Gabriele Cosmo
225 lines
8.2 KiB
C++
225 lines
8.2 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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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. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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// $Id: G4KleinNishinaCompton.cc,v 1.8 2006/06/29 19:53:04 gunter Exp $
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// GEANT4 tag $Name: geant4-08-02 $
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//
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// -------------------------------------------------------------------
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//
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// GEANT4 Class file
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//
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//
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// File name: G4KleinNishinaCompton
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//
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// Author: Vladimir Ivanchenko on base of Michel Maire code
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//
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// Creation date: 15.03.2005
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//
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// Modifications:
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// 18-04-05 Use G4ParticleChangeForGamma (V.Ivantchenko)
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// 27-03-06 Remove upper limit of cross section (V.Ivantchenko)
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//
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// Class Description:
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//
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// -------------------------------------------------------------------
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//
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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#include "G4KleinNishinaCompton.hh"
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#include "G4Electron.hh"
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#include "G4Gamma.hh"
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#include "Randomize.hh"
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#include "G4DataVector.hh"
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#include "G4ParticleChangeForGamma.hh"
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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using namespace std;
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G4KleinNishinaCompton::G4KleinNishinaCompton(const G4ParticleDefinition*,
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const G4String& nam)
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: G4VEmModel(nam)
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{
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theGamma = G4Gamma::Gamma();
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theElectron = G4Electron::Electron();
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lowestGammaEnergy = 1.0*eV;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4KleinNishinaCompton::~G4KleinNishinaCompton()
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{}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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void G4KleinNishinaCompton::Initialise(const G4ParticleDefinition*,
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const G4DataVector&)
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{
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if(pParticleChange)
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fParticleChange = reinterpret_cast<G4ParticleChangeForGamma*>(pParticleChange);
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else
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fParticleChange = new G4ParticleChangeForGamma();
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4KleinNishinaCompton::ComputeCrossSectionPerAtom(
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const G4ParticleDefinition*,
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G4double GammaEnergy,
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G4double Z, G4double,
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G4double, G4double)
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{
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G4double CrossSection = 0.0 ;
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if ( Z < 0.9999 ) return CrossSection;
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if ( GammaEnergy < 0.1*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 T0 = 15.0*keV;
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if (Z < 1.5) T0 = 40.0*keV;
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G4double X = max(GammaEnergy, T0) / electron_mass_c2;
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CrossSection = p1Z*std::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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// modification for low energy. (special case for Hydrogen)
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if (GammaEnergy < T0) {
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G4double dT0 = 1.*keV;
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X = (T0+dT0) / electron_mass_c2 ;
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G4double sigma = 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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G4double c1 = -T0*(sigma-CrossSection)/(CrossSection*dT0);
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G4double c2 = 0.150;
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if (Z > 1.5) c2 = 0.375-0.0556*log(Z);
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G4double y = log(GammaEnergy/T0);
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CrossSection *= exp(-y*(c1+c2*y));
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}
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// G4cout << "e= " << GammaEnergy << " Z= " << Z << " cross= " << CrossSection << G4endl;
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return CrossSection;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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std::vector<G4DynamicParticle*>* G4KleinNishinaCompton::SampleSecondaries(
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const G4MaterialCutsCouple*,
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const G4DynamicParticle* aDynamicGamma,
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G4double,
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G4double)
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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
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// (Nuc Phys 20(1960),15).
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// Note : Effects due to binding of atomic electrons are negliged.
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G4double gamEnergy0 = aDynamicGamma->GetKineticEnergy();
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G4double E0_m = gamEnergy0 / electron_mass_c2 ;
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G4ThreeVector gamDirection0 = 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);
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G4double epsilon0sq = epsilon0*epsilon0;
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G4double alpha1 = - log(epsilon0);
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G4double 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()); // epsilon0**r
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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;
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G4double 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 gamDirection1 ( dirx,diry,dirz );
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gamDirection1.rotateUz(gamDirection0);
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G4double gamEnergy1 = epsilon*gamEnergy0;
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fParticleChange->SetProposedKineticEnergy(gamEnergy1);
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if(gamEnergy1 > lowestGammaEnergy) {
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fParticleChange->ProposeMomentumDirection(gamDirection1);
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} else {
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fParticleChange->ProposeTrackStatus(fStopAndKill);
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gamEnergy1 += fParticleChange->GetLocalEnergyDeposit();
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fParticleChange->ProposeLocalEnergyDeposit(gamEnergy1);
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}
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std::vector<G4DynamicParticle*>* fvect = new std::vector<G4DynamicParticle*>;
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//
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// kinematic of the scattered electron
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//
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G4double eKinEnergy = gamEnergy0 - gamEnergy1;
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if(eKinEnergy > DBL_MIN) {
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G4ThreeVector eDirection = gamEnergy0*gamDirection0 - gamEnergy1*gamDirection1;
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eDirection = eDirection.unit();
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// create G4DynamicParticle object for the electron.
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G4DynamicParticle* dp = new G4DynamicParticle(theElectron,eDirection,eKinEnergy);
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fvect->push_back(dp);
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}
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return fvect;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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