Gabriele Cosmo
205 lines
8.5 KiB
C++
205 lines
8.5 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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////////////////////////////////////////////////////////////////////////////////
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// //
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// File: G4BetaPlusDecay.cc //
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// Author: D.H. Wright (SLAC) //
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// Date: 14 November 2014 //
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// //
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////////////////////////////////////////////////////////////////////////////////
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#include "G4BetaPlusDecay.hh"
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#include "G4BetaDecayCorrections.hh"
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#include "G4IonTable.hh"
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#include "G4ThreeVector.hh"
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#include "G4DynamicParticle.hh"
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#include "G4DecayProducts.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4SystemOfUnits.hh"
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#include <iostream>
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#include <iomanip>
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G4BetaPlusDecay::G4BetaPlusDecay(const G4ParticleDefinition* theParentNucleus,
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const G4double& branch, const G4double& e0,
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const G4double& excitationE,
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const G4Ions::G4FloatLevelBase& flb,
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const G4BetaDecayType& betaType)
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: G4NuclearDecay("beta+ decay", BetaPlus, excitationE, flb),
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endpointEnergy(e0 - 2.*CLHEP::electron_mass_c2)
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{
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SetParent(theParentNucleus); // Store name of parent nucleus, delete G4MT_parent
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SetBR(branch);
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SetNumberOfDaughters(3);
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G4IonTable* theIonTable =
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(G4IonTable*)(G4ParticleTable::GetParticleTable()->GetIonTable());
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G4int daughterZ = theParentNucleus->GetAtomicNumber() - 1;
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G4int daughterA = theParentNucleus->GetAtomicMass();
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SetDaughter(0, theIonTable->GetIon(daughterZ, daughterA, excitationE, flb) );
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SetUpBetaSpectrumSampler(daughterZ, daughterA, betaType);
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SetDaughter(1, "e+");
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SetDaughter(2, "nu_e");
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}
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G4BetaPlusDecay::~G4BetaPlusDecay()
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{
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delete spectrumSampler;
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}
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G4DecayProducts* G4BetaPlusDecay::DecayIt(G4double)
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{
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// Fill G4MT_parent with theParentNucleus (stored by SetParent in ctor)
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CheckAndFillParent();
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// Fill G4MT_daughters with e-, nu and residual nucleus (stored by SetDaughter)
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CheckAndFillDaughters();
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G4double parentMass = G4MT_parent->GetPDGMass();
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G4double eMass = G4MT_daughters[1]->GetPDGMass();
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G4double nucleusMass = G4MT_daughters[0]->GetPDGMass();
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// Set up final state
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// parentParticle is set at rest here because boost with correct momentum
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// is done later
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G4DynamicParticle parentParticle(G4MT_parent, G4ThreeVector(0,0,0), 0.0);
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G4DecayProducts* products = new G4DecayProducts(parentParticle);
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if (spectrumSampler) {
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// Generate positron isotropic in angle, with energy from stored spectrum
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G4double eKE = endpointEnergy*spectrumSampler->shoot(G4Random::getTheEngine() );
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G4double eMomentum = std::sqrt(eKE*(eKE + 2.*eMass) );
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G4double cosTheta = 2.*G4UniformRand() - 1.0;
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G4double sinTheta = std::sqrt(1.0 - cosTheta*cosTheta);
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G4double phi = twopi*G4UniformRand()*rad;
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G4double sinPhi = std::sin(phi);
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G4double cosPhi = std::cos(phi);
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G4ParticleMomentum eDirection(sinTheta*cosPhi, sinTheta*sinPhi, cosTheta);
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G4DynamicParticle* dynamicPositron
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= new G4DynamicParticle(G4MT_daughters[1], eDirection*eMomentum);
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products->PushProducts(dynamicPositron);
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// Generate neutrino with angle relative to positron, and energy from
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// energy-momentum conservation using endpoint energy of reaction
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G4double cosThetaENu = 2.*G4UniformRand() - 1.;
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G4double eTE = eMass + eKE;
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G4double nuEnergy = ((endpointEnergy - eKE)*(parentMass + nucleusMass - eTE)
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- eMomentum*eMomentum)/(parentMass - eTE + eMomentum*cosThetaENu)/2.;
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G4double sinThetaENu = std::sqrt(1.0 - cosThetaENu*cosThetaENu);
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phi = twopi*G4UniformRand()*rad;
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G4double sinPhiNu = std::sin(phi);
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G4double cosPhiNu = std::cos(phi);
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G4ParticleMomentum nuDirection;
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nuDirection.setX(sinThetaENu*cosPhiNu*cosTheta*cosPhi -
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sinThetaENu*sinPhiNu*sinPhi + cosThetaENu*sinTheta*cosPhi);
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nuDirection.setY(sinThetaENu*cosPhiNu*cosTheta*sinPhi +
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sinThetaENu*sinPhiNu*cosPhi + cosThetaENu*sinTheta*sinPhi);
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nuDirection.setZ(-sinThetaENu*cosPhiNu*sinTheta + cosThetaENu*cosTheta);
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G4DynamicParticle* dynamicNeutrino
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= new G4DynamicParticle(G4MT_daughters[2], nuDirection*nuEnergy);
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products->PushProducts(dynamicNeutrino);
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// Generate daughter nucleus from sum of positron and neutrino 4-vectors:
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// p_D = - p_e - p_nu
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G4DynamicParticle* dynamicDaughter =
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new G4DynamicParticle(G4MT_daughters[0],
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-eDirection*eMomentum - nuDirection*nuEnergy);
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products->PushProducts(dynamicDaughter);
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} else {
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// positron energy below threshold -> no decay
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G4DynamicParticle* noDecay =
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new G4DynamicParticle(G4MT_parent, G4ThreeVector(0,0,0), 0.0);
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products->PushProducts(noDecay);
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}
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// Check energy conservation against endpoint value, not nuclear masses
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/*
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G4int nProd = products->entries();
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G4DynamicParticle* temp = 0;
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G4double Esum = 0.0;
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for (G4int i = 0; i < nProd; i++) {
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temp = products->operator[](i);
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Esum += temp->GetKineticEnergy();
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}
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G4double eCons = (endpointEnergy - Esum)/keV;
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if (eCons > 0.001) G4cout << " Beta+ check: eCons (keV) = " << eCons << G4endl;
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*/
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return products;
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}
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void
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G4BetaPlusDecay::SetUpBetaSpectrumSampler(const G4int& daughterZ,
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const G4int& daughterA,
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const G4BetaDecayType& betaType)
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{
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G4double e0 = endpointEnergy/CLHEP::electron_mass_c2;
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G4BetaDecayCorrections corrections(-daughterZ, daughterA);
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spectrumSampler = 0;
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// Check for cases in which Q < 2Me (e.g. z67.a162)
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if (e0 > 0.) {
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// Array to store spectrum pdf
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G4int npti = 100;
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G4double* pdf = new G4double[npti];
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G4double e; // Total positron energy in units of electron mass
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G4double p; // Positron momentum in units of electron mass
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G4double f; // Spectral shap function
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for (G4int ptn = 0; ptn < npti; ptn++) {
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// Calculate simple phase space
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e = 1. + e0*(ptn + 0.5)/G4double(npti);
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p = std::sqrt(e*e - 1.);
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f = p*e*(e0 - e + 1.)*(e0 - e + 1.);
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// Apply Fermi factor to get allowed shape
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f *= corrections.FermiFunction(e);
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// Apply shape factor for forbidden transitions
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f *= corrections.ShapeFactor(betaType, p, e0-e+1.);
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pdf[ptn] = f;
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}
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spectrumSampler = new G4RandGeneral(pdf, npti);
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delete[] pdf;
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}
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}
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void G4BetaPlusDecay::DumpNuclearInfo()
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{
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G4cout << " G4BetaPlusDecay for parent nucleus " << GetParentName() << G4endl;
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G4cout << " decays to " << GetDaughterName(0) << " , " << GetDaughterName(1)
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<< " and " << GetDaughterName(2) << " with branching ratio " << GetBR()
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<< "% and endpoint energy " << endpointEnergy/keV << " keV " << G4endl;
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}
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