Kinoshita, Phys. Rev. D26 (1982) 2347
52
53
54//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
55//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
56
57#include "G4mplIonisationModel.hh"
58#include "Randomize.hh"
59#include "G4LossTableManager.hh"
60#include "G4ParticleChangeForLoss.hh"
61
62//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
63
64using namespace std;
65
66G4mplIonisationModel::G4mplIonisationModel(G4double mCharge, const G4String& nam)
67  : G4VEmModel(nam),G4VEmFluctuationModel(nam),
68  magCharge(mCharge),
69  twoln10(log(100.0)),
70  betalow(0.01),
71  betalim(0.1),
72  beta2lim(betalim*betalim),
73  bg2lim(beta2lim*(1.0 + beta2lim))
74{
75  nmpl         = G4int(abs(magCharge) * 2 * fine_structure_const + 0.5);
76  if(nmpl > 6)      { nmpl = 6; }
77  else if(nmpl < 1) { nmpl = 1; }
78  pi_hbarc2_over_mc2 = pi * hbarc * hbarc / electron_mass_c2;
79  chargeSquare = magCharge * magCharge;
80  dedxlim = 45.*nmpl*nmpl*GeV*cm2/g;
81  fParticleChange = 0;
82  mass = 0.0;
83}
84
85//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
86
87G4mplIonisationModel::~G4mplIonisationModel()
88{}
89
90//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
91
92void G4mplIonisationModel::Initialise(const G4ParticleDefinition* p,
93                                      const G4DataVector&)
94{
95  monopole = p;
96  mass     = monopole->GetPDGMass();
97  if(!fParticleChange) { fParticleChange = GetParticleChangeForLoss(); }
98}
99
100//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
101
102G4double G4mplIonisationModel::ComputeDEDXPerVolume(const G4Material* material,
103                                                    const G4ParticleDefinition*,
104                                                    G4double kineticEnergy,
105                                                    G4double)
106{
107  G4double tau   = kineticEnergy / mass;
108  G4double gam   = tau + 1.0;
109  G4double bg2   = tau * (tau + 2.0);
110  G4double beta2 = bg2 / (gam * gam);
111  G4double beta  = sqrt(beta2);
112
113  // low-energy asymptotic formula
114  G4double dedx  = dedxlim*beta*material->GetDensity();
115
116  // above asymptotic
117  if(beta > betalow) {
118
119    // high energy
120    if(beta >= betalim) {
121      dedx = ComputeDEDXAhlen(material, bg2);
122
123    } else {
124
125      G4double dedx1 = dedxlim*betalow*material->GetDensity();
126      G4double dedx2 = ComputeDEDXAhlen(material, bg2lim);
127
128      // extrapolation between two formula
129      G4double kapa2 = beta - betalow;
130      G4double kapa1 = betalim - beta;
131      dedx = (kapa1*dedx1 + kapa2*dedx2)/(kapa1 + kapa2);
132    }
133  }
134  return dedx;
135}
136
137//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
138
139G4double G4mplIonisationModel::ComputeDEDXAhlen(const G4Material* material, 
140                                                G4double bg2)
141{
142  G4double eDensity = material->GetElectronDensity();
143  G4double eexc  = material->GetIonisation()->GetMeanExcitationEnergy();
144  G4double cden  = material->GetIonisation()->GetCdensity();
145  G4double mden  = material->GetIonisation()->GetMdensity();
146  G4double aden  = material->GetIonisation()->GetAdensity();
147  G4double x0den = material->GetIonisation()->GetX0density();
148  G4double x1den = material->GetIonisation()->GetX1density();
149
150  // Ahlen's formula for nonconductors, [1]p157, f(5.7)
151  G4double dedx = log(2.0 * electron_mass_c2 * bg2 / eexc) - 0.5;
152
153  // Kazama et al. cross-section correction
154  G4double  k = 0.406;
155  if(nmpl > 1) k = 0.346;
156
157  // Bloch correction
158  const G4double B[7] = { 0.0, 0.248, 0.672, 1.022, 1.243, 1.464, 1.685}; 
159
160  dedx += 0.5 * k - B[nmpl];
161
162  // density effect correction
163  G4double deltam;
164  G4double x = log(bg2) / twoln10;
165  if ( x >= x0den ) {
166    deltam = twoln10 * x - cden;
167    if ( x < x1den ) deltam += aden * pow((x1den-x), mden);
168    dedx -= 0.5 * deltam;
169  }
170
171  // now compute the total ionization loss
172  dedx *=  pi_hbarc2_over_mc2 * eDensity * nmpl * nmpl;
173
174  if (dedx < 0.0) dedx = 0;
175  return dedx;
176}
177
178//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
179
180void G4mplIonisationModel::SampleSecondaries(std::vector<G4DynamicParticle*>*,
181                                             const G4MaterialCutsCouple*,
182                                             const G4DynamicParticle*,
183                                             G4double,
184                                             G4double)
185{}
186
187//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
188
189G4double G4mplIonisationModel::SampleFluctuations(
190                                       const G4Material* material,
191                                       const G4DynamicParticle* dp,
192                                       G4double& tmax,
193                                       G4double& length,
194                                       G4double& meanLoss)
195{
196  G4double siga = Dispersion(material,dp,tmax,length);
197  G4double loss = meanLoss;
198  siga = sqrt(siga);
199  G4double twomeanLoss = meanLoss + meanLoss;
200
201  if(twomeanLoss < siga) {
202    G4double x;
203    do {
204      loss = twomeanLoss*G4UniformRand();
205      x = (loss - meanLoss)/siga;
206    } while (1.0 - 0.5*x*x < G4UniformRand());
207  } else {
208    do {
209      loss = G4RandGauss::shoot(meanLoss,siga);
210    } while (0.0 > loss || loss > twomeanLoss);
211  }
212  return loss;
213}
214
215//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
216
217G4double G4mplIonisationModel::Dispersion(const G4Material* material,
218                                          const G4DynamicParticle* dp,
219                                          G4double& tmax,
220                                          G4double& length)
221{
222  G4double siga = 0.0;
223  G4double tau   = dp->GetKineticEnergy()/mass;
224  if(tau > 0.0) { 
225    G4double electronDensity = material->GetElectronDensity();
226    G4double gam   = tau + 1.0;
227    G4double invbeta2 = (gam*gam)/(tau * (tau+2.0));
228    siga  = (invbeta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
229      * electronDensity * chargeSquare;
230  }
231  return siga;
232}
233
234//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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