G4WentzelVIRelXSection.cc

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// $Id: G4WentzelVIRelXSection.cc 85306 2014-10-27 14:17:47Z gcosmo $
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:   G4WentzelVIRelXSection
//
// Author:      V.Ivanchenko 
//
// Creation date: 08.06.2012 from G4WentzelOKandVIxSection
//
// Modifications:
//
//

// -------------------------------------------------------------------
//

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#include "G4WentzelVIRelXSection.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"
#include "G4Electron.hh"
#include "G4Positron.hh"
#include "G4Proton.hh"
#include "G4EmParameters.hh"
#include "G4Log.hh"

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G4double G4WentzelVIRelXSection::ScreenRSquare[] = {0.0};
G4double G4WentzelVIRelXSection::FormFactor[]    = {0.0};

using namespace std;

G4WentzelVIRelXSection::G4WentzelVIRelXSection(G4bool combined) :
  numlimit(0.1),
  nwarnings(0),
  nwarnlimit(50),
  isCombined(combined),
  alpha2(fine_structure_const*fine_structure_const)
{
  fNistManager = G4NistManager::Instance();
  fG4pow = G4Pow::GetInstance();
  theElectron = G4Electron::Electron();
  thePositron = G4Positron::Positron();
  theProton   = G4Proton::Proton();
  lowEnergyLimit = 1.0*eV;
  G4double p0 = electron_mass_c2*classic_electr_radius;
  coeff = twopi*p0*p0;
  particle = 0;

  // Thomas-Fermi screening radii
  // Formfactors from A.V. Butkevich et al., NIM A 488 (2002) 282

  if(0.0 == ScreenRSquare[0]) {
    G4double a0 = electron_mass_c2/0.88534; 
    G4double constn = 6.937e-6/(MeV*MeV);

    ScreenRSquare[0] = alpha2*a0*a0;
    for(G4int j=1; j<100; ++j) {
      G4double x = a0*fG4pow->Z13(j);
      //ScreenRSquare[j] = 0.5*(1 + exp(-j*j*0.001))*alpha2*x*x;
      ScreenRSquare[j] = 0.5*alpha2*x*x;
      x = fNistManager->GetA27(j);
      FormFactor[j] = constn*x*x;
    } 
  }
  currentMaterial = 0;
  elecXSRatio = factB = factD = formfactA = screenZ = 0.0;
  cosTetMaxElec = cosTetMaxNuc = invbeta2 = kinFactor = gam0pcmp = pcmp2 = 1.0;
  cosThetaMax = 1.0;

  factB1= 0.5*CLHEP::pi*fine_structure_const;

  Initialise(theElectron, 1.0);
  targetMass = proton_mass_c2;
}

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G4WentzelVIRelXSection::~G4WentzelVIRelXSection()
{}

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void G4WentzelVIRelXSection::Initialise(const G4ParticleDefinition* p, 
                                        G4double cosThetaLim)
{
  SetupParticle(p);
  tkin = mom2 = momCM2 = 0.0;
  ecut = etag = DBL_MAX;
  targetZ = 0;

  // cosThetaMax is below 1.0 only when MSC is combined with SS
  if(isCombined) { cosThetaMax = cosThetaLim; }

  G4double a = G4EmParameters::Instance()->FactorForAngleLimit()
    *CLHEP::hbarc/CLHEP::fermi;
  factorA2 = 0.5*a*a;
  currentMaterial = 0;
}

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void G4WentzelVIRelXSection::SetupParticle(const G4ParticleDefinition* p)
{
  particle = p;
  mass = particle->GetPDGMass();
  spin = particle->GetPDGSpin();
  if(0.0 != spin) { spin = 0.5; }
  G4double q = std::fabs(particle->GetPDGCharge()/eplus);
  chargeSquare = q*q;
  charge3 = chargeSquare*q;
  tkin = 0.0;
  currentMaterial = 0;
  targetZ = 0;
}

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G4double
G4WentzelVIRelXSection::SetupTarget(G4int Z, G4double cut)
{
  G4double cosTetMaxNuc2 = cosTetMaxNuc;
  if(Z != targetZ || tkin != etag) {
    etag    = tkin; 
    targetZ = Z;
    if(targetZ > 99) { targetZ = 99; }
    SetTargetMass(fNistManager->GetAtomicMassAmu(targetZ)*CLHEP::amu_c2);
    //G4double tmass2 = targetMass*targetMass;
    //G4double etot = tkin + mass;
    //G4double invmass2 = mass*mass + tmass2 + 2*etot*targetMass;
    //momCM2 = mom2*tmass2/invmass2;
    //gam0pcmp = (etot + targetMass)*targetMass/invmass2;
    //pcmp2    = tmass2/invmass2;

    kinFactor = coeff*targetZ*chargeSquare*invbeta2/mom2;

    screenZ = ScreenRSquare[targetZ]/mom2;
    if(Z > 1) {
      screenZ *= std::min(Z*1.13,1.13 +3.76*Z*Z*invbeta2*alpha2*chargeSquare);
      /*
      if(mass > MeV) {
        screenZ *= std::min(Z*1.13,1.13 +3.76*Z*Z*invbeta2*alpha2*chargeSquare);
      } else {
        G4double tau = tkin/mass;
        //      screenZ *= std::min(Z*invbeta2,
        screenZ *= std::min(Z*1.13,
        (1.13 +3.76*Z*Z*invbeta2*alpha2*std::sqrt(tau/(tau + fG4pow->Z23(Z)))));
      }
      */
    }
    if(targetZ == 1 && cosTetMaxNuc2 < 0.0 && particle == theProton) {
      cosTetMaxNuc2 = 0.0;
    }
    formfactA = FormFactor[targetZ]*mom2;

    cosTetMaxElec = 1.0;
    ComputeMaxElectronScattering(cut); 
  }
  return cosTetMaxNuc2;
} 

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G4double 
G4WentzelVIRelXSection::ComputeTransportCrossSectionPerAtom(G4double cosTMax)
{
  G4double xsec = 0.0;
  if(cosTMax >= 1.0) { return xsec; }
 
  G4double xSection = 0.0;
  G4double x = 0; 
  G4double y = 0;
  G4double x1= 0;
  G4double x2= 0;
  G4double xlog = 0.0;

  G4double costm = std::max(cosTMax,cosTetMaxElec); 
  G4double fb = screenZ*factB;

  // scattering off electrons
  if(costm < 1.0) {
    x = (1.0 - costm)/screenZ;
    if(x < numlimit) { 
      x2 = 0.5*x*x;
      y  = x2*(1.0 - 1.3333333*x + 3*x2);
      if(0.0 < factB) { y -= fb*x2*x*(0.6666667 - x); }
    } else { 
      x1= x/(1 + x);
      xlog = G4Log(1.0 + x);  
      y = xlog - x1; 
      if(0.0 < factB) { y -= fb*(x + x1 - 2*xlog); }
    }

    if(y < 0.0) {
      ++nwarnings;
      if(nwarnings < nwarnlimit) {
        G4cout << "G4WentzelVIRelXSection::ComputeTransportCrossSectionPerAtom scattering on e- <0"
               << G4endl;
        G4cout << "y= " << y 
               << " e(MeV)= " << tkin << " p(MeV/c)= " << sqrt(mom2) 
               << " Z= " << targetZ << "  " 
               << particle->GetParticleName() << G4endl;
        G4cout << " 1-costm= " << 1.0-costm << " screenZ= " << screenZ 
               << " x= " << x << G4endl;
      }
      y = 0.0;
    }
    xSection = y;
  }
  /* 
  G4cout << "G4WentzelVI:XS per A " << " Z= " << targetZ 
         << " e(MeV)= " << tkin/MeV << " XSel= " << xSection
         << " cut(MeV)= " << ecut/MeV  
         << " zmaxE= " << (1.0 - cosTetMaxElec)/screenZ 
         << " zmaxN= " << (1.0 - cosThetaMax)/screenZ 
         << " 1-costm= " << 1.0 - cosThetaMax << G4endl;
  */
  // scattering off nucleus
  if(cosTMax < 1.0) {
    x = (1.0 - cosTMax)/screenZ;
    if(x < numlimit) { 
      x2 = 0.5*x*x;
      y  = x2*(1.0 - 1.3333333*x + 3*x2); 
      if(0.0 < factB) { y -= fb*x2*x*(0.6666667 - x); }
    } else { 
      x1= x/(1 + x);
      xlog = G4Log(1.0 + x);  
      y = xlog - x1; 
      if(0.0 < factB) { y -= fb*(x + x1 - 2*xlog); }
    }

    if(y < 0.0) {
      ++nwarnings;
      if(nwarnings < nwarnlimit) {
        G4cout << "G4WentzelVIRelXSection::ComputeTransportCrossSectionPerAtom scattering on e- <0"
               << G4endl;
        G4cout << "y= " << y 
               << " e(MeV)= " << tkin << " Z= " << targetZ << "  " 
               << particle->GetParticleName() << G4endl;
        G4cout << " formfactA= " << formfactA << " screenZ= " << screenZ 
               << " x= " << " x1= " << x1 <<G4endl;
      }
      y = 0.0;
    }
    xSection += y*targetZ; 
  }
  xSection *= kinFactor;
  /*
  G4cout << "Z= " << targetZ << " XStot= " << xSection/barn 
         << " screenZ= " << screenZ << " formF= " << formfactA 
         << " for " << particle->GetParticleName() 
         << " m= " << mass << " 1/v= " << sqrt(invbeta2) << " p= " << sqrt(mom2)
         << " x= " << x 
         << G4endl;
  */
  return xSection; 
}

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G4ThreeVector
G4WentzelVIRelXSection::SampleSingleScattering(G4double cosTMin,
                                                 G4double cosTMax,
                                                 G4double elecRatio)
{
  G4ThreeVector v(0.0,0.0,1.0);
 
  G4double formf = formfactA;
  G4double cost1 = cosTMin;
  G4double cost2 = cosTMax;
  if(elecRatio > 0.0) {
    if(G4UniformRand() <= elecRatio) {
      formf = 0.0;
      cost1 = std::max(cost1,cosTetMaxElec);
      cost2 = std::max(cost2,cosTetMaxElec);
    }
  }
  if(cost1 < cost2) { return v; }

  G4double w1 = 1. - cost1 + screenZ;
  G4double w2 = 1. - cost2 + screenZ;
  G4double z1 = w1*w2/(w1 + G4UniformRand()*(w2 - w1)) - screenZ;

  //G4double fm =  1.0 + formf*z1/(1.0 + (mass + tkin)*z1/targetMass);
  G4double fm =  1.0 + formf*z1;
  //G4double grej = (1. - z1*factB)/( (1.0 + z1*factD)*fm*fm );
  G4double grej = (1. - z1*factB + factB1*targetZ*sqrt(z1*factB)*(2 - z1))/( (1.0 + z1*factD)*fm*fm );
  // "false" scattering
  if( G4UniformRand() > grej ) { return v; }
    // } 
  G4double cost = 1.0 - z1;

  if(cost > 1.0)       { cost = 1.0; }
  else if(cost < -1.0) { cost =-1.0; }
  G4double sint = sqrt((1.0 - cost)*(1.0 + cost));
  //G4cout << "sint= " << sint << G4endl;
  G4double phi  = twopi*G4UniformRand();
  G4double vx1 = sint*cos(phi);
  G4double vy1 = sint*sin(phi);

  // only direction is changed
  v.set(vx1,vy1,cost);
  return v;
}

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void 
G4WentzelVIRelXSection::ComputeMaxElectronScattering(G4double cutEnergy)
{
  if(mass > MeV) {
    G4double ratio = electron_mass_c2/mass;
    G4double tau = tkin/mass;
    G4double tmax = 2.0*electron_mass_c2*tau*(tau + 2.)/
      (1.0 + 2.0*ratio*(tau + 1.0) + ratio*ratio);
    //tmax = std::min(tmax, targetZ*targetZ*10*eV); 
    cosTetMaxElec = 1.0 - std::min(cutEnergy, tmax)*electron_mass_c2/mom2;
  } else {

    G4double tmax = tkin;
    if(particle == theElectron) { tmax *= 0.5; }
    //tmax = std::min(tmax, targetZ*targetZ*10*eV); 
    G4double t = std::min(cutEnergy, tmax);
    G4double mom21 = t*(t + 2.0*electron_mass_c2);
    G4double t1 = tkin - t;
    //G4cout <<"tkin=" <<tkin<<" tmax= "<<tmax<<" t= " 
    //<<t<< " t1= "<<t1<<" cut= "<<ecut<<G4endl;
    if(t1 > 0.0) {
      G4double mom22 = t1*(t1 + 2.0*mass);
      G4double ctm = (mom2 + mom22 - mom21)*0.5/sqrt(mom2*mom22);
      if(ctm <  1.0) { cosTetMaxElec = ctm; }
      if(particle == theElectron && cosTetMaxElec < 0.0) { cosTetMaxElec = 0.0; }
    }
  }
}

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