G4NeutronDecay.cc

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//                                                                            //
//  File:   G4NeutronDecay.cc                                                 //
//  Author: L.G. Sarmiento (Lund)                                             //
//  Date:   10 October 2015                                                   //
//                                                                            //

#include "G4NeutronDecay.hh"
#include "G4IonTable.hh"
#include "Randomize.hh"
#include "G4ThreeVector.hh"
#include "G4DynamicParticle.hh"
#include "G4DecayProducts.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include <iostream>
#include <iomanip>

G4NeutronDecay::G4NeutronDecay(const G4ParticleDefinition* theParentNucleus,
                            const G4double& branch, const G4double& Qvalue,
                            const G4double& excitationE)
 : G4NuclearDecay("neutron decay", Neutron, excitationE), transitionQ(Qvalue)
{
  SetParent(theParentNucleus);  // Store name of parent nucleus, delete G4MT_parent
  SetBR(branch);

  SetNumberOfDaughters(2);
  G4IonTable* theIonTable =
    (G4IonTable*)(G4ParticleTable::GetParticleTable()->GetIonTable());
  G4int daughterZ = theParentNucleus->GetAtomicNumber();
  G4int daughterA = theParentNucleus->GetAtomicMass() - 1;
  SetDaughter(0, theIonTable->GetIon(daughterZ, daughterA, excitationE) );
  SetDaughter(1, "neutron");
}


G4NeutronDecay::~G4NeutronDecay()
{}


G4DecayProducts* G4NeutronDecay::DecayIt(G4double)
{
  // Fill G4MT_parent with theParentNucleus (stored by SetParent in ctor)  
  CheckAndFillParent();

  // Fill G4MT_daughters with neutron and residual nucleus (stored by SetDaughter)  
  CheckAndFillDaughters();

  G4double neutronMass = G4MT_daughters[1]->GetPDGMass();
  // Excitation energy included in PDG mass
  G4double nucleusMass = G4MT_daughters[0]->GetPDGMass();

  // Q value was calculated from atomic masses.
  // Use it to get correct neutron energy.
  G4double cmMomentum = std::sqrt(transitionQ*(transitionQ + 2.*neutronMass)*
                                (transitionQ + 2.*nucleusMass)*
                                (transitionQ + 2.*neutronMass + 2.*nucleusMass) )/
                                (transitionQ + neutronMass + nucleusMass)/2.; 

  // Set up final state
  // parentParticle is set at rest here because boost with correct momentum 
  // is done later
  G4DynamicParticle parentParticle(G4MT_parent, G4ThreeVector(0,0,0), 0.0);
  G4DecayProducts* products = new G4DecayProducts(parentParticle);

  G4double costheta = 2.*G4UniformRand()-1.0;
  G4double sintheta = std::sqrt(1.0 - costheta*costheta);
  G4double phi  = twopi*G4UniformRand()*rad;
  G4ThreeVector direction(sintheta*std::cos(phi),sintheta*std::sin(phi),
                          costheta);

  G4double KE = std::sqrt(cmMomentum*cmMomentum + neutronMass*neutronMass)
              - neutronMass;
  G4DynamicParticle* daughterparticle =
    new G4DynamicParticle(G4MT_daughters[1], direction, KE, neutronMass);
  products->PushProducts(daughterparticle);

  KE = std::sqrt(cmMomentum*cmMomentum + nucleusMass*nucleusMass) - nucleusMass;
  daughterparticle =
    new G4DynamicParticle(G4MT_daughters[0], -1.0*direction, KE, nucleusMass);
  products->PushProducts(daughterparticle);

  // Energy conservation check
  // For neutron decays, do final energy check against reaction Q value
  // which is well-measured using atomic mass differences.  Nuclear masses
  // should not be used since they are not usually directly measured and we
  // always decay atoms and not fully stripped nuclei.
  /*
  G4int nProd = products->entries();
  G4DynamicParticle* temp = 0;
  G4double Esum = 0.0;
  for (G4int i = 0; i < nProd; i++) {
    temp = products->operator[](i);
    Esum += temp->GetKineticEnergy();
  }
  G4double eCons = (transitionQ - Esum)/keV;
  if (eCons > 1.e-07) G4cout << " Neutron decay check: Ediff (keV) = " << eCons << G4endl;
  */
  return products;
}


void G4NeutronDecay::DumpNuclearInfo()
{
  G4cout << " G4NeutronDecay for parent nucleus " << GetParentName() << G4endl;
  G4cout << " decays to " << GetDaughterName(0) << " + " << GetDaughterName(1)
         << " with branching ratio " << GetBR() << "% and Q value "
         << transitionQ << G4endl;
}