G4ionEffectiveCharge.cc

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//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4ionEffectiveCharge
//
// Author:        Vladimir Ivanchenko
//
// Creation date: 07.05.2002
//
// Modifications:
// 12.09.2004 Set low energy limit to 1 keV (V.Ivanchenko) 
// 25.01.2005 Add protection - min Charge 0.1 eplus (V.Ivanchenko) 
// 28.04.2006 Set upper energy limit to 50 MeV (V.Ivanchenko) 
// 23.05.2006 Set upper energy limit to Z*10 MeV (V.Ivanchenko) 
// 15.08.2006 Add protection for not defined material (V.Ivanchenko) 
// 27-09-2007 Use Fermi energy from material, optimazed formulas (V.Ivanchenko)
//
 
// -------------------------------------------------------------------
//
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#include "G4ionEffectiveCharge.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4UnitsTable.hh"
#include "G4Material.hh"
#include "G4NistManager.hh"
#include "G4Log.hh"
#include "G4Exp.hh"
#include "G4Pow.hh"
 
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G4ionEffectiveCharge::G4ionEffectiveCharge()
{
  chargeCorrection = 1.0;
  energyHighLimit  = 20.0*CLHEP::MeV;
  energyLowLimit   = 1.0*CLHEP::keV;
  energyBohr       = 25.*CLHEP::keV;
  massFactor       = CLHEP::amu_c2/(CLHEP::proton_mass_c2*CLHEP::keV);
  minCharge        = 1.0;
  lastKinEnergy    = 0.0;
  effCharge        = CLHEP::eplus;
  inveplus         = 1.0/CLHEP::eplus;
  g4calc = G4Pow::GetInstance();
}
 
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G4double G4ionEffectiveCharge::EffectiveCharge(const G4ParticleDefinition* p,
                                               const G4Material* material,
                                               G4double kineticEnergy)
{
  if(p == lastPart && material == lastMat && kineticEnergy == lastKinEnergy)
    return effCharge;
 
  lastPart      = p;
  lastMat       = material;
  lastKinEnergy = kineticEnergy;
 
  G4double mass   = p->GetPDGMass();
  effCharge = p->GetPDGCharge();
  G4int Zi = G4lrint(effCharge*inveplus);
  chargeCorrection = 1.0;
 
  // The aproximation of ion effective charge from:
  // J.F.Ziegler, J.P. Biersack, U. Littmark
  // The Stopping and Range of Ions in Matter,
  // Vol.1, Pergamon Press, 1985
  // Fast ions or hadrons
  G4double reducedEnergy = kineticEnergy * CLHEP::proton_mass_c2/mass;
 
  //G4cout << "e= " << reducedEnergy << " Zi= " << Zi << "  " 
  //<< material->GetName() << G4endl;
 
  if(Zi <= 1 || reducedEnergy > effCharge*energyHighLimit ) {
    return effCharge;
  }
  G4double z = material->GetIonisation()->GetZeffective();
  reducedEnergy = std::max(reducedEnergy,energyLowLimit);
 
  // Helium ion case
  if( Zi <= 2 ) {
 
    static const G4double c[6] = 
      {0.2865,0.1266,-0.001429,0.02402,-0.01135,0.001475};
 
    G4double Q = std::max(0.0,G4Log(reducedEnergy*massFactor));
    G4double x = c[0];
    G4double y = 1.0;
    for (G4int i=1; i<6; ++i) {
      y *= Q;
      x += y * c[i] ;
    }
    G4double ex = (x < 0.2) ? x * (1 - 0.5*x) : 1. - G4Exp(-x);
 
    G4double tq = 7.6 - Q;
    G4double tq2= tq*tq;
    G4double tt = ( 0.007 + 0.00005 * z );
    if(tq2 < 0.2) { tt *= (1.0 - tq2 + 0.5*tq2*tq2); }
    else          { tt *= G4Exp(-tq2); }
 
    effCharge *= (1.0 + tt) * std::sqrt(ex);
 
    // Heavy ion case
  } else {
    
    G4double zi13 = g4calc->Z13(Zi);
    G4double zi23 = zi13*zi13;
 
    // v1 is ion velocity in vF unit
    G4double eF   = material->GetIonisation()->GetFermiEnergy();
    G4double v1sq = reducedEnergy/eF;
    G4double vFsq = eF/energyBohr;
    G4double vF   = std::sqrt(eF/energyBohr);
 
    G4double y = ( v1sq > 1.0 ) 
      // Faster than Fermi velocity
      ? vF * std::sqrt(v1sq) * ( 1.0 + 0.2/v1sq ) / zi23
      // Slower than Fermi velocity
      : 0.692308 * vF * (1.0 + 0.666666*v1sq + v1sq*v1sq/15.0) / zi23;
 
    G4double y3 = G4Exp(0.3*G4Log(y));
    // G4cout<<"y= "<<y<<" y3= "<<y3<<" v1= "<<v1<<" vF= "<<vF<<G4endl; 
    G4double q = std::max(1.0 - G4Exp( 0.803*y3 - 1.3167*y3*y3 - 0.38157*y
                                     - 0.008983*y*y), minCharge/effCharge);
    
    // compute charge correction
    G4double tq = 7.6 - G4Log(reducedEnergy/CLHEP::keV);
    G4double tq2= tq*tq;
    G4double sq = 1.0 + ( 0.18 + 0.0015 * z )*G4Exp(-tq2)/ (Zi*Zi); 
    //    G4cout << "sq= " << sq << G4endl;
 
    // Screen length according to
    // J.F.Ziegler and J.M.Manoyan, The stopping of ions in compaunds,
    // Nucl. Inst. & Meth. in Phys. Res. B35 (1988) 215-228.
 
    G4double lambda = 10.0 * vF *g4calc->A23(1.0 - q)/ (zi13 * (6.0 + q));
    G4double lambda2 = lambda*lambda;
    G4double xx = (0.5/q - 0.5)*G4Log(1.0 + lambda2)/vFsq;
 
    effCharge *= q;
    chargeCorrection = sq * (1.0 + xx);
  }
  //  G4cout << "G4ionEffectiveCharge: charge= " << charge << " q= " << q 
  //         << " chargeCor= " << chargeCorrection 
  //           << " e(MeV)= " << kineticEnergy/MeV << G4endl;
  return effCharge;
}
 
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