Geant4: G4KleinNishinaCompton Class Reference

G4KleinNishinaCompton::G4KleinNishinaCompton	(	const G4ParticleDefinition *	p = `0`,
		const G4String &	nam = `"Klein-Nishina"`
	)

Definition at line 63 of file G4KleinNishinaCompton.cc.

References G4Electron::Electron(), fParticleChange, G4Gamma::Gamma(), lowestGammaEnergy, theElectron, and theGamma.

00065   : G4VEmModel(nam)
00066 {
00067   theGamma = G4Gamma::Gamma();
00068   theElectron = G4Electron::Electron();
00069   lowestGammaEnergy = 1.0*eV;
00070   fParticleChange = 0;
00071 }

G4KleinNishinaCompton::~G4KleinNishinaCompton ( ) [virtual]

Definition at line 75 of file G4KleinNishinaCompton.cc.

00076 {}

G4double G4KleinNishinaCompton::ComputeCrossSectionPerAtom	(	const G4ParticleDefinition *	,
		G4double	kinEnergy,
		G4double	Z,
		G4double	A,
		G4double	cut,
		G4double	emax
	)			`[virtual]`

Reimplemented from G4VEmModel.

Reimplemented in G4PolarizedComptonModel.

Definition at line 88 of file G4KleinNishinaCompton.cc.

Referenced by G4PolarizedComptonModel::ComputeCrossSectionPerAtom().

00093 {
00094   G4double xSection = 0.0 ;
00095   if ( Z < 0.9999 )                 return xSection;
00096   if ( GammaEnergy < 0.1*keV      ) return xSection;
00097   //  if ( GammaEnergy > (100.*GeV/Z) ) return xSection;
00098 
00099   static const G4double a = 20.0 , b = 230.0 , c = 440.0;
00100   
00101   static const G4double
00102     d1= 2.7965e-1*barn, d2=-1.8300e-1*barn, d3= 6.7527   *barn, d4=-1.9798e+1*barn,
00103     e1= 1.9756e-5*barn, e2=-1.0205e-2*barn, e3=-7.3913e-2*barn, e4= 2.7079e-2*barn,
00104     f1=-3.9178e-7*barn, f2= 6.8241e-5*barn, f3= 6.0480e-5*barn, f4= 3.0274e-4*barn;
00105      
00106   G4double p1Z = Z*(d1 + e1*Z + f1*Z*Z), p2Z = Z*(d2 + e2*Z + f2*Z*Z),
00107            p3Z = Z*(d3 + e3*Z + f3*Z*Z), p4Z = Z*(d4 + e4*Z + f4*Z*Z);
00108 
00109   G4double T0  = 15.0*keV; 
00110   if (Z < 1.5) T0 = 40.0*keV; 
00111 
00112   G4double X   = max(GammaEnergy, T0) / electron_mass_c2;
00113   xSection = p1Z*std::log(1.+2.*X)/X
00114                + (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
00115                 
00116   //  modification for low energy. (special case for Hydrogen)
00117   if (GammaEnergy < T0) {
00118     G4double dT0 = 1.*keV;
00119     X = (T0+dT0) / electron_mass_c2 ;
00120     G4double sigma = p1Z*log(1.+2*X)/X
00121                     + (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
00122     G4double   c1 = -T0*(sigma-xSection)/(xSection*dT0);             
00123     G4double   c2 = 0.150; 
00124     if (Z > 1.5) c2 = 0.375-0.0556*log(Z);
00125     G4double    y = log(GammaEnergy/T0);
00126     xSection *= exp(-y*(c1+c2*y));          
00127   }
00128   //  G4cout << "e= " << GammaEnergy << " Z= " << Z << " cross= " << xSection << G4endl;
00129   return xSection;
00130 }

void G4KleinNishinaCompton::Initialise	(	const G4ParticleDefinition *	,
		const G4DataVector &
	)			`[virtual]`

Implements G4VEmModel.

Definition at line 80 of file G4KleinNishinaCompton.cc.

References fParticleChange, and G4VEmModel::GetParticleChangeForGamma().

00082 {
00083   if(!fParticleChange) { fParticleChange = GetParticleChangeForGamma(); }
00084 }

void G4KleinNishinaCompton::SampleSecondaries	(	std::vector< G4DynamicParticle * > *	,
		const G4MaterialCutsCouple *	,
		const G4DynamicParticle *	,
		G4double	tmin,
		G4double	maxEnergy
	)			`[virtual]`

Implements G4VEmModel.

Reimplemented in G4PolarizedComptonModel.

Definition at line 134 of file G4KleinNishinaCompton.cc.

References DBL_MIN, fParticleChange, fStopAndKill, G4UniformRand, G4DynamicParticle::GetKineticEnergy(), G4DynamicParticle::GetMomentumDirection(), lowestGammaEnergy, G4VParticleChange::ProposeLocalEnergyDeposit(), G4ParticleChangeForGamma::ProposeMomentumDirection(), G4VParticleChange::ProposeTrackStatus(), G4ParticleChangeForGamma::SetProposedKineticEnergy(), and theElectron.

00139 {
00140   // The scattered gamma energy is sampled according to Klein - Nishina formula.
00141   // The random number techniques of Butcher & Messel are used 
00142   // (Nuc Phys 20(1960),15).
00143   // Note : Effects due to binding of atomic electrons are negliged.
00144  
00145   G4double gamEnergy0 = aDynamicGamma->GetKineticEnergy();
00146 
00147   // extra protection
00148   if(gamEnergy0 < lowestGammaEnergy) {
00149     fParticleChange->ProposeTrackStatus(fStopAndKill);
00150     fParticleChange->ProposeLocalEnergyDeposit(gamEnergy0);
00151     fParticleChange->SetProposedKineticEnergy(0.0);
00152     return;
00153   }
00154 
00155   G4double E0_m = gamEnergy0 / electron_mass_c2 ;
00156 
00157   G4ThreeVector gamDirection0 = aDynamicGamma->GetMomentumDirection();
00158 
00159   //
00160   // sample the energy rate of the scattered gamma 
00161   //
00162 
00163   G4double epsilon, epsilonsq, onecost, sint2, greject ;
00164 
00165   G4double eps0       = 1./(1. + 2.*E0_m);
00166   G4double epsilon0sq = eps0*eps0;
00167   G4double alpha1     = - log(eps0);
00168   G4double alpha2     = 0.5*(1.- epsilon0sq);
00169 
00170   do {
00171     if ( alpha1/(alpha1+alpha2) > G4UniformRand() ) {
00172       epsilon   = exp(-alpha1*G4UniformRand());   // eps0**r
00173       epsilonsq = epsilon*epsilon; 
00174 
00175     } else {
00176       epsilonsq = epsilon0sq + (1.- epsilon0sq)*G4UniformRand();
00177       epsilon   = sqrt(epsilonsq);
00178     };
00179 
00180     onecost = (1.- epsilon)/(epsilon*E0_m);
00181     sint2   = onecost*(2.-onecost);
00182     greject = 1. - epsilon*sint2/(1.+ epsilonsq);
00183 
00184   } while (greject < G4UniformRand());
00185  
00186   //
00187   // scattered gamma angles. ( Z - axis along the parent gamma)
00188   //
00189 
00190   if(sint2 < 0.0) { sint2 = 0.0; }
00191   G4double cosTeta = 1. - onecost; 
00192   G4double sinTeta = sqrt (sint2);
00193   G4double Phi     = twopi * G4UniformRand();
00194 
00195   //
00196   // update G4VParticleChange for the scattered gamma
00197   //
00198    
00199   G4ThreeVector gamDirection1(sinTeta*cos(Phi), sinTeta*sin(Phi), cosTeta);
00200   gamDirection1.rotateUz(gamDirection0);
00201   G4double gamEnergy1 = epsilon*gamEnergy0;
00202   if(gamEnergy1 > lowestGammaEnergy) {
00203     fParticleChange->ProposeMomentumDirection(gamDirection1);
00204     fParticleChange->SetProposedKineticEnergy(gamEnergy1);
00205   } else { 
00206     fParticleChange->ProposeTrackStatus(fStopAndKill);
00207     fParticleChange->ProposeLocalEnergyDeposit(gamEnergy1);
00208     fParticleChange->SetProposedKineticEnergy(0.0);
00209   }
00210 
00211   //
00212   // kinematic of the scattered electron
00213   //
00214 
00215   G4double eKinEnergy = gamEnergy0 - gamEnergy1;
00216 
00217   if(eKinEnergy > DBL_MIN) {
00218     G4ThreeVector eDirection = gamEnergy0*gamDirection0 - gamEnergy1*gamDirection1;
00219     eDirection = eDirection.unit();
00220 
00221     // create G4DynamicParticle object for the electron.
00222     G4DynamicParticle* dp = new G4DynamicParticle(theElectron,eDirection,eKinEnergy);
00223     fvect->push_back(dp);
00224   }
00225 }

G4ParticleChangeForGamma* G4KleinNishinaCompton::fParticleChange [protected]

Definition at line 88 of file G4KleinNishinaCompton.hh.

Referenced by G4KleinNishinaCompton(), Initialise(), G4PolarizedComptonModel::SampleSecondaries(), and SampleSecondaries().

G4double G4KleinNishinaCompton::lowestGammaEnergy [protected]

Definition at line 89 of file G4KleinNishinaCompton.hh.

Referenced by G4KleinNishinaCompton(), G4PolarizedComptonModel::SampleSecondaries(), and SampleSecondaries().

G4ParticleDefinition* G4KleinNishinaCompton::theElectron [protected]

Definition at line 87 of file G4KleinNishinaCompton.hh.

Referenced by G4KleinNishinaCompton(), G4PolarizedComptonModel::SampleSecondaries(), and SampleSecondaries().

G4ParticleDefinition* G4KleinNishinaCompton::theGamma [protected]

Definition at line 86 of file G4KleinNishinaCompton.hh.

Referenced by G4KleinNishinaCompton().


Public Member Functions
	G4KleinNishinaCompton (const G4ParticleDefinition *p=0, const G4String &nam="Klein-Nishina")
virtual	~G4KleinNishinaCompton ()
virtual void	Initialise (const G4ParticleDefinition *, const G4DataVector &)
virtual G4double	ComputeCrossSectionPerAtom (const G4ParticleDefinition *, G4double kinEnergy, G4double Z, G4double A, G4double cut, G4double emax)
virtual void	SampleSecondaries (std::vector< G4DynamicParticle * > , const G4MaterialCutsCouple , const G4DynamicParticle *, G4double tmin, G4double maxEnergy)
Protected Attributes
G4ParticleDefinition *	theGamma
G4ParticleDefinition *	theElectron
G4ParticleChangeForGamma *	fParticleChange
G4double	lowestGammaEnergy

G4KleinNishinaCompton Class Reference

Public Member Functions

Protected Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Field Documentation