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geant4/source/processes/electromagnetic/standard/src/G4KleinNishinaModel.cc
T
Gabriele Cosmo 89a9605df1 Import Geant4 9.4.0 source tree
2016-06-09 16:25:56 +02:00

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//
// ********************************************************************
// * License and Disclaimer *
// * *
// * The Geant4 software is copyright of the Copyright Holders of *
// * the Geant4 Collaboration. It is provided under the terms and *
// * conditions of the Geant4 Software License, included in the file *
// * LICENSE and available at http://cern.ch/geant4/license . These *
// * include a list of copyright holders. *
// * *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work make any representation or warranty, express or implied, *
// * regarding this software system or assume any liability for its *
// * use. Please see the license in the file LICENSE and URL above *
// * for the full disclaimer and the limitation of liability. *
// * *
// * This code implementation is the result of the scientific and *
// * technical work of the GEANT4 collaboration. *
// * By using, copying, modifying or distributing the software (or *
// * any work based on the software) you agree to acknowledge its *
// * use in resulting scientific publications, and indicate your *
// * acceptance of all terms of the Geant4 Software license. *
// ********************************************************************
//
// $Id: G4KleinNishinaModel.cc,v 1.4 2010/11/21 16:08:37 vnivanch Exp $
// GEANT4 tag $Name: geant4-09-04 $
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name: G4KleinNishinaModel
//
// Author: Vladimir Ivanchenko on base of G4KleinNishinaCompton
//
// Creation date: 13.06.2010
//
// Modifications:
//
// Class Description:
//
// -------------------------------------------------------------------
//
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
#include "G4KleinNishinaModel.hh"
#include "G4Electron.hh"
#include "G4Gamma.hh"
#include "Randomize.hh"
#include "G4RandomDirection.hh"
#include "G4DataVector.hh"
#include "G4ParticleChangeForGamma.hh"
#include "G4VAtomDeexcitation.hh"
#include "G4LossTableManager.hh"
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
using namespace std;
G4KleinNishinaModel::G4KleinNishinaModel(const G4String& nam)
: G4VEmModel(nam),isInitialized(false)
{
theGamma = G4Gamma::Gamma();
theElectron = G4Electron::Electron();
lowestGammaEnergy = 1.0*eV;
fProbabilities.resize(9,0.0);
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
G4KleinNishinaModel::~G4KleinNishinaModel()
{}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
void G4KleinNishinaModel::Initialise(const G4ParticleDefinition* p,
const G4DataVector& cuts)
{
fAtomDeexcitation = G4LossTableManager::Instance()->AtomDeexcitation();
InitialiseElementSelectors(p, cuts);
if (isInitialized) { return; }
fParticleChange = GetParticleChangeForGamma();
isInitialized = true;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
G4double
G4KleinNishinaModel::ComputeCrossSectionPerAtom(const G4ParticleDefinition*,
G4double GammaEnergy,
G4double Z, G4double,
G4double, G4double)
{
G4double CrossSection = 0.0 ;
if ( Z < 0.9999 || GammaEnergy < 0.1*keV) { return CrossSection; }
static const G4double a = 20.0 , b = 230.0 , c = 440.0;
static const G4double
d1= 2.7965e-1*barn, d2=-1.8300e-1*barn, d3= 6.7527 *barn, d4=-1.9798e+1*barn,
e1= 1.9756e-5*barn, e2=-1.0205e-2*barn, e3=-7.3913e-2*barn, e4= 2.7079e-2*barn,
f1=-3.9178e-7*barn, f2= 6.8241e-5*barn, f3= 6.0480e-5*barn, f4= 3.0274e-4*barn;
G4double p1Z = Z*(d1 + e1*Z + f1*Z*Z), p2Z = Z*(d2 + e2*Z + f2*Z*Z),
p3Z = Z*(d3 + e3*Z + f3*Z*Z), p4Z = Z*(d4 + e4*Z + f4*Z*Z);
G4double T0 = 15.0*keV;
if (Z < 1.5) { T0 = 40.0*keV; }
G4double X = max(GammaEnergy, T0) / electron_mass_c2;
CrossSection = p1Z*std::log(1.+2.*X)/X
+ (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
// modification for low energy. (special case for Hydrogen)
if (GammaEnergy < T0) {
G4double dT0 = keV;
X = (T0+dT0) / electron_mass_c2 ;
G4double sigma = p1Z*log(1.+2*X)/X
+ (p2Z + p3Z*X + p4Z*X*X)/(1. + a*X + b*X*X + c*X*X*X);
G4double c1 = -T0*(sigma-CrossSection)/(CrossSection*dT0);
G4double c2 = 0.150;
if (Z > 1.5) { c2 = 0.375-0.0556*log(Z); }
G4double y = log(GammaEnergy/T0);
CrossSection *= exp(-y*(c1+c2*y));
}
// G4cout << "e= " << GammaEnergy << " Z= " << Z
// << " cross= " << CrossSection << G4endl;
return CrossSection;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
void G4KleinNishinaModel::SampleSecondaries(
std::vector<G4DynamicParticle*>* fvect,
const G4MaterialCutsCouple* couple,
const G4DynamicParticle* aDynamicGamma,
G4double,
G4double)
{
G4double energy = aDynamicGamma->GetKineticEnergy();
G4ThreeVector direction = aDynamicGamma->GetMomentumDirection();
// select atom
const G4Element* elm = SelectRandomAtom(couple, theGamma, energy);
// select shell first
G4int Z = (G4int)elm->GetZ();
G4int nShells = elm->GetNbOfAtomicShells();
if(nShells > (G4int)fProbabilities.size()) { fProbabilities.resize(nShells); }
G4double totprob = 0.0;
G4int i = 0;
for(; i<nShells; ++i) {
G4double prob = 0.0;
if(energy > elm->GetAtomicShell(i)) {
prob = (G4double)elm->GetNbOfShellElectrons(i);
}
totprob += prob;
fProbabilities[i] = totprob;
}
if(totprob == 0.0) { return; }
G4LorentzVector lv1, lv2, lv3;
G4LorentzVector lv0(energy*direction.x(),energy*direction.y(),
energy*direction.z(),energy);
G4double eKinEnergy = 0.0;
G4double gamEnergy1 = 0.0;
// Loop on sampling
G4double bindingEnergy;
do {
G4double xprob = totprob*G4UniformRand();
for(i=0; i<nShells; ++i) { if(xprob <= fProbabilities[i]) {break;} }
if( i == nShells ) { return; }
bindingEnergy = elm->GetAtomicShell(i);
G4double tkin = bindingEnergy*0.5;
G4double eEnergy = tkin + electron_mass_c2;
G4double eTotMomentum = sqrt(tkin*(tkin + electron_mass_c2*2));
G4ThreeVector eDir = G4RandomDirection();
lv1 = lv0;
lv2.set(eTotMomentum*eDir.x(),eTotMomentum*eDir.y(),
eTotMomentum*eDir.z(),eEnergy);
G4ThreeVector bst = lv2.boostVector();
lv1.boost(-bst);
// In the rest frame of an electron
// The scattered gamma energy is sampled according to Klein - Nishina formula.
// The random number techniques of Butcher & Messel are used
// (Nuc Phys 20(1960),15).
G4double gamEnergy0 = lv1.e();
G4double E0_m = gamEnergy0 / electron_mass_c2 ;
G4ThreeVector gamDirection0 = (lv1.vect()).unit();
//
// sample the energy rate of the scattered gamma
//
G4double epsilon, epsilonsq, onecost, sint2, greject ;
G4double epsilon0 = 1./(1. + 2.*E0_m);
G4double epsilon0sq = epsilon0*epsilon0;
G4double alpha1 = - log(epsilon0);
G4double alpha2 = 0.5*(1.- epsilon0sq);
do {
if ( alpha1/(alpha1+alpha2) > G4UniformRand() ) {
epsilon = exp(-alpha1*G4UniformRand()); // epsilon0**r
epsilonsq = epsilon*epsilon;
} else {
epsilonsq = epsilon0sq + (1.- epsilon0sq)*G4UniformRand();
epsilon = sqrt(epsilonsq);
};
onecost = (1.- epsilon)/(epsilon*E0_m);
sint2 = onecost*(2.-onecost);
greject = 1. - epsilon*sint2/(1.+ epsilonsq);
} while (greject < G4UniformRand());
//
// scattered gamma angles. ( Z - axis along the parent gamma)
//
G4double cosTeta = 1. - onecost;
G4double sinTeta = sqrt (sint2);
G4double Phi = twopi * G4UniformRand();
G4double dirx = sinTeta*cos(Phi), diry = sinTeta*sin(Phi), dirz = cosTeta;
//
// update G4VParticleChange for the scattered gamma
//
G4ThreeVector gamDirection1 ( dirx,diry,dirz );
gamDirection1.rotateUz(gamDirection0);
gamEnergy1 = epsilon*gamEnergy0;
// before scattering
lv2.set(0.0,0.0,0.0,electron_mass_c2);
lv2 += lv1;
// after scattering
lv1.set(gamEnergy1*gamDirection1.x(),gamEnergy1*gamDirection1.y(),
gamEnergy1*gamDirection1.z(),gamEnergy1);
lv2 -= lv1;
lv2.boost(bst);
lv1.boost(bst);
eKinEnergy = lv2.e() - electron_mass_c2 - bindingEnergy;
} while ( eKinEnergy < 0.0 );
// gamma kinematics
gamEnergy1 = lv1.e();
G4double edep = bindingEnergy;
if(gamEnergy1 > lowestGammaEnergy) {
fParticleChange->SetProposedKineticEnergy(gamEnergy1);
fParticleChange->ProposeMomentumDirection((lv1.vect()).unit());
} else {
fParticleChange->ProposeTrackStatus(fStopAndKill);
fParticleChange->SetProposedKineticEnergy(0.0);
edep += gamEnergy1;
}
//
// kinematic of the scattered electron
//
if(eKinEnergy > DBL_MIN) {
G4ThreeVector eDirection = (lv2.vect()).unit();
G4DynamicParticle* dp = new G4DynamicParticle(theElectron,eDirection,eKinEnergy);
fvect->push_back(dp);
}
// sample deexcitation
//
if(fAtomDeexcitation) {
G4int index = couple->GetIndex();
if(fAtomDeexcitation->CheckDeexcitationActiveRegion(index)) {
G4AtomicShellEnumerator as = G4AtomicShellEnumerator(i);
const G4AtomicShell* shell = fAtomDeexcitation->GetAtomicShell(Z, as);
size_t nbefore = fvect->size();
fAtomDeexcitation->GenerateParticles(fvect, shell, Z, index);
size_t nafter = fvect->size();
if(nafter > nbefore) {
for (size_t i=nbefore; i<nafter; ++i) {
edep -= ((*fvect)[i])->GetKineticEnergy();
}
}
}
}
// energy balance
fParticleChange->ProposeLocalEnergyDeposit(edep);
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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