1 | <!-- ******************************************************** --> |
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2 | <!-- --> |
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3 | <!-- [History] --> |
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4 | <!-- Changed by: Katsuya Amako, 4-Aug-1998 --> |
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5 | <!-- Changed by: Dennis Wright, 29-Nov-2001 --> |
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6 | <!-- Proof read by: Joe Chuma, 15-Jun-1999 --> |
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7 | <!-- Converted to DocBook: Katsuya Amako, Aug-2006 --> |
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8 | <!-- --> |
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9 | <!-- ******************************************************** --> |
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10 | |
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11 | |
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12 | <!-- ******************* Section (Level#1) ****************** --> |
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13 | <sect1 id="sect.HowToGenEvent"> |
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14 | <title> |
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15 | How to Generate a Primary Event |
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16 | </title> |
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17 | |
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18 | <!-- ******************* Section (Level#2) ****************** --> |
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19 | <sect2 id="sect.HowToGenEvent.GenPrimary"> |
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20 | <title> |
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21 | Generating Primary Events |
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22 | </title> |
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23 | |
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24 | <para> |
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25 | <emphasis>G4VuserPrimaryGeneratorAction</emphasis> is one of the mandatory |
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26 | classes available for deriving your own concrete class. In your |
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27 | concrete class, you have to specify how a primary event should be |
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28 | generated. Actual generation of primary particles will be done by |
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29 | concrete classes of <emphasis>G4VPrimaryGenerator</emphasis>, explained in the |
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30 | following sub-section. Your <emphasis>G4VUserPrimaryGeneratorAction</emphasis> |
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31 | concrete class just arranges the way primary particles are generated. |
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32 | |
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33 | <example id="programlist_HowToGenEvent_1"> |
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34 | <title> |
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35 | An example of a <emphasis>G4VUserPrimaryGeneratorAction</emphasis> |
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36 | concrete class using <emphasis>G4ParticleGun</emphasis>. |
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37 | For the usage of <emphasis>G4ParticleGun</emphasis> refer to the |
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38 | next subsection. |
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39 | </title> |
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40 | |
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41 | <programlisting> |
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42 | #ifndef ExN01PrimaryGeneratorAction_h |
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43 | #define ExN01PrimaryGeneratorAction_h 1 |
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44 | |
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45 | #include "G4VUserPrimaryGeneratorAction.hh" |
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46 | |
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47 | class G4ParticleGun; |
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48 | class G4Event; |
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49 | |
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50 | class ExN01PrimaryGeneratorAction : public G4VUserPrimaryGeneratorAction |
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51 | { |
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52 | public: |
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53 | ExN01PrimaryGeneratorAction(); |
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54 | ~ExN01PrimaryGeneratorAction(); |
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55 | |
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56 | public: |
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57 | void generatePrimaries(G4Event* anEvent); |
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58 | |
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59 | private: |
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60 | G4ParticleGun* particleGun; |
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61 | }; |
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62 | |
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63 | #endif |
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64 | |
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65 | #include "ExN01PrimaryGeneratorAction.hh" |
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66 | #include "G4Event.hh" |
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67 | #include "G4ParticleGun.hh" |
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68 | #include "G4ThreeVector.hh" |
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69 | #include "G4Geantino.hh" |
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70 | #include "globals.hh" |
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71 | |
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72 | ExN01PrimaryGeneratorAction::ExN01PrimaryGeneratorAction() |
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73 | { |
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74 | G4int n_particle = 1; |
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75 | particleGun = new G4ParticleGun(n_particle); |
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76 | |
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77 | particleGun->SetParticleDefinition(G4Geantino::GeantinoDefinition()); |
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78 | particleGun->SetParticleEnergy(1.0*GeV); |
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79 | particleGun->SetParticlePosition(G4ThreeVector(-2.0*m,0.0*m,0.0*m)); |
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80 | } |
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81 | |
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82 | ExN01PrimaryGeneratorAction::~ExN01PrimaryGeneratorAction() |
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83 | { |
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84 | delete particleGun; |
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85 | } |
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86 | |
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87 | void ExN01PrimaryGeneratorAction::generatePrimaries(G4Event* anEvent) |
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88 | { |
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89 | G4int i = anEvent->get_eventID() % 3; |
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90 | switch(i) |
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91 | { |
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92 | case 0: |
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93 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.0,0.0)); |
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94 | break; |
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95 | case 1: |
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96 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.1,0.0)); |
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97 | break; |
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98 | case 2: |
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99 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.0,0.1)); |
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100 | break; |
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101 | } |
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102 | |
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103 | particleGun->generatePrimaryVertex(anEvent); |
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104 | } |
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105 | </programlisting> |
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106 | </example> |
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107 | |
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108 | </para> |
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109 | |
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110 | |
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111 | <!-- ******************* Section (Level#3) ****************** --> |
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112 | <sect3 id="sect.HowToGenEvent.GenPrimary.SelectGenerator"> |
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113 | <title> |
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114 | Selection of the generator |
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115 | </title> |
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116 | |
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117 | <para> |
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118 | In the constructor of your <emphasis>G4VUserPrimaryGeneratorAction</emphasis>, |
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119 | you should instantiate the primary generator(s). If necessary, you |
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120 | need to set some initial conditions for the generator(s). |
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121 | </para> |
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122 | |
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123 | <para> |
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124 | In <xref linkend="programlist_HowToGenEvent_1" />, |
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125 | <emphasis>G4ParticleGun</emphasis> is constructed to |
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126 | use as the actual primary particle generator. Methods of |
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127 | <emphasis>G4ParticleGun</emphasis> are described in the following section. Please |
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128 | note that the primary generator object(s) you construct in your |
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129 | <emphasis>G4VUserPrimaryGeneratorAction</emphasis> concrete class must be deleted |
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130 | in your destructor. |
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131 | </para> |
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132 | |
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133 | </sect3> |
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134 | |
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135 | <!-- ******************* Section (Level#3) ****************** --> |
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136 | <sect3 id="sect.HowToGenEvent.GenPrimary.GenEvent"> |
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137 | <title> |
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138 | Generation of an event |
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139 | </title> |
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140 | |
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141 | <para> |
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142 | <emphasis>G4VUserPrimaryGeneratorAction</emphasis> has a pure virtual method |
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143 | named <literal>generatePrimaries()</literal>. This method is invoked at the |
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144 | beginning of each event. In this method, you have to invoke the |
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145 | <emphasis>G4VPrimaryGenerator</emphasis> concrete class you instantiated via the |
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146 | <literal>generatePrimaryVertex()</literal> method. |
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147 | </para> |
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148 | |
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149 | <para> |
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150 | You can invoke more than one generator and/or invoke one |
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151 | generator more than once. Mixing up several generators can produce |
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152 | a more complicated primary event. |
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153 | </para> |
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154 | |
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155 | </sect3> |
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156 | </sect2> |
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157 | |
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158 | |
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159 | <!-- ******************* Section (Level#2) ****************** --> |
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160 | <sect2 id="sect.HowToGenEvent.G4VPrimGen"> |
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161 | <title> |
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162 | G4VPrimaryGenerator |
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163 | </title> |
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164 | |
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165 | <para> |
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166 | Geant4 provides two <emphasis>G4VPrimaryGenerator</emphasis> concrete classes. |
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167 | One is <emphasis>G4ParticleGun</emphasis>, which will be discussed here, and the |
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168 | other is <emphasis>G4HEPEvtInterface</emphasis>, which will be discussed in |
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169 | <xref linkend="sect.EventGen" />. |
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170 | </para> |
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171 | |
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172 | |
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173 | <!-- ******************* Section (Level#3) ****************** --> |
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174 | <sect3 id="sect.HowToGenEvent.G4VPrimGen.G4PartGun"> |
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175 | <title> |
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176 | G4ParticleGun |
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177 | </title> |
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178 | |
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179 | <para> |
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180 | <emphasis>G4ParticleGun</emphasis> is a generator provided by Geant4. This class |
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181 | generates primary particle(s) with a given momentum and position. |
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182 | It does not provide any sort of randomizing. The constructor of |
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183 | <emphasis>G4ParticleGun</emphasis> takes an integer which causes the generation |
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184 | of one or more primaries of exactly same kinematics. It is a rather |
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185 | frequent user requirement to generate a primary with randomized |
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186 | energy, momentum, and/or position. Such randomization can be |
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187 | achieved by invoking various set methods provided by |
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188 | <emphasis>G4ParticleGun</emphasis>. The invocation of these methods should be |
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189 | implemented in the <literal>generatePrimaries()</literal> method of your |
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190 | concrete <emphasis>G4VUserPrimaryGeneratorAction</emphasis> class before invoking |
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191 | <literal>generatePrimaryVertex()</literal> of |
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192 | <emphasis>G4ParticleGun</emphasis>. |
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193 | Geant4 provides various random number generation methods with various |
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194 | distributions (see <xref linkend="sect.GlobClass" />). |
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195 | </para> |
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196 | |
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197 | </sect3> |
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198 | |
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199 | <!-- ******************* Section (Level#3) ****************** --> |
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200 | <sect3 id="sect.HowToGenEvent.G4VPrimGen.PublicMethG4PartGun"> |
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201 | <title> |
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202 | Public methods of <emphasis>G4ParticleGun</emphasis> |
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203 | </title> |
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204 | |
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205 | <para> |
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206 | The following methods are provided by <emphasis>G4ParticleGun</emphasis>, and all |
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207 | of them can be invoked from the <literal>generatePrimaries()</literal> method |
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208 | in your concrete <emphasis>G4VUserPrimaryGeneratorAction</emphasis> class. |
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209 | |
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210 | <itemizedlist spacing="compact"> |
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211 | <listitem><para> |
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212 | <literal>void SetParticleDefinition(G4ParticleDefinition*)</literal> |
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213 | </para></listitem> |
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214 | <listitem><para> |
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215 | <literal>void SetParticleMomentum(G4ParticleMomentum)</literal> |
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216 | </para></listitem> |
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217 | <listitem><para> |
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218 | <literal>void SetParticleMomentumDirection(G4ThreeVector)</literal> |
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219 | </para></listitem> |
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220 | <listitem><para> |
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221 | <literal>void SetParticleEnergy(G4double)</literal> |
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222 | </para></listitem> |
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223 | <listitem><para> |
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224 | <literal>void SetParticleTime(G4double)</literal> |
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225 | </para></listitem> |
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226 | <listitem><para> |
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227 | <literal>void SetParticlePosition(G4ThreeVector)</literal> |
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228 | </para></listitem> |
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229 | <listitem><para> |
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230 | <literal>void SetParticlePolarization(G4ThreeVector)</literal> |
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231 | </para></listitem> |
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232 | <listitem><para> |
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233 | <literal>void SetNumberOfParticles(G4int)</literal> |
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234 | </para></listitem> |
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235 | </itemizedlist> |
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236 | </para> |
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237 | |
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238 | |
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239 | </sect3> |
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240 | </sect2> |
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241 | </sect1> |
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