Import Geant4 0.0.0 source tree
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Gabriele Cosmo
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// This code implementation is the intellectual property of
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// the RD44 GEANT4 collaboration.
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//
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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 statement,
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// and all its terms.
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//
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// $Id: G4PolarizedComptonScattering.cc,v 2.3 1998/12/14 17:50:29 maire Exp $
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// GEANT4 tag $Name: geant4-00 $
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//
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// --------------------------------------------------------------
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// GEANT 4 class implementation file
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// CERN Geneva Switzerland
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//
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// For information related to this code contact:
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// CERN, IT Division, ASD group
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//
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// ---------- G4PolarizedComptonScattering physics process --------
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// by Vicente Lara, March 1998
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// **************************************************************
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//
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// --------------------------------------------------------------
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#include "G4PolarizedComptonScattering.hh"
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#include "G4EnergyLossTables.hh"
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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// constructor
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G4PolarizedComptonScattering::G4PolarizedComptonScattering(const G4String& processName)
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: G4ComptonScattering (processName)
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{ }
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4VParticleChange* G4PolarizedComptonScattering::PostStepDoIt(const G4Track& aTrack,
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const G4Step& aStep)
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//
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// The scattered gamma energy is sampled according to Klein - Nishina formula.
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// The random number techniques of Butcher & Messel are used (Nuc Phys 20(1960),15).
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// GEANT4 internal units
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//
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// Note : Effects due to binding of atomic electrons are negliged.
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{
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aParticleChange.Initialize(aTrack);
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G4Material* aMaterial = aTrack.GetMaterial();
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const G4DynamicParticle* aDynamicGamma = aTrack.GetDynamicParticle();
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G4ThreeVector GammaPolarization0 = aDynamicGamma->GetPolarization();
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if (abs(GammaPolarization0.mag() - 1.e0) > 1.e-14)
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G4ComptonScattering::PostStepDoIt(aTrack,aStep);
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G4double GammaEnergy0 = aDynamicGamma->GetKineticEnergy();
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G4double E0_m = GammaEnergy0 / electron_mass_c2 ;
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G4ParticleMomentum GammaDirection0 = aDynamicGamma->GetMomentumDirection();
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//
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// sample the energy rate of the scattered gamma
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//
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G4double epsilon, epsilonsq, onecost, sint2, greject ;
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G4double epsilon0 = 1./(1. + 2*E0_m) , epsilon0sq = epsilon0*epsilon0;
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G4double alpha1 = - log(epsilon0) , alpha2 = 0.5*(1.- epsilon0sq);
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do {
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if ( alpha1/(alpha1+alpha2) > G4UniformRand() )
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{ epsilon = exp(-alpha1*G4UniformRand()); // pow(epsilon0,G4UniformRand())
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epsilonsq = epsilon*epsilon; }
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else {
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epsilonsq = epsilon0sq + (1.- epsilon0sq)*G4UniformRand();
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epsilon = sqrt(epsilonsq);
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};
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onecost = (1.- epsilon)/(epsilon*E0_m);
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sint2 = onecost*(2.-onecost);
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greject = 1. - epsilon*sint2/(1.+ epsilonsq);
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} while (greject < G4UniformRand());
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//
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// scattered gamma angles. ( Z - axis along the parent gamma)
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//
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G4double cosTeta = 1. - onecost , sinTeta = sqrt (sint2);
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G4double Phi = twopi * G4UniformRand() ;
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G4double dirx = sinTeta*cos(Phi) , diry = sinTeta*sin(Phi) , dirz = cosTeta ;
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//
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// update G4VParticleChange for the scattered gamma
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//
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G4double GammaEnergy1 = epsilon*GammaEnergy0;
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// New polarization
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G4ThreeVector GammaPolarization1 = SetNewPolarization(epsilon,sint2,Phi,
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cosTeta,
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GammaPolarization0);
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// Set new direction
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G4ThreeVector GammaDirection1 ( dirx,diry,dirz );
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// Change reference frame.
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SystemOfRefChange(GammaDirection0,GammaDirection1,
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GammaPolarization0,GammaPolarization1);
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if (GammaEnergy1 > 0.)
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{
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aParticleChange.SetEnergyChange( GammaEnergy1 ) ;
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}
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else
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{
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aParticleChange.SetEnergyChange(0.) ;
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aParticleChange.SetStatusChange(fStopAndKill);
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}
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//
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// kinematic of the scattered electron
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//
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G4double ElecKineEnergy = GammaEnergy0 - GammaEnergy1 ;
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if((G4EnergyLossTables::GetRange(G4Electron::Electron(),
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ElecKineEnergy,aMaterial)>aStep.GetPostStepPoint()->GetSafety())
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||
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(ElecKineEnergy >
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(G4Electron::Electron()->GetCutsInEnergy())[aMaterial->GetIndex()]))
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{
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G4double ElecMomentum = sqrt(ElecKineEnergy*(ElecKineEnergy+2.*electron_mass_c2));
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G4ThreeVector ElecDirection (
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(GammaEnergy0*GammaDirection0 - GammaEnergy1*GammaDirection1)*(1./ElecMomentum) );
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// create G4DynamicParticle object for the electron.
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G4DynamicParticle* aElectron= new G4DynamicParticle (G4Electron::Electron(),
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ElecDirection, ElecKineEnergy) ;
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aParticleChange.SetNumberOfSecondaries(1) ;
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aParticleChange.AddSecondary( aElectron ) ;
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aParticleChange.SetLocalEnergyDeposit (0.) ;
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}
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else
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{
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aParticleChange.SetNumberOfSecondaries(0) ;
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aParticleChange.SetLocalEnergyDeposit (ElecKineEnergy) ;
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}
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// Reset NbOfInteractionLengthLeft and return aParticleChange
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return G4VDiscreteProcess::PostStepDoIt( aTrack, aStep);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4ThreeVector G4PolarizedComptonScattering::SetNewPolarization(G4double EnergyRate,
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G4double sinsqrth,
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G4double phi,
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G4double costheta,
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G4ThreeVector& GammaPolarization0)
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{
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G4double cosphi = cos(phi), sinphi = sin(phi);
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G4double ParallelIntensityPolar = EnergyRate + 1./EnergyRate + 2. - 4.*sinsqrth*cosphi*cosphi;
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G4double PerpendiIntensityPolar = EnergyRate + 1./EnergyRate - 2.;
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G4double PolarizationDegree = sqrt(sinsqrth*sinphi*sinphi + costheta*costheta);
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G4double sintheta = sqrt(sinsqrth);
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G4ThreeVector GammaPolarization1;
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// depolarization probability (1-P)
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if ( G4UniformRand() > 0.5*(PerpendiIntensityPolar/ParallelIntensityPolar) )
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{
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// Parallel to initial polarization
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GammaPolarization1.setX(PolarizationDegree);
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GammaPolarization1.setY(-sinsqrth*sinphi*cosphi/PolarizationDegree);
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GammaPolarization1.setZ(-sintheta*costheta*cosphi/PolarizationDegree);
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}
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else
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{
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// Perpendicular to initial polarization
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GammaPolarization1.setX(0.);
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GammaPolarization1.setY(costheta/PolarizationDegree);
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GammaPolarization1.setZ(-sintheta*sinphi/PolarizationDegree);
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};
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return GammaPolarization1;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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void G4PolarizedComptonScattering::SystemOfRefChange(G4ThreeVector& Direction0,
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G4ThreeVector& Direction1,
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G4ThreeVector& Polarization0,
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G4ThreeVector& Polarization1)
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{
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// Angles for go back to the original RS
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G4double cosTeta0 = Direction0.cosTheta(), sinTeta0 = sin(Direction0.theta());
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G4double cosPhi0 = cos(Direction0.phi()), sinPhi0 = sin(Direction0.phi());
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G4double cosPsi, sinPsi;
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if (sinTeta0 != 0. ) {
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cosPsi = -Polarization0.z()/sinTeta0;
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if (cosPhi0 != 0. ) {
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sinPsi = (Polarization0.y() - cosTeta0*sinPhi0*cosPsi)/cosPhi0;
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} else {
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sinPsi = -Polarization0.x()/sinPhi0;
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}
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} else {
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cosPsi = Polarization0.x()/cosTeta0;
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sinPsi = Polarization0.y();
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}
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G4double Psi = atan(sinPsi/cosPsi);
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// Rotation along Z axe
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Direction1.rotateZ(Psi);
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//
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Direction1.rotateUz(Direction0);
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aParticleChange.SetMomentumChange( Direction1 ) ;
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// 3 Euler angles rotation for scattered photon polarization
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Polarization1.rotateZ(Psi);
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Polarization1.rotateUz(Direction0);
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aParticleChange.SetPolarizationChange( Polarization1 );
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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