G4NeutronBetaDecayChannel.cc

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// G4NeutronBetaDecayChannel class implementation
//
// Author: H.Kurashige, 18 September 2001
// --------------------------------------------------------------------
 
#include "G4NeutronBetaDecayChannel.hh"
 
#include "G4DecayProducts.hh"
#include "G4LorentzRotation.hh"
#include "G4LorentzVector.hh"
#include "G4ParticleDefinition.hh"
#include "G4PhysicalConstants.hh"
#include "G4RotationMatrix.hh"
#include "G4SystemOfUnits.hh"
#include "G4VDecayChannel.hh"
#include "Randomize.hh"
 
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(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;
  auto parentparticle = new G4DynamicParticle(G4MT_parent, dummy, 0.0);
 
  // create G4Decayproducts
  auto 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;
  auto 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;
  auto 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;
  auto 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;
}