G4Fancy3DNucleus.cc

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//
// ------------------------------------------------------------
//      GEANT 4 class implementation file
//
//      ---------------- G4Fancy3DNucleus ----------------
//             by Gunter Folger, May 1998.
//       class for a 3D nucleus, arranging nucleons in space and momentum.
// ------------------------------------------------------------
// 20110805  M. Kelsey -- Remove C-style array (pointer) of G4Nucleons,
//              make vector a container of objects.  Move Helper class
//              to .hh.  Move testSums, places, momentum and fermiM to
//              class data members for reuse.

#include <algorithm>

#include "G4Fancy3DNucleus.hh"
#include "G4Fancy3DNucleusHelper.hh"
#include "G4NuclearFermiDensity.hh"
#include "G4NuclearShellModelDensity.hh"
#include "G4NucleiProperties.hh"
#include "G4Nucleon.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"
#include "G4ios.hh"
#include "G4HadronicException.hh"


G4Fancy3DNucleus::G4Fancy3DNucleus()
  : myA(0), myZ(0), theNucleons(250), currentNucleon(-1), theDensity(0), 
    nucleondistance(0.8*fermi), places(250), momentum(250), fermiM(250),
    testSums(250)
{
//G4cout <<"G4Fancy3DNucleus::G4Fancy3DNucleus()"<<G4endl;
}

G4Fancy3DNucleus::~G4Fancy3DNucleus()
{
  if(theDensity) delete theDensity;
}

#if defined(NON_INTEGER_A_Z)
void G4Fancy3DNucleus::Init(G4double theA, G4double theZ)
{
  G4int intZ = G4int(theZ);
  G4int intA= ( G4UniformRand()>theA-G4int(theA) ) ? G4int(theA) : G4int(theA)+1;
   // forward to integer Init()
  Init(intA, intZ);

}
#endif

void G4Fancy3DNucleus::Init(G4int theA, G4int theZ)
{
//  G4cout << "G4Fancy3DNucleus::Init(theA, theZ) called"<<G4endl;
  currentNucleon=-1;
  theNucleons.clear();

  myZ = theZ;
  myA= theA;

  theNucleons.resize(myA);      // Pre-loads vector with empty elements
  
//  G4cout << "myA, myZ" << myA << ", " << myZ << G4endl;

  if(theDensity) delete theDensity;
  if ( myA < 17 ) {
     theDensity = new G4NuclearShellModelDensity(myA, myZ);
  } else {
     theDensity = new G4NuclearFermiDensity(myA, myZ);
  }

  theFermi.Init(myA, myZ);
  
  ChooseNucleons();
  
  ChoosePositions();
  
//  CenterNucleons();   // This would introduce a bias 

  ChooseFermiMomenta();
  
  G4double Ebinding= BindingEnergy()/myA;
  
  for (G4int aNucleon=0; aNucleon < myA; aNucleon++)
  {
        theNucleons[aNucleon].SetBindingEnergy(Ebinding);
  }
  
  
  return;
}

G4bool G4Fancy3DNucleus::StartLoop()
{
        currentNucleon=0;
        return (theNucleons.size()>0);
}       

// Returns by pointer; null pointer indicates end of loop
G4Nucleon * G4Fancy3DNucleus::GetNextNucleon()
{
  return ( (currentNucleon>=0 && currentNucleon<myA) ? 
           &theNucleons[currentNucleon++] : 0 );
}

const std::vector<G4Nucleon> & G4Fancy3DNucleus::GetNucleons()
{
  return theNucleons;
}


// Class-scope function to sort nucleons by Z coordinate
bool G4Fancy3DNucleusHelperForSortInZ(const G4Nucleon& nuc1, const G4Nucleon& nuc2)
{
        return nuc1.GetPosition().z() < nuc2.GetPosition().z();
}

void G4Fancy3DNucleus::SortNucleonsIncZ() // on increased Z-coordinates Uzhi 29.08.08
{
  if (theNucleons.size() < 2 ) return;          // Avoid unnecesary work

  std::sort(theNucleons.begin(), theNucleons.end(),
            G4Fancy3DNucleusHelperForSortInZ); 
}

void G4Fancy3DNucleus::SortNucleonsDecZ() // on decreased Z-coordinates Uzhi 29.08.08
{
  if (theNucleons.size() < 2 ) return;          // Avoid unnecessary work
  SortNucleonsIncZ();

  std::reverse(theNucleons.begin(), theNucleons.end());
}


G4double G4Fancy3DNucleus::BindingEnergy()
{
  return G4NucleiProperties::GetBindingEnergy(myA,myZ);
}


G4double G4Fancy3DNucleus::GetNuclearRadius()
{
        return GetNuclearRadius(0.5);
}

G4double G4Fancy3DNucleus::GetNuclearRadius(const G4double maxRelativeDensity)
{       
        return theDensity->GetRadius(maxRelativeDensity);
}

G4double G4Fancy3DNucleus::GetOuterRadius()
{
        G4double maxradius2=0;
        
        for (int i=0; i<myA; i++)
        {
           if ( theNucleons[i].GetPosition().mag2() > maxradius2 )
           {
                maxradius2=theNucleons[i].GetPosition().mag2();
           }
        }
        return std::sqrt(maxradius2)+nucleondistance;
}

G4double G4Fancy3DNucleus::GetMass()
{
        return   myZ*G4Proton::Proton()->GetPDGMass() + 
                 (myA-myZ)*G4Neutron::Neutron()->GetPDGMass() -
                 BindingEnergy();
}



void G4Fancy3DNucleus::DoLorentzBoost(const G4LorentzVector & theBoost)
{
        for (G4int i=0; i<myA; i++){
            theNucleons[i].Boost(theBoost);
        }
}

void G4Fancy3DNucleus::DoLorentzBoost(const G4ThreeVector & theBeta)
{
        for (G4int i=0; i<myA; i++){
            theNucleons[i].Boost(theBeta);
        }
}

void G4Fancy3DNucleus::DoLorentzContraction(const G4ThreeVector & theBeta)
{
        G4double factor=(1-std::sqrt(1-theBeta.mag2()))/theBeta.mag2(); // (gamma-1)/gamma/beta**2
        G4ThreeVector rprime;
        for (G4int i=0; i< myA; i++) {
          rprime = theNucleons[i].GetPosition() - 
            factor * (theBeta*theNucleons[i].GetPosition()) * theBeta;  
          theNucleons[i].SetPosition(rprime);
        }    
}

void G4Fancy3DNucleus::DoLorentzContraction(const G4LorentzVector & theBoost)
{
        G4ThreeVector beta = theBoost.vect()/theBoost.e();
        // DoLorentzBoost(beta); 
        DoLorentzContraction(beta);
}



void G4Fancy3DNucleus::CenterNucleons()
{
        G4ThreeVector   center;
        
        for (G4int i=0; i<myA; i++ )
        {
           center+=theNucleons[i].GetPosition();
        }   
        center /= -myA;
        DoTranslation(center);
}

void G4Fancy3DNucleus::DoTranslation(const G4ThreeVector & theShift)
{
  G4ThreeVector tempV;
  for (G4int i=0; i<myA; i++ )
    {
      tempV = theNucleons[i].GetPosition() + theShift;
      theNucleons[i].SetPosition(tempV);
    }   
}

const G4VNuclearDensity * G4Fancy3DNucleus::GetNuclearDensity() const
{
        return theDensity;
}

//----------------------- private Implementation Methods-------------

void G4Fancy3DNucleus::ChooseNucleons()
{
        G4int protons=0,nucleons=0;
        
        while (nucleons < myA )
        {
          if ( protons < myZ && G4UniformRand() < (G4double)(myZ-protons)/(G4double)(myA-nucleons) )
          {
             protons++;
             theNucleons[nucleons++].SetParticleType(G4Proton::Proton());
          }
          else if ( (nucleons-protons) < (myA-myZ) )
          {
               theNucleons[nucleons++].SetParticleType(G4Neutron::Neutron());
          }
          else G4cout << "G4Fancy3DNucleus::ChooseNucleons not efficient" << G4endl;
        }
        return;
}

void G4Fancy3DNucleus::ChoosePositions()
{
        G4int i=0;
        G4ThreeVector   aPos, delta;
        G4bool          freeplace;
        static G4double nd2 = sqr(nucleondistance);
        G4double maxR=GetNuclearRadius(0.001);   //  there are no nucleons at a
                                                //  relative Density of 0.01
        G4int jr=0;
        G4int jx,jy;
        G4double arand[600];
        G4double *prand=arand;

        places.clear();                         // Reset data buffer

        while ( i < myA )
        {
           do
           {    
                if ( jr < 3 ) 
                {
                    jr=std::min(600,9*(myA - i));
                    CLHEP::RandFlat::shootArray(jr, prand );
                }
                jx=--jr;
                jy=--jr;
                aPos.set((2*arand[jx]-1.), (2*arand[jy]-1.), (2*arand[--jr]-1.));
           } while (aPos.mag2() > 1. );
           aPos *=maxR;
           G4double density=theDensity->GetRelativeDensity(aPos);
           if (G4UniformRand() < density)
           {
              freeplace= true;
              std::vector<G4ThreeVector>::iterator iplace;
              for( iplace=places.begin(); iplace!=places.end() && freeplace;++iplace)
              {
                delta = *iplace - aPos;
                freeplace= delta.mag2() > nd2;
              }
              
              if ( freeplace )
              {
                  G4double pFermi=theFermi.GetFermiMomentum(theDensity->GetDensity(aPos));
                    // protons must at least have binding energy of CoulombBarrier, so
                    //  assuming the Fermi energy corresponds to a potential, we must place these such
                    //  that the Fermi Energy > CoulombBarrier
                  if (theNucleons[i].GetDefinition() == G4Proton::Proton())
                  {
                    G4double nucMass = theNucleons[i].GetDefinition()->GetPDGMass();
                    G4double eFermi= std::sqrt( sqr(pFermi) + sqr(nucMass) )
                                      - nucMass;
                    if (eFermi <= CoulombBarrier() ) freeplace=false;
                  }
              }
              if ( freeplace )
              {
                  theNucleons[i].SetPosition(aPos);
                  places.push_back(aPos);
                  ++i;
              }
           }
        }

}

void G4Fancy3DNucleus::ChooseFermiMomenta()
{
    G4int i;
    G4double density;

    // Pre-allocate buffers for filling by index
    momentum.resize(myA, G4ThreeVector(0.,0.,0.));
    fermiM.resize(myA, 0.*GeV);

    for (G4int ntry=0; ntry<1 ; ntry ++ )
    {
        for (i=0; i < myA; i++ )    // momenta for all, including last, in case we swap nucleons
        {
           density = theDensity->GetDensity(theNucleons[i].GetPosition());
           fermiM[i] = theFermi.GetFermiMomentum(density);
           G4ThreeVector mom=theFermi.GetMomentum(density);
           if (theNucleons[i].GetDefinition() == G4Proton::Proton())
           {
              G4double eMax = std::sqrt(sqr(fermiM[i]) +sqr(theNucleons[i].GetDefinition()->GetPDGMass()) )
                              - CoulombBarrier();
              if ( eMax > theNucleons[i].GetDefinition()->GetPDGMass() )
              {
                  G4double pmax2= sqr(eMax) - sqr(theNucleons[i].GetDefinition()->GetPDGMass());
                  fermiM[i] = std::sqrt(pmax2);
                  while ( mom.mag2() > pmax2 )
                  {
                      mom=theFermi.GetMomentum(density, fermiM[i]);
                  }
              }  else
              {
                  G4cerr << "G4Fancy3DNucleus: difficulty finding proton momentum" << G4endl;
                  mom=G4ThreeVector(0,0,0);
              }

           }
           momentum[i]= mom;
        }

        if ( ReduceSum() ) break;
//       G4cout <<" G4FancyNucleus: iterating to find momenta: "<< ntry<< G4endl;
    }

//     G4ThreeVector sum;
//     for (G4int index=0; index<myA;sum+=momentum[index++])
//     ;
//     G4cout << "final sum / mag() " << sum << " / " << sum.mag() << G4endl;

    G4double energy;
    for ( i=0; i< myA ; i++ )
    {
       energy = theNucleons[i].GetParticleType()->GetPDGMass()
                - BindingEnergy()/myA;
       G4LorentzVector tempV(momentum[i],energy);
       theNucleons[i].SetMomentum(tempV);
       // GF 11-05-2011: set BindingEnergy to be T of Nucleon with p , ~ p**2/2m
       //theNucleons[i].SetBindingEnergy(
       //     0.5*sqr(fermiM[i])/theNucleons[i].GetParticleType()->GetPDGMass());
    }
}


G4bool G4Fancy3DNucleus::ReduceSum()
{
        G4ThreeVector sum;
        G4double PFermi=fermiM[myA-1];

        for (G4int i=0; i < myA-1 ; i++ )
             { sum+=momentum[i]; }

// check if have to do anything at all..
        if ( sum.mag() <= PFermi )
        {
                momentum[myA-1]=-sum;
                return true;
        }

// find all possible changes in momentum, changing only the component parallel to sum
        G4ThreeVector testDir=sum.unit();
        testSums.clear();
        testSums.resize(myA-1);         // Allocate block for filling below

        G4ThreeVector delta;
        for (G4int aNucleon=0; aNucleon < myA-1; aNucleon++) {
          delta = 2.*((momentum[aNucleon]*testDir)*testDir);

          testSums[aNucleon].Fill(delta, delta.mag(), aNucleon);
        }

        std::sort(testSums.begin(), testSums.end());

//    reduce Momentum Sum until the next would be allowed.
        G4int index=testSums.size();
        while ( (sum-testSums[--index].Vector).mag()>PFermi && index>0)
        {
          // Only take one which improve, ie. don't change sign and overshoot...
          if ( sum.mag() > (sum-testSums[index].Vector).mag() ) {
            momentum[testSums[index].Index]-=testSums[index].Vector;
            sum-=testSums[index].Vector;
          }
        }

        if ( (sum-testSums[index].Vector).mag() <= PFermi )
        {
                G4int best=-1;
                G4double pBest=2*PFermi; // anything larger than PFermi
                for ( G4int aNucleon=0; aNucleon<=index; aNucleon++)
                {
                        // find the momentum closest to choosen momentum for last Nucleon.
                        G4double pTry=(testSums[aNucleon].Vector-sum).mag();
                        if ( pTry < PFermi
                         &&  std::abs(momentum[myA-1].mag() - pTry ) < pBest )
                        {
                           pBest=std::abs(momentum[myA-1].mag() - pTry );
                           best=aNucleon;
                        }
                }
                if ( best < 0 )  
                {
                  G4String text = "G4Fancy3DNucleus.cc: Logic error in ReduceSum()";
                  throw G4HadronicException(__FILE__, __LINE__, text);
                }
                momentum[testSums[best].Index]-=testSums[best].Vector;
                momentum[myA-1]=testSums[best].Vector-sum;

                return true;

        }

        // try to compensate momentum using another Nucleon....
        G4int swapit=-1;
        while (swapit<myA-1)
        {
          if ( fermiM[++swapit] > PFermi ) break;
        }
        if (swapit == myA-1 ) return false;

        // Now we have a nucleon with a bigger Fermi Momentum.
        // Exchange with last nucleon.. and iterate.
        std::swap(theNucleons[swapit], theNucleons[myA-1]);
        std::swap(momentum[swapit], momentum[myA-1]);
        std::swap(fermiM[swapit], fermiM[myA-1]);
        return ReduceSum();
}

G4double G4Fancy3DNucleus::CoulombBarrier()
{
  G4double coulombBarrier = (1.44/1.14) * MeV * myZ / (1.0 + std::pow(G4double(myA),1./3.));
  return coulombBarrier;
}

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