G4IonCoulombCrossSection.cc

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//      G4IonCoulombCrossSection.cc
//-------------------------------------------------------------------
//
// GEANT4 Class header file
//
// File name:    G4IonCoulombCrossSection
//
// Author:      Cristina Consolandi
//
// Creation date: 05.10.2010 from G4eCoulombScatteringModel 
//                                 
// Class Description:
//      Computation of Screen-Coulomb Cross Section 
//      for protons, alpha and heavy Ions
//
//
// Reference:
//      M.J. Boschini et al. "Nuclear and Non-Ionizing Energy-Loss 
//      for Coulomb Scattered Particles from Low Energy up to Relativistic 
//      Regime in Space Radiation Environment"
//      Accepted for publication in the Proceedings of  the  ICATPP Conference
//      on Cosmic Rays for Particle and Astroparticle Physics, Villa  Olmo, 7-8
//      October,  2010, to be published by World Scientific (Singapore).
//
//      Available for downloading at:
//      http://arxiv.org/abs/1011.4822
//
// -------------------------------------------------------------------
//
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#include "G4IonCoulombCrossSection.hh"
#include "G4PhysicalConstants.hh"
#include "Randomize.hh"
#include "G4Proton.hh"
#include "G4LossTableManager.hh"

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using namespace std;

G4IonCoulombCrossSection::G4IonCoulombCrossSection():
   cosThetaMin(1.0),
   cosThetaMax(-1.0),
   alpha2(fine_structure_const*fine_structure_const)
{
        fNistManager = G4NistManager::Instance();
        theProton   = G4Proton::Proton();
        particle=0;

        G4double p0 = electron_mass_c2*classic_electr_radius;
        coeff  = twopi*p0*p0;

        cosTetMinNuc=0;
        cosTetMaxNuc=0;
        nucXSection =0;


        chargeSquare = spin = mass =0;
        tkinLab = momLab2 = invbetaLab2=0;
        tkin = mom2 = invbeta2=0;

        targetZ = targetMass = screenZ =0;
        ScreenRSquare=0.;

        etag = ecut = 0.0;

}
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G4IonCoulombCrossSection::~G4IonCoulombCrossSection()
{}
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void G4IonCoulombCrossSection::Initialise(const G4ParticleDefinition* p,
                                          G4double CosThetaLim)
{

        SetupParticle(p);
        nucXSection = 0.0;
        tkin = targetZ = mom2 = DBL_MIN;
        ecut = etag = DBL_MAX;
        particle = p;

                
        cosThetaMin = CosThetaLim; 

}
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void G4IonCoulombCrossSection::SetupKinematic(G4double ekin,
                                                     G4double cut,G4int iz )
{
  if(ekin != tkinLab || ecut != cut) {

    // lab
    tkinLab = ekin;
    momLab2 = tkinLab*(tkinLab + 2.0*mass);
    invbetaLab2 = 1.0 +  mass*mass/momLab2;

    G4double etot = tkinLab + mass;
    G4double ptot = sqrt(momLab2);
    G4double m12  = mass*mass;

    targetMass=fNistManager->GetAtomicMassAmu(iz)*amu_c2;

    // relativistic reduced mass from publucation
    // A.P. Martynenko, R.N. Faustov, Teoret. mat. Fiz. 64 (1985) 179
        
    //incident particle & target nucleus
    G4double Ecm=sqrt(m12 + targetMass*targetMass + 2.0*etot*targetMass);
    G4double mu_rel=mass*targetMass/Ecm;
    G4double momCM= ptot*targetMass/Ecm;
    // relative system
    mom2 = momCM*momCM;
    invbeta2 = 1.0 +  mu_rel*mu_rel/mom2;
    tkin = momCM*sqrt(invbeta2) - mu_rel;//Ekin of mu_rel
    //.........................................................

    cosTetMinNuc = cosThetaMin;
    cosTetMaxNuc = cosThetaMax;

  }

}
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void G4IonCoulombCrossSection::SetupTarget(G4double Z, G4double e, G4int heavycorr)
{
        if(Z != targetZ || e != etag) {
                etag    = e;
                targetZ = Z;
                G4int iz= G4int(Z);

                SetScreenRSquare(iz);
                screenZ =0;
                screenZ = ScreenRSquare/mom2;

        //      G4cout<< "heavycorr "<<heavycorr<<G4endl;

                if(heavycorr!=0 && particle != theProton){
                        G4double corr=5.*twopi*Z*std::sqrt(chargeSquare*alpha2);
                        corr=std::pow(corr,0.12);
                        screenZ *=(1.13 + corr*3.76*Z*Z*chargeSquare*invbeta2*alpha2)/2.;
//                      G4cout<<" heavycorr Z e corr....2As "<< heavycorr << "\t"
//                              <<Z <<"\t"<<e/MeV <<"\t"<<screenZ<<G4endl;

                }else{ screenZ *=(1.13 + 3.76*Z*Z*chargeSquare*invbeta2*alpha2)/2.;
//                        G4cout<<"  heavycorr Z e....2As "<< heavycorr << "\t"
//                              <<Z <<"\t"<< e/MeV <<"\t"  <<screenZ<<G4endl;
                }

                if(1 == iz && particle == theProton && cosTetMaxNuc < 0.0) {
                        cosTetMaxNuc = 0.0;
                }

        }
}

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void G4IonCoulombCrossSection::SetScreenRSquare(G4int iz){

                G4double a0 = electron_mass_c2/0.88534;

                //target nucleus
                G4double Z1=std::sqrt(chargeSquare);
                G4double Z2=targetZ;
        
                G4double Z1023=std::pow(Z1,0.23);
                G4double Z2023=std::pow(Z2,0.23);
        
                // Universal screening length
                G4double x=a0*(Z1023+Z2023);

                //for proton Thomas-Fermi screening length      
                if(particle == theProton){ 
                                x = a0*fNistManager->GetZ13(iz);
                                }               
                ScreenRSquare  = alpha2*x*x;

         
}
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G4double G4IonCoulombCrossSection::NuclearCrossSection()
{
        // This method needs initialisation before be called

        // scattering with target nucleus
        G4double fac = coeff*targetZ*targetZ*chargeSquare*invbeta2/mom2;

        nucXSection  = 0.0;

        G4double x  = 1.0 - cosTetMinNuc;
        G4double x1 = x + screenZ;

        // scattering with nucleus
        if(cosTetMaxNuc < cosTetMinNuc) {

                nucXSection =fac*(cosTetMinNuc - cosTetMaxNuc)/
                        (x1*(1.0 - cosTetMaxNuc + screenZ));

                }

  return nucXSection;
}

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G4double G4IonCoulombCrossSection::SampleCosineTheta()
{
        
        if(cosTetMaxNuc >= cosTetMinNuc) return 0.0;

        G4double x1 = 1. - cosTetMinNuc + screenZ;
        G4double x2 = 1. - cosTetMaxNuc + screenZ;
        G4double dx = cosTetMinNuc - cosTetMaxNuc;
        G4double /*grej,*/ z1;

                z1 = x1*x2/(x1 + G4UniformRand()*dx) - screenZ;
                //grej = 1.0/(1.0 + z1);
  return z1;
}

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