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25 //
26 /// \file processes/phonon/src/G4PhononDownconversion.cc
27 /// \brief Implementation of the G4PhononDownconversion class
28 //
29 //
30 // 20131111 Add verbose output for MFP calculation
31 // 20131115 Initialize data buffers in ctor
32
33 #include "G4PhononDownconversion.hh"
34 #include "G4LatticePhysical.hh"
35 #include "G4PhononLong.hh"
36 #include "G4PhononPolarization.hh"
37 #include "G4PhononTrackMap.hh"
38 #include "G4PhononTransFast.hh"
39 #include "G4PhononTransSlow.hh"
40 #include "G4PhysicalConstants.hh"
41 #include "G4RandomDirection.hh"
42 #include "G4Step.hh"
43 #include "G4SystemOfUnits.hh"
44 #include "G4VParticleChange.hh"
45 #include "Randomize.hh"
46 #include <cmath>
47
48
49
50 G4PhononDownconversion::G4PhononDownconversion(const G4String& aName)
51 : G4VPhononProcess(aName), fBeta(0.), fGamma(0.), fLambda(0.), fMu(0.) {;}
52
53 G4PhononDownconversion::~G4PhononDownconversion() {;}
54
55 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
56
57 G4double G4PhononDownconversion::GetMeanFreePath(const G4Track& aTrack,
58 G4double /*previousStepSize*/,
59 G4ForceCondition* condition) {
60 //Determines mean free path for longitudinal phonons to split
61 G4double A = theLattice->GetAnhDecConstant();
62 G4double Eoverh = aTrack.GetKineticEnergy()/h_Planck;
63
64 //Calculate mean free path for anh. decay
65 G4double mfp = aTrack.GetVelocity()/(Eoverh*Eoverh*Eoverh*Eoverh*Eoverh*A);
66
67 if (verboseLevel > 1)
68 G4cout << "G4PhononDownconversion::GetMeanFreePath = " << mfp << G4endl;
69
70 *condition = NotForced;
71 return mfp;
72 }
73
74 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
75
76
77 G4VParticleChange* G4PhononDownconversion::PostStepDoIt( const G4Track& aTrack,
78 const G4Step&) {
79 aParticleChange.Initialize(aTrack);
80
81 //Obtain dynamical constants from this volume's lattice
82 fBeta=theLattice->GetBeta();
83 fGamma=theLattice->GetGamma();
84 fLambda=theLattice->GetLambda();
85 fMu=theLattice->GetMu();
86
87 //Destroy the parent phonon and create the daughter phonons.
88 //74% chance that daughter phonons are both transverse
89 //26% Transverse and Longitudinal
90 if (G4UniformRand()>0.740) MakeLTSecondaries(aTrack);
91 else MakeTTSecondaries(aTrack);
92
93 aParticleChange.ProposeEnergy(0.);
94 aParticleChange.ProposeTrackStatus(fStopAndKill);
95
96 return &aParticleChange;
97 }
98
99 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
100
101 G4bool G4PhononDownconversion::IsApplicable(const G4ParticleDefinition& aPD) {
102 //Only L-phonons decay
103 return (&aPD==G4PhononLong::PhononDefinition());
104 }
105
106 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
107
108 //probability density of energy distribution of L'-phonon in L->L'+T process
109
110 G4double G4PhononDownconversion::GetLTDecayProb(G4double d, G4double x) const {
111 //d=delta= ratio of group velocities vl/vt and x is the fraction of energy in the longitudinal mode, i.e. x=EL'/EL
112 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));
113 }
114
115 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
116
117 //probability density of energy distribution of T-phonon in L->T+T process
118 G4double G4PhononDownconversion::GetTTDecayProb(G4double d, G4double x) const {
119 //dynamic constants from Tamura, PRL31, 1985
120 G4double A = 0.5*(1-d*d)*(fBeta+fLambda+(1+d*d)*(fGamma+fMu));
121 G4double B = fBeta+fLambda+2*d*d*(fGamma+fMu);
122 G4double C = fBeta + fLambda + 2*(fGamma+fMu);
123 G4double D = (1-d*d)*(2*fBeta+4*fGamma+fLambda+3*fMu);
124
125 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)));
126 }
127
128 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
129
130
131 G4double G4PhononDownconversion::MakeLDeviation(G4double d, G4double x) const {
132 //change in L'-phonon propagation direction after decay
133
134 return std::acos((1+(x*x)-((d*d)*(1-x)*(1-x)))/(2*x));
135 }
136
137 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
138
139
140 G4double G4PhononDownconversion::MakeTDeviation(G4double d, G4double x) const {
141 //change in T-phonon propagation direction after decay (L->L+T process)
142
143 return std::acos((1-x*x+d*d*(1-x)*(1-x))/(2*d*(1-x)));
144 }
145
146 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
147
148
149 G4double G4PhononDownconversion::MakeTTDeviation(G4double d, G4double x) const {
150 //change in T-phonon propagation direction after decay (L->T+T process)
151
152 return std::acos((1-d*d*(1-x)*(1-x)+d*d*x*x)/(2*d*x));
153 }
154
155 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
156
157
158 //Generate daughter phonons from L->T+T process
159
160 void G4PhononDownconversion::MakeTTSecondaries(const G4Track& aTrack) {
161 //d is the velocity ratio vL/vT
162 G4double d=1.6338;
163 G4double upperBound=(1+(1/d))/2;
164 G4double lowerBound=(1-(1/d))/2;
165
166 //Use MC method to generate point from distribution:
167 //if a random point on the energy-probability plane is
168 //smaller that the curve of the probability density,
169 //then accept that point.
170 //x=fraction of parent phonon energy in first T phonon
171 G4double x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
172 G4double p = 1.5*G4UniformRand();
173 while(p >= GetTTDecayProb(d, x*d)) {
174 x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
175 p = 1.5*G4UniformRand();
176 }
177
178 //using energy fraction x to calculate daughter phonon directions
179 G4double theta1=MakeTTDeviation(d, x);
180 G4double theta2=MakeTTDeviation(d, 1-x);
181 G4ThreeVector dir1=trackKmap->GetK(aTrack);
182 G4ThreeVector dir2=dir1;
183
184 // FIXME: These extra randoms change timing and causting outputs of example!
185 G4ThreeVector ran = G4RandomDirection(); // FIXME: Drop this line
186
187 G4double ph=G4UniformRand()*twopi;
188 dir1 = dir1.rotate(dir1.orthogonal(),theta1).rotate(dir1, ph);
189 dir2 = dir2.rotate(dir2.orthogonal(),-theta2).rotate(dir2,ph);
190
191 G4double E=aTrack.GetKineticEnergy();
192 G4double Esec1 = x*E, Esec2 = E-Esec1;
193
194 // Make FT or ST phonon (0. means no longitudinal)
195 G4int polarization1 = ChoosePolarization(0., theLattice->GetSTDOS(),
196 theLattice->GetFTDOS());
197
198 // Make FT or ST phonon (0. means no longitudinal)
199 G4int polarization2 = ChoosePolarization(0., theLattice->GetSTDOS(),
200 theLattice->GetFTDOS());
201
202 // Construct the secondaries and set their wavevectors
203 G4Track* sec1 = CreateSecondary(polarization1, dir1, Esec1);
204 G4Track* sec2 = CreateSecondary(polarization2, dir2, Esec2);
205
206 aParticleChange.SetNumberOfSecondaries(2);
207 aParticleChange.AddSecondary(sec1);
208 aParticleChange.AddSecondary(sec2);
209 }
210
211 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
212
213
214 //Generate daughter phonons from L->L'+T process
215
216 void G4PhononDownconversion::MakeLTSecondaries(const G4Track& aTrack) {
217 //d is the velocity ratio vL/v
218 G4double d=1.6338;
219 G4double upperBound=1;
220 G4double lowerBound=(d-1)/(d+1);
221
222 //Use MC method to generate point from distribution:
223 //if a random point on the energy-probability plane is
224 //smaller that the curve of the probability density,
225 //then accept that point.
226 //x=fraction of parent phonon energy in L phonon
227 G4double x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
228 G4double p = 4.0*G4UniformRand();
229 while(p >= GetLTDecayProb(d, x)) {
230 x = G4UniformRand()*(upperBound-lowerBound) + lowerBound;
231 p = 4.0*G4UniformRand(); //4.0 is about the max in the PDF
232 }
233
234 //using energy fraction x to calculate daughter phonon directions
235 G4double thetaL=MakeLDeviation(d, x);
236 G4double thetaT=MakeTDeviation(d, x); // FIXME: Should be 1-x?
237 G4ThreeVector dir1=trackKmap->GetK(aTrack);
238 G4ThreeVector dir2=dir1;
239
240 G4double ph=G4UniformRand()*twopi;
241 dir1 = dir1.rotate(dir1.orthogonal(),thetaL).rotate(dir1, ph);
242 dir2 = dir2.rotate(dir2.orthogonal(),-thetaT).rotate(dir2,ph);
243
244 G4double E=aTrack.GetKineticEnergy();
245 G4double Esec1 = x*E, Esec2 = E-Esec1;
246
247 // First secondary is longitudnal
248 G4int polarization1 = G4PhononPolarization::Long;
249
250 // Make FT or ST phonon (0. means no longitudinal)
251 G4int polarization2 = ChoosePolarization(0., theLattice->GetSTDOS(),
252 theLattice->GetFTDOS());
253
254 // Construct the secondaries and set their wavevectors
255 G4Track* sec1 = CreateSecondary(polarization1, dir1, Esec1);
256 G4Track* sec2 = CreateSecondary(polarization2, dir2, Esec2);
257
258 aParticleChange.SetNumberOfSecondaries(2);
259 aParticleChange.AddSecondary(sec1);
260 aParticleChange.AddSecondary(sec2);
261 }
262
263 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
264
265