G4GammaTransition.cc

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//
// -------------------------------------------------------------------
//      GEANT 4 class file 
//
//      CERN, Geneva, Switzerland
//
//      File name:     G4GammaTransition
//
//      Author V.Ivanchenko 27 February 2015
//
// -------------------------------------------------------------------

#include "G4GammaTransition.hh"
#include "G4AtomicShells.hh"
#include "Randomize.hh"
#include "G4RandomDirection.hh"
#include "G4Gamma.hh"
#include "G4Electron.hh"
#include "G4LorentzVector.hh"
#include "G4SystemOfUnits.hh"
#include "G4PhysicalConstants.hh"

G4GammaTransition::G4GammaTransition() 
  : polarFlag(false), fDirection(0.,0.,0.), fTwoJMAX(10), fVerbose(0)
{}

G4GammaTransition::~G4GammaTransition() 
{}
  
G4Fragment* 
G4GammaTransition::SampleTransition(G4Fragment* nucleus,
            G4double newExcEnergy,
            G4double mpRatio,
            G4int  JP1,
            G4int  JP2,
            G4int  MP,
            G4int  shell,
            G4bool isDiscrete,
            G4bool isGamma)
{
  G4Fragment* result = nullptr;
  G4double bond_energy = 0.0;

  if (!isGamma) { 
    if(0 <= shell) {
      G4int Z = nucleus->GetZ_asInt();
      if(Z <= 100) {
  G4int idx = (G4int)shell;
  idx = std::min(idx, G4AtomicShells::GetNumberOfShells(Z)-1);
  bond_energy = G4AtomicShells::GetBindingEnergy(Z, idx);
      }
    }
  }
  G4double etrans = nucleus->GetExcitationEnergy() - newExcEnergy 
    - bond_energy;
  if(fVerbose > 2) {
    G4cout << "G4GammaTransition::GenerateGamma - Etrans(MeV)= " 
     << etrans << "  Eexnew= " << newExcEnergy 
     << " Ebond= " << bond_energy << G4endl;
  } 
  if(etrans <= 0.0) { 
    etrans += bond_energy;
    bond_energy = 0.0;
  }
  
  // Do complete Lorentz computation 
  G4LorentzVector lv = nucleus->GetMomentum();
  G4double mass = nucleus->GetGroundStateMass() + newExcEnergy;

  // select secondary
  G4ParticleDefinition* part;

  if(isGamma) { part =  G4Gamma::Gamma(); }
  else {
    part = G4Electron::Electron();
    G4int ne = std::max(nucleus->GetNumberOfElectrons() - 1, 0);
    nucleus->SetNumberOfElectrons(ne);
  }

  if(polarFlag && isDiscrete && JP1 <= fTwoJMAX) {
    SampleDirection(nucleus, mpRatio, JP1, JP2, MP);
  } else {
    fDirection = G4RandomDirection();
  }

  G4double emass = part->GetPDGMass();

  // 2-body decay in rest frame
  G4double ecm       = lv.mag();
  G4ThreeVector bst  = lv.boostVector();
  if(!isGamma) { ecm += (CLHEP::electron_mass_c2 - bond_energy); }

  //G4cout << "Ecm= " << ecm << " mass= " << mass << " emass= " << emass << G4endl;

  ecm = std::max(ecm, mass + emass);
  G4double energy = 0.5*((ecm - mass)*(ecm + mass) + emass*emass)/ecm;
  G4double mom = (emass > 0.0) ? std::sqrt((energy - emass)*(energy + emass))
    : energy;

  // emitted gamma or e-
  G4LorentzVector res4mom(mom * fDirection.x(),
        mom * fDirection.y(),
        mom * fDirection.z(), energy);
  // residual
  energy = std::max(ecm - energy, mass);
  lv.set(-mom*fDirection.x(), -mom*fDirection.y(), -mom*fDirection.z(), energy);

  // Lab system transform for short lived level
  lv.boost(bst);

  // modified primary fragment 
  nucleus->SetExcEnergyAndMomentum(newExcEnergy, lv);

  // gamma or e- are produced
  res4mom.boost(bst); 
  result = new G4Fragment(res4mom, part);

  //G4cout << " DeltaE= " << e0 - lv.e() - res4mom.e() + emass
  //   << "   Emass= " << emass << G4endl;
  if(fVerbose > 2) {
    G4cout << "G4GammaTransition::SampleTransition : " << *result << G4endl;
    G4cout << "       Left nucleus: " << *nucleus << G4endl;
  }
  return result;
}

void G4GammaTransition::SampleDirection(G4Fragment* nuc, G4double ratio, 
          G4int twoJ1, G4int twoJ2, G4int mp)
{
  G4double cosTheta, phi;
  G4NuclearPolarization* np = nuc->GetNuclearPolarization(); 
  if(fVerbose > 2) {
    G4cout << "G4GammaTransition::SampleDirection : 2J1= " << twoJ1 
     << " 2J2= " << twoJ2 << " ratio= " << ratio 
     << " mp= " << mp << G4endl;
    G4cout << "  Nucleus: " << *nuc << G4endl;
  }
  if(nullptr == np) {
    cosTheta = 2*G4UniformRand() - 1.0;
    phi = CLHEP::twopi*G4UniformRand();

  } else {
    // PhotonEvaporation dataset:
    // The multipolarity number with 1,2,3,4,5,6,7 representing E0,E1,M1,E2,M2,E3,M3
    // monopole transition and 100*Nx+Ny representing multipolarity transition with
    // Ny and Ny taking the value 1,2,3,4,5,6,7 referring to E0,E1,M1,E2,M2,E3,M3,..
    // For example a M1+E2 transition would be written 304.
    // M1 is the primary transition (L) and E2 is the secondary (L')

    G4double mpRatio = ratio;

    G4int L0 = 0, Lp = 0;
    if (mp > 99) {
      L0 = mp/200;
      Lp = (mp%100)/2;
    } else {
      L0 = mp/2;
      Lp = 0;
      mpRatio = 0.;
    } 
    fPolTrans.SampleGammaTransition(np, twoJ1, twoJ2, L0, Lp, mpRatio, cosTheta, phi);
  }

  G4double sinTheta = std::sqrt((1.-cosTheta)*(1.+cosTheta));
  fDirection.set(sinTheta*std::cos(phi),sinTheta*std::sin(phi),cosTheta);
  if(fVerbose > 3) {
    G4cout << "G4GammaTransition::SampleDirection done: " << fDirection << G4endl;
    if(np) { G4cout << *np << G4endl; }
  }
}