G4AlphaDecay.cc

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//                                                                            //
//  File:   G4AlphaDecay.cc                                                   //
//  Author: D.H. Wright (SLAC)                                                //
//  Date:   20 October 2014                                                   //
//                                                                            //

#include "G4AlphaDecay.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>

G4AlphaDecay::G4AlphaDecay(const G4ParticleDefinition* theParentNucleus,
                           const G4double& branch, const G4double& Qvalue,
                           const G4double& excitationE)
 : G4VDecayChannel("alpha decay"), transitionQ(Qvalue), daughterEx(excitationE),
   halflifeThreshold(nanosecond)
{
  SetParent(theParentNucleus);  // Store name of parent nucleus, delete G4MT_parent 
  SetBR(branch);

  SetNumberOfDaughters(2);
  SetDaughter(0, "alpha");      // Store name of 1st daughter
  G4IonTable* theIonTable =
    (G4IonTable*)(G4ParticleTable::GetParticleTable()->GetIonTable());
  G4int daughterZ = theParentNucleus->GetAtomicNumber() - 2;
  G4int daughterA = theParentNucleus->GetAtomicMass() - 4; 
  SetDaughter(1, theIonTable->GetIon(daughterZ, daughterA, daughterEx) );
}


G4AlphaDecay::G4AlphaDecay(const G4AlphaDecay& right)
 : G4VDecayChannel(right), transitionQ(right.transitionQ),
   daughterEx(right.daughterEx), halflifeThreshold(right.halflifeThreshold)
{}


G4AlphaDecay::~G4AlphaDecay()
{}


G4DecayProducts* G4AlphaDecay::DecayIt(G4double)
{
  // Fill G4MT_parent with theParentNucleus (stored by SetParent in ctor)  
  if (G4MT_parent == 0) FillParent();

  // Fill G4MT_daughters with alpha and residual nucleus (stored by SetDaughter)  
  if (G4MT_daughters == 0) FillDaughters();

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

  // Q value was calculated from atomic masses.
  // Use it to get correct alpha energy.
  G4double cmMomentum = std::sqrt(transitionQ*(transitionQ + 2.*alphaMass)*
                                (transitionQ + 2.*nucleusMass)*
                                (transitionQ + 2.*alphaMass + 2.*nucleusMass) )/
                                (transitionQ + alphaMass + 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 + alphaMass*alphaMass)
              - alphaMass;
  G4DynamicParticle* daughterparticle =
    new G4DynamicParticle(G4MT_daughters[0], direction, KE, alphaMass);
  products->PushProducts(daughterparticle);

  KE = std::sqrt(cmMomentum*cmMomentum + nucleusMass*nucleusMass) - nucleusMass;
  daughterparticle =
    new G4DynamicParticle(G4MT_daughters[1], -1.0*direction, KE, nucleusMass);
  products->PushProducts(daughterparticle);

  return products;
}


void G4AlphaDecay::DumpInfo()
{
  G4cout << " G4AlphaDecay for parent nucleus " << GetParentName() << G4endl;
  G4cout << " decays to " << GetDaughterName(0) << " + " << GetDaughterName(1)
         << " with branching ratio " << GetBR() << " and Q value "
         << transitionQ << G4endl;
}