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25 //
26 //
27 // GEANT4 Class file
28 //
29 //
30 // File name: G4AllisonPositronAtRestModel
31 //
32 // Author: Vladimir Ivanchenko
33 //
34 // Creation date: 14 May 2024
35 //
36 // -------------------------------------------
37 //
38
39 #include "G4AllisonPositronAtRestModel.hh"
40 #include "G4DynamicParticle.hh"
41 #include "G4Material.hh"
42 #include "Randomize.hh"
43 #include "G4Gamma.hh"
44 #include "G4RandomDirection.hh"
45 #include "G4ThreeVector.hh"
46 #include "G4PhysicalConstants.hh"
47 #include "G4SystemOfUnits.hh"
48
49 //....oooOO0OOooo........oooOO0OOooo........oo
50
51 G4AllisonPositronAtRestModel::G4AllisonPositro
52 : G4VPositronAtRestModel("Allison")
53 {}
54
55 //....oooOO0OOooo........oooOO0OOooo........oo
56
57 void G4AllisonPositronAtRestModel::SampleSecon
58 std::vector<G4DynamicParticle*>&
59 G4double&, const G4Material* mate
60 {
61 const G4double eGamma = CLHEP::electron_mass
62
63 // In rest frame of positronium gammas are b
64 const G4ThreeVector& dir1 = G4RandomDirectio
65 const G4ThreeVector& dir2 = -dir1;
66 auto aGamma1 = new G4DynamicParticle(G4Gamma
67 auto aGamma2 = new G4DynamicParticle(G4Gamma
68
69 // In rest frame the gammas are polarised pe
70 // Pryce and Ward, Nature No 4065 (1947) p.4
71 // Snyder et al, Physical Review 73 (1948) p
72 G4ThreeVector pol1 = (G4RandomDirection().cr
73 G4ThreeVector pol2 = (pol1.cross(dir2)).unit
74
75 // A positron in matter slows down and combi
76 // make a neutral atom called positronium, a
77 // atom. I expect that when the energy of th
78 // less than the binding energy of positroni
79 // energetically favourable for an electron
80 // nearby atom or molecule to transfer and b
81 // ionic bond, leaving behind a mildly ionis
82 // would expect the positronium to come away
83 // few eV on average. In its para (spin 0) s
84 // photons, which in the rest frame of the p
85 // (back-to-back) due to momentum conservati
86 // positronium, photons will be not quite ba
87
88 // The positroniuim acquires an energy of or
89 // doesn't have time to thermalise. Neverthe
90 // energy distribution by a Maxwell-Boltzman
91 // of a more familiar concept of temperature
92 // of energy of translational motion, <KE>=3
93 // has a distribution exp(-mv^2/2kT), which
94 // and variance kT/m=2<KE>/3m, where m is th
95
96 const G4double meanEnergyPerIonPair = materi
97 const G4double& meanKE = meanEnergyPerIonPai
98
99 if (meanKE > 0.) { // Positronium has motio
100 // Mass of positronium
101 const G4double mass = 2.*CLHEP::electron_m
102 // Mean <KE>=3kT/2, as described above
103 // const G4double T = 2.*meanKE/(3.*k_Bolt
104 // Component velocities: Gaussian, varianc
105 const G4double sigmav = std::sqrt(2.*meanK
106 // This is in units where c=1
107 const G4double vx = G4RandGauss::shoot(0.,
108 const G4double vy = G4RandGauss::shoot(0.,
109 const G4double vz = G4RandGauss::shoot(0.,
110 const G4ThreeVector v(vx,vy,vz); // In un
111 const G4ThreeVector& beta = v; // so be
112 aGamma1->Set4Momentum(aGamma1->Get4Momentu
113 aGamma2->Set4Momentum(aGamma2->Get4Momentu
114
115 // Rotate polarisation vectors
116 const G4ThreeVector& newDir1 = aGamma1->Ge
117 const G4ThreeVector& newDir2 = aGamma2->Ge
118 const G4ThreeVector& axis1 = dir1.cross(ne
119 const G4ThreeVector& axis2 = dir2.cross(ne
120 const G4double& angle1 = std::acos(dir1*ne
121 const G4double& angle2 = std::acos(dir2*ne
122 pol1.rotate(axis1, angle1);
123 pol2.rotate(axis2, angle2);
124 }
125
126 // use constructors optimal for massless par
127 aGamma1->SetPolarization(pol1);
128 aGamma2->SetPolarization(pol2);
129
130 secParticles.push_back(aGamma1);
131 secParticles.push_back(aGamma2);
132 }
133
134 //....oooOO0OOooo........oooOO0OOooo........oo
135
136 void G4AllisonPositronAtRestModel::PrintGenera
137 {
138 G4cout << "\n" << G4endl;
139 G4cout << "Allison AtRest positron 2-gamma a
140 G4cout << "Takes into account positronium mo
141 }
142
143 //....oooOO0OOooo........oooOO0OOooo........oo
144