| 1 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>2.6. How to Generate a Primary Event</title><link rel="stylesheet" href="../xml/XSLCustomizationLayer/G4HTMLStylesheet.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.1"><link rel="start" href="index.html" title="Geant4 User's Guide for Application Developers"><link rel="up" href="ch02.html" title="Chapter 2. Getting Started with Geant4 - Running a Simple Example"><link rel="prev" href="ch02s05.html" title="2.5. How to Specify Physics Processes"><link rel="next" href="ch02s07.html" title="2.7. How to Make an Executable Program"><script language="JavaScript">
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| 8 | </script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">2.6.
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| 9 | How to Generate a Primary Event
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| 10 | </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s05.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><th width="60%" align="center">Chapter 2.
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| 11 | Getting Started with Geant4 - Running a Simple Example
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| 12 | </th><td width="20%" align="right"> <a accesskey="n" href="ch02s07.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr></table><hr></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sect.HowToGenEvent"></a>2.6.
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| 13 | How to Generate a Primary Event
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| 14 | </h2></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.HowToGenEvent.GenPrimary"></a>2.6.1.
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| 15 | Generating Primary Events
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| 16 | </h3></div></div></div><p>
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| 17 | <span class="emphasis"><em>G4VuserPrimaryGeneratorAction</em></span> is one of the mandatory
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| 18 | classes available for deriving your own concrete class. In your
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| 19 | concrete class, you have to specify how a primary event should be
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| 20 | generated. Actual generation of primary particles will be done by
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| 21 | concrete classes of <span class="emphasis"><em>G4VPrimaryGenerator</em></span>, explained in the
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| 22 | following sub-section. Your <span class="emphasis"><em>G4VUserPrimaryGeneratorAction</em></span>
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| 23 | concrete class just arranges the way primary particles are generated.
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| 24 |
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| 25 | </p><div class="example"><a name="programlist_HowToGenEvent_1"></a><p class="title"><b>Example 2.19.
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| 26 | An example of a <span class="emphasis"><em>G4VUserPrimaryGeneratorAction</em></span>
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| 27 | concrete class using <span class="emphasis"><em>G4ParticleGun</em></span>.
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| 28 | For the usage of <span class="emphasis"><em>G4ParticleGun</em></span> refer to the
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| 29 | next subsection.
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| 30 | </b></p><div class="example-contents"><pre class="programlisting">
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| 31 | #ifndef ExN01PrimaryGeneratorAction_h
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| 32 | #define ExN01PrimaryGeneratorAction_h 1
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| 33 |
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| 34 | #include "G4VUserPrimaryGeneratorAction.hh"
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| 35 |
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| 36 | class G4ParticleGun;
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| 37 | class G4Event;
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| 38 |
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| 39 | class ExN01PrimaryGeneratorAction : public G4VUserPrimaryGeneratorAction
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| 40 | {
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| 41 | public:
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| 42 | ExN01PrimaryGeneratorAction();
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| 43 | ~ExN01PrimaryGeneratorAction();
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| 44 |
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| 45 | public:
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| 46 | void generatePrimaries(G4Event* anEvent);
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| 47 |
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| 48 | private:
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| 49 | G4ParticleGun* particleGun;
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| 50 | };
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| 51 |
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| 52 | #endif
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| 53 |
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| 54 | #include "ExN01PrimaryGeneratorAction.hh"
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| 55 | #include "G4Event.hh"
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| 56 | #include "G4ParticleGun.hh"
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| 57 | #include "G4ThreeVector.hh"
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| 58 | #include "G4Geantino.hh"
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| 59 | #include "globals.hh"
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| 60 |
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| 61 | ExN01PrimaryGeneratorAction::ExN01PrimaryGeneratorAction()
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| 62 | {
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| 63 | G4int n_particle = 1;
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| 64 | particleGun = new G4ParticleGun(n_particle);
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| 65 |
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| 66 | particleGun->SetParticleDefinition(G4Geantino::GeantinoDefinition());
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| 67 | particleGun->SetParticleEnergy(1.0*GeV);
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| 68 | particleGun->SetParticlePosition(G4ThreeVector(-2.0*m,0.0*m,0.0*m));
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| 69 | }
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| 70 |
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| 71 | ExN01PrimaryGeneratorAction::~ExN01PrimaryGeneratorAction()
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| 72 | {
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| 73 | delete particleGun;
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| 74 | }
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| 75 |
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| 76 | void ExN01PrimaryGeneratorAction::generatePrimaries(G4Event* anEvent)
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| 77 | {
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| 78 | G4int i = anEvent->get_eventID() % 3;
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| 79 | switch(i)
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| 80 | {
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| 81 | case 0:
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| 82 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.0,0.0));
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| 83 | break;
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| 84 | case 1:
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| 85 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.1,0.0));
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| 86 | break;
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| 87 | case 2:
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| 88 | particleGun->SetParticleMomentumDirection(G4ThreeVector(1.0,0.0,0.1));
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| 89 | break;
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| 90 | }
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| 91 |
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| 92 | particleGun->generatePrimaryVertex(anEvent);
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| 93 | }
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| 94 | </pre></div></div><p><br class="example-break">
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| 95 |
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| 96 | </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.HowToGenEvent.GenPrimary.SelectGenerator"></a>2.6.1.1.
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| 97 | Selection of the generator
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| 98 | </h4></div></div></div><p>
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| 99 | In the constructor of your <span class="emphasis"><em>G4VUserPrimaryGeneratorAction</em></span>,
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| 100 | you should instantiate the primary generator(s). If necessary, you
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| 101 | need to set some initial conditions for the generator(s).
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| 102 | </p><p>
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| 103 | In <a href="ch02s06.html#programlist_HowToGenEvent_1" title="Example 2.19.
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| 104 | An example of a G4VUserPrimaryGeneratorAction
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| 105 | concrete class using G4ParticleGun.
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| 106 | For the usage of G4ParticleGun refer to the
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| 107 | next subsection.
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| 108 | ">Example 2.19</a>,
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| 109 | <span class="emphasis"><em>G4ParticleGun</em></span> is constructed to
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| 110 | use as the actual primary particle generator. Methods of
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| 111 | <span class="emphasis"><em>G4ParticleGun</em></span> are described in the following section. Please
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| 112 | note that the primary generator object(s) you construct in your
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| 113 | <span class="emphasis"><em>G4VUserPrimaryGeneratorAction</em></span> concrete class must be deleted
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| 114 | in your destructor.
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| 115 | </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.HowToGenEvent.GenPrimary.GenEvent"></a>2.6.1.2.
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| 116 | Generation of an event
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| 117 | </h4></div></div></div><p>
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| 118 | <span class="emphasis"><em>G4VUserPrimaryGeneratorAction</em></span> has a pure virtual method
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| 119 | named <code class="literal">generatePrimaries()</code>. This method is invoked at the
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| 120 | beginning of each event. In this method, you have to invoke the
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| 121 | <span class="emphasis"><em>G4VPrimaryGenerator</em></span> concrete class you instantiated via the
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| 122 | <code class="literal">generatePrimaryVertex()</code> method.
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| 123 | </p><p>
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| 124 | You can invoke more than one generator and/or invoke one
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| 125 | generator more than once. Mixing up several generators can produce
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| 126 | a more complicated primary event.
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| 127 | </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.HowToGenEvent.G4VPrimGen"></a>2.6.2.
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| 128 | G4VPrimaryGenerator
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| 129 | </h3></div></div></div><p>
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| 130 | Geant4 provides two <span class="emphasis"><em>G4VPrimaryGenerator</em></span> concrete classes.
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| 131 | One is <span class="emphasis"><em>G4ParticleGun</em></span>, which will be discussed here, and the
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| 132 | other is <span class="emphasis"><em>G4HEPEvtInterface</em></span>, which will be discussed in
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| 133 | <a href="ch03s06.html" title="3.6.
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| 134 | Event Generator Interface
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| 135 | ">Section 3.6</a>.
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| 136 | </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.HowToGenEvent.G4VPrimGen.G4PartGun"></a>2.6.2.1.
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| 137 | G4ParticleGun
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| 138 | </h4></div></div></div><p>
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| 139 | <span class="emphasis"><em>G4ParticleGun</em></span> is a generator provided by Geant4. This class
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| 140 | generates primary particle(s) with a given momentum and position.
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| 141 | It does not provide any sort of randomizing. The constructor of
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| 142 | <span class="emphasis"><em>G4ParticleGun</em></span> takes an integer which causes the generation
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| 143 | of one or more primaries of exactly same kinematics. It is a rather
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| 144 | frequent user requirement to generate a primary with randomized
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| 145 | energy, momentum, and/or position. Such randomization can be
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| 146 | achieved by invoking various set methods provided by
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| 147 | <span class="emphasis"><em>G4ParticleGun</em></span>. The invocation of these methods should be
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| 148 | implemented in the <code class="literal">generatePrimaries()</code> method of your
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| 149 | concrete <span class="emphasis"><em>G4VUserPrimaryGeneratorAction</em></span> class before invoking
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| 150 | <code class="literal">generatePrimaryVertex()</code> of
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| 151 | <span class="emphasis"><em>G4ParticleGun</em></span>.
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| 152 | Geant4 provides various random number generation methods with various
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| 153 | distributions (see <a href="ch03s02.html" title="3.2.
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| 154 | Global Usage Classes
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| 155 | ">Section 3.2</a>).
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| 156 | </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.HowToGenEvent.G4VPrimGen.PublicMethG4PartGun"></a>2.6.2.2.
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| 157 | Public methods of <span class="emphasis"><em>G4ParticleGun</em></span>
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| 158 | </h4></div></div></div><p>
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| 159 | The following methods are provided by <span class="emphasis"><em>G4ParticleGun</em></span>, and all
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| 160 | of them can be invoked from the <code class="literal">generatePrimaries()</code> method
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| 161 | in your concrete <span class="emphasis"><em>G4VUserPrimaryGeneratorAction</em></span> class.
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| 162 |
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| 163 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
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| 164 | <code class="literal">void SetParticleDefinition(G4ParticleDefinition*)</code>
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| 165 | </p></li><li><p>
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| 166 | <code class="literal">void SetParticleMomentum(G4ParticleMomentum)</code>
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| 167 | </p></li><li><p>
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| 168 | <code class="literal">void SetParticleMomentumDirection(G4ThreeVector)</code>
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| 169 | </p></li><li><p>
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| 170 | <code class="literal">void SetParticleEnergy(G4double)</code>
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| 171 | </p></li><li><p>
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| 172 | <code class="literal">void SetParticleTime(G4double)</code>
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| 173 | </p></li><li><p>
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| 174 | <code class="literal">void SetParticlePosition(G4ThreeVector)</code>
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| 175 | </p></li><li><p>
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| 176 | <code class="literal">void SetParticlePolarization(G4ThreeVector)</code>
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| 177 | </p></li><li><p>
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| 178 | <code class="literal">void SetNumberOfParticles(G4int)</code>
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| 179 | </p></li></ul></div><p>
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| 180 | </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s05.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><td width="20%" align="center"><a accesskey="u" href="ch02.html"><img src="AllResources/IconsGIF/up.gif" alt="Up"></a></td><td width="40%" align="right"> <a accesskey="n" href="ch02s07.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr><tr><td width="40%" align="left" valign="top">2.5.
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| 181 | How to Specify Physics Processes
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| 182 | </td><td width="20%" align="center"><a accesskey="h" href="index.html"><img src="AllResources/IconsGIF/home.gif" alt="Home"></a></td><td width="40%" align="right" valign="top"> 2.7.
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| 183 | How to Make an Executable Program
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