Gabriele Cosmo
289 lines
10 KiB
C++
289 lines
10 KiB
C++
// This code implementation is the intellectual property of
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// the 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: G4ComptonScattering.cc,v 1.4 2000/11/17 15:03:17 maire Exp $
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// GEANT4 tag $Name: geant4-03-00 $
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//
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//
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//------------ G4ComptonScattering physics process --------
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// by Michel Maire, April 1996
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//
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// --------------------------------------------------------------
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// 28-05-96, DoIt() small change in ElecDirection, by M.Maire
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// 10-06-96, simplification in ComputeMicroscopicCrossSection(), by M.Maire
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// 21-06-96, SetCuts implementation, M.Maire
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// 13-09-96, small changes in DoIt for better efficiency. Thanks to P.Urban
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// 06-01-97, crossection table + meanfreepath table, M.Maire
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// 05-03-97, new Physics scheme, M.Maire
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// 28-03-97, protection in BuildPhysicsTable, M.Maire
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// 07-04-98, remove 'tracking cut' of the scattered gamma, MMa
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// 04-06-98, in DoIt, secondary production condition: range>G4std::min(threshold,safety)
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// 13-08-98, new methods SetBining() PrintInfo()
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// 15-12-98, cross section=0 below 10 keV
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// --------------------------------------------------------------
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#include "G4ComptonScattering.hh"
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#include "G4EnergyLossTables.hh"
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#include "G4UnitsTable.hh"
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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// constructor
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G4ComptonScattering::G4ComptonScattering(const G4String& processName)
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: G4VDiscreteProcess (processName),
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theCrossSectionTable(NULL),
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theMeanFreePathTable(NULL),
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LowestEnergyLimit ( 10*keV), // initialization
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HighestEnergyLimit(100*GeV),
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NumbBinTable(100)
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{ }
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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// destructor
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G4ComptonScattering::~G4ComptonScattering()
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{
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if (theCrossSectionTable) {
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theCrossSectionTable->clearAndDestroy();
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delete theCrossSectionTable;
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}
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if (theMeanFreePathTable) {
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theMeanFreePathTable->clearAndDestroy();
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delete theMeanFreePathTable;
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}
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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void G4ComptonScattering::SetPhysicsTableBining(G4double lowE, G4double highE, G4int nBins)
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{
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LowestEnergyLimit = lowE; HighestEnergyLimit = highE; NumbBinTable = nBins;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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void G4ComptonScattering::BuildPhysicsTable(const G4ParticleDefinition& GammaType)
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// Build microscopic cross section table and mean free path table
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{
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G4double LowEdgeEnergy, Value;
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G4PhysicsLogVector* ptrVector;
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// Build microscopic cross section tables for the Compton Scattering process
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if (theCrossSectionTable) {
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theCrossSectionTable->clearAndDestroy(); delete theCrossSectionTable; }
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theCrossSectionTable = new G4PhysicsTable(G4Element::GetNumberOfElements()) ;
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const G4ElementTable* theElementTable = G4Element::GetElementTable() ;
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G4double AtomicNumber;
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G4int J;
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for ( J=0 ; J < G4Element::GetNumberOfElements(); J++ )
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{
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//create physics vector then fill it ....
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ptrVector = new G4PhysicsLogVector(LowestEnergyLimit, HighestEnergyLimit,
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NumbBinTable ) ;
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AtomicNumber = (*theElementTable)(J)->GetZ();
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for ( G4int i = 0 ; i < NumbBinTable ; i++ )
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{
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LowEdgeEnergy = ptrVector->GetLowEdgeEnergy( i ) ;
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Value = ComputeCrossSectionPerAtom( LowEdgeEnergy, AtomicNumber);
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ptrVector->PutValue( i , Value ) ;
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}
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theCrossSectionTable->insertAt( J , ptrVector ) ;
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}
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// Build mean free path table for the Compton Scattering process
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if (theMeanFreePathTable) {
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theMeanFreePathTable->clearAndDestroy(); delete theMeanFreePathTable; }
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theMeanFreePathTable = new G4PhysicsTable(G4Material::GetNumberOfMaterials());
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const G4MaterialTable* theMaterialTable = G4Material::GetMaterialTable() ;
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G4Material* material;
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for ( J=0 ; J < G4Material::GetNumberOfMaterials(); J++ )
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{
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//create physics vector then fill it ....
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ptrVector = new G4PhysicsLogVector(LowestEnergyLimit, HighestEnergyLimit,
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NumbBinTable ) ;
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material = (*theMaterialTable)(J);
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for ( G4int i = 0 ; i < NumbBinTable ; i++ )
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{
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LowEdgeEnergy = ptrVector->GetLowEdgeEnergy( i ) ;
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Value = ComputeMeanFreePath( LowEdgeEnergy, material);
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ptrVector->PutValue( i , Value ) ;
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}
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theMeanFreePathTable->insertAt( J , ptrVector ) ;
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}
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PrintInfoDefinition();
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4ComptonScattering::ComputeCrossSectionPerAtom
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(G4double GammaEnergy, G4double Z)
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// Calculates the microscopic cross section in GEANT4 internal units.
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// A parametrized formula from L. Urban is used to estimate the total cross section.
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// It gives a good description of the data from 10 keV to 100/Z GeV.
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{
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G4double CrossSection = 0.0 ;
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if ( Z < 1. ) return CrossSection;
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if ( GammaEnergy < 10.*keV ) return CrossSection;
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if ( GammaEnergy > (100.*GeV/Z) ) return CrossSection;
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static const G4double a = 20.0 , b = 230.0 , c = 440.0 ;
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static const G4double
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d1= 2.7965e-1*barn, d2=-1.8300e-1*barn, d3= 6.7527 *barn, d4=-1.9798e+1*barn,
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e1= 1.9756e-5*barn, e2=-1.0205e-2*barn, e3=-7.3913e-2*barn, e4= 2.7079e-2*barn,
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f1=-3.9178e-7*barn, f2= 6.8241e-5*barn, f3= 6.0480e-5*barn, f4= 3.0274e-4*barn;
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G4double p1Z = Z*(d1 + e1*Z + f1*Z*Z), p2Z = Z*(d2 + e2*Z + f2*Z*Z),
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p3Z = Z*(d3 + e3*Z + f3*Z*Z), p4Z = Z*(d4 + e4*Z + f4*Z*Z);
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G4double X = GammaEnergy / electron_mass_c2 ;
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return CrossSection = p1Z*log(1.+2*X)/X
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+ (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4VParticleChange* G4ComptonScattering::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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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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G4ThreeVector GammaDirection1 ( dirx,diry,dirz );
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GammaDirection1.rotateUz(GammaDirection0);
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aParticleChange.SetMomentumChange( GammaDirection1 ) ;
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G4double GammaEnergy1 = epsilon*GammaEnergy0;
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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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// condition changed!
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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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void G4ComptonScattering::PrintInfoDefinition()
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{
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G4String comments = "Total cross sections from a parametrisation. ";
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comments += "Good description from 10 KeV to (100/Z) GeV. \n";
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comments += " Scattered gamma energy according Klein-Nishina.";
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G4cout << G4endl << GetProcessName() << ": " << comments
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<< "\n PhysicsTables from " << G4BestUnit(LowestEnergyLimit,"Energy")
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<< " to " << G4BestUnit(HighestEnergyLimit,"Energy")
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<< " in " << NumbBinTable << " bins. \n";
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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