G4BetheBlochModel.cc

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// $Id: G4BetheBlochModel.cc 79188 2014-02-20 09:22:48Z gcosmo $
//
// -------------------------------------------------------------------
//
// GEANT4 Class header file
//
//
// File name:     G4BetheBlochModel
//
// Author:        Vladimir Ivanchenko on base of Laszlo Urban code
//
// Creation date: 03.01.2002
//
// Modifications:
//
// 04-12-02 Fix problem of G4DynamicParticle constructor (V.Ivanchenko)
// 23-12-02 Change interface in order to move to cut per region (V.Ivanchenko)
// 27-01-03 Make models region aware (V.Ivanchenko)
// 13-02-03 Add name (V.Ivanchenko)
// 24-03-05 Add G4EmCorrections (V.Ivanchenko)
// 11-04-05 Major optimisation of internal interfaces (V.Ivanchenko)
// 11-02-06 ComputeCrossSectionPerElectron, ComputeCrossSectionPerAtom (mma)
// 12-02-06 move G4LossTableManager::Instance()->EmCorrections() 
//          in constructor (mma)
// 12-08-08 Added methods GetParticleCharge, GetChargeSquareRatio, 
//          CorrectionsAlongStep needed for ions(V.Ivanchenko)
//
// -------------------------------------------------------------------
//


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#include "G4BetheBlochModel.hh"
#include "Randomize.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4Electron.hh"
#include "G4LossTableManager.hh"
#include "G4EmCorrections.hh"
#include "G4ParticleChangeForLoss.hh"
#include "G4Log.hh"
#include "G4DeltaAngle.hh"

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using namespace std;

G4BetheBlochModel::G4BetheBlochModel(const G4ParticleDefinition* p, 
                                     const G4String& nam)
  : G4VEmModel(nam),
    particle(0),
    tlimit(DBL_MAX),
    twoln10(2.0*G4Log(10.0)),
    bg2lim(0.0169),
    taulim(8.4146e-3),
    isIon(false),
    isInitialised(false)
{
  fParticleChange = 0;
  theElectron = G4Electron::Electron();
  if(p) {
    SetGenericIon(p);
    SetParticle(p);
  } else {
    SetParticle(theElectron);
  }
  corr = G4LossTableManager::Instance()->EmCorrections();  
  nist = G4NistManager::Instance();
  SetLowEnergyLimit(2.0*MeV);
}

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G4BetheBlochModel::~G4BetheBlochModel()
{}

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void G4BetheBlochModel::Initialise(const G4ParticleDefinition* p,
                                   const G4DataVector&)
{
  SetGenericIon(p);
  SetParticle(p);

  //G4cout << "G4BetheBlochModel::Initialise for " << p->GetParticleName()
  //     << "  isIon= " << isIon 
  //     << G4endl;

  // always false before the run
  SetDeexcitationFlag(false);

  if(!isInitialised) {
    isInitialised = true;
    fParticleChange = GetParticleChangeForLoss();
    if(UseAngularGeneratorFlag() && !GetAngularDistribution()) {
      SetAngularDistribution(new G4DeltaAngle());
    }
  }
}

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G4double G4BetheBlochModel::GetChargeSquareRatio(const G4ParticleDefinition* p,
                                                 const G4Material* mat,
                                                 G4double kineticEnergy)
{
  // this method is called only for ions
  G4double q2 = corr->EffectiveChargeSquareRatio(p,mat,kineticEnergy);
  corrFactor = q2*corr->EffectiveChargeCorrection(p,mat,kineticEnergy);
  return corrFactor;
}

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G4double G4BetheBlochModel::GetParticleCharge(const G4ParticleDefinition* p,
                                              const G4Material* mat,
                                              G4double kineticEnergy)
{
  //G4cout<<"G4BetheBlochModel::GetParticleCharge e= "<<kineticEnergy <<
  //  " q= " <<  corr->GetParticleCharge(p,mat,kineticEnergy) <<G4endl;
  // this method is called only for ions, so no check if it is an ion
  return corr->GetParticleCharge(p,mat,kineticEnergy);
}

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void G4BetheBlochModel::SetupParameters()
{
  mass = particle->GetPDGMass();
  spin = particle->GetPDGSpin();
  G4double q = particle->GetPDGCharge()/eplus;
  chargeSquare = q*q;
  corrFactor = chargeSquare;
  ratio = electron_mass_c2/mass;
  G4double magmom = 
    particle->GetPDGMagneticMoment()*mass/(0.5*eplus*hbar_Planck*c_squared);
  magMoment2 = magmom*magmom - 1.0;
  formfact = 0.0;
  if(particle->GetLeptonNumber() == 0) {
    G4double x = 0.8426*GeV;
    if(spin == 0.0 && mass < GeV) {x = 0.736*GeV;}
    else if(mass > GeV) {
      x /= nist->GetZ13(mass/proton_mass_c2);
      //        tlimit = 51.2*GeV*A13[iz]*A13[iz];
    }
    formfact = 2.0*electron_mass_c2/(x*x);
    tlimit   = 2.0/formfact;
  }
}

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G4double G4BetheBlochModel::MinEnergyCut(const G4ParticleDefinition*,
                                         const G4MaterialCutsCouple* couple)
{
  return couple->GetMaterial()->GetIonisation()->GetMeanExcitationEnergy();
}

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G4double 
G4BetheBlochModel::ComputeCrossSectionPerElectron(const G4ParticleDefinition* p,
                                                  G4double kineticEnergy,
                                                  G4double cutEnergy,
                                                  G4double maxKinEnergy)        
{
  G4double cross = 0.0;
  G4double tmax = MaxSecondaryEnergy(p, kineticEnergy);
  G4double maxEnergy = min(tmax,maxKinEnergy);
  if(cutEnergy < maxEnergy) {

    G4double totEnergy = kineticEnergy + mass;
    G4double energy2   = totEnergy*totEnergy;
    G4double beta2     = kineticEnergy*(kineticEnergy + 2.0*mass)/energy2;

    cross = 1.0/cutEnergy - 1.0/maxEnergy 
      - beta2*G4Log(maxEnergy/cutEnergy)/tmax;

    // +term for spin=1/2 particle
    if( 0.5 == spin ) { cross += 0.5*(maxEnergy - cutEnergy)/energy2; }

    // High order correction different for hadrons and ions
    // nevetheless they are applied to reduce high energy transfers
    //    if(!isIon) 
    //cross += corr->FiniteSizeCorrectionXS(p,currentMaterial,
    //                                    kineticEnergy,cutEnergy);

    cross *= twopi_mc2_rcl2*chargeSquare/beta2;
  }
  
   // G4cout << "BB: e= " << kineticEnergy << " tmin= " << cutEnergy 
   //        << " tmax= " << tmax << " cross= " << cross << G4endl;
  
  return cross;
}

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G4double G4BetheBlochModel::ComputeCrossSectionPerAtom(
                                           const G4ParticleDefinition* p,
                                                 G4double kineticEnergy,
                                                 G4double Z, G4double,
                                                 G4double cutEnergy,
                                                 G4double maxEnergy)
{
  G4double cross = Z*ComputeCrossSectionPerElectron
                                         (p,kineticEnergy,cutEnergy,maxEnergy);
  return cross;
}

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G4double G4BetheBlochModel::CrossSectionPerVolume(
                                           const G4Material* material,
                                           const G4ParticleDefinition* p,
                                                 G4double kineticEnergy,
                                                 G4double cutEnergy,
                                                 G4double maxEnergy)
{
  G4double eDensity = material->GetElectronDensity();
  G4double cross = eDensity*ComputeCrossSectionPerElectron
                                         (p,kineticEnergy,cutEnergy,maxEnergy);
  return cross;
}

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G4double G4BetheBlochModel::ComputeDEDXPerVolume(const G4Material* material,
                                                 const G4ParticleDefinition* p,
                                                 G4double kineticEnergy,
                                                 G4double cut)
{
  G4double tmax      = MaxSecondaryEnergy(p, kineticEnergy);
  G4double cutEnergy = std::min(cut,tmax);

  G4double tau   = kineticEnergy/mass;
  G4double gam   = tau + 1.0;
  G4double bg2   = tau * (tau+2.0);
  G4double beta2 = bg2/(gam*gam);

  G4double eexc  = material->GetIonisation()->GetMeanExcitationEnergy();
  G4double eexc2 = eexc*eexc;

  G4double eDensity = material->GetElectronDensity();

  G4double dedx = G4Log(2.0*electron_mass_c2*bg2*cutEnergy/eexc2)
                - (1.0 + cutEnergy/tmax)*beta2;

  if(0.5 == spin) {
    G4double del = 0.5*cutEnergy/(kineticEnergy + mass);
    dedx += del*del;
  }

  // density correction
  G4double x = G4Log(bg2)/twoln10;
  dedx -= material->GetIonisation()->DensityCorrection(x);

  // shell correction
  dedx -= 2.0*corr->ShellCorrection(p,material,kineticEnergy);

  // now compute the total ionization loss
  dedx *= twopi_mc2_rcl2*chargeSquare*eDensity/beta2;

  //High order correction different for hadrons and ions
  if(isIon) {
    dedx += corr->IonBarkasCorrection(p,material,kineticEnergy);
  } else {      
    dedx += corr->HighOrderCorrections(p,material,kineticEnergy,cutEnergy);
  }

  if (dedx < 0.0) { dedx = 0.0; }

  //G4cout << "E(MeV)= " << kineticEnergy/MeV << " dedx= " << dedx 
  //     << "  " << material->GetName() << G4endl;

  return dedx;
}

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void G4BetheBlochModel::CorrectionsAlongStep(const G4MaterialCutsCouple* couple,
                                             const G4DynamicParticle* dp,
                                             G4double& eloss,
                                             G4double&,
                                             G4double length)
{
  if(isIon) {
    const G4ParticleDefinition* p = dp->GetDefinition();
    const G4Material* mat = couple->GetMaterial();
    G4double preKinEnergy = dp->GetKineticEnergy();
    G4double e = preKinEnergy - eloss*0.5;
    if(e < preKinEnergy*0.75) { e = preKinEnergy*0.75; }

    G4double q2 = corr->EffectiveChargeSquareRatio(p,mat,e);
    GetModelOfFluctuations()->SetParticleAndCharge(p, q2);
    G4double qfactor = q2*corr->EffectiveChargeCorrection(p,mat,e)/corrFactor;
    G4double highOrder = length*corr->IonHighOrderCorrections(p,couple,e);
    G4double elossnew  = eloss*qfactor + highOrder;
    if(elossnew > preKinEnergy)   { elossnew = preKinEnergy; }
    else if(elossnew < eloss*0.5) { elossnew = eloss*0.5; }
    eloss = elossnew;
    //G4cout << "G4BetheBlochModel::CorrectionsAlongStep: e= " << preKinEnergy
    //     << " qfactor= " << qfactor 
    //     << " highOrder= " << highOrder << " (" 
    // << highOrder/eloss << ")" << G4endl;    
  }
}

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void G4BetheBlochModel::SampleSecondaries(vector<G4DynamicParticle*>* vdp,
                                          const G4MaterialCutsCouple* couple,
                                          const G4DynamicParticle* dp,
                                          G4double minKinEnergy,
                                          G4double maxEnergy)
{
  G4double kineticEnergy = dp->GetKineticEnergy();
  G4double tmax = MaxSecondaryEnergy(dp->GetDefinition(),kineticEnergy);

  G4double maxKinEnergy = std::min(maxEnergy,tmax);
  if(minKinEnergy >= maxKinEnergy) { return; }

  G4double totEnergy     = kineticEnergy + mass;
  G4double etot2         = totEnergy*totEnergy;
  G4double beta2         = kineticEnergy*(kineticEnergy + 2.0*mass)/etot2;

  G4double deltaKinEnergy, f; 
  G4double f1 = 0.0;
  G4double fmax = 1.0;
  if( 0.5 == spin ) { fmax += 0.5*maxKinEnergy*maxKinEnergy/etot2; }

  // sampling without nuclear size effect
  do {
    G4double q = G4UniformRand();
    deltaKinEnergy = minKinEnergy*maxKinEnergy
                    /(minKinEnergy*(1.0 - q) + maxKinEnergy*q);

    f = 1.0 - beta2*deltaKinEnergy/tmax;
    if( 0.5 == spin ) {
      f1 = 0.5*deltaKinEnergy*deltaKinEnergy/etot2;
      f += f1;
    }

  } while( fmax*G4UniformRand() > f);

  // projectile formfactor - suppresion of high energy
  // delta-electron production at high energy
  
  G4double x = formfact*deltaKinEnergy;
  if(x > 1.e-6) {

    G4double x1 = 1.0 + x;
    G4double grej  = 1.0/(x1*x1);
    if( 0.5 == spin ) {
      G4double x2 = 0.5*electron_mass_c2*deltaKinEnergy/(mass*mass);
      grej *= (1.0 + magMoment2*(x2 - f1/f)/(1.0 + x2));
    }
    if(grej > 1.1) {
      G4cout << "### G4BetheBlochModel WARNING: grej= " << grej
             << "  " << dp->GetDefinition()->GetParticleName()
             << " Ekin(MeV)= " <<  kineticEnergy
             << " delEkin(MeV)= " << deltaKinEnergy
             << G4endl;
    }
    if(G4UniformRand() > grej) return;
  }

  G4ThreeVector deltaDirection;

  if(UseAngularGeneratorFlag()) {

    const G4Material* mat =  couple->GetMaterial();
    G4int Z = SelectRandomAtomNumber(mat);

    deltaDirection = 
      GetAngularDistribution()->SampleDirection(dp, deltaKinEnergy, Z, mat);

  } else {
 
    G4double deltaMomentum =
      sqrt(deltaKinEnergy * (deltaKinEnergy + 2.0*electron_mass_c2));
    G4double cost = deltaKinEnergy * (totEnergy + electron_mass_c2) /
      (deltaMomentum * dp->GetTotalMomentum());
    if(cost > 1.0) { cost = 1.0; }
    G4double sint = sqrt((1.0 - cost)*(1.0 + cost));

    G4double phi = twopi * G4UniformRand() ;

    deltaDirection.set(sint*cos(phi),sint*sin(phi), cost) ;
    deltaDirection.rotateUz(dp->GetMomentumDirection());
  }  

  /*
    G4cout << "### G4BetheBlochModel " 
           << dp->GetDefinition()->GetParticleName()
           << " Ekin(MeV)= " <<  kineticEnergy
           << " delEkin(MeV)= " << deltaKinEnergy
           << " tmin(MeV)= " << minKinEnergy
           << " tmax(MeV)= " << maxKinEnergy
           << " dir= " << dp->GetMomentumDirection()
           << " dirDelta= " << deltaDirection
           << G4endl;
  }
  */

  // create G4DynamicParticle object for delta ray
  G4DynamicParticle* delta = 
    new G4DynamicParticle(theElectron,deltaDirection,deltaKinEnergy);

  vdp->push_back(delta);

  // Change kinematics of primary particle
  kineticEnergy -= deltaKinEnergy;
  G4ThreeVector finalP = dp->GetMomentum() - delta->GetMomentum();
  finalP               = finalP.unit();
  
  fParticleChange->SetProposedKineticEnergy(kineticEnergy);
  fParticleChange->SetProposedMomentumDirection(finalP);
}

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G4double G4BetheBlochModel::MaxSecondaryEnergy(const G4ParticleDefinition* pd,
                                               G4double kinEnergy) 
{
  // here particle type is checked for any method
  SetParticle(pd);
  G4double tau  = kinEnergy/mass;
  G4double tmax = 2.0*electron_mass_c2*tau*(tau + 2.) /
                  (1. + 2.0*(tau + 1.)*ratio + ratio*ratio);
  return std::min(tmax,tlimit);
}

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