G4hPairProductionModel.cc

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00025 //
00026 // $Id: G4hPairProductionModel.cc 66996 2013-01-29 14:50:52Z gcosmo $
00027 //
00028 // -------------------------------------------------------------------
00029 //
00030 // GEANT4 Class file
00031 //
00032 //
00033 // File name:     G4hPairProductionModel
00034 //
00035 // Author:        Vladimir Ivanchenko on base of G4MuPairProductionModel
00036 //
00037 // Creation date: 28.02.2008
00038 //
00039 // Modifications:
00040 //
00041 
00042 //
00043 // Class Description:
00044 //
00045 //
00046 // -------------------------------------------------------------------
00047 //
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00049 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
00050 
00051 #include "G4hPairProductionModel.hh"
00052 #include "G4PhysicalConstants.hh"
00053 
00054 using namespace std;
00055 
00056 G4hPairProductionModel::G4hPairProductionModel(const G4ParticleDefinition* p,
00057                                                const G4String& nam)
00058   : G4MuPairProductionModel(p, nam)
00059 {}
00060 
00061 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
00062 
00063 G4hPairProductionModel::~G4hPairProductionModel()
00064 {}
00065 
00066 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
00067 
00068 G4double G4hPairProductionModel::ComputeDMicroscopicCrossSection(
00069                                            G4double tkin,
00070                                            G4double Z,
00071                                            G4double pairEnergy)
00072 //  differential cross section
00073 {
00074   G4double bbbtf= 183. ;
00075   G4double bbbh = 202.4 ;
00076   G4double g1tf = 1.95e-5 ;
00077   G4double g2tf = 5.3e-5 ;
00078   G4double g1h  = 4.4e-5 ;
00079   G4double g2h  = 4.8e-5 ;
00080 
00081   G4double totalEnergy  = tkin + particleMass;
00082   G4double residEnergy  = totalEnergy - pairEnergy;
00083   G4double massratio    = particleMass/electron_mass_c2 ;
00084   G4double massratio2   = massratio*massratio ;
00085   G4double cross = 0.;
00086 
00087   SetCurrentElement(Z);
00088 
00089   G4double c3 = 0.75*sqrte*particleMass;
00090   if (residEnergy <= c3*z13) return cross;
00091 
00092   G4double c7 = 4.*electron_mass_c2;
00093   G4double c8 = 6.*particleMass*particleMass;
00094   G4double alf = c7/pairEnergy;
00095   G4double a3 = 1. - alf;
00096   if (a3 <= 0.) return cross;
00097 
00098   // zeta calculation
00099   G4double bbb,g1,g2;
00100   if( Z < 1.5 ) { bbb = bbbh ; g1 = g1h ; g2 = g2h ; }
00101   else          { bbb = bbbtf; g1 = g1tf; g2 = g2tf; }
00102 
00103   G4double zeta = 0;
00104   G4double zeta1 = 0.073*log(totalEnergy/(particleMass+g1*z23*totalEnergy))-0.26;
00105   if ( zeta1 > 0.)
00106   {
00107     G4double zeta2 = 0.058*log(totalEnergy/(particleMass+g2*z13*totalEnergy))-0.14;
00108     zeta  = zeta1/zeta2 ;
00109   }
00110 
00111   G4double z2 = Z*(Z+zeta);
00112   G4double screen0 = 2.*electron_mass_c2*sqrte*bbb/(z13*pairEnergy);
00113   G4double a0 = totalEnergy*residEnergy;
00114   G4double a1 = pairEnergy*pairEnergy/a0;
00115   G4double bet = 0.5*a1;
00116   G4double xi0 = 0.25*massratio2*a1;
00117   G4double del = c8/a0;
00118 
00119   G4double rta3 = sqrt(a3);
00120   G4double tmnexp = alf/(1. + rta3) + del*rta3;
00121   if(tmnexp >= 1.0) return cross;
00122 
00123   G4double tmn = log(tmnexp);
00124   G4double sum = 0.;
00125 
00126   // Gaussian integration in ln(1-ro) ( with 8 points)
00127   for (G4int i=0; i<8; i++)
00128   {
00129     G4double a4 = exp(tmn*xgi[i]);     // a4 = (1.-asymmetry)
00130     G4double a5 = a4*(2.-a4) ;
00131     G4double a6 = 1.-a5 ;
00132     G4double a7 = 1.+a6 ;
00133     G4double a9 = 3.+a6 ;
00134     G4double xi = xi0*a5 ;
00135     G4double xii = 1./xi ;
00136     G4double xi1 = 1.+xi ;
00137     G4double screen = screen0*xi1/a5 ;
00138     G4double yeu = 5.-a6+4.*bet*a7 ;
00139     G4double yed = 2.*(1.+3.*bet)*log(3.+xii)-a6-a1*(2.-a6) ;
00140     G4double ye1 = 1.+yeu/yed ;
00141     G4double ale=log(bbb/z13*sqrt(xi1*ye1)/(1.+screen*ye1)) ;
00142     G4double cre = 0.5*log(1.+2.25*z23*xi1*ye1/massratio2) ;
00143     G4double be;
00144 
00145     if (xi <= 1.e3) be = ((2.+a6)*(1.+bet)+xi*a9)*log(1.+xii)+(a5-bet)/xi1-a9;
00146     else            be = (3.-a6+a1*a7)/(2.*xi);
00147 
00148     G4double fe = (ale-cre)*be;
00149     if ( fe < 0.) fe = 0. ;
00150 
00151     G4double ymu = 4.+a6 +3.*bet*a7 ;
00152     G4double ymd = a7*(1.5+a1)*log(3.+xi)+1.-1.5*a6 ;
00153     G4double ym1 = 1.+ymu/ymd ;
00154     G4double alm_crm = log(bbb*massratio/(1.5*z23*(1.+screen*ym1)));
00155     G4double a10,bm;
00156     if ( xi >= 1.e-3)
00157     {
00158       a10 = (1.+a1)*a5 ;
00159       bm  = (a7*(1.+1.5*bet)-a10*xii)*log(xi1)+xi*(a5-bet)/xi1+a10;
00160     } else {
00161       bm = (5.-a6+bet*a9)*(xi/2.);
00162     }
00163 
00164     G4double fm = alm_crm*bm;
00165     if ( fm < 0.) fm = 0. ;
00166 
00167     sum += wgi[i]*a4*(fe+fm/massratio2);
00168   }
00169 
00170   cross = -tmn*sum*factorForCross*z2*residEnergy/(totalEnergy*pairEnergy);
00171 
00172   return cross;
00173 }
00174 
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