Gabriele Cosmo
352 lines
12 KiB
C++
352 lines
12 KiB
C++
//
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// ********************************************************************
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// * DISCLAIMER *
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// * *
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// * The following disclaimer summarizes all the specific disclaimers *
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// * of contributors to this software. The specific disclaimers,which *
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// * govern, are listed with their locations in: *
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// * http://cern.ch/geant4/license *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. *
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// * *
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// * This code implementation is the intellectual property of the *
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// * GEANT4 collaboration. *
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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 *
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// * statement, and all its terms. *
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// ********************************************************************
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//
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// --------------------------------------------------------------------
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///
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// $Id: G4LowEnergyGammaConversion.cc,v 1.26 2001/11/07 21:31:16 pia Exp $
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// GEANT4 tag $Name: geant4-04-00 $
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//
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//
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// --------------------------------------------------------------
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//
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// Author: A. Forti
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// Maria Grazia Pia (Maria.Grazia.Pia@cern.ch)
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//
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// History:
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// --------
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// 02/03/1999 A. Forti 1st implementation
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// 14.03.2000 Veronique Lefebure;
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// Change initialisation of lowestEnergyLimit from 1.22 to 1.022.
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// Note that the hard coded value 1.022 should be used instead of
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// 2*electron_mass_c2 in order to agree with the value of the data bank EPDL97
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// 24.04.01 V.Ivanchenko remove RogueWave
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// 27.07.01 F.Longo correct bug in energy distribution
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//
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// --------------------------------------------------------------
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#include "G4LowEnergyGammaConversion.hh"
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#include "Randomize.hh"
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#include "G4ParticleDefinition.hh"
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#include "G4Track.hh"
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#include "G4Step.hh"
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#include "G4ForceCondition.hh"
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#include "G4Gamma.hh"
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#include "G4Electron.hh"
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#include "G4DynamicParticle.hh"
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#include "G4VParticleChange.hh"
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#include "G4ThreeVector.hh"
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#include "G4Positron.hh"
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#include "G4IonisParamElm.hh"
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#include "G4Material.hh"
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#include "G4VCrossSectionHandler.hh"
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#include "G4CrossSectionHandler.hh"
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#include "G4VEMDataSet.hh"
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#include "G4VDataSetAlgorithm.hh"
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#include "G4LogLogInterpolation.hh"
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#include "G4VRangeTest.hh"
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#include "G4RangeTest.hh"
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#include "G4CutsPerMaterialWarning.hh"
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G4LowEnergyGammaConversion::G4LowEnergyGammaConversion(const G4String& processName)
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: G4VDiscreteProcess(processName),
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lowEnergyLimit(1.022000*MeV),
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highEnergyLimit(100*GeV),
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intrinsicLowEnergyLimit(1.022000*MeV),
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intrinsicHighEnergyLimit(100*GeV),
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smallEnergy(2.*MeV)
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{
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if (lowEnergyLimit < intrinsicLowEnergyLimit ||
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highEnergyLimit > intrinsicHighEnergyLimit)
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{
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G4Exception("G4LowEnergyGammaConversion::G4LowEnergyGammaConversion - energy limit outside intrinsic process validity range");
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}
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// The following pointer is owned by G4DataHandler
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crossSectionHandler = new G4CrossSectionHandler();
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crossSectionHandler->Initialise(0,1.0220*MeV,100.*GeV,400);
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meanFreePathTable = 0;
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rangeTest = new G4RangeTest;
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if (verboseLevel > 0)
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{
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G4cout << GetProcessName() << " is created " << G4endl
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<< "Energy range: "
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<< lowEnergyLimit / MeV << " MeV - "
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<< highEnergyLimit / GeV << " GeV"
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<< G4endl;
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}
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}
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G4LowEnergyGammaConversion::~G4LowEnergyGammaConversion()
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{
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delete meanFreePathTable;
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delete crossSectionHandler;
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delete rangeTest;
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}
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void G4LowEnergyGammaConversion::BuildPhysicsTable(const G4ParticleDefinition& photon)
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{
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G4CutsPerMaterialWarning warning;
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warning.PrintWarning(&photon);
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crossSectionHandler->Clear();
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G4String crossSectionFile = "pair/pp-cs-";
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crossSectionHandler->LoadData(crossSectionFile);
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delete meanFreePathTable;
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meanFreePathTable = crossSectionHandler->BuildMeanFreePathForMaterials();
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}
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G4VParticleChange* G4LowEnergyGammaConversion::PostStepDoIt(const G4Track& aTrack,
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const G4Step& aStep)
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{
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// The energies of the e+ e- secondaries 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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// 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* material = aTrack.GetMaterial();
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const G4DynamicParticle* incidentPhoton = aTrack.GetDynamicParticle();
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G4double photonEnergy = incidentPhoton->GetKineticEnergy();
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G4ParticleMomentum photonDirection = incidentPhoton->GetMomentumDirection();
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G4double epsilon ;
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G4double epsilon0 = electron_mass_c2 / photonEnergy ;
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// Do it fast if photon energy < 2. MeV
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if (photonEnergy < smallEnergy )
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{
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epsilon = epsilon0 + (0.5 - epsilon0) * G4UniformRand();
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}
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else
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{
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// Select randomly one element in the current material
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const G4Element* element = crossSectionHandler->SelectRandomElement(material,photonEnergy);
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if (element == 0)
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{
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G4cout << "G4LowEnergyGammaConversion::PostStepDoIt - element = 0" << G4endl;
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}
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G4IonisParamElm* ionisation = element->GetIonisation();
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if (ionisation == 0)
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{
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G4cout << "G4LowEnergyGammaConversion::PostStepDoIt - ionisation = 0" << G4endl;
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}
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// Extract Coulomb factor for this Element
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G4double fZ = 8. * (ionisation->GetlogZ3());
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if (photonEnergy > 50. * MeV) fZ += 8. * (element->GetfCoulomb());
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// Limits of the screening variable
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G4double screenFactor = 136. * epsilon0 / (element->GetIonisation()->GetZ3()) ;
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G4double screenMax = exp ((42.24 - fZ)/8.368) - 0.952 ;
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G4double screenMin = G4std::min(4.*screenFactor,screenMax) ;
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// Limits of the energy sampling
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G4double epsilon1 = 0.5 - 0.5 * sqrt(1. - screenMin / screenMax) ;
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G4double epsilonMin = G4std::max(epsilon0,epsilon1);
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G4double epsilonRange = 0.5 - epsilonMin ;
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// Sample the energy rate of the created electron (or positron)
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G4double screen;
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G4double gReject ;
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G4double f10 = ScreenFunction1(screenMin) - fZ;
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G4double f20 = ScreenFunction2(screenMin) - fZ;
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G4double normF1 = G4std::max(f10 * epsilonRange * epsilonRange,0.);
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G4double normF2 = G4std::max(1.5 * f20,0.);
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do {
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if (normF1 / (normF1 + normF2) > G4UniformRand() )
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{
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epsilon = 0.5 - epsilonRange * pow(G4UniformRand(), 0.3333) ;
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screen = screenFactor / (epsilon * (1. - epsilon));
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gReject = (ScreenFunction1(screen) - fZ) / f10 ;
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}
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else
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{
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epsilon = epsilonMin + epsilonRange * G4UniformRand();
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screen = screenFactor / (epsilon * (1 - epsilon));
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gReject = (ScreenFunction2(screen) - fZ) / f20 ;
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}
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} while ( gReject < G4UniformRand() );
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} // End of epsilon sampling
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// Fix charges randomly
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G4double electronTotEnergy;
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G4double positronTotEnergy;
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if (RandBit::shootBit())
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{
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electronTotEnergy = (1. - epsilon) * photonEnergy;
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positronTotEnergy = epsilon * photonEnergy;
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}
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else
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{
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positronTotEnergy = (1. - epsilon) * photonEnergy;
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electronTotEnergy = epsilon * photonEnergy;
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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;
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G4double a2 = 3. * a1;
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// G4double d = 27. ;
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// if (9. / (9. + d) > G4UniformRand())
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if (0.25 > G4UniformRand())
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{
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u = - log(G4UniformRand() * G4UniformRand()) / a1 ;
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}
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else
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{
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u = - log(G4UniformRand() * G4UniformRand()) / a2 ;
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}
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G4double theta = u * electron_mass_c2 / photonEnergy ;
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G4double phi = twopi * G4UniformRand() ;
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G4double dirX = sin(theta) * cos(phi);
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G4double dirY = sin(theta) * sin(phi);
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G4double dirZ = cos(theta);
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// Kinematics 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 localEnergyDeposit = 0. ;
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aParticleChange.SetNumberOfSecondaries(2.) ;
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G4double electronKineEnergy = G4std::max(0.,electronTotEnergy - electron_mass_c2) ;
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// Generate the electron only if with large enough range w.r.t. cuts and safety
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G4double safety = aStep.GetPostStepPoint()->GetSafety();
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if (rangeTest->Escape(G4Electron::Electron(),material,electronKineEnergy,safety))
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{
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G4ThreeVector electronDirection ( dirX, dirY, dirZ );
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electronDirection.rotateUz(photonDirection);
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G4DynamicParticle* particle1 = new G4DynamicParticle (G4Electron::Electron(),
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electronDirection,
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electronKineEnergy);
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aParticleChange.AddSecondary(particle1) ;
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}
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else
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{
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localEnergyDeposit += electronKineEnergy ;
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}
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// The e+ is always created (even with kinetic energy = 0) for further annihilation
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G4double positronKineEnergy = G4std::max(0.,positronTotEnergy - electron_mass_c2) ;
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// Is the local energy deposit correct, if the positron is always created?
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if (! (rangeTest->Escape(G4Positron::Positron(),material,positronKineEnergy,safety)))
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{
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localEnergyDeposit += positronKineEnergy ;
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positronKineEnergy = 0. ;
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}
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G4ThreeVector positronDirection(-dirX,-dirY,dirZ);
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positronDirection.rotateUz(photonDirection);
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// Create G4DynamicParticle object for the particle2
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G4DynamicParticle* particle2 = new G4DynamicParticle(G4Positron::Positron(),
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positronDirection, positronKineEnergy);
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aParticleChange.AddSecondary(particle2) ;
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aParticleChange.SetLocalEnergyDeposit(localEnergyDeposit) ;
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// Kill the incident photon
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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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// Reset NbOfInteractionLengthLeft and return aParticleChange
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return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
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}
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G4bool G4LowEnergyGammaConversion::IsApplicable(const G4ParticleDefinition& particle)
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{
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return ( &particle == G4Gamma::Gamma() );
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}
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G4double G4LowEnergyGammaConversion::GetMeanFreePath(const G4Track& track,
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G4double previousStepSize,
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G4ForceCondition*)
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{
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const G4DynamicParticle* photon = track.GetDynamicParticle();
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G4double energy = photon->GetKineticEnergy();
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G4Material* material = track.GetMaterial();
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size_t materialIndex = material->GetIndex();
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G4double meanFreePath;
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if (energy > highEnergyLimit) meanFreePath = meanFreePathTable->FindValue(highEnergyLimit,materialIndex);
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else if (energy < lowEnergyLimit) meanFreePath = DBL_MAX;
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else meanFreePath = meanFreePathTable->FindValue(energy,materialIndex);
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return meanFreePath;
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}
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G4double G4LowEnergyGammaConversion::ScreenFunction1(G4double screenVariable)
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{
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// Compute the value of the screening function 3*phi1 - phi2
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G4double value;
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if (screenVariable > 1.)
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value = 42.24 - 8.368 * log(screenVariable + 0.952);
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else
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value = 42.392 - screenVariable * (7.796 - 1.961 * screenVariable);
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return value;
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}
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G4double G4LowEnergyGammaConversion::ScreenFunction2(G4double screenVariable)
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{
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// Compute the value of the screening function 1.5*phi1 - 0.5*phi2
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G4double value;
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if (screenVariable > 1.)
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value = 42.24 - 8.368 * log(screenVariable + 0.952);
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else
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value = 41.405 - screenVariable * (5.828 - 0.8945 * screenVariable);
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return value;
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}
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