Gabriele Cosmo
265 lines
10 KiB
C++
265 lines
10 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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/// \file processes/phonon/src/G4PhononDownconversion.cc
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/// \brief Implementation of the G4PhononDownconversion class
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//
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//
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// 20131111 Add verbose output for MFP calculation
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// 20131115 Initialize data buffers in ctor
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#include "G4PhononDownconversion.hh"
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#include "G4LatticePhysical.hh"
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#include "G4PhononLong.hh"
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#include "G4PhononPolarization.hh"
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#include "G4PhononTrackMap.hh"
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#include "G4PhononTransFast.hh"
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#include "G4PhononTransSlow.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4RandomDirection.hh"
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#include "G4Step.hh"
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#include "G4SystemOfUnits.hh"
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#include "G4VParticleChange.hh"
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#include "Randomize.hh"
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#include <cmath>
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G4PhononDownconversion::G4PhononDownconversion(const G4String& aName)
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: G4VPhononProcess(aName), fBeta(0.), fGamma(0.), fLambda(0.), fMu(0.) {;}
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G4PhononDownconversion::~G4PhononDownconversion() {;}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4PhononDownconversion::GetMeanFreePath(const G4Track& aTrack,
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G4double /*previousStepSize*/,
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G4ForceCondition* condition) {
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//Determines mean free path for longitudinal phonons to split
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G4double A = theLattice->GetAnhDecConstant();
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G4double Eoverh = aTrack.GetKineticEnergy()/h_Planck;
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//Calculate mean free path for anh. decay
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G4double mfp = aTrack.GetVelocity()/(Eoverh*Eoverh*Eoverh*Eoverh*Eoverh*A);
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if (verboseLevel > 1)
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G4cout << "G4PhononDownconversion::GetMeanFreePath = " << mfp << G4endl;
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*condition = NotForced;
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return mfp;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4VParticleChange* G4PhononDownconversion::PostStepDoIt( const G4Track& aTrack,
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const G4Step&) {
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aParticleChange.Initialize(aTrack);
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//Obtain dynamical constants from this volume's lattice
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fBeta=theLattice->GetBeta();
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fGamma=theLattice->GetGamma();
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fLambda=theLattice->GetLambda();
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fMu=theLattice->GetMu();
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//Destroy the parent phonon and create the daughter phonons.
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//74% chance that daughter phonons are both transverse
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//26% Transverse and Longitudinal
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if (G4UniformRand()>0.740) MakeLTSecondaries(aTrack);
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else MakeTTSecondaries(aTrack);
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aParticleChange.ProposeEnergy(0.);
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aParticleChange.ProposeTrackStatus(fStopAndKill);
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return &aParticleChange;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4bool G4PhononDownconversion::IsApplicable(const G4ParticleDefinition& aPD) {
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//Only L-phonons decay
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return (&aPD==G4PhononLong::PhononDefinition());
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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//probability density of energy distribution of L'-phonon in L->L'+T process
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G4double G4PhononDownconversion::GetLTDecayProb(G4double d, G4double x) const {
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//d=delta= ratio of group velocities vl/vt and x is the fraction of energy in the longitudinal mode, i.e. x=EL'/EL
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return (1/(x*x))*(1-x*x)*(1-x*x)*((1+x)*(1+x)-d*d*((1-x)*(1-x)))*(1+x*x-d*d*(1-x)*(1-x))*(1+x*x-d*d*(1-x)*(1-x));
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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//probability density of energy distribution of T-phonon in L->T+T process
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G4double G4PhononDownconversion::GetTTDecayProb(G4double d, G4double x) const {
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//dynamic constants from Tamura, PRL31, 1985
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G4double A = 0.5*(1-d*d)*(fBeta+fLambda+(1+d*d)*(fGamma+fMu));
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G4double B = fBeta+fLambda+2*d*d*(fGamma+fMu);
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G4double C = fBeta + fLambda + 2*(fGamma+fMu);
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G4double D = (1-d*d)*(2*fBeta+4*fGamma+fLambda+3*fMu);
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return (A+B*d*x-B*x*x)*(A+B*d*x-B*x*x)+(C*x*(d-x)-D/(d-x)*(x-d-(1-d*d)/(4*x)))*(C*x*(d-x)-D/(d-x)*(x-d-(1-d*d)/(4*x)));
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4PhononDownconversion::MakeLDeviation(G4double d, G4double x) const {
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//change in L'-phonon propagation direction after decay
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return std::acos((1+(x*x)-((d*d)*(1-x)*(1-x)))/(2*x));
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4PhononDownconversion::MakeTDeviation(G4double d, G4double x) const {
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//change in T-phonon propagation direction after decay (L->L+T process)
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return std::acos((1-x*x+d*d*(1-x)*(1-x))/(2*d*(1-x)));
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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G4double G4PhononDownconversion::MakeTTDeviation(G4double d, G4double x) const {
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//change in T-phonon propagation direction after decay (L->T+T process)
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return std::acos((1-d*d*(1-x)*(1-x)+d*d*x*x)/(2*d*x));
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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//Generate daughter phonons from L->T+T process
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void G4PhononDownconversion::MakeTTSecondaries(const G4Track& aTrack) {
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//d is the velocity ratio vL/vT
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G4double d=1.6338;
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G4double upperBound=(1+(1/d))/2;
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G4double lowerBound=(1-(1/d))/2;
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//Use MC method to generate point from distribution:
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//if a random point on the energy-probability plane is
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//smaller that the curve of the probability density,
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//then accept that point.
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//x=fraction of parent phonon energy in first T phonon
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G4double x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
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G4double p = 1.5*G4UniformRand();
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while(p >= GetTTDecayProb(d, x*d)) {
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x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
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p = 1.5*G4UniformRand();
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}
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//using energy fraction x to calculate daughter phonon directions
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G4double theta1=MakeTTDeviation(d, x);
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G4double theta2=MakeTTDeviation(d, 1-x);
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G4ThreeVector dir1=trackKmap->GetK(aTrack);
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G4ThreeVector dir2=dir1;
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// FIXME: These extra randoms change timing and causting outputs of example!
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G4ThreeVector ran = G4RandomDirection(); // FIXME: Drop this line
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G4double ph=G4UniformRand()*twopi;
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dir1 = dir1.rotate(dir1.orthogonal(),theta1).rotate(dir1, ph);
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dir2 = dir2.rotate(dir2.orthogonal(),-theta2).rotate(dir2,ph);
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G4double E=aTrack.GetKineticEnergy();
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G4double Esec1 = x*E, Esec2 = E-Esec1;
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// Make FT or ST phonon (0. means no longitudinal)
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G4int polarization1 = ChoosePolarization(0., theLattice->GetSTDOS(),
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theLattice->GetFTDOS());
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// Make FT or ST phonon (0. means no longitudinal)
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G4int polarization2 = ChoosePolarization(0., theLattice->GetSTDOS(),
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theLattice->GetFTDOS());
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// Construct the secondaries and set their wavevectors
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G4Track* sec1 = CreateSecondary(polarization1, dir1, Esec1);
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G4Track* sec2 = CreateSecondary(polarization2, dir2, Esec2);
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aParticleChange.SetNumberOfSecondaries(2);
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aParticleChange.AddSecondary(sec1);
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aParticleChange.AddSecondary(sec2);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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//Generate daughter phonons from L->L'+T process
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void G4PhononDownconversion::MakeLTSecondaries(const G4Track& aTrack) {
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//d is the velocity ratio vL/v
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G4double d=1.6338;
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G4double upperBound=1;
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G4double lowerBound=(d-1)/(d+1);
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//Use MC method to generate point from distribution:
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//if a random point on the energy-probability plane is
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//smaller that the curve of the probability density,
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//then accept that point.
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//x=fraction of parent phonon energy in L phonon
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G4double x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
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G4double p = 4.0*G4UniformRand();
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while(p >= GetLTDecayProb(d, x)) {
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x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
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p = 4.0*G4UniformRand(); //4.0 is about the max in the PDF
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}
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//using energy fraction x to calculate daughter phonon directions
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G4double thetaL=MakeLDeviation(d, x);
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G4double thetaT=MakeTDeviation(d, x); // FIXME: Should be 1-x?
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G4ThreeVector dir1=trackKmap->GetK(aTrack);
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G4ThreeVector dir2=dir1;
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G4double ph=G4UniformRand()*twopi;
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dir1 = dir1.rotate(dir1.orthogonal(),thetaL).rotate(dir1, ph);
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dir2 = dir2.rotate(dir2.orthogonal(),-thetaT).rotate(dir2,ph);
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G4double E=aTrack.GetKineticEnergy();
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G4double Esec1 = x*E, Esec2 = E-Esec1;
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// First secondary is longitudnal
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G4int polarization1 = G4PhononPolarization::Long;
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// Make FT or ST phonon (0. means no longitudinal)
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G4int polarization2 = ChoosePolarization(0., theLattice->GetSTDOS(),
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theLattice->GetFTDOS());
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// Construct the secondaries and set their wavevectors
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G4Track* sec1 = CreateSecondary(polarization1, dir1, Esec1);
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G4Track* sec2 = CreateSecondary(polarization2, dir2, Esec2);
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aParticleChange.SetNumberOfSecondaries(2);
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aParticleChange.AddSecondary(sec1);
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aParticleChange.AddSecondary(sec2);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
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