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Gabriele Cosmo
2016-06-01 15:25:35 +02:00
parent 54d6b71f95
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source/processes/electromagnetic/standard/src/G4GammaConversion.cc
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// This code implementation is the intellectual property of
// the RD44 GEANT4 collaboration.
//
// By copying, distributing or modifying the Program (or any work
// based on the Program) you indicate your acceptance of this statement,
// and all its terms.
//
// $Id: G4GammaConversion.cc,v 2.9 1998/11/13 13:41:56 maire Exp $
// GEANT4 tag $Name: geant4-00 $
//
//
// --------------------------------------------------------------
// GEANT 4 class implementation file
// CERN Geneva Switzerland
//
// For information related to this code contact:
// CERN, IT Division, ASD group
// History: first implementation, based on object model of
// 2nd December 1995, G.Cosmo
// ------------ G4GammaConversion physics process --------
// by Michel Maire, 24 May 1996
// **************************************************************
// 11-06-96, Added SelectRandomAtom() method, M.Maire
// 21-06-96, SetCuts implementation, M.Maire
// 24-06-96, simplification in ComputeMicroscopicCrossSection, M.Maire
// 24-06-96, in DoIt : change the particleType stuff, M.Maire
// 25-06-96, modification in the generation of the teta angle, M.Maire
// 16-09-96, minors optimisations in DoIt. Thanks to P.Urban
// dynamical array PartialSumSigma
// 13-12-96, fast sampling of epsil below 2 MeV, L.Urban
// 14-01-97, crossection table + meanfreepath table.
// PartialSumSigma removed, M.Maire
// 14-01-97, in DoIt the positron is always created, even with Ekine=0,
// for further annihilation, M.Maire
// 14-03-97, new Physics scheme for geant4alpha, M.Maire
// 28-03-97, protection in BuildPhysicsTable, M.Maire
// 19-06-97, correction in ComputeMicroscopicCrossSection, L.Urban
// 04-06-98, in DoIt, secondary production condition: range>min(threshold,safety)
// 13-08-98, new methods SetBining() PrintInfo()
// --------------------------------------------------------------
#include "G4GammaConversion.hh"
#include "G4EnergyLossTables.hh"
#include "G4UnitsTable.hh"
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
// constructor
G4GammaConversion::G4GammaConversion(const G4String& processName)
: G4VDiscreteProcess (processName), // initialization
theCrossSectionTable(NULL),
theMeanFreePathTable(NULL),
LowestEnergyLimit (2*electron_mass_c2),
HighestEnergyLimit(100*GeV),
NumbBinTable(100)
{ }
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
// destructor
G4GammaConversion::~G4GammaConversion()
{
if (theCrossSectionTable) {
theCrossSectionTable->clearAndDestroy();
delete theCrossSectionTable;
}
if (theMeanFreePathTable) {
theMeanFreePathTable->clearAndDestroy();
delete theMeanFreePathTable;
}
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
void G4GammaConversion::SetPhysicsTableBining(G4double lowE, G4double highE, G4int nBins)
{
LowestEnergyLimit = lowE; HighestEnergyLimit = highE; NumbBinTable = nBins;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
void G4GammaConversion::BuildPhysicsTable(const G4ParticleDefinition& GammaType)
// Build microscopic cross section table and mean free path table
{
G4double LowEdgeEnergy, Value;
G4PhysicsLogVector* ptrVector;
// Build microscopic cross section tables for the e+e- pair creation
if (theCrossSectionTable) {
theCrossSectionTable->clearAndDestroy(); delete theCrossSectionTable; }
theCrossSectionTable = new G4PhysicsTable(G4Element::GetNumberOfElements()) ;
const G4ElementTable* theElementTable = G4Element::GetElementTable() ;
G4double AtomicNumber;
G4int J;
for ( J=0 ; J < G4Element::GetNumberOfElements(); J++ )
{
//create physics vector then fill it ....
ptrVector = new G4PhysicsLogVector(LowestEnergyLimit, HighestEnergyLimit,
NumbBinTable ) ;
AtomicNumber = (*theElementTable)(J)->GetZ();
for ( G4int i = 0 ; i < NumbBinTable ; i++ )
{
LowEdgeEnergy = ptrVector->GetLowEdgeEnergy( i ) ;
Value = ComputeMicroscopicCrossSection( LowEdgeEnergy, AtomicNumber);
ptrVector->PutValue( i , Value ) ;
}
theCrossSectionTable->insertAt( J , ptrVector ) ;
}
// Build mean free path table for the e+e- pair creation
if (theMeanFreePathTable) {
theMeanFreePathTable->clearAndDestroy(); delete theMeanFreePathTable; }
theMeanFreePathTable = new G4PhysicsTable( G4Material::GetNumberOfMaterials() ) ;
const G4MaterialTable* theMaterialTable = G4Material::GetMaterialTable() ;
G4Material* material;
for ( J=0 ; J < G4Material::GetNumberOfMaterials(); J++ )
{
//create physics vector then fill it ....
ptrVector = new G4PhysicsLogVector(LowestEnergyLimit, HighestEnergyLimit,
NumbBinTable ) ;
material = (*theMaterialTable)(J);
for ( G4int i = 0 ; i < NumbBinTable ; i++ )
{
LowEdgeEnergy = ptrVector->GetLowEdgeEnergy( i ) ;
Value = ComputeMeanFreePath( LowEdgeEnergy, material);
ptrVector->PutValue( i , Value ) ;
}
theMeanFreePathTable->insertAt( J , ptrVector ) ;
}
PrintInfoDefinition();
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
G4double G4GammaConversion::ComputeMicroscopicCrossSection
(G4double GammaEnergy, G4double AtomicNumber)
// Calculates the microscopic cross section in GEANT4 internal units.
// A parametrized formula from L. Urban is used to estimate the total cross section.
// It gives a good description of the data from 1.5 MeV to 100 GeV.
// below 1.5 MeV: sigma=sigma(1.5MeV)*(GammaEnergy-2electronmass)*(GammaEnergy-2electronmass)
{
G4double GammaEnergyLimit = 1.5*MeV;
G4double CrossSection = 0.0 ;
if ( AtomicNumber < 1. ) return CrossSection;
if ( GammaEnergy < 2*electron_mass_c2 ) return CrossSection ;
static const G4double
a0= 8.7842e+2*microbarn, a1=-1.9625e+3*microbarn, a2= 1.2949e+3*microbarn,
a3=-2.0028e+2*microbarn, a4= 1.2575e+1*microbarn, a5=-2.8333e-1*microbarn;
static const G4double
b0=-1.0342e+1*microbarn, b1= 1.7692e+1*microbarn, b2=-8.2381 *microbarn,
b3= 1.3063 *microbarn, b4=-9.0815e-2*microbarn, b5= 2.3586e-3*microbarn;
static const G4double
c0=-4.5263e+2*microbarn, c1= 1.1161e+3*microbarn, c2=-8.6749e+2*microbarn,
c3= 2.1773e+2*microbarn, c4=-2.0467e+1*microbarn, c5= 6.5372e-1*microbarn;
G4double GammaEnergySave = GammaEnergy ;
if (GammaEnergy < GammaEnergyLimit) GammaEnergy = GammaEnergyLimit ;
G4double X = log(GammaEnergy/electron_mass_c2), X2=X*X, X3=X2*X, X4=X3*X, X5=X4*X;
G4double F1 = a0 + a1*X + a2*X2 + a3*X3 + a4*X4 + a5*X5,
F2 = b0 + b1*X + b2*X2 + b3*X3 + b4*X4 + b5*X5,
F3 = c0 + c1*X + c2*X2 + c3*X3 + c4*X4 + c5*X5;
CrossSection = (AtomicNumber+1.)*
(F1*AtomicNumber + F2*AtomicNumber*AtomicNumber + F3);
if (GammaEnergySave < GammaEnergyLimit)
{
X=GammaEnergySave-2.*electron_mass_c2;
CrossSection *= X*X ;
}
if (CrossSection < 0.) CrossSection = 0.;
return CrossSection;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
G4VParticleChange* G4GammaConversion::PostStepDoIt(const G4Track& aTrack,
const G4Step& aStep)
//
// The secondaries e+e- energies are sampled using the Bethe - Heitler cross sections
// with Coulomb correction.
// A modified version of the random number techniques of Butcher & Messel is used
// (Nuc Phys 20(1960),15).
//
// GEANT4 internal units.
//
// Note 1 : Effects due to the breakdown of the Born approximation at low energy
// are ignored.
// Note 2 : The differential cross section implicitly takes account of pair creation
// in both nuclear and atomic electron fields. However triplet prodution is
// not generated.
{
aParticleChange.Initialize(aTrack);
G4Material* aMaterial = aTrack.GetMaterial();
const G4DynamicParticle* aDynamicGamma = aTrack.GetDynamicParticle();
G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection();
G4double epsil ;
G4double epsil0 = electron_mass_c2/GammaEnergy ;
// do it fast if GammaEnergy < 2. MeV
const G4double Egsmall=2.*MeV;
if (GammaEnergy<Egsmall) { epsil = epsil0 + (0.5-epsil0)*G4UniformRand(); }
else
{ // now comes the case with GammaEnergy >= 2. MeV
// select randomly one element constituing the material
G4Element* anElement = SelectRandomAtom(aDynamicGamma, aMaterial);
// Extract Coulomb factor for this Element
G4double FZ = 8.*(anElement->GetIonisation()->GetlogZ3());
if (GammaEnergy > 50.*MeV) FZ += 8.*(anElement->GetfCoulomb());
// limits of the screening variable
G4double screenfac = 136.*epsil0/(anElement->GetIonisation()->GetZ3()) ;
G4double screenmax = exp ((42.24 - FZ)/8.368) - 0.952 ;
G4double screenmin = min(4.*screenfac,screenmax) ;
// limits of the energy sampling
G4double epsil1 = 0.5 - 0.5*sqrt(1. - screenmin/screenmax) ;
G4double epsilmin = max(epsil0,epsil1) , epsilrange = 0.5 - epsilmin ;
//
// sample the energy rate of the created electron (or positron)
//
//G4double epsil, screenvar, greject ;
G4double screenvar, greject ;
G4double F10 = ScreenFunction1(screenmin) - FZ , F20 = ScreenFunction2(screenmin) - FZ;
G4double NormF1 = max(F10*epsilrange*epsilrange,0.) , NormF2 = max(1.5*F20,0.);
do {
if ( NormF1/(NormF1+NormF2) > G4UniformRand() )
{ epsil = 0.5 - epsilrange*pow(G4UniformRand(), 1/3) ;
screenvar = screenfac/(epsil*(1-epsil));
greject = (ScreenFunction1(screenvar) - FZ)/F10 ;
}
else { epsil = epsilmin + epsilrange*G4UniformRand();
screenvar = screenfac/(epsil*(1-epsil));
greject = (ScreenFunction2(screenvar) - FZ)/F20 ;
}
} while( greject < G4UniformRand() );
} // end of epsil sampling.........................
//
// fixe charges randomly
//
G4double ElectTotEnergy, PositTotEnergy;
if (RandFlat::shootBit())
{
ElectTotEnergy = (1.-epsil)*GammaEnergy;
PositTotEnergy = epsil*GammaEnergy;
}
else
{
PositTotEnergy = (1.-epsil)*GammaEnergy;
ElectTotEnergy = epsil*GammaEnergy;
}
//
// scattered electron (positron) angles. ( Z - axis along the parent photon)
//
// universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211),
// derived from Tsai distribution (Rev Mod Phys 49,421(1977))
G4double u;
const G4double a1 = 0.625 , a2 = 3.*a1 , d = 27. ;
if (9./(9.+d) > G4UniformRand()) u = - log(G4UniformRand()*G4UniformRand())/a1 ;
else u = - log(G4UniformRand()*G4UniformRand())/a2 ;
G4double Teta = u*electron_mass_c2/GammaEnergy ;
G4double Phi = twopi * G4UniformRand() ;
G4double dirx = sin(Teta)*cos(Phi) , diry = sin(Teta)*sin(Phi) , dirz = cos(Teta) ;
//
// kinematic of the created pair
//
// the electron and positron are assumed to have a symetric angular distribution
// with respect to the Z axis along the parent photon.
G4double LocalEnerDeposit = 0. ;
aParticleChange.SetNumberOfSecondaries(2) ;
G4double ElectKineEnergy = max(0.,ElectTotEnergy - electron_mass_c2) ;
// condition changed !
if((G4EnergyLossTables::GetRange(G4Electron::Electron(),
ElectKineEnergy,aMaterial)>aStep.GetPostStepPoint()->GetSafety())
||
(ElectKineEnergy >
(G4Electron::Electron()->GetCutsInEnergy())[aMaterial->GetIndex()]))
{
G4ThreeVector ElectDirection ( dirx, diry, dirz );
ElectDirection.rotateUz(GammaDirection);
// create G4DynamicParticle object for the particle1
G4DynamicParticle* aParticle1= new G4DynamicParticle (G4Electron::Electron(),
ElectDirection, ElectKineEnergy);
aParticleChange.AddSecondary( aParticle1 ) ;
}
else
{ LocalEnerDeposit += ElectKineEnergy ; }
// the e+ is always created (even with Ekine=0) for further annihilation.
G4double PositKineEnergy = max(0.,PositTotEnergy - electron_mass_c2) ;
// if (G4EnergyLossTables::GetRange(G4Positron::Positron(),PositKineEnergy,aMaterial)
// < min(G4Positron::GetCuts(), aStep.GetPostStepPoint()->GetSafety()) )
if((G4EnergyLossTables::GetRange(G4Positron::Positron(),
PositKineEnergy,aMaterial)<aStep.GetPostStepPoint()->GetSafety())
&&
(PositKineEnergy <
(G4Positron::Positron()->GetCutsInEnergy())[aMaterial->GetIndex()]))
{
LocalEnerDeposit += PositKineEnergy ;
PositKineEnergy = 0. ;
}
G4ThreeVector PositDirection ( -dirx, -diry, dirz );
PositDirection.rotateUz(GammaDirection);
// create G4DynamicParticle object for the particle2
G4DynamicParticle* aParticle2= new G4DynamicParticle (G4Positron::Positron(),
PositDirection, PositKineEnergy);
aParticleChange.AddSecondary( aParticle2 ) ;
aParticleChange.SetLocalEnergyDeposit( LocalEnerDeposit ) ;
//
// Kill the incident photon
//
aParticleChange.SetMomentumChange( 0., 0., 0. ) ;
aParticleChange.SetEnergyChange( 0. ) ;
aParticleChange.SetStatusChange( fStopAndKill ) ;
// Reset NbOfInteractionLengthLeft and return aParticleChange
return G4VDiscreteProcess::PostStepDoIt( aTrack, aStep );
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
G4Element* G4GammaConversion::SelectRandomAtom(const G4DynamicParticle* aDynamicGamma,
G4Material* aMaterial)
{
// select randomly 1 element within the material
const G4int NumberOfElements = aMaterial->GetNumberOfElements();
const G4ElementVector* theElementVector = aMaterial->GetElementVector();
if (NumberOfElements == 1) return (*theElementVector)(0);
const G4double* theAtomNumDensityVector = aMaterial->GetAtomicNumDensityVector();
G4double PartialSumSigma = 0. ;
G4double rval = G4UniformRand()/MeanFreePath;
for ( G4int i=0 ; i < NumberOfElements ; i++ )
{ PartialSumSigma += theAtomNumDensityVector[i] *
GetMicroscopicCrossSection(aDynamicGamma, (*theElementVector)(i));
if (rval <= PartialSumSigma) return ((*theElementVector)(i));
}
G4cout << " WARNING !!! - The Material '"<< aMaterial->GetName()
<< "' has no elements, NULL pointer returned." << endl;
return NULL;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
void G4GammaConversion::PrintInfoDefinition()
{
G4String comments = "Total cross sections from a parametrisation(L.Urban). ";
comments += "Good description from 1.5 MeV to 100 GeV for all Z. \n";
comments += " e+e- energies according Bethe-Heitler";
G4cout << endl << GetProcessName() << ": " << comments
<< "\n PhysicsTables from " << G4BestUnit(LowestEnergyLimit,"Energy")
<< " to " << G4BestUnit(HighestEnergyLimit,"Energy")
<< " in " << NumbBinTable << " bins. \n";
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....