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This commit is contained in:
Gabriele Cosmo
2016-06-08 16:39:52 +02:00
parent 921d3b1cda
commit 330b82b769
4524 changed files with 178689 additions and 43575 deletions
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source/processes/electromagnetic/standard/src/G4GammaConversionToMuons.cc
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//
// ********************************************************************
// * DISCLAIMER *
// * *
// * The following disclaimer summarizes all the specific disclaimers *
// * of contributors to this software. The specific disclaimers,which *
// * govern, are listed with their locations in: *
// * http://cern.ch/geant4/license *
// * *
// * 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. *
// * *
// * This code implementation is the intellectual property of the *
// * GEANT4 collaboration. *
// * By copying, distributing or modifying the Program (or any work *
// * based on the Program) you indicate your acceptance of this *
// * statement, and all its terms. *
// ********************************************************************
//
//
// $Id: G4GammaConversionToMuons.cc,v 1.3 2002/05/06 09:32:41 maire Exp $
// GEANT4 tag $Name: geant4-04-01 $
//
// ------------ G4GammaConversionToMuons physics process ------
// by H.Burkhardt, S. Kelner and R. Kokoulin, April 2002
// ---------------------------------------------------------------------------
#include "G4GammaConversionToMuons.hh"
#include "G4EnergyLossTables.hh"
#include "G4UnitsTable.hh"
#include "G4MuonPlus.hh"
#include "G4MuonMinus.hh"
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
// constructor
G4GammaConversionToMuons::G4GammaConversionToMuons(const G4String& processName)
: G4VDiscreteProcess (processName),
LowestEnergyLimit (4*G4MuonPlus::MuonPlus()->GetPDGMass()), // 4*Mmuon
HighestEnergyLimit(1e21*eV), // ok to 1e21eV=1e12GeV, then LPM suppression
CrossSecFactor(1.)
{ }
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
// destructor
G4GammaConversionToMuons::~G4GammaConversionToMuons() // (empty) destructor
{ }
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
void G4GammaConversionToMuons::BuildPhysicsTable(const G4ParticleDefinition&)
// Build cross section and mean free path tables
{ //here no tables, just calling PrintInfoDefinition
PrintInfoDefinition();
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
void G4GammaConversionToMuons::SetCrossSecFactor(G4double fac)
// Set the factor to artificially increase the cross section
{ CrossSecFactor=fac;
G4cout << "The cross section for GammaConversionToMuons is artificially "
<< "increased by the CrossSecFactor=" << CrossSecFactor << G4endl;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
G4double G4GammaConversionToMuons::ComputeCrossSectionPerAtom(
G4double Egam, G4double Z, G4double A)
// Calculates the microscopic cross section in GEANT4 internal units.
// Total cross section parametrisation from H.Burkhardt
// It gives a good description at any energy (from 0 to 10**21 eV)
{ static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
static const G4double Mele=electron_mass_c2;
static const G4double GammaEnergyLimit=4* Mmuon;
static const G4double Rc=elm_coupling/Mmuon; // classical particle radius
static const G4double sqrte=sqrt(exp(1.));
static const G4double PowSat=-0.88;
static G4double CrossSection = 0.0 ;
if ( A < 1. ) return 0;
if ( Egam < 4*Mmuon ) return 0 ; // below threshold return 0
static G4double EgamLast=0,Zlast=0,PowThres,Ecor,B,Dn,Zthird,Winfty,WMedAppr,
Wsatur,sigfac;
if(Zlast==Z && Egam==EgamLast) return CrossSection; // already calculated
EgamLast=Egam;
if(Zlast!=Z) // new element
{ Zlast=Z;
if(Z==1) // special case of Hydrogen
{ B=202.4;
Dn=1.49;
}
else
{ B=183.;
Dn=1.54*pow(A,0.27);
}
Zthird=pow(Z,-1./3.); // Z**(-1/3)
Winfty=B*Zthird*Mmuon/(Dn*Mele);
WMedAppr=1./(4.*Dn*sqrte*Mmuon);
Wsatur=Winfty/WMedAppr;
sigfac=4.*fine_structure_const*Z*Z*Rc*Rc;
PowThres=1.479+0.00799*Dn;
Ecor=-18.+4347./(B*Zthird);
}
G4double CorFuc=1.+.04*log(1.+Ecor/Egam);
G4double Eg=pow(1.-4.*Mmuon/Egam,PowThres)*pow( pow(Wsatur,PowSat)+
pow(Egam,PowSat),1./PowSat); // threshold and saturation
CrossSection=7./9.*sigfac*log(1.+WMedAppr*CorFuc*Eg);
CrossSection*=CrossSecFactor; // increase the CrossSection by (by default 1)
return CrossSection;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
G4VParticleChange* G4GammaConversionToMuons::PostStepDoIt(
const G4Track& aTrack,
const G4Step& aStep)
//
// generation of gamma->mu+mu-
//
{
aParticleChange.Initialize(aTrack);
G4Material* aMaterial = aTrack.GetMaterial();
static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
static const G4double Mele=electron_mass_c2;
static const G4double sqrte=sqrt(exp(1.));
// current Gamma energy and direction, return if energy too low
const G4DynamicParticle *aDynamicGamma = aTrack.GetDynamicParticle();
G4double Egam = aDynamicGamma->GetKineticEnergy();
if (Egam < 4*Mmuon) return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
G4ParticleMomentum GammaDirection = aDynamicGamma->GetMomentumDirection();
// select randomly one element constituting the material
const G4Element& anElement = *SelectRandomAtom(aDynamicGamma, aMaterial);
G4double Z = anElement.GetZ();
G4double A = anElement.GetA()/(g/mole);
static G4double Zlast=0,B,Dn,Zthird,Winfty,A027,C1Num2,C2Term2;
if(Zlast!=Z) // the element has changed
{ Zlast=Z;
if(Z==1) // special case of Hydrogen
{ B=202.4;
Dn=1.49;
}
else
{ B=183.;
Dn=1.54*pow(A,0.27);
}
Zthird=pow(Z,-1./3.); // Z**(-1/3)
Winfty=B*Zthird*Mmuon/(Dn*Mele);
A027=pow(A,0.27);
G4double C1Num=0.35*A027;
C1Num2=C1Num*C1Num;
C2Term2=Mele/(183.*Zthird*Mmuon);
}
G4double GammaMuonInv=Mmuon/Egam;
G4double sqrtx=sqrt(.25-GammaMuonInv);
G4double xmax=.5+sqrtx;
G4double xmin=.5-sqrtx;
// generate xPlus according to the differential cross section by rejection
G4double Ds2=(Dn*sqrte-2.);
G4double sBZ=sqrte*B*Zthird/Mele;
G4double LogWmaxInv=1./log(Winfty*(1.+2.*Ds2*GammaMuonInv)
/(1.+2.*sBZ*Mmuon*GammaMuonInv));
G4double xPlus,xMinus,xPM,result,W;
do
{ xPlus=xmin+G4UniformRand()*(xmax-xmin);
xMinus=1.-xPlus;
xPM=xPlus*xMinus;
G4double del=Mmuon*Mmuon/(2.*Egam*xPM);
W=Winfty*(1.+Ds2*del/Mmuon)/(1.+sBZ*del);
if(W<1.) W=1.; // to avoid negative cross section at xmin
G4double xxp=1.-4./3.*xPM; // the main xPlus dependence
result=xxp*log(W)*LogWmaxInv;
if(result>1.)
{ G4cout << "error in dSigxPlusGen, result=" << result << " is >1" << '\n';
exit(10);
}
}
while (G4UniformRand() > result);
// now generate the angular variables via the auxilary variables t,psi,rho
G4double t;
G4double psi;
G4double rho;
G4double thetaPlus,thetaMinus,phiHalf; // final angular variables
do // t, psi, rho generation start (while angle < pi)
{
//generate t by the rejection method
G4double C1=C1Num2* GammaMuonInv/xPM;
G4double f1_max=(1.-xPM) / (1.+C1);
G4double f1; // the probability density
do
{ t=G4UniformRand();
f1=(1.-2.*xPM+4.*xPM*t*(1.-t)) / (1.+C1/(t*t));
if(f1<0 | f1> f1_max) // should never happend
{ G4cout << "outside allowed range f1=" << f1 << G4endl;
exit(1);
}
}
while ( G4UniformRand()*f1_max > f1);
// generate psi by the rejection method
G4double f2_max=1.-2.*xPM*(1.-4.*t*(1.-t));
// long version
G4double f2;
do
{ psi=2.*pi*G4UniformRand();
f2=1.-2.*xPM+4.*xPM*t*(1.-t)*(1.+cos(2.*psi));
if(f2<0 | f2> f2_max) // should never happend
{ G4cout << "outside allowed range f2=" << f2 << G4endl;
exit(1);
}
}
while ( G4UniformRand()*f2_max > f2);
// generate rho by direct transformation
G4double C2Term1=GammaMuonInv/(2.*xPM*t);
G4double C2=4./sqrt(xPM)*pow(C2Term1*C2Term1+C2Term2*C2Term2,2);
G4double rhomax=1.9/A027*(1./t-1.);
G4double beta=log( (C2+pow(rhomax,4))/C2 );
rho=pow(C2 *( exp(beta*G4UniformRand())-1. ) ,0.25);
//now get from t and psi the kinematical variables
G4double u=sqrt(1./t-1.);
G4double xiHalf=0.5*rho*cos(psi);
phiHalf=0.5*rho/u*sin(psi);
thetaPlus =GammaMuonInv*(u+xiHalf)/xPlus;
thetaMinus=GammaMuonInv*(u-xiHalf)/xMinus;
} while ( abs(thetaPlus)>pi | abs(thetaMinus) >pi);
// now construct the vectors
// azimuthal symmetry, take phi0 at random between 0 and 2 pi
G4double phi0=2.*pi*G4UniformRand();
G4double EPlus=xPlus*Egam;
G4double EMinus=xMinus*Egam;
// mu+ mu- directions for gamma in z-direction
G4ThreeVector MuPlusDirection ( sin(thetaPlus) *cos(phi0+phiHalf),
sin(thetaPlus) *sin(phi0+phiHalf), cos(thetaPlus) );
G4ThreeVector MuMinusDirection (-sin(thetaMinus)*cos(phi0-phiHalf),
-sin(thetaMinus) *sin(phi0-phiHalf), cos(thetaMinus) );
// rotate to actual gamma direction
MuPlusDirection.rotateUz(GammaDirection);
MuMinusDirection.rotateUz(GammaDirection);
aParticleChange.SetNumberOfSecondaries(2);
// create G4DynamicParticle object for the particle1
G4DynamicParticle* aParticle1= new G4DynamicParticle(
G4MuonPlus::MuonPlus(),MuPlusDirection,EPlus-Mmuon);
aParticleChange.AddSecondary(aParticle1);
// create G4DynamicParticle object for the particle2
G4DynamicParticle* aParticle2= new G4DynamicParticle(
G4MuonMinus::MuonMinus(),MuMinusDirection,EMinus-Mmuon);
aParticleChange.AddSecondary(aParticle2);
//
// Kill the incident photon
//
aParticleChange.SetMomentumChange( 0., 0., 0. ) ;
aParticleChange.SetEnergyChange( 0. ) ;
aParticleChange.SetStatusChange( fStopAndKill ) ;
// Reset NbOfInteractionLengthLeft and return aParticleChange
return G4VDiscreteProcess::PostStepDoIt( aTrack, aStep );
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
G4Element* G4GammaConversionToMuons::SelectRandomAtom(
const G4DynamicParticle* aDynamicGamma,
G4Material* aMaterial)
{
// select randomly 1 element within the material, invoked by PostStepDoIt
const G4int NumberOfElements = aMaterial->GetNumberOfElements();
const G4ElementVector* theElementVector = aMaterial->GetElementVector();
if (NumberOfElements == 1) return (*theElementVector)[0];
const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
G4double PartialSumSigma = 0. ;
G4double rval = G4UniformRand()/MeanFreePath;
for ( G4int i=0 ; i < NumberOfElements ; i++ )
{ PartialSumSigma += NbOfAtomsPerVolume[i] *
GetCrossSectionPerAtom(aDynamicGamma, (*theElementVector)[i]);
if (rval <= PartialSumSigma) return ((*theElementVector)[i]);
}
G4cout << " WARNING !!! - The Material '"<< aMaterial->GetName()
<< "' has no elements, NULL pointer returned." << G4endl;
return NULL;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo.....
void G4GammaConversionToMuons::PrintInfoDefinition()
{
G4String comments ="gamma->mu+mu- Bethe Heitler process.\n";
G4cout << G4endl << GetProcessName() << ": " << comments
<< " good cross section parametrization from "
<< G4BestUnit(LowestEnergyLimit,"Energy")
<< " to " << HighestEnergyLimit/GeV << " GeV for all Z." << G4endl;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....