[904] | 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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[1211] | 8 | <!-- Added GPS description: Katsuya Amako, Dec-2009 --> |
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[904] | 9 | <!-- --> |
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| 10 | <!-- ******************************************************** --> |
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| 11 | |
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| 12 | |
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| 13 | <!-- ******************* Section (Level#1) ****************** --> |
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| 14 | <sect1 id="sect.HowToGenEvent"> |
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| 15 | <title> |
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| 16 | How to Generate a Primary Event |
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| 17 | </title> |
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| 18 | |
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| 19 | <!-- ******************* Section (Level#2) ****************** --> |
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| 20 | <sect2 id="sect.HowToGenEvent.GenPrimary"> |
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| 21 | <title> |
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| 22 | Generating Primary Events |
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| 23 | </title> |
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| 24 | |
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| 25 | <para> |
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| 26 | <emphasis>G4VuserPrimaryGeneratorAction</emphasis> is one of the mandatory |
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| 27 | classes available for deriving your own concrete class. In your |
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| 28 | concrete class, you have to specify how a primary event should be |
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| 29 | generated. Actual generation of primary particles will be done by |
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| 30 | concrete classes of <emphasis>G4VPrimaryGenerator</emphasis>, explained in the |
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| 31 | following sub-section. Your <emphasis>G4VUserPrimaryGeneratorAction</emphasis> |
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| 32 | concrete class just arranges the way primary particles are generated. |
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| 33 | |
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| 34 | <example id="programlist_HowToGenEvent_1"> |
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| 35 | <title> |
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| 36 | An example of a <emphasis>G4VUserPrimaryGeneratorAction</emphasis> |
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| 37 | concrete class using <emphasis>G4ParticleGun</emphasis>. |
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| 38 | For the usage of <emphasis>G4ParticleGun</emphasis> refer to the |
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| 39 | next subsection. |
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| 40 | </title> |
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| 41 | |
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| 42 | <programlisting> |
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| 43 | #ifndef ExN01PrimaryGeneratorAction_h |
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| 44 | #define ExN01PrimaryGeneratorAction_h 1 |
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| 45 | |
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| 46 | #include "G4VUserPrimaryGeneratorAction.hh" |
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| 47 | |
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| 48 | class G4ParticleGun; |
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| 49 | class G4Event; |
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| 50 | |
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| 51 | class ExN01PrimaryGeneratorAction : public G4VUserPrimaryGeneratorAction |
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| 52 | { |
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| 53 | public: |
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| 54 | ExN01PrimaryGeneratorAction(); |
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| 55 | ~ExN01PrimaryGeneratorAction(); |
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| 56 | |
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| 57 | public: |
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| 58 | void generatePrimaries(G4Event* anEvent); |
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| 59 | |
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| 60 | private: |
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| 61 | G4ParticleGun* particleGun; |
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| 62 | }; |
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| 63 | |
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| 64 | #endif |
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| 65 | |
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| 66 | #include "ExN01PrimaryGeneratorAction.hh" |
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| 67 | #include "G4Event.hh" |
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| 68 | #include "G4ParticleGun.hh" |
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| 69 | #include "G4ThreeVector.hh" |
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| 70 | #include "G4Geantino.hh" |
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| 71 | #include "globals.hh" |
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| 72 | |
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| 73 | ExN01PrimaryGeneratorAction::ExN01PrimaryGeneratorAction() |
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| 74 | { |
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| 75 | G4int n_particle = 1; |
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| 76 | particleGun = new G4ParticleGun(n_particle); |
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| 77 | |
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| 78 | particleGun->SetParticleDefinition(G4Geantino::GeantinoDefinition()); |
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| 79 | particleGun->SetParticleEnergy(1.0*GeV); |
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| 80 | particleGun->SetParticlePosition(G4ThreeVector(-2.0*m,0.0*m,0.0*m)); |
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| 81 | } |
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| 82 | |
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| 83 | ExN01PrimaryGeneratorAction::~ExN01PrimaryGeneratorAction() |
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| 84 | { |
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| 85 | delete particleGun; |
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| 86 | } |
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| 87 | |
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| 88 | void ExN01PrimaryGeneratorAction::generatePrimaries(G4Event* anEvent) |
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| 89 | { |
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| 90 | G4int i = anEvent->get_eventID() % 3; |
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| 91 | switch(i) |
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| 92 | { |
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| 93 | case 0: |
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| 94 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.0,0.0)); |
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| 95 | break; |
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| 96 | case 1: |
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| 97 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.1,0.0)); |
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| 98 | break; |
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| 99 | case 2: |
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| 100 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.0,0.1)); |
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| 101 | break; |
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| 102 | } |
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| 103 | |
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| 104 | particleGun->generatePrimaryVertex(anEvent); |
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| 105 | } |
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| 106 | </programlisting> |
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| 107 | </example> |
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| 108 | |
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| 109 | </para> |
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| 110 | |
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| 111 | |
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| 112 | <!-- ******************* Section (Level#3) ****************** --> |
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| 113 | <sect3 id="sect.HowToGenEvent.GenPrimary.SelectGenerator"> |
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| 114 | <title> |
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| 115 | Selection of the generator |
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| 116 | </title> |
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| 117 | |
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| 118 | <para> |
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| 119 | In the constructor of your <emphasis>G4VUserPrimaryGeneratorAction</emphasis>, |
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| 120 | you should instantiate the primary generator(s). If necessary, you |
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| 121 | need to set some initial conditions for the generator(s). |
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| 122 | </para> |
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| 123 | |
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| 124 | <para> |
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| 125 | In <xref linkend="programlist_HowToGenEvent_1" />, |
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| 126 | <emphasis>G4ParticleGun</emphasis> is constructed to |
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| 127 | use as the actual primary particle generator. Methods of |
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| 128 | <emphasis>G4ParticleGun</emphasis> are described in the following section. Please |
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| 129 | note that the primary generator object(s) you construct in your |
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| 130 | <emphasis>G4VUserPrimaryGeneratorAction</emphasis> concrete class must be deleted |
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| 131 | in your destructor. |
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| 132 | </para> |
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| 133 | |
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| 134 | </sect3> |
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| 135 | |
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| 136 | <!-- ******************* Section (Level#3) ****************** --> |
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| 137 | <sect3 id="sect.HowToGenEvent.GenPrimary.GenEvent"> |
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| 138 | <title> |
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| 139 | Generation of an event |
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| 140 | </title> |
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| 141 | |
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| 142 | <para> |
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| 143 | <emphasis>G4VUserPrimaryGeneratorAction</emphasis> has a pure virtual method |
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| 144 | named <literal>generatePrimaries()</literal>. This method is invoked at the |
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| 145 | beginning of each event. In this method, you have to invoke the |
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| 146 | <emphasis>G4VPrimaryGenerator</emphasis> concrete class you instantiated via the |
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| 147 | <literal>generatePrimaryVertex()</literal> method. |
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| 148 | </para> |
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| 149 | |
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| 150 | <para> |
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| 151 | You can invoke more than one generator and/or invoke one |
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| 152 | generator more than once. Mixing up several generators can produce |
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| 153 | a more complicated primary event. |
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| 154 | </para> |
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| 155 | |
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| 156 | </sect3> |
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| 157 | </sect2> |
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| 158 | |
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| 159 | |
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| 160 | <!-- ******************* Section (Level#2) ****************** --> |
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| 161 | <sect2 id="sect.HowToGenEvent.G4VPrimGen"> |
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| 162 | <title> |
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| 163 | G4VPrimaryGenerator |
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| 164 | </title> |
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| 165 | |
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| 166 | <para> |
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[1211] | 167 | Geant4 provides three <emphasis>G4VPrimaryGenerator</emphasis> concrete |
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| 168 | classes. Among these <emphasis>G4ParticleGun</emphasis> and |
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| 169 | <emphasis> G4GeneralParticleSource</emphasis> will be discussed here. |
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| 170 | The third one is <emphasis>G4HEPEvtInterface</emphasis>, which will be |
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| 171 | discussed in <xref linkend="sect.EventGen" />. |
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[904] | 172 | </para> |
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| 173 | |
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| 174 | |
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| 175 | <!-- ******************* Section (Level#3) ****************** --> |
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| 176 | <sect3 id="sect.HowToGenEvent.G4VPrimGen.G4PartGun"> |
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| 177 | <title> |
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| 178 | G4ParticleGun |
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| 179 | </title> |
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| 180 | |
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| 181 | <para> |
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| 182 | <emphasis>G4ParticleGun</emphasis> is a generator provided by Geant4. This class |
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| 183 | generates primary particle(s) with a given momentum and position. |
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| 184 | It does not provide any sort of randomizing. The constructor of |
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| 185 | <emphasis>G4ParticleGun</emphasis> takes an integer which causes the generation |
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| 186 | of one or more primaries of exactly same kinematics. It is a rather |
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| 187 | frequent user requirement to generate a primary with randomized |
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| 188 | energy, momentum, and/or position. Such randomization can be |
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| 189 | achieved by invoking various set methods provided by |
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| 190 | <emphasis>G4ParticleGun</emphasis>. The invocation of these methods should be |
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| 191 | implemented in the <literal>generatePrimaries()</literal> method of your |
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| 192 | concrete <emphasis>G4VUserPrimaryGeneratorAction</emphasis> class before invoking |
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| 193 | <literal>generatePrimaryVertex()</literal> of |
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| 194 | <emphasis>G4ParticleGun</emphasis>. |
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| 195 | Geant4 provides various random number generation methods with various |
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| 196 | distributions (see <xref linkend="sect.GlobClass" />). |
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| 197 | </para> |
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| 198 | |
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| 199 | </sect3> |
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| 200 | |
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| 201 | <!-- ******************* Section (Level#3) ****************** --> |
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| 202 | <sect3 id="sect.HowToGenEvent.G4VPrimGen.PublicMethG4PartGun"> |
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| 203 | <title> |
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| 204 | Public methods of <emphasis>G4ParticleGun</emphasis> |
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| 205 | </title> |
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| 206 | |
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| 207 | <para> |
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| 208 | The following methods are provided by <emphasis>G4ParticleGun</emphasis>, and all |
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| 209 | of them can be invoked from the <literal>generatePrimaries()</literal> method |
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| 210 | in your concrete <emphasis>G4VUserPrimaryGeneratorAction</emphasis> class. |
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| 211 | |
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| 212 | <itemizedlist spacing="compact"> |
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| 213 | <listitem><para> |
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| 214 | <literal>void SetParticleDefinition(G4ParticleDefinition*)</literal> |
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| 215 | </para></listitem> |
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| 216 | <listitem><para> |
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| 217 | <literal>void SetParticleMomentum(G4ParticleMomentum)</literal> |
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| 218 | </para></listitem> |
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| 219 | <listitem><para> |
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| 220 | <literal>void SetParticleMomentumDirection(G4ThreeVector)</literal> |
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| 221 | </para></listitem> |
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| 222 | <listitem><para> |
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| 223 | <literal>void SetParticleEnergy(G4double)</literal> |
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| 224 | </para></listitem> |
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| 225 | <listitem><para> |
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| 226 | <literal>void SetParticleTime(G4double)</literal> |
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| 227 | </para></listitem> |
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| 228 | <listitem><para> |
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| 229 | <literal>void SetParticlePosition(G4ThreeVector)</literal> |
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| 230 | </para></listitem> |
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| 231 | <listitem><para> |
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| 232 | <literal>void SetParticlePolarization(G4ThreeVector)</literal> |
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| 233 | </para></listitem> |
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| 234 | <listitem><para> |
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| 235 | <literal>void SetNumberOfParticles(G4int)</literal> |
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| 236 | </para></listitem> |
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| 237 | </itemizedlist> |
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| 238 | </para> |
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[1211] | 239 | </sect3> |
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[904] | 240 | |
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[1211] | 241 | <!-- ******************* Section (Level#3) ****************** --> |
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| 242 | <sect3 id="sect.HowToGenEvent.G4VPrimGen.G4GPS"> |
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| 243 | <title> |
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| 244 | G4GeneralParticleSource |
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| 245 | </title> |
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[904] | 246 | |
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[1211] | 247 | <para> |
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| 248 | For many applications <literal>G4ParticleGun</literal> is a suitable |
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| 249 | particle generator. Howevr if you want to generate primary particles |
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| 250 | in more sophisticated manner, you can utilize |
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| 251 | <literal>G4GeneralParticleSource</literal> - Geant4 General Particle |
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| 252 | Source module (GPS). |
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| 253 | </para> |
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| 254 | |
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| 255 | <para> |
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| 256 | Using this tool, you can control the following characteristics of |
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| 257 | primary particles: |
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| 258 | |
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| 259 | |
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| 260 | <itemizedlist spacing="compact"> |
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| 261 | <listitem><para> |
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| 262 | Spectrum: linear, exponential, power-law, Gaussian, blackbody, or |
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| 263 | piece-wise fits to data. |
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| 264 | </para></listitem> |
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| 265 | <listitem><para> |
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| 266 | Angular distribution: unidirectional, isotropic, cosine-law, |
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| 267 | beam or arbitrary (user defined). |
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| 268 | </para></listitem> |
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| 269 | <listitem><para> |
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| 270 | Spatial sampling: on simple 2D or 3D surfaces such as discs, spheres, |
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| 271 | and boxes. |
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| 272 | </para></listitem> |
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| 273 | <listitem><para> |
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| 274 | Multiple sources: multiple independent sources can be used in the same run. |
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| 275 | </para></listitem> |
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| 276 | </itemizedlist> |
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| 277 | </para> |
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| 278 | |
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| 279 | <para> |
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| 280 | Details of information on the General Source Particle Module can be |
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| 281 | found in the documents |
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| 282 | <ulink url="http://reat.space.qinetiq.com/gps/"> |
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| 283 | Geant4 General Particle Source</ulink>. |
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| 284 | </para> |
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| 285 | |
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[904] | 286 | </sect3> |
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| 287 | </sect2> |
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| 288 | </sect1> |
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