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25 //
26 //
27 /// \file PrimaryGeneratorAction.cc
28 /// \brief Implementation of the PrimaryGeneratorAction class
29
30 #include "PrimaryGeneratorAction.hh"
31
32 #include "G4Event.hh"
33 #include "G4ParticleGun.hh"
34 #include "G4PhysicalConstants.hh"
35 #include "G4SystemOfUnits.hh"
36 #include "Randomize.hh"
37
38 #include <fstream>
39
40 PrimaryGeneratorAction::PrimaryGeneratorAction(DetectorConstruction* detector)
41 : G4VUserPrimaryGeneratorAction(), fDetector(detector)
42 {
43 fpParticleGun = std::make_unique<G4ParticleGun>();
44 fpParticleGun->SetParticleEnergy(-1); // default value - can be overridden in the macro file
45 }
46
47 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
48
49 void PrimaryGeneratorAction::GeneratePrimaries(G4Event* anEvent)
50 {
51 // user can set the energy in the macro file
52 G4double energy = fpParticleGun->GetParticleEnergy();
53
54 // only first check is important as only user can set energy to -1,
55 // hopefully...
56 if (energy == -1) { // if energy is larger than zero, then the beam is
57 // mono-energetic if the energy is set to zero, then the
58 // energy is randomized, based on spectrum file
59 fMonoEnergetic = false;
60 }
61
62 if (!fMonoEnergetic) {
63 energy = GenerateParticleEnergy();
64 }
65
66 fpParticleGun->SetParticleEnergy(energy);
67 fpParticleGun->SetParticlePosition(GenerateParticlePosition()); // point of emission
68 fpParticleGun->SetParticleMomentumDirection(
69 GenerateParticleDirection()); // direction of emission
70
71 fpParticleGun->GeneratePrimaryVertex(anEvent); // sending the particle
72 }
73
74 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
75
76 G4double PrimaryGeneratorAction::GenerateParticleEnergy()
77 {
78 if (fEnergySpectrum_length == 0) { // reading the spectrum file if not loaded yet
79 std::ifstream fin(fEnergySpectrumFilename);
80 G4String len, gain, offset, counts;
81 fin >> len >> gain >> offset;
82 fEnergySpectrum_length = std::stoi(len);
83 fEnergySpectrum_gain = std::stod(gain);
84 fEnergySpectrum_offset = std::stod(offset);
85
86 fEnergySpectrum_counts.resize(fEnergySpectrum_length);
87 for (G4int i = 0; i < fEnergySpectrum_length; i++) {
88 fin >> counts;
89 fEnergySpectrum_counts[i] = std::stoi(counts);
90 }
91 }
92
93 auto max_en_counter = fEnergySpectrum_counts[fEnergySpectrum_length - 1] - 1;
94 auto rand_count = 1 + G4int(G4UniformRand() * max_en_counter);
95
96 // primitive search for lowest en_id that gives higher count value than
97 // rand_count:
98 G4int en_id = 0;
99 for (; rand_count > fEnergySpectrum_counts[en_id]; en_id++)
100 ;
101
102 G4int left = fEnergySpectrum_counts[en_id - 1];
103 G4int right = fEnergySpectrum_counts[en_id];
104
105 G4double en_left = (en_id - 1) * fEnergySpectrum_gain + fEnergySpectrum_offset;
106 G4double en_right = en_id * fEnergySpectrum_gain + fEnergySpectrum_offset;
107
108 // linear interpolation:
109 G4double slope = (en_right - en_left) / (right - left);
110 return (en_left + slope * (rand_count - left)) * MeV;
111 }
112
113 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
114
115 G4ThreeVector PrimaryGeneratorAction::GenerateParticlePosition()
116 {
117 // the source is an infinitely thin disk of radius r
118 G4double r = std::sqrt(G4UniformRand()) * fDetector->GetCollDiameter() / 2.;
119 G4double phi = G4UniformRand() * twopi;
120
121 G4double x = fDetector->GetCollExitPosistion() - fDetector->GetCollLength();
122 G4double y = r * std::cos(phi);
123 G4double z = r * std::sin(phi);
124
125 return {x, y, z};
126 }
127
128 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
129
130 G4ThreeVector PrimaryGeneratorAction::GenerateParticleDirection()
131 {
132 G4double phi, theta;
133 G4double px, py, pz;
134
135 phi = G4UniformRand() * twopi;
136
137 // For convenience theta is measured along the beam axis, which is x-axis.
138 // To reduce the number of events, when the projectile hits the collimator,
139 // only forward angles in the range [0, max_theta] are considered.
140 // If theta is larger, then the projectile will hit the collimator anyway.
141 // Even with this restriction only 1 in 4 projectiles pass through the
142 // collimator.
143 G4double cos_max_theta =
144 std::cos(std::atan(fDetector->GetCollDiameter() / fDetector->GetCollLength()));
145 theta = std::acos(cos_max_theta + G4UniformRand() * (1 - cos_max_theta));
146
147 px = std::cos(theta);
148 py = std::sin(theta) * std::sin(phi);
149 pz = std::sin(theta) * std::cos(phi);
150
151 return {px, py, pz};
152 }
153 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
154