G4EvaporationProbability.cc

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//J.M. Quesada (August2008). Based on:
//
// Hadronic Process: Nuclear De-excitations
// by V. Lara (Oct 1998)
//
// Modif (03 September 2008) by J. M. Quesada for external choice of inverse 
// cross section option
// JMQ (06 September 2008) Also external choices have been added for 
// superimposed Coulomb barrier (if useSICB is set true, by default is false) 
//
// JMQ (14 february 2009) bug fixed in emission width: hbarc instead of 
//                        hbar_Planck in the denominator
//
#include "G4EvaporationProbability.hh"
#include "G4NuclearLevelData.hh"
#include "G4VCoulombBarrier.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4PairingCorrection.hh"
#include "G4NucleiProperties.hh"
#include "G4KalbachCrossSection.hh"
#include "G4ChatterjeeCrossSection.hh"
#include "Randomize.hh"
#include "G4Exp.hh"

using namespace std;

G4EvaporationProbability::G4EvaporationProbability(G4int anA, G4int aZ, 
                           G4double aGamma, 
                           G4VCoulombBarrier*) 
  : theA(anA),
    theZ(aZ),
    Gamma(aGamma)
{
  resZ = resA = fragA = fragZ = 0;
  resA13 = muu = resMass = Mass = U = delta0 = delta1 = a0 = probmax = 0.0;
  partMass = G4NucleiProperties::GetNuclearMass(theA, theZ);
  pcoeff = Gamma*partMass*CLHEP::millibarn
    /((CLHEP::pi*CLHEP::hbarc)*(CLHEP::pi*CLHEP::hbarc)); 

  if(0 == theZ)      { index = 0; }
  else if(1 == theZ) { index = theA; }
  else               { index = theA + 1; }
  fLevelData = G4NuclearLevelData::GetInstance(); 
}

G4EvaporationProbability::~G4EvaporationProbability() 
{}

// obsolete method  
G4double G4EvaporationProbability::EmissionProbability(
         const G4Fragment&, G4double)
{
  return 0.0;
}

G4double G4EvaporationProbability::TotalProbability(
  const G4Fragment & fragment, G4double minEnergy, G4double maxEnergy, 
  G4double CoulombBarrier)
{
  fragA = fragment.GetA_asInt();
  fragZ = fragment.GetZ_asInt();
  resA  = fragA - theA;
  resZ  = fragZ - theZ;

  G4double fragMass = fragment.GetGroundStateMass();
  U = fragment.GetExcitationEnergy();
  Mass = fragMass + U;
  delta0 = std::max(0.0, fPairCorr->GetPairingCorrection(fragA,fragZ));
  delta1 = std::max(0.0, fPairCorr->GetPairingCorrection(resA,resZ));
  resMass = G4NucleiProperties::GetNuclearMass(resA, resZ);
  resA13 = fG4pow->Z13(resA);
  a0 = LevelDensity*fragA;
  /*    
  G4cout << "G4EvaporationProbability: resZ= " << resZ << " resA= " << resA 
     << " fragZ= " << fragZ << " fragA= " << fragA << " U= " 
     << U << " d0= " << delta0 << G4endl;
  */
  if(U < delta0 || maxEnergy <= minEnergy) { return 0.0; }
   
  G4double Width = 0.0;
  if (OPTxs==0) {

    G4double SystemEntropy = 2.0*std::sqrt(a0*(U-delta0));
                                  
    static const G4double RN2 = 
      2.25*fermi*fermi/(twopi* hbar_Planck*hbar_Planck);

    G4double Alpha = CalcAlphaParam(fragment);
    G4double Beta = CalcBetaParam(fragment);

    // to be checked where to use a0, where - a1    
    G4double a1 = LevelDensity*resA;
    G4double GlobalFactor = Gamma*Alpha*partMass*RN2*resA13*resA13/(a1*a1);
    
    G4double maxea = maxEnergy*a1;
    G4double Term1 = Beta*a1 - 1.5 + maxea;
    G4double Term2 = (2.0*Beta*a1-3.0)*std::sqrt(maxea) + 2*maxea;
    
    static const G4double explim = 350.;
    G4double ExpTerm1 = (SystemEntropy <= explim) ? G4Exp(-SystemEntropy) : 0.0;
    
    G4double ExpTerm2 = 2.*std::sqrt(maxea) - SystemEntropy;
    ExpTerm2 = std::min(ExpTerm2, explim);
    ExpTerm2 = G4Exp(ExpTerm2);
    
    Width = GlobalFactor*(Term1*ExpTerm1 + Term2*ExpTerm2);
             
  } else {

    // compute power once
    if(OPTxs <= 2) { 
      muu =  G4ChatterjeeCrossSection::ComputePowerParameter(resA, index);
    } else {
      muu = G4KalbachCrossSection::ComputePowerParameter(resA, index);
    }
    // if Coulomb barrier cutoff is superimposed for all cross sections 
    // then the limit is the Coulomb Barrier
    Width = IntegrateEmissionProbability(minEnergy, maxEnergy, 
                     CoulombBarrier);
  }
  return Width;
}

G4double G4EvaporationProbability::IntegrateEmissionProbability(
     G4double low, G4double up, G4double cb)
{
  static const G4double den = 2.0/CLHEP::MeV;
  G4double del = (up - low);
  G4int nbins  = std::max(3,(G4int)(del*den));
  del /= (G4double)nbins;
  G4double e = low;
  G4double y0 = ProbabilityDistributionFunction(e, cb);
  probmax = y0;
  //G4cout << "    0. e= " << low << "  y= " << y0 << G4endl;

  G4double sum(0.0), ds(0.0), y;
  for (G4int i=0; i<nbins; ++i) {
    e += del;
    y = ProbabilityDistributionFunction(e, cb); 
    probmax = std::max(probmax, y);
    ds = y0 + y;
    sum += ds;
    if(ds < sum*0.01) { break; }
    //G4cout << "   " << i << ". e= " << e << "  y= " << y << " sum= " << sum << G4endl;
    y0 = y;
  }
  sum *= del*0.5;
  //G4cout << "Evap prob: " << sum << " probmax= " << probmax << G4endl;
  return sum;
}

G4double G4EvaporationProbability::ProbabilityDistributionFunction(G4double K, 
                                   G4double cb)
{ 
  //G4cout << "### G4EvaporationProbability::ProbabilityDistributionFunction" 
  //  << G4endl;

  G4double E0 = U - delta0;
  //G4double E1 = Mass - partMass - resMass - delta1 - K;
  G4double E1 = sqrt((Mass - partMass)*(Mass - partMass) - 2*Mass*K) 
    - resMass - delta1;
  /*
  G4cout << "PDF: FragZ= " << fragZ << " FragA= " << fragA
     << " Z= " << theZ << "  A= " << theA 
     << " K= " << K << " E0= " << E0 << " E1= " << E1 << G4endl;
  */
  if(E1 < 0.0) { return 0.0; }

  G4double a1 = LevelDensity*resA;

  //JMQ 14/02/09 BUG fixed: hbarc should be in the denominator instead 
  //             of hbar_Planck; without 1/hbar_Panck remains as a width

  G4double Prob = pcoeff*G4Exp(2.0*(std::sqrt(a1*E1) - std::sqrt(a0*E0)))
    *K*CrossSection(K, cb);

  return Prob;
}

G4double 
G4EvaporationProbability::CrossSection(G4double K, G4double cb)
{
  G4double res;
  if(OPTxs <= 2) { 
    res = G4ChatterjeeCrossSection::ComputeCrossSection(K, cb, resA13, muu,
                            index, theZ, resA); 
  } else { 
    res = G4KalbachCrossSection::ComputeCrossSection(K, cb, resA13, muu,
                             index, theZ, theA, resA);
  }
  //G4cout << "     K= " << K << "  res= " << res << " muu= " << muu << G4endl;
  return res;
}  

G4double 
G4EvaporationProbability::SampleKineticEnergy(G4double minKinEnergy, 
                          G4double maxKinEnergy,
                          G4double cb)
{
  /*
    G4cout << "### Sample probability Emin= " << minKinEnergy 
       << " Emax= " << maxKinEnergy << "  CoulombBarrier= " 
       << cb << "  Z= " << theZ << " A= " << theA << G4endl;
  */
  G4double T = 0.0;
  CLHEP::HepRandomEngine* rndm = G4Random::getTheEngine();
  static const G4int nmax = 100;
  if (OPTxs==0) {
    // JMQ:
    // It uses Dostrovsky's approximation for the inverse reaction cross
    // in the probability for fragment emission
    // MaximalKineticEnergy energy in the original version (V.Lara) was 
    // calculated at the Coulomb barrier.
    
    G4double Rb = 4.0*a0*maxKinEnergy;
    G4double RbSqrt = std::sqrt(Rb);
    G4double PEX1 = 0.0;
    if (RbSqrt < 160.0) { PEX1 = G4Exp(-RbSqrt); }
    G4double Rk = 0.0;
    G4double FRk = 0.0;
    G4int nn = 0;
    do {
      G4double RandNumber = rndm->flat();
      Rk = 1.0 + (1./RbSqrt)*G4Log(RandNumber + (1.0-RandNumber)*PEX1);
      G4double Q1 = 1.0;
      G4double Q2 = 1.0;
      if (theZ == 0) { // for emitted neutron
        G4double Beta = (2.12/(resA13*resA13) - 0.05)*MeV/(0.76 + 2.2/resA13);
        Q1 = 1.0 + Beta/maxKinEnergy;
        Q2 = Q1*std::sqrt(Q1);
      } 
      
      static const G4double ssqr3  = 1.5*std::sqrt(3.0);
      FRk = ssqr3 * Rk * (Q1 - Rk*Rk)/Q2;
      if(nn > nmax) { break; }
      ++nn;
      // Loop checking, 05-Aug-2015, Vladimir Ivanchenko
    } while (FRk < rndm->flat());
    
    T = maxKinEnergy * (1.0-Rk*Rk) + minKinEnergy;

  } else { 

    G4double delta = maxKinEnergy - minKinEnergy;
    probmax *= 1.25;
    for(G4int i=0; i<nmax; ++i) {
      T = minKinEnergy + delta*rndm->flat();
      G4double prob = ProbabilityDistributionFunction(T, cb);
      /*     
      if(probmax < prob) {
        G4cout << "### G4EvaporationProbability::SampleKineticEnergy: "
           << " prob= " << prob << " > probmax= " << probmax
           << " T= " << T << " Emin= " << minKinEnergy
           << " Emax= " << maxKinEnergy << " Z= " << theZ
           << " A= " << theA << " FragZ= " << fragZ 
           << " FragA= " << fragA << " i= " << i << G4endl; 
      }
      */
      if(probmax*rndm->flat() <= prob) { break; }
    }
  }
  //G4cout << "-- new Z= " << theZ << " A= " << theA << " ekin= " << T << G4endl; 
  return T;
  //return fLevelData->FindLevel(resZ, resA, resMass, Mass, partMass, T);
}