Geant4_10
G4hPairProductionModel.cc
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26 // $Id: G4hPairProductionModel.cc 74020 2013-09-19 13:38:38Z gcosmo $
27 //
28 // -------------------------------------------------------------------
29 //
30 // GEANT4 Class file
31 //
32 //
33 // File name: G4hPairProductionModel
34 //
35 // Author: Vladimir Ivanchenko on base of G4MuPairProductionModel
36 //
37 // Creation date: 28.02.2008
38 //
39 // Modifications:
40 //
41 
42 //
43 // Class Description:
44 //
45 //
46 // -------------------------------------------------------------------
47 //
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50 
52 #include "G4PhysicalConstants.hh"
53 #include "G4Log.hh"
54 #include "G4Exp.hh"
55 
56 using namespace std;
57 
59  const G4String& nam)
60  : G4MuPairProductionModel(p, nam)
61 {}
62 
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64 
66 {}
67 
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69 
71  G4double tkin,
72  G4double Z,
73  G4double pairEnergy)
74 // differential cross section
75 {
76  static const G4double bbbtf= 183. ;
77  static const G4double bbbh = 202.4 ;
78  static const G4double g1tf = 1.95e-5 ;
79  static const G4double g2tf = 5.3e-5 ;
80  static const G4double g1h = 4.4e-5 ;
81  static const G4double g2h = 4.8e-5 ;
82 
83  G4double totalEnergy = tkin + particleMass;
84  G4double residEnergy = totalEnergy - pairEnergy;
85  G4double massratio = particleMass/electron_mass_c2 ;
86  G4double massratio2 = massratio*massratio ;
87  G4double cross = 0.;
88 
89  G4double c3 = 0.75*sqrte*particleMass;
90  if (residEnergy <= c3*z13) { return cross; }
91 
92  G4double c7 = 4.*CLHEP::electron_mass_c2;
93  G4double c8 = 6.*particleMass*particleMass;
94  G4double alf = c7/pairEnergy;
95  G4double a3 = 1. - alf;
96  if (a3 <= 0.) { return cross; }
97 
98  // zeta calculation
99  G4double bbb,g1,g2;
100  if( Z < 1.5 ) { bbb = bbbh ; g1 = g1h ; g2 = g2h ; }
101  else { bbb = bbbtf; g1 = g1tf; g2 = g2tf; }
102 
103  G4double zeta = 0;
104  G4double zeta1 =
105  0.073*G4Log(totalEnergy/(particleMass+g1*z23*totalEnergy))-0.26;
106  if ( zeta1 > 0.)
107  {
108  G4double zeta2 =
109  0.058*G4Log(totalEnergy/(particleMass+g2*z13*totalEnergy))-0.14;
110  zeta = zeta1/zeta2 ;
111  }
112 
113  G4double z2 = Z*(Z+zeta);
114  G4double screen0 = 2.*electron_mass_c2*sqrte*bbb/(z13*pairEnergy);
115  G4double a0 = totalEnergy*residEnergy;
116  G4double a1 = pairEnergy*pairEnergy/a0;
117  G4double bet = 0.5*a1;
118  G4double xi0 = 0.25*massratio2*a1;
119  G4double del = c8/a0;
120 
121  G4double rta3 = sqrt(a3);
122  G4double tmnexp = alf/(1. + rta3) + del*rta3;
123  if(tmnexp >= 1.0) { return cross; }
124 
125  G4double tmn = G4Log(tmnexp);
126  G4double sum = 0.;
127 
128  // Gaussian integration in ln(1-ro) ( with 8 points)
129  for (G4int i=0; i<8; i++)
130  {
131  G4double a4 = G4Exp(tmn*xgi[i]); // a4 = (1.-asymmetry)
132  G4double a5 = a4*(2.-a4) ;
133  G4double a6 = 1.-a5 ;
134  G4double a7 = 1.+a6 ;
135  G4double a9 = 3.+a6 ;
136  G4double xi = xi0*a5 ;
137  G4double xii = 1./xi ;
138  G4double xi1 = 1.+xi ;
139  G4double screen = screen0*xi1/a5 ;
140  G4double yeu = 5.-a6+4.*bet*a7 ;
141  G4double yed = 2.*(1.+3.*bet)*G4Log(3.+xii)-a6-a1*(2.-a6) ;
142  G4double ye1 = 1.+yeu/yed ;
143  G4double ale=G4Log(bbb/z13*sqrt(xi1*ye1)/(1.+screen*ye1)) ;
144  G4double cre = 0.5*G4Log(1.+2.25*z23*xi1*ye1/massratio2) ;
145  G4double be;
146 
147  if (xi <= 1.e3) {
148  be = ((2.+a6)*(1.+bet)+xi*a9)*G4Log(1.+xii)+(a5-bet)/xi1-a9;
149  } else {
150  be = (3.-a6+a1*a7)/(2.*xi);
151  }
152  G4double fe = (ale-cre)*be;
153  if ( fe < 0.) { fe = 0.; }
154 
155  G4double ymu = 4.+a6 +3.*bet*a7 ;
156  G4double ymd = a7*(1.5+a1)*G4Log(3.+xi)+1.-1.5*a6 ;
157  G4double ym1 = 1.+ymu/ymd ;
158  G4double alm_crm = G4Log(bbb*massratio/(1.5*z23*(1.+screen*ym1)));
159  G4double a10,bm;
160  if ( xi >= 1.e-3)
161  {
162  a10 = (1.+a1)*a5 ;
163  bm = (a7*(1.+1.5*bet)-a10*xii)*G4Log(xi1)+xi*(a5-bet)/xi1+a10;
164  } else {
165  bm = (5.-a6+bet*a9)*(xi/2.);
166  }
167 
168  G4double fm = alm_crm*bm;
169  if ( fm < 0.) { fm = 0.; }
170 
171  sum += wgi[i]*a4*(fe+fm/massratio2);
172  }
173 
174  cross = -tmn*sum*factorForCross*z2*residEnergy/(totalEnergy*pairEnergy);
175 
176  return cross;
177 }
178 
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G4hPairProductionModel(const G4ParticleDefinition *p=0, const G4String &nam="hPairProd")
static const G4double xgi[8]
const char * p
Definition: xmltok.h:285
int G4int
Definition: G4Types.hh:78
virtual G4double ComputeDMicroscopicCrossSection(G4double tkin, G4double Z, G4double pairEnergy)
Float_t Z
Definition: plot.C:39
float electron_mass_c2
Definition: hepunit.py:274
G4double G4Log(G4double x)
Definition: G4Log.hh:227
G4double G4Exp(G4double initial_x)
Exponential Function double precision.
Definition: G4Exp.hh:180
#define fm
static const G4double wgi[8]
double G4double
Definition: G4Types.hh:76
G4fissionEvent * fe