source: trunk/source/processes/hadronic/models/de_excitation/photon_evaporation/src/G4E1Probability.cc @ 1340

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// $Id: G4E1Probability.cc,v 1.9 2010/05/25 10:47:24 vnivanch Exp $
// GEANT4 tag $Name: geant4-09-03-ref-09 $
//
//---------------------------------------------------------------------
//
// Geant4 class G4E1Probability
//
// by V. Lara (May 2003)
//
// Modifications:
// 18.05.2010 V.Ivanchenko trying to speedup the most slow method
//            by usage of G4Pow, integer A and introduction of const members
//
//

#include "G4E1Probability.hh"
//#include "G4ConstantLevelDensityParameter.hh"
#include "Randomize.hh"
#include "G4Pow.hh"

// Constructors and operators
//

G4E1Probability::G4E1Probability():G4VEmissionProbability()
{
  G4double x = CLHEP::pi*CLHEP::hbarc;
  normC = 1.0 / (x*x);
  theLevelDensityParameter = 0.125/MeV;
  fG4pow = G4Pow::GetInstance(); 
}

G4E1Probability::~G4E1Probability()
{}

// Calculate the emission probability
//

G4double G4E1Probability::EmissionProbDensity(const G4Fragment& frag, 
                                              const G4double gammaE)
{

  // Calculate the probability density here

  // From nuclear fragment properties and the excitation energy, calculate
  // the probability density for photon evaporation from U to U - gammaE
  // (U = nucleus excitation energy, gammaE = total evaporated photon
  // energy). Fragment = nuclear fragment BEFORE de-excitation

  G4double theProb = 0.0;

  G4int Afrag = frag.GetA_asInt();
  G4double Uexcite = frag.GetExcitationEnergy();

  if( (Uexcite-gammaE) < 0.0 || gammaE < 0) { return theProb; }

  // Need a level density parameter.
  // For now, just use the constant approximation (not reliable near magic
  // nuclei).

  G4double aLevelDensityParam = Afrag*theLevelDensityParameter;

  //  G4double levelDensBef = std::exp(2*std::sqrt(aLevelDensityParam*Uexcite));
  //  G4double levelDensAft = std::exp(2*std::sqrt(aLevelDensityParam*(Uexcite-gammaE)));
  // VI reduce number of calls to exp 
  G4double levelDens = 1.0;
  if( aLevelDensityParam > 0.0 ) {
    levelDens = std::exp(2*(std::sqrt(aLevelDensityParam*(Uexcite-gammaE)) 
      - std::sqrt(aLevelDensityParam*Uexcite))); 
  }
  // Now form the probability density

  // Define constants for the photoabsorption cross-section (the reverse
  // process of our de-excitation)

  G4double sigma0 = 2.5 * Afrag * millibarn;  // millibarns

  G4double Egdp   = (40.3 / fG4pow->powZ(Afrag,0.2) )*MeV;
  G4double GammaR = 0.30 * Egdp;
 
  // CD
  //cout<<"  PROB TESTS "<<G4endl;
  //cout<<" hbarc = "<<hbarc<<G4endl;
  //cout<<" pi = "<<pi<<G4endl;
  //cout<<" Uexcite, gammaE = "<<Uexcite<<"  "<<gammaE<<G4endl;
  //cout<<" Uexcite, gammaE = "<<Uexcite*MeV<<"  "<<gammaE*MeV<<G4endl;
  //cout<<" lev density param = "<<aLevelDensityParam<<G4endl;
  //cout<<" level densities = "<<levelDensBef<<"  "<<levelDensAft<<G4endl;
  //cout<<" sigma0 = "<<sigma0<<G4endl;
  //cout<<" Egdp, GammaR = "<<Egdp<<"  "<<GammaR<<G4endl;
  //cout<<" normC = "<<normC<<G4endl;

  // VI implementation 18.05.2010
  G4double gammaE2 = gammaE*gammaE;
  G4double gammaR2 = gammaE2*GammaR*GammaR;
  G4double egdp2   = gammaE2 - Egdp*Egdp;
  G4double sigmaAbs = sigma0*gammaR2/(egdp2*egdp2 + gammaR2); 
  theProb = normC * sigmaAbs * gammaE2 * levelDens;

  // old implementation
  //  G4double numerator = sigma0 * gammaE*gammaE * GammaR*GammaR;
  // G4double denominator = (gammaE*gammaE - Egdp*Egdp)*
  //         (gammaE*gammaE - Egdp*Egdp) + GammaR*GammaR*gammaE*gammaE;

  //G4double sigmaAbs = numerator/denominator; 
  //theProb = normC * sigmaAbs * gammaE2 * levelDensAft/levelDensBef;

  // CD
  //cout<<" sigmaAbs = "<<sigmaAbs<<G4endl;
  //cout<<" Probability = "<<theProb<<G4endl;

  return theProb;

}

G4double G4E1Probability::EmissionProbability(const G4Fragment& frag, 
                                                 const G4double gammaE)
{

  // From nuclear fragment properties and the excitation energy, calculate
  // the probability for photon evaporation down to last ground level.
  // fragment = nuclear fragment BEFORE de-excitation

  G4double theProb = 0.0;

  G4double Uafter = 0.0;
  const G4double Uexcite = frag.GetExcitationEnergy();

  G4double normC = 3.0;

  const G4double upperLim = Uexcite;
  const G4double lowerLim = Uafter;
  const G4int numIters = 100;

  // Fall-back is a uniform random number

  //G4double uniformNum = G4UniformRand();
  //theProb = uniformNum;

  // Need to integrate EmissionProbDensity from lowerLim to upperLim 
  // and multiply by normC

  G4double integ = normC *
           EmissionIntegration(frag,gammaE,lowerLim,upperLim,numIters);
  if(integ > 0.0) theProb = integ/(upperLim-lowerLim);

  return theProb;

}

G4double G4E1Probability::EmissionIntegration(const G4Fragment& frag, 
                             const G4double ,
                             const G4double lowLim, const G4double upLim,
                             const G4int numIters)

{

  // Simple Gaussian quadrature integration

  G4double x;
  G4double root3 = 1.0/std::sqrt(3.0);

  G4double Step = (upLim-lowLim)/(2.0*numIters);
  G4double Delta = Step*root3;

  G4double mean = 0.0;

  G4double theInt = 0.0;

  for(G4int i = 0; i < numIters; i++) {

    x = (2*i + 1)*Step;
    G4double E1ProbDensityA = EmissionProbDensity(frag,x+Delta);
    G4double E1ProbDensityB = EmissionProbDensity(frag,x-Delta);

    mean += E1ProbDensityA + E1ProbDensityB;

  }

  if(mean*Step > 0.0) theInt = mean*Step;

  return theInt;

}