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Gabriele Cosmo
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//
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// ********************************************************************
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// * DISCLAIMER *
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// * *
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// * The following disclaimer summarizes all the specific disclaimers *
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// * of contributors to this software. The specific disclaimers,which *
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// * govern, are listed with their locations in: *
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// * http://cern.ch/geant4/license *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. *
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// * *
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// * This code implementation is the intellectual property of the *
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// * GEANT4 collaboration. *
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// * By copying, distributing or modifying the Program (or any work *
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// * based on the Program) you indicate your acceptance of this *
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// * statement, and all its terms. *
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// ********************************************************************
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//
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//
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// -------------------------------------------------------------------
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//
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// GEANT4 Class file
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//
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//
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// File name: G4MollerBhabhaModel
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//
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// Author: Vladimir Ivanchenko on base of Laszlo Urban code
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//
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// Creation date: 03.01.2002
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//
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// Modifications: 13.11.2002 Minor fix - use normalised direction (VI)
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// 04.12.2002 Change G4DynamicParticle constructor in PostStepDoIt (VI)
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//
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//
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// Class Description:
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//
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// Implementation of energy loss and delta-electron production by e+/e-
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//
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// -------------------------------------------------------------------
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//
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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#include "G4MollerBhabhaModel.hh"
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#include "G4Electron.hh"
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#include "G4Positron.hh"
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#include "Randomize.hh"
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4MollerBhabhaModel::G4MollerBhabhaModel(const G4ParticleDefinition* p)
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: G4VEmModel(),
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particle(0),
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highKinEnergy(100.*TeV),
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lowKinEnergy(0.1*keV),
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twoln10(2.0*log(10.0)),
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lowLimit(0.2*keV),
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isElectron(true)
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{
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if(p) SetParticle(p);
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theElectron = G4Electron::Electron();
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4MollerBhabhaModel::~G4MollerBhabhaModel()
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{}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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void G4MollerBhabhaModel::SetParticle(const G4ParticleDefinition* p)
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{
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particle = p;
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if(p != theElectron) isElectron = false;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4MollerBhabhaModel::HighEnergyLimit(const G4ParticleDefinition* p,
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const G4Material*)
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{
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return highKinEnergy;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4MollerBhabhaModel::LowEnergyLimit(const G4ParticleDefinition* p,
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const G4Material*)
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{
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return lowKinEnergy;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4MollerBhabhaModel::MinEnergyCut(const G4ParticleDefinition* p,
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const G4Material* material)
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{
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return material->GetIonisation()->GetMeanExcitationEnergy();
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4bool G4MollerBhabhaModel::IsInCharge(const G4ParticleDefinition* p,
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const G4Material*)
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{
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return (p == theElectron || p == G4Positron::Positron());
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4MollerBhabhaModel::ComputeDEDX(const G4Material* material,
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const G4ParticleDefinition* p,
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G4double kineticEnergy,
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G4double cutEnergy)
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{
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if(!particle) SetParticle(p);
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// calculate the dE/dx due to the ionization by Seltzer-Berger formula
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G4double electronDensity = material->GetElectronDensity();
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G4double Zeff = electronDensity/material->GetTotNbOfAtomsPerVolume();
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G4double th = 0.25*sqrt(Zeff)*keV;
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G4double tkin = kineticEnergy;
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if (kineticEnergy < th) tkin = th;
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G4double tau = tkin/electron_mass_c2;
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G4double gam = tau + 1.0;
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G4double gamma2= gam*gam;
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G4double beta2 = 1. - 1./gamma2;
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G4double bg2 = beta2*gamma2;
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G4double eexc = material->GetIonisation()->GetMeanExcitationEnergy();
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eexc /= electron_mass_c2;
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G4double eexc2 = eexc*eexc;
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G4double dedx;
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G4double d = G4std::min(cutEnergy, MaxSecondaryEnergy(p, tkin))/electron_mass_c2;
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// electron
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if (isElectron) {
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dedx = log(2.0*(tau + 2.0)/eexc2) - 1.0 - beta2
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+ log((tau-d)*d) + tau/(tau-d)
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+ (0.5*d*d + (2.0*tau + 1.)*log(1. - d/tau))/gamma2;
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//positron
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} else {
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G4double d2 = d*d*0.5;
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G4double d3 = d2*d/1.5;
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G4double d4 = d3*d*3.75;
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G4double y = 1.0/(1.0 + gam);
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dedx = log(2.0*(tau + 2.0)/eexc2) + log(tau*d)
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- beta2*(tau + 2.0*d - y*(3.0*d2
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+ y*(d - d3 + y*(d2 - tau*d3 + d4))))/tau;
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}
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//density correction
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G4double cden = material->GetIonisation()->GetCdensity();
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G4double mden = material->GetIonisation()->GetMdensity();
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G4double aden = material->GetIonisation()->GetAdensity();
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G4double x0den = material->GetIonisation()->GetX0density();
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G4double x1den = material->GetIonisation()->GetX1density();
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G4double x = log(bg2)/twoln10;
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if (x >= x0den) {
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dedx -= twoln10*x - cden;
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if (x < x1den) dedx -= aden*pow(x1den-x, mden);
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}
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// now you can compute the total ionization loss
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dedx *= twopi_mc2_rcl2*electronDensity/beta2;
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if (dedx < 0.0) dedx = 0.0;
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// lowenergy extrapolation
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if (kineticEnergy < tkin) {
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if (kineticEnergy >= lowLimit) dedx *= sqrt(kineticEnergy/tkin);
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else dedx *= sqrt(kineticEnergy*tkin)/lowLimit;
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}
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return dedx;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4MollerBhabhaModel::CrossSection(const G4Material* material,
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const G4ParticleDefinition* p,
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G4double kineticEnergy,
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G4double cutEnergy,
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G4double maxEnergy)
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{
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if(!particle) SetParticle(p);
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G4double cross = 0.0;
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G4double tmax = MaxSecondaryEnergy(p, kineticEnergy);
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tmax = G4std::min(maxEnergy, tmax);
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if(cutEnergy < tmax) {
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G4double xmin = cutEnergy/kineticEnergy;
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G4double xmax = tmax/kineticEnergy;
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G4double gam = kineticEnergy/electron_mass_c2 + 1.0;
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G4double gamma2= gam*gam;
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G4double beta2 = 1.0 - 1.0/gamma2;
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//Moller (e-e-) scattering
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if (isElectron) {
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G4double g = (2.0*gam - 1.0)/gamma2;
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cross = ((xmax - xmin)*(1.0 - g + 1.0/(xmin*xmax)
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+ 1.0/((1.0-xmin)*(1.0 - xmax)))
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- g*log( xmax*(1.0 - xmin)/(xmin*(1.0 - xmax)) ) ) / beta2;
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//Bhabha (e+e-) scattering
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} else {
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G4double y = 1.0/(1.0 + gam);
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G4double y2 = y*y;
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G4double y12 = 1.0 - 2.0*y;
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G4double b1 = 2.0 - y2;
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G4double b2 = y12*(3.0 + y2);
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G4double y122= y12*y12;
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G4double b4 = y122*y12;
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G4double b3 = b4 + y122;
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cross = (xmax - xmin)*(1.0/(beta2*xmin*xmax) + b2
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- 0.5*b3*(xmin + xmax)
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+ b4*(xmin*xmin + xmin*xmax + xmax*xmax)/3.0)
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- b1*log(xmax/xmin);
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}
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cross *= twopi_mc2_rcl2*(material->GetElectronDensity())/kineticEnergy;
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}
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return cross;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4std::vector<G4DynamicParticle*>* G4MollerBhabhaModel::SampleSecondary(
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const G4Material* material,
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const G4DynamicParticle* dp,
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G4double tmin,
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G4double maxEnergy)
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{
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G4double tmax = G4std::min(maxEnergy, MaxSecondaryEnergy(dp));
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if(tmin >= tmax) return 0;
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G4double kineticEnergy = dp->GetKineticEnergy();
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G4double energy = kineticEnergy + electron_mass_c2;
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G4double totalMomentum = sqrt(kineticEnergy*(energy + electron_mass_c2));
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G4double xmin = tmin/kineticEnergy;
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G4double xmax = tmax/kineticEnergy;
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G4double gam = energy/electron_mass_c2;
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G4double gamma2 = gam*gam;
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G4double beta2 = 1.0 - 1.0/gamma2;
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G4double x, z, q, grej;
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G4ThreeVector momentum = dp->GetMomentumDirection();
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//Moller (e-e-) scattering
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if (isElectron) {
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G4double g = (2.0*gam - 1.0)/gamma2;
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G4double y = 1.0 - xmax;
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grej = 1.0 - g*xmax + xmax*xmax*(1.0 - g + (1.0 - g*y)/(y*y));
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do {
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q = G4UniformRand();
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x = xmin*xmax/(xmin*(1.0 - q) + xmax*q);
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y = 1.0 - x;
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z = 1.0 - g*x + x*x*(1.0 - g + (1.0 - g*y)/(y*y));
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if(z > grej) {
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G4cout << "G4MollerBhabhaModel::SampleSecondary Warning! "
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<< "Majorant " << grej << " < "
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<< z << " for x= " << x
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<< " e-e- scattering"
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<< G4endl;
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}
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} while(grej * G4UniformRand() > z);
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//Bhabha (e+e-) scattering
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} else {
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G4double y = 1.0/(1.0 + gam);
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G4double y2 = y*y;
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G4double y12 = 1.0 - 2.0*y;
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G4double b1 = 2.0 - y2;
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G4double b2 = y12*(3.0 + y2);
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G4double y122= y12*y12;
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G4double b4 = y122*y12;
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G4double b3 = b4 + y122;
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y = xmax*xmax;
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grej = -xmin*b1;
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grej += y*b2;
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grej -= xmin*xmin*xmin*b3;
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grej += y*y*b4;
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grej *= beta2;
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grej += 1.0;
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do {
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q = G4UniformRand();
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x = xmin*xmax/(xmin*(1.0 - q) + xmax*q);
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z = -x*b1;
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y = x*x;
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z += y*b2;
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y *= x;
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z -= y*b3;
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y *= x;
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z += y*b4;
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z *= beta2;
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z += 1.0;
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if(z > grej) {
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G4cout << "G4MollerBhabhaModel::SampleSecondary Warning! "
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<< "Majorant " << grej << " < "
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<< z << " for x= " << x
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<< " e+e- scattering"
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<< G4endl;
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}
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} while(grej * G4UniformRand() > z);
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}
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G4double deltaKinEnergy = x * kineticEnergy;
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G4double deltaMomentum =
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sqrt(deltaKinEnergy * (deltaKinEnergy + 2.0*electron_mass_c2));
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G4double cost = deltaKinEnergy * (energy + electron_mass_c2) /
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(deltaMomentum * totalMomentum);
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G4double sint = sqrt(1.0 - cost*cost);
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G4double phi = twopi * G4UniformRand() ;
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G4ThreeVector deltaDirection(sint*cos(phi),sint*sin(phi), cost) ;
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deltaDirection.rotateUz(momentum);
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// create G4DynamicParticle object for delta ray
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G4DynamicParticle* delta = new G4DynamicParticle();
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delta->SetDefinition(theElectron);
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delta->SetKineticEnergy(deltaKinEnergy);
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delta->SetMomentumDirection(deltaDirection);
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G4std::vector<G4DynamicParticle*>* vdp = new G4std::vector<G4DynamicParticle*>;
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vdp->push_back(delta);
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return vdp;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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