G4mplIonisationModel.cc

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// $Id: G4mplIonisationModel.cc 66996 2013-01-29 14:50:52Z gcosmo $
//
// -------------------------------------------------------------------
//
// GEANT4 Class header file
//
//
// File name:     G4mplIonisationModel
//
// Author:        Vladimir Ivanchenko 
//
// Creation date: 06.09.2005
//
// Modifications:
// 12.08.2007 Changing low energy approximation and extrapolation. 
//            Small bug fixing and refactoring (M. Vladymyrov)
// 13.11.2007 Use low-energy asymptotic from [3] (V.Ivanchenko) 
//
//
// -------------------------------------------------------------------
// References
// [1] Steven P. Ahlen: Energy loss of relativistic heavy ionizing particles, 
//     S.P. Ahlen, Rev. Mod. Phys 52(1980), p121
// [2] K.A. Milton arXiv:hep-ex/0602040
// [3] S.P. Ahlen and K. Kinoshita, Phys. Rev. D26 (1982) 2347


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#include "G4mplIonisationModel.hh"
#include "Randomize.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4LossTableManager.hh"
#include "G4ParticleChangeForLoss.hh"

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using namespace std;

G4mplIonisationModel::G4mplIonisationModel(G4double mCharge, const G4String& nam)
  : G4VEmModel(nam),G4VEmFluctuationModel(nam),
  magCharge(mCharge),
  twoln10(log(100.0)),
  betalow(0.01),
  betalim(0.1),
  beta2lim(betalim*betalim),
  bg2lim(beta2lim*(1.0 + beta2lim))
{
  nmpl         = G4int(abs(magCharge) * 2 * fine_structure_const + 0.5);
  if(nmpl > 6)      { nmpl = 6; }
  else if(nmpl < 1) { nmpl = 1; }
  pi_hbarc2_over_mc2 = pi * hbarc * hbarc / electron_mass_c2;
  chargeSquare = magCharge * magCharge;
  dedxlim = 45.*nmpl*nmpl*GeV*cm2/g;
  fParticleChange = 0;
  monopole = 0;
  mass = 0.0;
}

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G4mplIonisationModel::~G4mplIonisationModel()
{}

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void G4mplIonisationModel::SetParticle(const G4ParticleDefinition* p)
{
  monopole = p;
  mass     = monopole->GetPDGMass();
  G4double emin = 
    std::min(LowEnergyLimit(),0.1*mass*(1/sqrt(1 - betalow*betalow) - 1)); 
  G4double emax = 
    std::max(HighEnergyLimit(),10*mass*(1/sqrt(1 - beta2lim) - 1)); 
  SetLowEnergyLimit(emin);
  SetHighEnergyLimit(emax);
}

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void G4mplIonisationModel::Initialise(const G4ParticleDefinition* p,
                                      const G4DataVector&)
{
  if(!monopole) { SetParticle(p); }
  if(!fParticleChange) { fParticleChange = GetParticleChangeForLoss(); }
}

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G4double G4mplIonisationModel::ComputeDEDXPerVolume(const G4Material* material,
                                                    const G4ParticleDefinition* p,
                                                    G4double kineticEnergy,
                                                    G4double)
{
  if(!monopole) { SetParticle(p); }
  G4double tau   = kineticEnergy / mass;
  G4double gam   = tau + 1.0;
  G4double bg2   = tau * (tau + 2.0);
  G4double beta2 = bg2 / (gam * gam);
  G4double beta  = sqrt(beta2);

  // low-energy asymptotic formula
  G4double dedx  = dedxlim*beta*material->GetDensity();

  // above asymptotic
  if(beta > betalow) {

    // high energy
    if(beta >= betalim) {
      dedx = ComputeDEDXAhlen(material, bg2);

    } else {

      G4double dedx1 = dedxlim*betalow*material->GetDensity();
      G4double dedx2 = ComputeDEDXAhlen(material, bg2lim);

      // extrapolation between two formula 
      G4double kapa2 = beta - betalow;
      G4double kapa1 = betalim - beta;
      dedx = (kapa1*dedx1 + kapa2*dedx2)/(kapa1 + kapa2);
    }
  }
  return dedx;
}

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G4double G4mplIonisationModel::ComputeDEDXAhlen(const G4Material* material, 
                                                G4double bg2)
{
  G4double eDensity = material->GetElectronDensity();
  G4double eexc  = material->GetIonisation()->GetMeanExcitationEnergy();
  G4double cden  = material->GetIonisation()->GetCdensity();
  G4double mden  = material->GetIonisation()->GetMdensity();
  G4double aden  = material->GetIonisation()->GetAdensity();
  G4double x0den = material->GetIonisation()->GetX0density();
  G4double x1den = material->GetIonisation()->GetX1density();

  // Ahlen's formula for nonconductors, [1]p157, f(5.7)
  G4double dedx = log(2.0 * electron_mass_c2 * bg2 / eexc) - 0.5;

  // Kazama et al. cross-section correction
  G4double  k = 0.406;
  if(nmpl > 1) k = 0.346;

  // Bloch correction
  const G4double B[7] = { 0.0, 0.248, 0.672, 1.022, 1.243, 1.464, 1.685}; 

  dedx += 0.5 * k - B[nmpl];

  // density effect correction
  G4double deltam;
  G4double x = log(bg2) / twoln10;
  if ( x >= x0den ) {
    deltam = twoln10 * x - cden;
    if ( x < x1den ) deltam += aden * pow((x1den-x), mden);
    dedx -= 0.5 * deltam;
  }

  // now compute the total ionization loss
  dedx *=  pi_hbarc2_over_mc2 * eDensity * nmpl * nmpl;

  if (dedx < 0.0) dedx = 0;
  return dedx;
}

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void G4mplIonisationModel::SampleSecondaries(std::vector<G4DynamicParticle*>*,
                                             const G4MaterialCutsCouple*,
                                             const G4DynamicParticle*,
                                             G4double,
                                             G4double)
{}

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G4double G4mplIonisationModel::SampleFluctuations(
                                       const G4Material* material,
                                       const G4DynamicParticle* dp,
                                       G4double& tmax,
                                       G4double& length,
                                       G4double& meanLoss)
{
  G4double siga = Dispersion(material,dp,tmax,length);
  G4double loss = meanLoss;
  siga = sqrt(siga);
  G4double twomeanLoss = meanLoss + meanLoss;

  if(twomeanLoss < siga) {
    G4double x;
    do {
      loss = twomeanLoss*G4UniformRand();
      x = (loss - meanLoss)/siga;
    } while (1.0 - 0.5*x*x < G4UniformRand());
  } else {
    do {
      loss = G4RandGauss::shoot(meanLoss,siga);
    } while (0.0 > loss || loss > twomeanLoss);
  }
  return loss;
}

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G4double G4mplIonisationModel::Dispersion(const G4Material* material,
                                          const G4DynamicParticle* dp,
                                          G4double& tmax,
                                          G4double& length)
{
  G4double siga = 0.0;
  G4double tau   = dp->GetKineticEnergy()/mass;
  if(tau > 0.0) { 
    G4double electronDensity = material->GetElectronDensity();
    G4double gam   = tau + 1.0;
    G4double invbeta2 = (gam*gam)/(tau * (tau+2.0));
    siga  = (invbeta2 - 0.5) * twopi_mc2_rcl2 * tmax * length
      * electronDensity * chargeSquare;
  }
  return siga;
}

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