Gabriele Cosmo
426 lines
13 KiB
C++
426 lines
13 KiB
C++
// 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: G4LowEnergyGammaConversion.cc,v 1.9 1999/06/28 15:46:00 aforti Exp $
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// GEANT4 tag $Name: geant4-00-01 $
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//
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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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// History: first implementation, based on object model of
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// 2nd December 1995, G.Cosmo
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// ------------ G4LowEnergyGammaConversion physics process --------
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// by Michel Maire, 24 May 1996
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// **************************************************************
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// 11-06-96, Added SelectRandomAtom() method, M.Maire
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// 21-06-96, SetCuts implementation, M.Maire
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// 24-06-96, simplification in ComputeMicroscopicCrossSection, M.Maire
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// 24-06-96, in DoIt : change the particleType stuff, M.Maire
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// 25-06-96, modification in the generation of the teta angle, M.Maire
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// 16-09-96, minors optimisations in DoIt. Thanks to P.Urban
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// dynamical array PartialSumSigma
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// 13-12-96, fast sampling of epsil below 2 MeV, L.Urban
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// 14-01-97, crossection table + meanfreepath table.
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// PartialSumSigma removed, M.Maire
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// 14-01-97, in DoIt the positron is always created, even with Ekine=0,
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// for further annihilation, M.Maire
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// 14-03-97, new Physics scheme for geant4alpha, M.Maire
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// 28-03-97, protection in BuildPhysicsTable, M.Maire
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// 19-06-97, correction in ComputeMicroscopicCrossSection, L.Urban
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// 04-06-98, in DoIt, secondary production condition: range>min(threshold,safety)
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// --------------------------------------------------------------
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// This Class Header
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#include "G4LowEnergyGammaConversion.hh"
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// Collaborating Class Headers
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#include "G4EnergyLossTables.hh"
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#include "G4Electron.hh"
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#include "G4Positron.hh"
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// constructor
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G4LowEnergyGammaConversion::G4LowEnergyGammaConversion(const G4String& processName)
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: G4VDiscreteProcess(processName),
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theCrossSectionTable(0),
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theMeanFreePathTable(0),
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ZNumVec(0),
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LowestEnergyLimit (1.2200),
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HighestEnergyLimit(100*GeV),
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NumbBinTable(200)
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{
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if (verboseLevel>0) {
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G4cout << GetProcessName() << " is created "<< endl;
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G4cout << "LowestEnergy: " << LowestEnergyLimit/keV << "keV ";
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G4cout << "HighestEnergy: " << HighestEnergyLimit/GeV << "GeV " << endl;
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}
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}
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// destructor
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G4LowEnergyGammaConversion::~G4LowEnergyGammaConversion()
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{
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if (theCrossSectionTable) {
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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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if(ZNumVec){
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ZNumVec->clear();
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delete ZNumVec;
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}
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}
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// methods.............................................................................
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void G4LowEnergyGammaConversion::BuildPhysicsTable(const G4ParticleDefinition& GammaType){
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BuildZVec();
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// Build microscopic cross section tables for the Compton Scattering process
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BuildCrossSectionTable();
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// Build mean free path table for the Compton Scattering process
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BuildMeanFreePathTable();
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}
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void G4LowEnergyGammaConversion::BuildCrossSectionTable(){
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if (theCrossSectionTable) {
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delete theCrossSectionTable;
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}
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theCrossSectionTable = new G4SecondLevel();
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G4int dataNum = 2;
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for(G4int TableInd = 0; TableInd < ZNumVec->entries(); TableInd++){
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G4int AtomInd = (G4int) (*ZNumVec)[TableInd];
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G4FirstLevel* oneAtomCS = util.BuildFirstLevelTables(AtomInd, dataNum, "pair/pp-cs-");
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theCrossSectionTable->insert(oneAtomCS);
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}//end for on atoms
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}
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void G4LowEnergyGammaConversion::BuildZVec(){
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const G4MaterialTable* theMaterialTable=G4Material::GetMaterialTable();
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G4int numOfMaterials = theMaterialTable->length();
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if(ZNumVec){
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ZNumVec->clear();
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delete ZNumVec;
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}
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ZNumVec = new G4Data();
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for (G4int J=0 ; J < numOfMaterials; J++){
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const G4Material* material= (*theMaterialTable)[J];
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const G4ElementVector* theElementVector = material->GetElementVector();
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const G4int NumberOfElements = material->GetNumberOfElements() ;
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for (G4int iel=0; iel<NumberOfElements; iel++ ){
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G4double Zel = (*theElementVector)(iel)->GetZ();
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if(ZNumVec->contains(Zel) == FALSE){
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ZNumVec->insert(Zel);
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}
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else{
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continue;
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}
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}
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}
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}
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G4VParticleChange* G4LowEnergyGammaConversion::PostStepDoIt(const G4Track& aTrack, const G4Step& aStep){
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//
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// The secondaries e+e- energies are sampled using the Bethe - Heitler
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// cross sections with Coulomb correction. A modified version of the random
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// number techniques of Butcher & Messel is used (Nuc Phys 20(1960),15).
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//
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// GEANT4 internal units.
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//
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// Note 1 : Effects due to the breakdown of the Born approximation at low
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// energy are ignored.
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// Note 2 : The differential cross section implicitly takes account of
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// pair creation in both nuclear and atomic electron fields. However triplet
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// prodution is not generated.
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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 GammaEnergy = aDynamicGamma->GetKineticEnergy();
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G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection();
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G4double epsil ;
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G4double epsil0 = electron_mass_c2 / GammaEnergy ;
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// do it fast if GammaEnergy < 2. MeV
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const G4double Egsmall=2.*MeV;
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if (GammaEnergy<Egsmall) { epsil = epsil0 + (0.5-epsil0)*G4UniformRand(); }
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else{ // now comes the case with GammaEnergy >= 2. MeV
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// select randomly one element constituing the material
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G4Element* anElement = SelectRandomAtom(aDynamicGamma, aMaterial);
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// Extract Coulomb factor for this Element
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G4double FZ = 8.*(anElement->GetIonisation()->GetlogZ3());
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if (GammaEnergy > 50.*MeV) FZ += 8.*(anElement->GetfCoulomb());
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// limits of the screening variable
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G4double screenfac = 136.*epsil0/(anElement->GetIonisation()->GetZ3()) ;
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G4double screenmax = exp ((42.24 - FZ)/8.368) - 0.952 ;
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G4double screenmin = min(4.*screenfac,screenmax) ;
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// limits of the energy sampling
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G4double epsil1 = 0.5 - 0.5*sqrt(1. - screenmin/screenmax) ;
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G4double epsilmin = max(epsil0,epsil1) , epsilrange = 0.5 - epsilmin ;
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//
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// sample the energy rate of the created electron (or positron)
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//
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//G4double epsil, screenvar, greject ;
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G4double screenvar, greject ;
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G4double F10 = ScreenFunction1(screenmin) - FZ , F20 = ScreenFunction2(screenmin) - FZ;
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G4double NormF1 = max(F10*epsilrange*epsilrange,0.) , NormF2 = max(1.5*F20,0.);
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do {
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if ( NormF1/(NormF1+NormF2) > G4UniformRand() ){
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epsil = 0.5 - epsilrange*pow(G4UniformRand(), 1/3) ;
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screenvar = screenfac/(epsil*(1-epsil));
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greject = (ScreenFunction1(screenvar) - FZ)/F10 ;
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}
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else {
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epsil = epsilmin + epsilrange*G4UniformRand();
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screenvar = screenfac/(epsil*(1-epsil));
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greject = (ScreenFunction2(screenvar) - FZ)/F20 ;
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}
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} while( greject < G4UniformRand() );
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} // end of epsil sampling.........................
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//
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// fixe charges randomly
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//
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G4double ElectTotEnergy, PositTotEnergy;
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if (RandFlat::shootBit()){
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ElectTotEnergy = (1.-epsil)*GammaEnergy;
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PositTotEnergy = epsil*GammaEnergy;
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}
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else{
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PositTotEnergy = (1.-epsil)*GammaEnergy;
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ElectTotEnergy = epsil*GammaEnergy;
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}
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//
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// scattered electron (positron) angles. ( Z - axis along the parent photon)
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// universal distribution suggested by L. Urban (Geant3 manual (1993) Phys211),
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// derived from Tsai distribution (Rev Mod Phys 49,421(1977))
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G4double u;
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const G4double a1 = 0.625 , a2 = 3.*a1 , d = 27. ;
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if (9./(9.+d) > G4UniformRand()){
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u = - log(G4UniformRand()*G4UniformRand())/a1 ;
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}
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else{
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u = - log(G4UniformRand()*G4UniformRand())/a2 ;
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}
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G4double Teta = u*electron_mass_c2/GammaEnergy ;
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G4double Phi = twopi * G4UniformRand() ;
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G4double dirx = sin(Teta)*cos(Phi) , diry = sin(Teta)*sin(Phi) , dirz = cos(Teta);
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//
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// kinematic of the created pair
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// the electron and positron are assumed to have a symetric angular
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// distribution with respect to the Z axis along the parent photon.
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G4double LocalEnerDeposit = 0. ;
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aParticleChange.SetNumberOfSecondaries(2) ;
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G4double ElectKineEnergy = max(0.,ElectTotEnergy - electron_mass_c2) ;
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if (G4EnergyLossTables::GetRange(G4Electron::Electron(), ElectKineEnergy, aMaterial)
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>= min(G4Electron::GetCuts(), aStep.GetPostStepPoint()->GetSafety()) ){
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G4ThreeVector ElectDirection ( dirx, diry, dirz );
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ElectDirection.rotateUz(GammaDirection);
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// create G4DynamicParticle object for the particle1
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G4DynamicParticle* aParticle1= new G4DynamicParticle (G4Electron::Electron(),ElectDirection, ElectKineEnergy);
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aParticleChange.AddSecondary( aParticle1 ) ;
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}
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else{
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LocalEnerDeposit += ElectKineEnergy ;
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}
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// the e+ is always created (even with Ekine=0) for further annihilation.
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G4double PositKineEnergy = max(0.,PositTotEnergy - electron_mass_c2) ;
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if (G4EnergyLossTables::GetRange(G4Positron::Positron(),PositKineEnergy,aMaterial)
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< min(G4Positron::GetCuts(), aStep.GetPostStepPoint()->GetSafety()) ){
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LocalEnerDeposit += PositKineEnergy ;
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PositKineEnergy = 0. ;
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}
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G4ThreeVector PositDirection ( -dirx, -diry, dirz );
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PositDirection.rotateUz(GammaDirection);
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// create G4DynamicParticle object for the particle2
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G4DynamicParticle* aParticle2= new G4DynamicParticle (G4Positron::Positron(),
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PositDirection, PositKineEnergy);
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aParticleChange.AddSecondary( aParticle2 ) ;
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aParticleChange.SetLocalEnergyDeposit( LocalEnerDeposit ) ;
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//
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// Kill the incident photon
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//
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aParticleChange.SetMomentumChange( 0., 0., 0. ) ;
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aParticleChange.SetEnergyChange( 0. ) ;
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aParticleChange.SetStatusChange( fStopAndKill ) ;
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#ifdef G4VERBOSE
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if(verboseLevel > 15){
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G4cout<<"LE Gamma Conversion PostStepDoIt"<<endl;
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}
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#endif
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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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void G4LowEnergyGammaConversion::BuildMeanFreePathTable(){
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if (theMeanFreePathTable) {
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theMeanFreePathTable->clearAndDestroy(); delete theMeanFreePathTable; }
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// material
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G4double NumbOfMaterials = G4Material::GetNumberOfMaterials();
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const G4MaterialTable* theMaterialTable = G4Material::GetMaterialTable() ;
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G4Material* material;
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// MeanFreePath
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G4double LowEdgeEnergy, Value;
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theMeanFreePathTable = new G4PhysicsTable(NumbOfMaterials);
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G4PhysicsLogVector* ptrVector;
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for ( G4int J = 0 ; J < NumbOfMaterials; J++ ) { // For each material
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//create physics vector then fill it ....
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ptrVector = new G4PhysicsLogVector(LowestEnergyLimit, HighestEnergyLimit, NumbBinTable);
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material = (*theMaterialTable)(J);
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const G4ElementVector* theElementVector = material->GetElementVector();
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const G4double* theAtomNumDensityVector = material->GetAtomicNumDensityVector();
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for ( G4int i = 0 ; i < NumbBinTable ; i++ ){
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//For each energy
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LowEdgeEnergy = ptrVector->GetLowEdgeEnergy(i);
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const G4double BigPath= DBL_MAX;
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G4double SIGMA = 0 ;
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for ( G4int k=0 ; k < material->GetNumberOfElements() ; k++ ){
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// For each element
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G4int AtomIndex = (G4int) (*theElementVector)(k)->GetZ();
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const G4FirstLevel* oneAtomCS
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= (*theCrossSectionTable)[ZNumVec->index(AtomIndex)];
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G4double interCrsSec = util.DataLogInterpolation(LowEdgeEnergy,
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(*(*oneAtomCS)[0]),
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(*(*oneAtomCS)[1]))*barn;
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SIGMA += theAtomNumDensityVector[k]*interCrsSec;
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}
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Value = SIGMA<=0.0 ? BigPath : 1./SIGMA ;
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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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}
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G4Element* G4LowEnergyGammaConversion::SelectRandomAtom(const G4DynamicParticle* aDynamicGamma, G4Material* aMaterial){
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// select randomly 1 element within the material
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G4double GammaEnergy = aDynamicGamma->GetKineticEnergy();
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const G4int NumberOfElements = aMaterial->GetNumberOfElements();
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const G4ElementVector* theElementVector = aMaterial->GetElementVector();
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if (NumberOfElements == 1) return (*theElementVector)(0);
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const G4double* theAtomNumDensityVector = aMaterial->GetAtomicNumDensityVector();
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G4double PartialSumSigma = 0.;
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G4double rval = G4UniformRand()/MeanFreePath;
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for ( G4int i=0 ; i < NumberOfElements ; i++ ){
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G4double crossSection;
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if (GammaEnergy < LowestEnergyLimit)
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crossSection = 0. ;
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else {
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if (GammaEnergy > HighestEnergyLimit) GammaEnergy = 0.99*HighestEnergyLimit ;
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G4int AtomIndex = (G4int) (*theElementVector)(i)->GetZ();
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const G4FirstLevel* oneAtomCS
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= (*theCrossSectionTable)[ZNumVec->index(AtomIndex)];
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crossSection = util.DataLogInterpolation(GammaEnergy,
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(*(*oneAtomCS)[0]),
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(*(*oneAtomCS)[1]))*barn;
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}
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PartialSumSigma += theAtomNumDensityVector[i] * crossSection;
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if(rval <= PartialSumSigma) return ((*theElementVector)(i));
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}
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// G4cout << " WARNING !!! - The Material '"<< aMaterial->GetName()
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// << "' has no elements" << endl;
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return (*theElementVector)(0);
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}
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