G4HENeutronInelastic.cc

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// $Id$
//

// G4 Process: Gheisha High Energy Collision model.
// This includes the high energy cascading model, the two-body-resonance model
// and the low energy two-body model. Not included are the low energy stuff
// like nuclear reactions, nuclear fission without any cascading and all
// processes for particles at rest.  
// First work done by J.L.Chuma and F.W.Jones, TRIUMF, June 96.  
// H. Fesefeldt, RWTH-Aachen, 23-October-1996
 
#include "G4HENeutronInelastic.hh"
#include "globals.hh"
#include "G4ios.hh"
#include "G4PhysicalConstants.hh"

void G4HENeutronInelastic::ModelDescription(std::ostream& outFile) const
{
  outFile << "G4HENeutronInelastic is one of the High Energy\n"
          << "Parameterized (HEP) models used to implement inelastic\n"
          << "neutron scattering from nuclei.  It is a re-engineered\n"
          << "version of the GHEISHA code of H. Fesefeldt.  It divides the\n"
          << "initial collision products into backward- and forward-going\n"
          << "clusters which are then decayed into final state hadrons.\n"
          << "The model does not conserve energy on an event-by-event\n"
          << "basis.  It may be applied to neutrons with initial energies\n"
          << "above 20 GeV.\n";
}


G4HadFinalState*
G4HENeutronInelastic::ApplyYourself(const G4HadProjectile& aTrack,
                                    G4Nucleus& targetNucleus)
{
  G4HEVector* pv = new G4HEVector[MAXPART];
  const G4HadProjectile* aParticle = &aTrack;
  const G4double A = targetNucleus.GetA_asInt();
  const G4double Z = targetNucleus.GetZ_asInt();
  G4HEVector incidentParticle(aParticle);
     
  G4double atomicNumber = Z;
  G4double atomicWeight = A;

  G4int incidentCode = incidentParticle.getCode();
  G4double incidentMass = incidentParticle.getMass();
  G4double incidentTotalEnergy = incidentParticle.getEnergy();

  // G4double incidentTotalMomentum = incidentParticle.getTotalMomentum();
  // DHW 19 May 2011: variable set but not used

  G4double incidentKineticEnergy = incidentTotalEnergy - incidentMass;

  if (incidentKineticEnergy < 1.)
    G4cout << "GHENeutronInelastic: incident energy < 1 GeV" << G4endl;
    
  if (verboseLevel > 1) {
    G4cout << "G4HENeutronInelastic::ApplyYourself" << G4endl;
    G4cout << "incident particle " << incidentParticle.getName()
           << "mass "              << incidentMass
           << "kinetic energy "    << incidentKineticEnergy
           << G4endl;
    G4cout << "target material with (A,Z) = (" 
           << atomicWeight << "," << atomicNumber << ")" << G4endl;
  }
    
  G4double inelasticity = NuclearInelasticity(incidentKineticEnergy, 
                                              atomicWeight, atomicNumber);
  if (verboseLevel > 1)
    G4cout << "nuclear inelasticity = " << inelasticity << G4endl;
    
  incidentKineticEnergy -= inelasticity;
    
  G4double excitationEnergyGNP = 0.;
  G4double excitationEnergyDTA = 0.; 

  G4double excitation = NuclearExcitation(incidentKineticEnergy,
                                          atomicWeight, atomicNumber,
                                          excitationEnergyGNP,
                                          excitationEnergyDTA);
  if (verboseLevel > 1)
    G4cout << "nuclear excitation = " << excitation << excitationEnergyGNP 
           << excitationEnergyDTA << G4endl;             

  incidentKineticEnergy -= excitation;
  incidentTotalEnergy  = incidentKineticEnergy + incidentMass;
  // incidentTotalMomentum = std::sqrt( (incidentTotalEnergy-incidentMass)                    
  //                                   *(incidentTotalEnergy+incidentMass));
  // DHW 19 May 2011: variables et but not used

  G4HEVector targetParticle;
  if (G4UniformRand() < atomicNumber/atomicWeight) { 
    targetParticle.setDefinition("Proton");
  } else { 
    targetParticle.setDefinition("Neutron");
  }

  G4double targetMass = targetParticle.getMass();
  G4double centerOfMassEnergy = std::sqrt(incidentMass*incidentMass
                                        + targetMass*targetMass
                                        + 2.0*targetMass*incidentTotalEnergy);
  G4double availableEnergy = centerOfMassEnergy - targetMass - incidentMass;

  // In the original Gheisha code the inElastic flag was set as follows
  //   G4bool inElastic = InElasticCrossSectionInFirstInt
  //                      (availableEnergy, incidentCode, incidentTotalMomentum);  
  // For unknown reasons, it has been replaced by the following code in Geant???
  //
  G4bool inElastic = true;
  //   if (G4UniformRand() < elasticCrossSection/totalCrossSection) inElastic = false;    

  vecLength = 0;

  if (verboseLevel > 1)
    G4cout << "ApplyYourself: CallFirstIntInCascade for particle "
           << incidentCode << G4endl;

  G4bool successful = false; 
    
  FirstIntInCasNeutron(inElastic, availableEnergy, pv, vecLength,
                       incidentParticle, targetParticle, atomicWeight);

  if (verboseLevel > 1)
    G4cout << "ApplyYourself::StrangeParticlePairProduction" << G4endl;

  if ((vecLength > 0) && (availableEnergy > 1.)) 
    StrangeParticlePairProduction(availableEnergy, centerOfMassEnergy,
                                  pv, vecLength,
                                  incidentParticle, targetParticle);

  HighEnergyCascading(successful, pv, vecLength,
                      excitationEnergyGNP, excitationEnergyDTA,
                      incidentParticle, targetParticle,
                      atomicWeight, atomicNumber);
  if (!successful)
    HighEnergyClusterProduction(successful, pv, vecLength,
                                excitationEnergyGNP, excitationEnergyDTA,
                                incidentParticle, targetParticle,
                                atomicWeight, atomicNumber);
  if (!successful) 
    MediumEnergyCascading(successful, pv, vecLength, 
                          excitationEnergyGNP, excitationEnergyDTA, 
                          incidentParticle, targetParticle,
                          atomicWeight, atomicNumber);

  if (!successful)
    MediumEnergyClusterProduction(successful, pv, vecLength,
                                  excitationEnergyGNP, excitationEnergyDTA,       
                                  incidentParticle, targetParticle,
                                  atomicWeight, atomicNumber);
  if (!successful)
    QuasiElasticScattering(successful, pv, vecLength,
                           excitationEnergyGNP, excitationEnergyDTA,
                           incidentParticle, targetParticle, 
                           atomicWeight, atomicNumber);
  if (!successful)
    ElasticScattering(successful, pv, vecLength,
                      incidentParticle,    
                      atomicWeight, atomicNumber);

  if (!successful)
    G4cout << "GHEInelasticInteraction::ApplyYourself fails to produce final state particles" 
           << G4endl;

  FillParticleChange(pv, vecLength);
  delete [] pv;
  theParticleChange.SetStatusChange(stopAndKill);
  return &theParticleChange;
}


void
G4HENeutronInelastic::FirstIntInCasNeutron(G4bool& inElastic,
                                           const G4double availableEnergy,
                                           G4HEVector pv[],
                                           G4int& vecLen,
                                           const G4HEVector& incidentParticle,
                                           const G4HEVector& targetParticle,
                                           const G4double atomicWeight)

// Neutron undergoes interaction with nucleon within a nucleus.  Check if it is
// energetically possible to produce pions/kaons.  In not, assume nuclear excitation
// occurs and input particle is degraded in energy. No other particles are produced.
// If reaction is possible, find the correct number of pions/protons/neutrons
// produced using an interpolation to multiplicity data.  Replace some pions or
// protons/neutrons by kaons or strange baryons according to the average
// multiplicity per inelastic reaction.
{
  static const G4double expxu = 82.;     // upper bound for arg. of exp
  static const G4double expxl = -expxu;  // lower bound for arg. of exp

  static const G4double protb = 0.35;
  static const G4double neutb = 0.35;              
  static const G4double c = 1.25;

  static const G4int numMul = 1200;
  static const G4int numSec = 60;

  G4int neutronCode = Neutron.getCode();
  G4int protonCode  = Proton.getCode();

  G4int targetCode = targetParticle.getCode();
  G4double incidentTotalMomentum = incidentParticle.getTotalMomentum();

  static G4bool first = true;
  static G4double protmul[numMul], protnorm[numSec];  // proton constants
  static G4double neutmul[numMul], neutnorm[numSec];  // neutron constants

  //  misc. local variables
  //  npos = number of pi+,  nneg = number of pi-,  nzero = number of pi0

  G4int i, counter, nt, npos, nneg, nzero;

  if (first) {
    // compute normalization constants, this will only be done once
    first = false;
    for (i = 0; i < numMul; i++) protmul[i] = 0.0;
    for (i = 0; i < numSec; i++) protnorm[i] = 0.0;
    counter = -1;
    for (npos = 0; npos < (numSec/3); npos++) {
      for (nneg = std::max(0,npos-1); nneg <= (npos+1); nneg++) {
                 for( nzero=0; nzero<numSec/3; nzero++ ) 
                    {
                      if( ++counter < numMul ) 
                        {
                          nt = npos+nneg+nzero;
                          if( (nt>0) && (nt<=numSec) ) 
                            {
                              protmul[counter] = pmltpc(npos,nneg,nzero,nt,protb,c)
                                                 /(Factorial(1-npos+nneg)*Factorial(1+npos-nneg)) ;
                              protnorm[nt-1] += protmul[counter];
                            }
                        }
                    }
      }
    }

    for( i=0; i<numMul; i++ )neutmul[i]  = 0.0;
    for( i=0; i<numSec; i++ )neutnorm[i] = 0.0;
    counter = -1;
       for( npos=0; npos<numSec/3; npos++ ) 
          {
            for( nneg=npos; nneg<=(npos+2); nneg++ ) 
               {
                 for( nzero=0; nzero<numSec/3; nzero++ ) 
                    {
                      if( ++counter < numMul ) 
                        {
                          nt = npos+nneg+nzero;
                          if( (nt>0) && (nt<=numSec) ) 
                            {
                               neutmul[counter] = pmltpc(npos,nneg,nzero,nt,neutb,c)
                                                  /(Factorial(-npos+nneg)*Factorial(2+npos-nneg));
                               neutnorm[nt-1] += neutmul[counter];
                            }
                        }
                    }
               }
          }
       for( i=0; i<numSec; i++ ) 
          {
            if( protnorm[i] > 0.0 )protnorm[i] = 1.0/protnorm[i];
            if( neutnorm[i] > 0.0 )neutnorm[i] = 1.0/neutnorm[i];
          }
     }                                          // end of initialization

         
                                              // initialize the first two places
                                              // the same as beam and target                                    
   pv[0] = incidentParticle;
   pv[1] = targetParticle;
   vecLen = 2;

   if( !inElastic ) 
     {                                     // quasi-elastic scattering, no pions produced
       if( targetCode == protonCode ) 
         {
           G4double cech[] = {0.50, 0.45, 0.40, 0.35, 0.30, 0.25, 0.06, 0.04, 0.005, 0.};
           G4int iplab = G4int( std::min( 9.0, incidentTotalMomentum*2.5) );
           if( G4UniformRand() < cech[iplab]/std::pow(atomicWeight,0.42) ) 
             {                                            // charge exchange  n p -> p n
               pv[0] = Proton;
               pv[1] = Neutron;
             }
         }
       return;
     }
   else if (availableEnergy <= PionPlus.getMass())
       return;

                                                  //   inelastic scattering

   npos = 0, nneg = 0, nzero = 0;
   G4double eab = availableEnergy;
   G4int ieab = G4int( eab*5.0 );
   
   G4double supp[] = {0., 0.4, 0.55, 0.65, 0.75, 0.82, 0.86, 0.90, 0.94, 0.98};
   if( (ieab <= 9) && (G4UniformRand() >= supp[ieab]) ) 
     {
                                          //   suppress high multiplicity events at low momentum
                                          //   only one additional pion will be produced
       G4double w0, wp, wm, wt, ran;
       if( targetCode == neutronCode )                    // target is a neutron 
         {
           w0 = - sqr(1.+neutb)/(2.*c*c);
           wm = w0 = std::exp(w0);
           w0 = w0/2.;
           if( G4UniformRand() < w0/(w0+wm) )  
             { npos = 0; nneg = 0; nzero = 1; }
           else 
             { npos = 0; nneg = 1; nzero = 0; }       
         } 
       else 
         {                                               // target is a proton
           w0 = -sqr(1.+protb)/(2.*c*c);
           w0 = std::exp(w0);
           wp = w0/2.;
           wm = -sqr(-1.+protb)/(2.*c*c);
           wm = std::exp(wm)/2.;
           wt = w0+wp+wm;
           wp = w0+wp;
           ran = G4UniformRand();
           if( ran < w0/wt)
             { npos = 0; nneg = 0; nzero = 1; }       
           else if( ran < wp/wt)
             { npos = 1; nneg = 0; nzero = 0; }       
           else
             { npos = 0; nneg = 1; nzero = 0; }       
         }
     }
   else
     {
       // number of total particles vs. centre of mass Energy - 2*proton mass
   
       G4double aleab = std::log(availableEnergy);
       G4double n     = 3.62567+aleab*(0.665843+aleab*(0.336514
                    + aleab*(0.117712+0.0136912*aleab))) - 2.0;
   
       // normalization constant for kno-distribution.
       // calculate first the sum of all constants, check for numerical problems.   
       G4double test, dum, anpn = 0.0;

       for (nt=1; nt<=numSec; nt++) {
         test = std::exp( std::min( expxu, std::max( expxl, -(pi/4.0)*(nt*nt)/(n*n) ) ) );
         dum = pi*nt/(2.0*n*n);
         if (std::fabs(dum) < 1.0) { 
           if( test >= 1.0e-10 )anpn += dum*test;
         } else { 
           anpn += dum*test;
         }
       }
   
       G4double ran = G4UniformRand();
       G4double excs = 0.0;
       if( targetCode == protonCode ) 
         {
           counter = -1;
           for (npos=0; npos<numSec/3; npos++) {
             for (nneg=std::max(0,npos-1); nneg<=(npos+1); nneg++) {
               for (nzero=0; nzero<numSec/3; nzero++) {
                 if (++counter < numMul) {
                   nt = npos+nneg+nzero;
                   if ( (nt>0) && (nt<=numSec) ) {
                     test = std::exp( std::min( expxu, std::max( expxl, -(pi/4.0)*(nt*nt)/(n*n) ) ) );
                     dum = (pi/anpn)*nt*protmul[counter]*protnorm[nt-1]/(2.0*n*n);
                     if (std::fabs(dum) < 1.0) { 
                       if( test >= 1.0e-10 )excs += dum*test;
                     } else { 
                       excs += dum*test;
                     }
                     if (ran < excs) goto outOfLoop;      //----------------------->
                   }
                 }
               }
             }
           }
       
           // 3 previous loops continued to the end
           inElastic = false;                 // quasi-elastic scattering   
           return;
         }
       else   
         {                                         // target must be a neutron
           counter = -1;
           for (npos=0; npos<numSec/3; npos++) {
             for (nneg=npos; nneg<=(npos+2); nneg++) {
               for (nzero=0; nzero<numSec/3; nzero++) {
                 if (++counter < numMul) {
                   nt = npos+nneg+nzero;
                   if ( (nt>=1) && (nt<=numSec) ) {
                     test = std::exp( std::min( expxu, std::max( expxl, -(pi/4.0)*(nt*nt)/(n*n) ) ) );
                     dum = (pi/anpn)*nt*neutmul[counter]*neutnorm[nt-1]/(2.0*n*n);
                     if (std::fabs(dum) < 1.0) { 
                       if( test >= 1.0e-10 )excs += dum*test;
                     } else { 
                       excs += dum*test;
                     }
                     if (ran < excs) goto outOfLoop;       // -------------------------->
                   }
                 }
               }
             }
           }
           // 3 previous loops continued to the end
           inElastic = false;                     // quasi-elastic scattering.
           return;
         }
     } 
   outOfLoop:           //  <----------------------------------------------   
    
   if( targetCode == neutronCode)
     {
       if( npos == nneg)
         {
         }
       else if (npos == (nneg-1))
         {
           if( G4UniformRand() < 0.5)
             {
               pv[1] = Proton;
             }
           else
             {
               pv[0] = Proton;
             }
         }
       else      
         {
           pv[0] = Proton;
           pv[1] = Proton;
         } 
     }  
   else
     {
       if( npos == nneg)
         {
           if( G4UniformRand() < 0.25)
             {
               pv[0] = Proton;
               pv[1] = Neutron;
             }
           else
             {
             }
         } 
       else if ( npos == (1+nneg))
         {
           pv[1] = Neutron;
         }
       else
         {
           pv[0] = Proton;
         }
     }      


   nt = npos + nneg + nzero;
   while ( nt > 0)
       {
         G4double ran = G4UniformRand();
         if ( ran < (G4double)npos/nt)
            { 
              if( npos > 0 ) 
                { pv[vecLen++] = PionPlus;
                  npos--;
                }
            }
         else if ( ran < (G4double)(npos+nneg)/nt)
            {   
              if( nneg > 0 )
                { 
                  pv[vecLen++] = PionMinus;
                  nneg--;
                }
            }
         else
            {
              if( nzero > 0 )
                { 
                  pv[vecLen++] = PionZero;
                  nzero--;
                }
            }
         nt = npos + nneg + nzero;
       } 
   if (verboseLevel > 1)
      {
        G4cout << "Particles produced: " ;
        G4cout << pv[0].getName() << " " ;
        G4cout << pv[1].getName() << " " ;
        for (i=2; i < vecLen; i++)   
            { 
              G4cout << pv[i].getName() << " " ;
            }
         G4cout << G4endl;
      }
   return;
 }

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