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G4Generator2BS.cc
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25 //
26 //
27 // -------------------------------------------------------------------
28 //
29 // GEANT4 Class file
30 //
31 //
32 // File name: G4Generator2BS
33 //
34 // Author: Andreia Trindade (andreia@lip.pt)
35 // Pedro Rodrigues (psilva@lip.pt)
36 // Luis Peralta (luis@lip.pt)
37 //
38 // Creation date: 2 June 2003
39 //
40 // Modifications:
41 // 02 Jun 2003 First implementation acording with new design
42 // 05 Nov 2003 MGP Fixed std namespace
43 // 17 Nov 2003 MGP Fixed compilation problem on Windows
44 // 12 Oct 2010 V.Ivanchenko Moved RejectionFunction inline, use G4Pow to speadup
45 // 09 May 2011 L.Pandola Initialize private members, to avoid Coverity warning
46 //
47 // Class Description:
48 //
49 // Concrete base class for Bremsstrahlung Angular Distribution Generation
50 // 2BS Distribution
51 //
52 // Class Description: End
53 //
54 // -------------------------------------------------------------------
55 //
56 
57 #include "G4Generator2BS.hh"
58 #include "Randomize.hh"
59 #include "G4PhysicalConstants.hh"
60 #include "G4SystemOfUnits.hh"
61 #include "G4Pow.hh"
62 
63 G4Generator2BS::G4Generator2BS(const G4String&)
64  : G4VEmAngularDistribution("AngularGen2BS"),fz(1),ratio(1),
65  ratio1(1),ratio2(1),delta(0)
66 {
67  g4pow = G4Pow::GetInstance();
68  nwarn = 0;
69 }
70 
71 G4Generator2BS::~G4Generator2BS()
72 {}
73 
74 G4ThreeVector& G4Generator2BS::SampleDirection(const G4DynamicParticle* dp,
75  G4double final_energy,
76  G4int Z,
77  const G4Material*)
78 {
79 
80  // Adapted from "Improved bremsstrahlung photon angular sampling in the EGS4 code system"
81  // by Alex F. Bielajew, Rahde Mohan anc Chen-Shou Chui, PIRS-0203
82  // Ionizing Radiation Standards
83  // Institute for National Measurement Standards
84  // National Research Council of Canada
85  // Departement of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York
86 
87  G4double energy = dp->GetTotalEnergy();
88  ratio = final_energy/energy;
89  ratio1 = (1 + ratio)*(1 + ratio);
90  ratio2 = 1 + ratio*ratio;
91 
92  G4double gamma = energy/electron_mass_c2;
93  G4double beta = std::sqrt((gamma - 1)*(gamma + 1))/gamma;
94 
95  // VI speadup
96  fz = 0.00008116224*g4pow->Z13(Z)*g4pow->Z13(Z+1);
97 
98  // majoranta
99  G4double ymax = 2*beta*(1 + beta)*gamma*gamma;
100  G4double gMax = RejectionFunction(0.0);
101  gMax = std::max(gMax,RejectionFunction(ymax));
102 
103  G4double y, gfun;
104 
105  do{
106  G4double q = G4UniformRand();
107  y = q*ymax/(1 + ymax*(1 - q));
108  gfun = RejectionFunction(y);
109 
110  // violation point
111  if(gfun > gMax && nwarn >= 20) {
112  ++nwarn;
113  G4cout << "### WARNING in G4Generator2BS: Etot(MeV)= " << energy/MeV
114  << " Egamma(MeV)" << (energy - final_energy)/MeV
115  << " gMax= " << gMax << " < " << gfun
116  << " results are not reliable!"
117  << G4endl;
118  if(20 == nwarn) {
119  G4cout << " WARNING in G4Generator2BS is closed" << G4endl;
120  }
121  }
122 
123  } while(G4UniformRand()*gMax > gfun || y > ymax);
124 
125 
126  G4double cost = 1 - 2*y/ymax;
127  G4double sint = std::sqrt((1 - cost)*(1 + cost));
128  G4double phi = twopi*G4UniformRand();
129 
130  fLocalDirection.set(sint*std::cos(phi), sint*std::sin(phi),cost);
131  fLocalDirection.rotateUz(dp->GetMomentumDirection());
132 
133  return fLocalDirection;
134 }
135 
136 void G4Generator2BS::PrintGeneratorInformation() const
137 {
138  G4cout << "\n" << G4endl;
139  G4cout << "Bremsstrahlung Angular Generator is 2BS Generator "
140  << "from 2BS Koch & Motz distribution (Rev Mod Phys 31(4), 920 (1959))" << G4endl;
141  G4cout << "Sampling algorithm adapted from PIRS-0203" << G4endl;
142  G4cout << "\n" << G4endl;
143 }
144