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
//
// V.Ivanchenko general clean-up since 2010
//
#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"
#include "G4Log.hh"
#include "G4Pow.hh"
 
using namespace std;
 
static const G4double explim = 160.;
 
G4EvaporationProbability::G4EvaporationProbability(G4int anA, G4int aZ, 
                           G4double aGamma) 
  : G4VEmissionProbability(aZ, anA), fGamma(aGamma)
{
  resA13 = muu = freeU = a0 = delta1 = 0.0;
  pcoeff = fGamma*pEvapMass*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; }
  if(0 == aZ) {
    ResetIntegrator(30, 0.25*CLHEP::MeV, 0.02);
  } else {
    ResetIntegrator(30, 0.5*CLHEP::MeV, 0.03);
  }
  // G4cout << "G4EvaporationProbability: Z= " << theZ << " A= " << theA 
  // << " M(GeV)= " << pEvapMass/GeV << G4endl;
}
 
G4EvaporationProbability::~G4EvaporationProbability() 
{}
 
G4double G4EvaporationProbability::CalcAlphaParam(const G4Fragment&)
{
  return 1.0;
}
 
G4double G4EvaporationProbability::CalcBetaParam(const G4Fragment&)
{
  return 1.0;
}
 
G4double G4EvaporationProbability::TotalProbability(
  const G4Fragment& fragment, G4double minEnergy, G4double maxEnergy, 
  G4double CB, G4double exEnergy)
{
  G4int fragA = fragment.GetA_asInt();
  G4int fragZ = fragment.GetZ_asInt();
  G4double U = fragment.GetExcitationEnergy(); 
  a0 = pNuclearLevelData->GetLevelDensity(fragZ,fragA,U);
  freeU = exEnergy;
  resA13 = pG4pow->Z13(resA);
  delta1 = pNuclearLevelData->GetPairingCorrection(resZ,resA);
  /*    
  G4cout << "G4EvaporationProbability: Z= " << theZ << " A= " << theA 
     << " resZ= " << resZ << " resA= " << resA 
     << " fragZ= " << fragZ << " fragA= " << fragA 
     << "\n   freeU= " << freeU  
     << " a0= " << a0 << " OPT= " << OPTxs << " emin= " 
         << minEnergy << " emax= " << maxEnergy 
     << " CB= " << CB << G4endl;
  */
  if (OPTxs==0 || (OPTxs==4 && freeU < 10.)) {
 
    G4double SystemEntropy = 2.0*std::sqrt(a0*freeU);
                                  
    const G4double RN2 = 2.25*CLHEP::fermi*CLHEP::fermi
      /(CLHEP::twopi*CLHEP::hbar_Planck*hbar_Planck);
 
    G4double Alpha = CalcAlphaParam(fragment);
    G4double Beta = CalcBetaParam(fragment);
 
    // to be checked where to use a0, where - a1    
    G4double a1 = pNuclearLevelData->GetLevelDensity(resZ,resA,freeU);
    G4double GlobalFactor = fGamma*Alpha*pEvapMass*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;
    
    G4double ExpTerm1 = (SystemEntropy <= explim) ? G4Exp(-SystemEntropy) : 0.0;
    
    G4double ExpTerm2 = 2.*std::sqrt(maxea) - SystemEntropy;
    ExpTerm2 = std::min(ExpTerm2, explim);
    ExpTerm2 = G4Exp(ExpTerm2);
    
    pProbability = GlobalFactor*(Term1*ExpTerm1 + Term2*ExpTerm2);
             
  } else {
 
    // compute power once
    if(0 < index) { 
      muu = G4KalbachCrossSection::ComputePowerParameter(resA, index);
    }
    // if Coulomb barrier cutoff is superimposed for all cross sections 
    // then the limit is the Coulomb Barrier
    pProbability = IntegrateProbability(minEnergy, maxEnergy, CB);
  }
  return pProbability;
}
 
G4double G4EvaporationProbability::ComputeProbability(G4double K, G4double CB)
{ 
  //G4cout << "### G4EvaporationProbability::ProbabilityDistributionFunction" 
  //  << G4endl;
 
  G4double E0 = freeU;
  // abnormal case - should never happens
  if(pMass < pEvapMass + pResMass) { return 0.0; }
    
  G4double m02   = pMass*pMass;
  G4double m12   = pEvapMass*pEvapMass;
  G4double mres  = sqrt(m02 + m12 - 2.*pMass*(pEvapMass + K));
 
  G4double excRes = mres - pResMass;
  G4double E1 = excRes - delta1;
  if(E1 <= 0.0) { return 0.0; }
  G4double a1 = pNuclearLevelData->GetLevelDensity(resZ,resA,excRes);
  G4double xs = CrossSection(K, CB); 
  G4double prob = pcoeff*G4Exp(2.0*(std::sqrt(a1*E1) - std::sqrt(a0*E0)))*K*xs;
  /*  
  G4cout << "PDF: Z= " << theZ << "  A= " << theA 
     << " K= " << K << " E0= " << E0 << " E1= " << E1 << G4endl;
  G4cout << " prob= " << prob << " pcoeff= " << pcoeff 
         << " xs= " << xs << G4endl;
  */
  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 << "XS: K= "<<K<<" res= "<<res<<" cb= "<<CB<<" muu= "
  //       <<muu<<" index= " << index<< G4endl;
  return res;
}  
 
G4double 
G4EvaporationProbability::SampleKineticEnergy(G4double minKinEnergy, 
                          G4double maxKinEnergy,
                          G4double)
{
  /*
    G4cout << "### Sample probability Emin= " << minKinEnergy 
       << " Emax= " << maxKinEnergy 
       << "  Z= " << theZ << " A= " << theA << G4endl;
  */
  G4double T = 0.0;
  CLHEP::HepRandomEngine* rndm = G4Random::getTheEngine();
  if (OPTxs==0 || (OPTxs==4 && freeU < 10.)) {
    // 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 = (RbSqrt < explim) ? G4Exp(-RbSqrt) : 0.0;
    G4double Rk = 0.0;
    G4double FRk = 0.0;
    G4int nn = 0;
    const G4int nmax = 100;
    const G4double ssqr3  = 1.5*std::sqrt(3.0);
    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);
      } 
      
      FRk = ssqr3 * Rk * (Q1 - Rk*Rk)/Q2;
      if(nn > nmax) { break; }
      ++nn;
      // Loop checking, 05-Aug-2015, Vladimir Ivanchenko
    } while (FRk < rndm->flat());
    
    T = std::max(maxKinEnergy * (1.0-Rk*Rk), 0.0) + minKinEnergy;
 
  } else { 
    T = SampleEnergy();
  }
  //G4cout<<"-- new Z= "<<theZ<<" A= "<< theA << " ekin= " << T << G4endl; 
  return T;
}