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25 //
26 //
27 // -------------------------------------------------------------------
28 //
29 // GEANT4 Class file
30 //
31 //
32 // File name: G4SauterGavrilaAngularDistribution
33 //
34 // Author: Vladimir Ivanchenko using Michel Maire algorithm
35 // developed for Geant3
36 //
37 // Creation date: 23 July 2012
38 //
39 // Modified:
40 // 04.05.2017 Marilena Bandieramonte implemented Penelope 2014 algorithm
41 // -------------------------------------------------------------------
42 //
43
44 #include "G4SauterGavrilaAngularDistribution.hh"
45 #include "G4PhysicalConstants.hh"
46 #include "Randomize.hh"
47
48 G4SauterGavrilaAngularDistribution::G4SauterGavrilaAngularDistribution()
49 : G4VEmAngularDistribution("SauterGavrila")
50 {}
51
52 G4SauterGavrilaAngularDistribution::~G4SauterGavrilaAngularDistribution()
53 = default;
54
55 G4ThreeVector& G4SauterGavrilaAngularDistribution::SampleDirection(
56 const G4DynamicParticle* dp, G4double, G4int, const G4Material*)
57 {
58 static const G4double emin = 1*CLHEP::eV;
59 static const G4double emax = 100*CLHEP::MeV;
60
61 G4double energy = std::max(dp->GetKineticEnergy(), emin);
62 if (energy > emax) {
63 fLocalDirection = dp->GetMomentumDirection();
64 } else {
65 // Initial algorithm according Penelope 2008 manual and
66 // F.Sauter Ann. Physik 9, 217(1931); 11, 454(1931).
67 // Modified according Penelope 2014 manual
68 G4double costheta = 0.0;
69
70 // 1) initialize energy-dependent variables
71 // Variable naming according to Eq. (2.24) of Penelope Manual
72 // (pag. 44)
73 G4double tau = energy/electron_mass_c2;
74 G4double gamma = 1.0 + tau;
75 G4double beta = std::sqrt(tau*(tau + 2.0))/gamma;
76
77 // ac corresponds to "A" of Eq. (2.31)
78 //
79 G4double ac = (1.0 - beta)/beta;
80 G4double a1 = 0.5*beta*gamma*tau*(gamma-2.0);
81 G4double a2 = ac + 2.0;
82 // gtmax = maximum of the rejection function according to Eq. (2.28),
83 // obtained for tsam=0
84 G4double gtmax = 2.0*(a1 + 1.0/ac);
85
86 G4double tsam = 0.0;
87 G4double gtr = 0.0;
88
89 //2) sampling. Eq. (2.31) of Penelope Manual
90 // tsam = 1-std::cos(theta)
91 // gtr = rejection function according to Eq. (2.28)
92 do{
93 G4double rand = G4UniformRand();
94 tsam = 2.0*ac * (2.0*rand + a2*std::sqrt(rand)) / (a2*a2 - 4.0*rand);
95 gtr = (2.0 - tsam) * (a1 + 1.0/(ac+tsam));
96 // Loop checking, 03-Aug-2015, Vladimir Ivanchenko
97 } while(G4UniformRand()*gtmax > gtr);
98
99 costheta = 1.0 - tsam;
100
101 G4double sint = std::sqrt(tsam*(2.0 - tsam));
102 G4double phi = CLHEP::twopi*G4UniformRand();
103
104 fLocalDirection.set(sint*std::cos(phi), sint*std::sin(phi), costheta);
105 fLocalDirection.rotateUz(dp->GetMomentumDirection());
106 }
107 return fLocalDirection;
108 }
109
110 void G4SauterGavrilaAngularDistribution::PrintGeneratorInformation() const
111 {
112 G4cout << "\n" << G4endl;
113 G4cout << "Non-polarized photoelectric effect angular generator." << G4endl;
114 G4cout << "The Sauter-Gavrila distribution for the K-shell is used."<<G4endl;
115 G4cout << "Originally developed by M.Maire for Geant3"
116 << G4endl;
117 }
118
119