G4NeutronBetaDecayChannel.cc

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//
// G4NeutronBetaDecayChannel class implementation
//
// Author: H.Kurashige, 18 September 2001 
// --------------------------------------------------------------------
 
#include "G4ParticleDefinition.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4DecayProducts.hh"
#include "G4VDecayChannel.hh"
#include "G4NeutronBetaDecayChannel.hh"
#include "Randomize.hh"
#include "G4RotationMatrix.hh"
#include "G4LorentzVector.hh"
#include "G4LorentzRotation.hh"
 
G4NeutronBetaDecayChannel::G4NeutronBetaDecayChannel()
  : G4VDecayChannel()
{
}
 
G4NeutronBetaDecayChannel::
G4NeutronBetaDecayChannel(const G4String& theParentName, 
                                G4double  theBR)
  : G4VDecayChannel("Neutron Decay")
{
  // set names for daughter particles
  if (theParentName == "neutron")
  {
    SetBR(theBR);
    SetParent("neutron");
    SetNumberOfDaughters(3);
    SetDaughter(0, "e-");
    SetDaughter(1, "anti_nu_e");
    SetDaughter(2, "proton");
  }
  else if (theParentName == "anti_neutron")
  {
    SetBR(theBR);
    SetParent("anti_neutron");
    SetNumberOfDaughters(3);
    SetDaughter(0, "e+");
    SetDaughter(1, "nu_e");
    SetDaughter(2, "anti_proton");
  }
  else
  {
#ifdef G4VERBOSE
    if (GetVerboseLevel()>0)
    {
      G4cout << "G4NeutronBetaDecayChannel:: constructor :";
      G4cout << " parent particle is not neutron but ";
      G4cout << theParentName << G4endl;
    }
#endif
  }
}
 
G4NeutronBetaDecayChannel::~G4NeutronBetaDecayChannel()
{
}
 
G4NeutronBetaDecayChannel::
G4NeutronBetaDecayChannel(const G4NeutronBetaDecayChannel& right)
  : G4VDecayChannel(right)
{
}
 
G4NeutronBetaDecayChannel& G4NeutronBetaDecayChannel::
operator=(const G4NeutronBetaDecayChannel& right)
{
  if (this != &right)
  { 
    kinematics_name = right.kinematics_name;
    verboseLevel = right.verboseLevel;
    rbranch = right.rbranch;
 
    // copy parent name
    delete parent_name;
    parent_name = new G4String(*right.parent_name);
 
    // clear daughters_name array
    ClearDaughtersName();
 
    // recreate array
    numberOfDaughters = right.numberOfDaughters;
    if ( numberOfDaughters >0 )
    {
      daughters_name = new G4String*[numberOfDaughters];
      // copy daughters name
      for (G4int index=0; index<numberOfDaughters; ++index)
      {
        daughters_name[index] = new G4String(*right.daughters_name[index]);
      }
    }
  }
  return *this;
}
 
G4DecayProducts* G4NeutronBetaDecayChannel::DecayIt(G4double) 
{
  //  This class describes free neutron beta decay kinematics.
  //  This version neglects neutron/electron polarization  
  //  without Coulomb effect
 
#ifdef G4VERBOSE
  if (GetVerboseLevel()>1) G4cout << "G4NeutronBetaDecayChannel::DecayIt ";
#endif
 
  CheckAndFillParent();
  CheckAndFillDaughters();
 
  // parent mass
  G4double parentmass = G4MT_parent->GetPDGMass();
 
  // daughters'mass
  G4double daughtermass[3]; 
  G4double sumofdaughtermass = 0.0;
  for (G4int index=0; index<3; ++index)
  {
    daughtermass[index] = G4MT_daughters[index]->GetPDGMass();
    sumofdaughtermass += daughtermass[index];
  }
  G4double xmax = parentmass-sumofdaughtermass;  
 
  // create parent G4DynamicParticle at rest
  G4ThreeVector dummy;
  G4DynamicParticle* parentparticle
    = new G4DynamicParticle( G4MT_parent, dummy, 0.0);
 
  // create G4Decayproducts
  G4DecayProducts *products = new G4DecayProducts(*parentparticle);
  delete parentparticle;
 
  // calculate daughter momentum
  G4double daughtermomentum[3];
 
  // calcurate electron energy
  G4double x;                    // Ee
  G4double p;                    // Pe
  G4double dm = daughtermass[0]; //Me
  G4double w;                    // cosine of e-nu angle
  G4double r;  
  G4double r0;
  const std::size_t MAX_LOOP=10000;
  for (std::size_t loop_counter=0; loop_counter<MAX_LOOP; ++loop_counter)
  {
    x = xmax*G4UniformRand();
    p = std::sqrt(x*(x+2.0*dm));
    w = 1.0-2.0*G4UniformRand();
    r = p*(x+dm)*(xmax-x)*(xmax-x)*(1.0+aENuCorr*p/(x+dm)*w);
    r0 = G4UniformRand()*(xmax+dm)*(xmax+dm)*xmax*xmax*(1.0+aENuCorr);
    if  (r > r0) break;
  }  
 
  // create daughter G4DynamicParticle 
  // rotation materix to lab frame
  //
  G4double costheta = 2.*G4UniformRand()-1.0;
  G4double theta = std::acos(costheta)*rad;
  G4double phi  = twopi*G4UniformRand()*rad;
  G4RotationMatrix rm;
  rm.rotateY(theta);
  rm.rotateZ(phi);
 
  // daughter 0 (electron) in Z direction
  daughtermomentum[0] = p;
  G4ThreeVector direction0(0.0, 0.0, 1.0);
  direction0 = rm * direction0;
  G4DynamicParticle* daughterparticle0 
    = new G4DynamicParticle(G4MT_daughters[0], direction0*daughtermomentum[0]);
  products->PushProducts(daughterparticle0);
 
  // daughter 1 (nutrino) in XZ plane
  G4double eNu;    // Enu
  eNu = (parentmass-daughtermass[2])
      * (parentmass+daughtermass[2])+(dm*dm)-2.*parentmass*(x+dm);
  eNu /= 2.*(parentmass+p*w-(x+dm));
  G4double cosn = w;
  G4double phin  = twopi*G4UniformRand()*rad;
  G4double sinn = std::sqrt((1.0-cosn)*(1.0+cosn));
 
  G4ThreeVector direction1(sinn*std::cos(phin), sinn*std::sin(phin), cosn);
  direction1 = rm * direction1;
  G4DynamicParticle* daughterparticle1 
    = new G4DynamicParticle( G4MT_daughters[1], direction1*eNu);
  products->PushProducts(daughterparticle1);
 
  // daughter 2 (proton) at REST
  G4double eP;     // Eproton
  eP = parentmass-eNu-(x+dm)-daughtermass[2];
  G4double pPx = -eNu*sinn;
  G4double pPz = -p-eNu*cosn;
  G4double pP  = std::sqrt(eP*(eP+2.*daughtermass[2]));
  G4ThreeVector direction2(pPx/pP*std::cos(phin),
                           pPx/pP*std::sin(phin), pPz/pP);
  direction2 = rm * direction2;
  G4DynamicParticle* daughterparticle2 
    = new G4DynamicParticle( G4MT_daughters[2], direction2*pP);
  products->PushProducts(daughterparticle2);
 
  // output message
#ifdef G4VERBOSE
  if (GetVerboseLevel()>1)
  {
    G4cout << "G4NeutronBetaDecayChannel::DecayIt ";
    G4cout << "  create decay products in rest frame " <<G4endl;
    products->DumpInfo();
  }
#endif
  return products;
}