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G4mplIonisationModel.cc
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26 // $Id: G4mplIonisationModel.cc 66996 2013-01-29 14:50:52Z gcosmo $
27 //
28 // -------------------------------------------------------------------
29 //
30 // GEANT4 Class header file
31 //
32 //
33 // File name: G4mplIonisationModel
34 //
35 // Author: Vladimir Ivanchenko
36 //
37 // Creation date: 06.09.2005
38 //
39 // Modifications:
40 // 12.08.2007 Changing low energy approximation and extrapolation.
41 // Small bug fixing and refactoring (M. Vladymyrov)
42 // 13.11.2007 Use low-energy asymptotic from [3] (V.Ivanchenko)
43 //
44 //
45 // -------------------------------------------------------------------
46 // References
47 // [1] Steven P. Ahlen: Energy loss of relativistic heavy ionizing particles,
48 // S.P. Ahlen, Rev. Mod. Phys 52(1980), p121
49 // [2] K.A. Milton arXiv:hep-ex/0602040
50 // [3] S.P. Ahlen and K. Kinoshita, Phys. Rev. D26 (1982) 2347
51 
52 
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55 
56 #include "G4mplIonisationModel.hh"
57 #include "Randomize.hh"
58 #include "G4PhysicalConstants.hh"
59 #include "G4SystemOfUnits.hh"
60 #include "G4LossTableManager.hh"
61 #include "G4ParticleChangeForLoss.hh"
62 
63 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
64 
65 using namespace std;
66 
67 G4mplIonisationModel::G4mplIonisationModel(G4double mCharge, const G4String& nam)
68  : G4VEmModel(nam),G4VEmFluctuationModel(nam),
69  magCharge(mCharge),
70  twoln10(log(100.0)),
71  betalow(0.01),
72  betalim(0.1),
73  beta2lim(betalim*betalim),
74  bg2lim(beta2lim*(1.0 + beta2lim))
75 {
76  nmpl = G4int(abs(magCharge) * 2 * fine_structure_const + 0.5);
77  if(nmpl > 6) { nmpl = 6; }
78  else if(nmpl < 1) { nmpl = 1; }
79  pi_hbarc2_over_mc2 = pi * hbarc * hbarc / electron_mass_c2;
80  chargeSquare = magCharge * magCharge;
81  dedxlim = 45.*nmpl*nmpl*GeV*cm2/g;
82  fParticleChange = 0;
83  monopole = 0;
84  mass = 0.0;
85 }
86 
87 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
88 
89 G4mplIonisationModel::~G4mplIonisationModel()
90 {}
91 
92 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
93 
94 void G4mplIonisationModel::SetParticle(const G4ParticleDefinition* p)
95 {
96  monopole = p;
97  mass = monopole->GetPDGMass();
98  G4double emin =
99  std::min(LowEnergyLimit(),0.1*mass*(1/sqrt(1 - betalow*betalow) - 1));
100  G4double emax =
101  std::max(HighEnergyLimit(),10*mass*(1/sqrt(1 - beta2lim) - 1));
102  SetLowEnergyLimit(emin);
103  SetHighEnergyLimit(emax);
104 }
105 
106 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
107 
108 void G4mplIonisationModel::Initialise(const G4ParticleDefinition* p,
109  const G4DataVector&)
110 {
111  if(!monopole) { SetParticle(p); }
112  if(!fParticleChange) { fParticleChange = GetParticleChangeForLoss(); }
113 }
114 
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116 
117 G4double G4mplIonisationModel::ComputeDEDXPerVolume(const G4Material* material,
118  const G4ParticleDefinition* p,
119  G4double kineticEnergy,
120  G4double)
121 {
122  if(!monopole) { SetParticle(p); }
123  G4double tau = kineticEnergy / mass;
124  G4double gam = tau + 1.0;
125  G4double bg2 = tau * (tau + 2.0);
126  G4double beta2 = bg2 / (gam * gam);
127  G4double beta = sqrt(beta2);
128 
129  // low-energy asymptotic formula
130  G4double dedx = dedxlim*beta*material->GetDensity();
131 
132  // above asymptotic
133  if(beta > betalow) {
134 
135  // high energy
136  if(beta >= betalim) {
137  dedx = ComputeDEDXAhlen(material, bg2);
138 
139  } else {
140 
141  G4double dedx1 = dedxlim*betalow*material->GetDensity();
142  G4double dedx2 = ComputeDEDXAhlen(material, bg2lim);
143 
144  // extrapolation between two formula
145  G4double kapa2 = beta - betalow;
146  G4double kapa1 = betalim - beta;
147  dedx = (kapa1*dedx1 + kapa2*dedx2)/(kapa1 + kapa2);
148  }
149  }
150  return dedx;
151 }
152 
153 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
154 
155 G4double G4mplIonisationModel::ComputeDEDXAhlen(const G4Material* material,
156  G4double bg2)
157 {
158  G4double eDensity = material->GetElectronDensity();
159  G4double eexc = material->GetIonisation()->GetMeanExcitationEnergy();
160  G4double cden = material->GetIonisation()->GetCdensity();
161  G4double mden = material->GetIonisation()->GetMdensity();
162  G4double aden = material->GetIonisation()->GetAdensity();
163  G4double x0den = material->GetIonisation()->GetX0density();
164  G4double x1den = material->GetIonisation()->GetX1density();
165 
166  // Ahlen's formula for nonconductors, [1]p157, f(5.7)
167  G4double dedx = log(2.0 * electron_mass_c2 * bg2 / eexc) - 0.5;
168 
169  // Kazama et al. cross-section correction
170  G4double k = 0.406;
171  if(nmpl > 1) k = 0.346;
172 
173  // Bloch correction
174  const G4double B[7] = { 0.0, 0.248, 0.672, 1.022, 1.243, 1.464, 1.685};
175 
176  dedx += 0.5 * k - B[nmpl];
177 
178  // density effect correction
179  G4double deltam;
180  G4double x = log(bg2) / twoln10;
181  if ( x >= x0den ) {
182  deltam = twoln10 * x - cden;
183  if ( x < x1den ) deltam += aden * pow((x1den-x), mden);
184  dedx -= 0.5 * deltam;
185  }
186 
187  // now compute the total ionization loss
188  dedx *= pi_hbarc2_over_mc2 * eDensity * nmpl * nmpl;
189 
190  if (dedx < 0.0) dedx = 0;
191  return dedx;
192 }
193 
194 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
195 
196 void G4mplIonisationModel::SampleSecondaries(std::vector<G4DynamicParticle*>*,
197  const G4MaterialCutsCouple*,
198  const G4DynamicParticle*,
199  G4double,
200  G4double)
201 {}
202 
203 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
204 
205 G4double G4mplIonisationModel::SampleFluctuations(
206  const G4Material* material,
207  const G4DynamicParticle* dp,
208  G4double& tmax,
209  G4double& length,
210  G4double& meanLoss)
211 {
212  G4double siga = Dispersion(material,dp,tmax,length);
213  G4double loss = meanLoss;
214  siga = sqrt(siga);
215  G4double twomeanLoss = meanLoss + meanLoss;
216 
217  if(twomeanLoss < siga) {
218  G4double x;
219  do {
220  loss = twomeanLoss*G4UniformRand();
221  x = (loss - meanLoss)/siga;
222  } while (1.0 - 0.5*x*x < G4UniformRand());
223  } else {
224  do {
225  loss = G4RandGauss::shoot(meanLoss,siga);
226  } while (0.0 > loss || loss > twomeanLoss);
227  }
228  return loss;
229 }
230 
231 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
232 
233 G4double G4mplIonisationModel::Dispersion(const G4Material* material,
234  const G4DynamicParticle* dp,
235  G4double& tmax,
236  G4double& length)
237 {
238  G4double siga = 0.0;
239  G4double tau = dp->GetKineticEnergy()/mass;
240  if(tau > 0.0) {
241  G4double electronDensity = material->GetElectronDensity();
242  G4double gam = tau + 1.0;
243  G4double invbeta2 = (gam*gam)/(tau * (tau+2.0));
244  siga = (invbeta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
245  * electronDensity * chargeSquare;
246  }
247  return siga;
248 }
249 
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