[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 | <!-- Proof read by: Joe Chuma, 15-Jun-1999 --> |
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| 6 | <!-- Changed by: Hisaya Kurashige, 28-Oct-2001 --> |
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| 7 | <!-- Changed by: Dennis Wright, 29-Nov-2001 --> |
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| 8 | <!-- Converted to DocBook: Katsuya Amako, Aug-2006 --> |
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| 9 | <!-- Changed by: Hisaya Kurashige, 18-Jan-2007 --> |
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| 10 | <!-- Changed by: Hisaya Kurashige, 1-Dec-2007 --> |
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| 11 | <!-- --> |
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| 12 | <!-- ******************************************************** --> |
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| 13 | |
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| 14 | |
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| 15 | <!-- ******************* Section (Level#1) ****************** --> |
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| 16 | <sect1 id="sect.HowToSpecParti"> |
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| 17 | <title> |
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| 18 | How to Specify Particles |
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| 19 | </title> |
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| 20 | |
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| 21 | <para> |
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| 22 | <literal>G4VuserPhysicsList</literal> is one of the mandatory user base |
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| 23 | classes described in |
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| 24 | <xref linkend="sect.HowToDefMain" />. |
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| 25 | Within this class all particles and physics processes to be used in |
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| 26 | your simulation must be defined. The range cut-off parameter should |
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| 27 | also be defined in this class. |
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| 28 | </para> |
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| 29 | |
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| 30 | <para> |
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| 31 | The user must create a class derived from |
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| 32 | <literal>G4VuserPhysicsList</literal> and implement the following pure |
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| 33 | virtual methods: |
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| 34 | |
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| 35 | <informalexample> |
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| 36 | <programlisting> |
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| 37 | ConstructParticle(); // construction of particles |
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| 38 | ConstructProcess(); // construct processes and register them to particles |
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| 39 | SetCuts(); // setting a range cut value for all particles |
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| 40 | </programlisting> |
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| 41 | </informalexample> |
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| 42 | </para> |
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| 43 | |
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| 44 | <para> |
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| 45 | This section provides some simple examples of the |
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| 46 | <literal>ConstructParticle()</literal> and <literal>SetCuts()</literal> |
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| 47 | methods. |
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| 48 | For information on <literal>ConstructProcess()</literal> methods, please see |
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| 49 | <xref linkend="sect.HowToSpecPhysProc" />. |
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| 50 | |
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| 51 | </para> |
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| 52 | |
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| 53 | |
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| 54 | <!-- ******************* Section (Level#2) ****************** --> |
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| 55 | <sect2 id="sect.HowToSpecParti.PartiDef"> |
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| 56 | <title> |
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| 57 | Particle Definition |
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| 58 | </title> |
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| 59 | |
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| 60 | <para> |
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| 61 | Geant4 provides various types of particles for use in simulations: |
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| 62 | |
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| 63 | <itemizedlist spacing="compact"> |
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| 64 | <listitem><para> |
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| 65 | ordinary particles, such as electrons, protons, and gammas |
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| 66 | </para></listitem> |
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| 67 | <listitem><para> |
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| 68 | resonant particles with very short lifetimes, such as vector |
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| 69 | mesons and delta baryons |
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| 70 | </para></listitem> |
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| 71 | <listitem><para> |
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| 72 | nuclei, such as deuteron, alpha, and heavy ions (including hyper-nuclei) |
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| 73 | </para></listitem> |
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| 74 | <listitem><para> |
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| 75 | quarks, di-quarks, and gluon |
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| 76 | </para></listitem> |
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| 77 | </itemizedlist> |
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| 78 | </para> |
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| 79 | |
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| 80 | <para> |
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| 81 | Each particle is represented by its own class, which is derived |
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| 82 | from <literal>G4ParticleDefinition</literal>. |
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| 83 | (Exception: G4Ions represents all heavy nuclei. Please see |
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| 84 | <xref linkend="sect.Parti" />.) |
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| 85 | Particles are organized into six major categories: |
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| 86 | |
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| 87 | <itemizedlist spacing="compact"> |
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| 88 | <listitem><para> |
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| 89 | lepton, |
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| 90 | </para></listitem> |
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| 91 | <listitem><para> |
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| 92 | meson, |
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| 93 | </para></listitem> |
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| 94 | <listitem><para> |
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| 95 | baryon, |
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| 96 | </para></listitem> |
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| 97 | <listitem><para> |
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| 98 | boson, |
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| 99 | </para></listitem> |
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| 100 | <listitem><para> |
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| 101 | shortlived and |
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| 102 | </para></listitem> |
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| 103 | <listitem><para> |
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| 104 | ion, |
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| 105 | </para></listitem> |
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| 106 | </itemizedlist> |
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| 107 | |
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| 108 | each of which is defined in a corresponding sub-directory under |
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| 109 | <literal>geant4/source/particles</literal>. There is also a corresponding |
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| 110 | granular library for each particle category. |
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| 111 | </para> |
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| 112 | |
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| 113 | |
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| 114 | <!-- ******************* Section (Level#3) ****************** --> |
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| 115 | <sect3 id="sect.HowToSpecParti.PartiDef.G4ParticleDefinition"> |
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| 116 | <title> |
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| 117 | The <literal>G4ParticleDefinition</literal> Class |
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| 118 | </title> |
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| 119 | |
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| 120 | <para> |
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| 121 | <literal>G4ParticleDefinition</literal> has properties which characterize |
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| 122 | individual particles, such as, name, mass, charge, spin, and so on. |
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| 123 | Most of these properties are "read-only" and can not be changed directly. |
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| 124 | <literal>G4ParticlePropertyTable</literal> is used to retrieve (load) |
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| 125 | particle property of <literal>G4ParticleDefinition</literal> |
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| 126 | into (from) <literal>G4ParticlePropertyData</literal>. |
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| 127 | </para> |
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| 128 | |
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| 129 | </sect3> |
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| 130 | |
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| 131 | <!-- ******************* Section (Level#3) ****************** --> |
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| 132 | <sect3 id="sect.HowToSpecParti.PartiDef.HowToAccessParti"> |
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| 133 | <title> |
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| 134 | How to Access a Particle |
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| 135 | </title> |
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| 136 | |
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| 137 | <para> |
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| 138 | Each particle class type represents an individual particle type, |
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| 139 | and each class has a single object. This object can be accessed by |
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| 140 | using the static method of each class. |
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| 141 | There are some exceptions to this rule; please see |
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| 142 | <xref linkend="sect.Parti" /> for details. |
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| 143 | </para> |
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| 144 | |
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| 145 | <para> |
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| 146 | For example, the class <literal>G4Electron</literal> represents the |
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| 147 | electron and the member <literal>G4Electron::theInstance</literal> |
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| 148 | points its only object. |
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| 149 | The pointer to this object is available |
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| 150 | through the static methods |
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| 151 | <literal>G4Electron::ElectronDefinition()</literal>. |
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| 152 | <literal>G4Electron::Definition()</literal>. |
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| 153 | </para> |
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| 154 | |
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| 155 | <para> |
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| 156 | More than 100 types of particles are provided by default, to be |
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| 157 | used in various physics processes. In normal applications, users |
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| 158 | will not need to define their own particles. |
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| 159 | </para> |
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| 160 | |
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| 161 | <para> |
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| 162 | The unique object for each particle class is created when its static |
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| 163 | method to get the pointer is called iat the first time. |
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| 164 | Because particles are dynamic objects and should be instantiated before |
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| 165 | initialization of physics processes, |
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| 166 | you must explicitly invoke static methods of all particle classes |
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| 167 | required by your program at the initialization step. |
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| 168 | (NOTE: The particle object was static and created automatically before 8.0 release) |
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| 169 | </para> |
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| 170 | |
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| 171 | </sect3> |
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| 172 | |
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| 173 | <!-- ******************* Section (Level#3) ****************** --> |
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| 174 | <sect3 id="sect.HowToSpecParti.PartiDef.DictOfParti"> |
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| 175 | <title>Dictionary of Particles |
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| 176 | </title> |
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| 177 | |
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| 178 | <para> |
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| 179 | The <literal>G4ParticleTable</literal> class is provided as a dictionary of |
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| 180 | particles. Various utility methods are provided, such as: |
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| 181 | |
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| 182 | <informalexample> |
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| 183 | <programlisting> |
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| 184 | FindParticle(G4String name); // find the particle by name |
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| 185 | FindParticle(G4int PDGencoding) // find the particle by PDG encoding . |
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| 186 | </programlisting> |
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| 187 | </informalexample> |
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| 188 | </para> |
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| 189 | |
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| 190 | <para> |
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| 191 | <literal>G4ParticleTable</literal> is defined as a singleton object, |
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| 192 | and the static method <literal>G4ParticleTable::GetParticleTable()</literal> |
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| 193 | provides its pointer. |
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| 194 | </para> |
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| 195 | |
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| 196 | <para> |
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| 197 | As for heavy ions (including hyper-nuclei), objects are created |
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| 198 | dynamically by requests from users and processes. |
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| 199 | The <literal>G4ParticleTable</literal> class provides |
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| 200 | methods to create ions, such as: |
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| 201 | <informalexample> |
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| 202 | <programlisting> |
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| 203 | G4ParticleDefinition* GetIon( G4int atomicNumber, |
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| 204 | G4int atomicMass, |
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| 205 | G4double excitationEnergy); |
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| 206 | </programlisting> |
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| 207 | </informalexample> |
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| 208 | </para> |
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| 209 | |
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| 210 | <para> |
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| 211 | Particles are registered automatically during construction. The |
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| 212 | user has no control over particle registration. |
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| 213 | </para> |
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| 214 | |
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| 215 | |
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| 216 | </sect3> |
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| 217 | |
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| 218 | <!-- ******************* Section (Level#3) ****************** --> |
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| 219 | <sect3 id="sect.HowToSpecParti.PartiDef.ConstruParti"> |
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| 220 | <title> |
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| 221 | Constructing Particles |
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| 222 | </title> |
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| 223 | |
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| 224 | <para> |
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| 225 | <literal>ConstructParticle()</literal> is a pure virtual method, in which |
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| 226 | the static member functions for all the particles you require should be called. |
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| 227 | This ensures that objects of these particles are created. |
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| 228 | </para> |
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| 229 | |
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| 230 | <para> |
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| 231 | WARNING: You must define "All PARTICLE TYPES" which are used in your |
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| 232 | application, except for heavy ions. |
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| 233 | "All PARTICLE TYPES" means not only primary |
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| 234 | particles, but also all other particles which may appear as secondaries |
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| 235 | generated by physics processes you use. Beginning with Geant4 version 8.0, |
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| 236 | you should keep this rule strictly because all particle definitions are |
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| 237 | revised to "non-static" objects. |
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| 238 | </para> |
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| 239 | |
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| 240 | <para> |
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| 241 | For example, suppose you need a proton and a geantino, which is |
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| 242 | a virtual particle used for simulation and which does not interact |
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| 243 | with materials. The <literal>ConstructParticle()</literal> method is |
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| 244 | implemented as below: |
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| 245 | |
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| 246 | <example id="programlist_HowToSpecParti_1"> |
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| 247 | <title> |
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| 248 | Construct a proton and a geantino. |
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| 249 | </title> |
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| 250 | <programlisting> |
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| 251 | void ExN01PhysicsList::ConstructParticle() |
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| 252 | { |
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| 253 | G4Proton::ProtonDefinition(); |
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| 254 | G4Geantino::GeantinoDefinition(); |
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| 255 | } |
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| 256 | </programlisting> |
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| 257 | </example> |
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| 258 | </para> |
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| 259 | |
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| 260 | <para> |
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| 261 | Due to the large number of pre-defined particles in Geant4, it |
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| 262 | is cumbersome to list all the particles by this method. If you want |
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| 263 | all the particles in a Geant4 particle category, there are six |
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| 264 | utility classes, corresponding to each of the particle categories, |
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| 265 | which perform this function: |
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| 266 | |
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| 267 | <itemizedlist spacing="compact"> |
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| 268 | <listitem><para> |
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| 269 | <literal>G4BosonConstructor</literal> |
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| 270 | </para></listitem> |
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| 271 | <listitem><para> |
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| 272 | <literal>G4LeptonConstructor</literal> |
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| 273 | </para></listitem> |
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| 274 | <listitem><para> |
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| 275 | <literal>G4MesonConstructor</literal> |
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| 276 | </para></listitem> |
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| 277 | <listitem><para> |
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| 278 | <literal>G4BarionConstructor</literal> |
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| 279 | </para></listitem> |
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| 280 | <listitem><para> |
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| 281 | <literal>G4IonConstructor</literal> |
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| 282 | </para></listitem> |
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| 283 | <listitem><para> |
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| 284 | <literal>G4ShortlivedConstructor</literal>. |
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| 285 | </para></listitem> |
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| 286 | </itemizedlist> |
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| 287 | </para> |
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| 288 | |
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| 289 | <para> |
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| 290 | An example of this is shown in <literal>ExN05PhysicsList</literal>, |
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| 291 | listed below. |
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| 292 | |
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| 293 | <example id="programlist_HowToSpecParti_2"> |
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| 294 | <title> |
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| 295 | Construct all leptons. |
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| 296 | </title> |
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| 297 | <programlisting> |
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| 298 | void ExN05PhysicsList::ConstructLeptons() |
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| 299 | { |
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| 300 | // Construct all leptons |
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| 301 | G4LeptonConstructor pConstructor; |
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| 302 | pConstructor.ConstructParticle(); |
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| 303 | } |
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| 304 | </programlisting> |
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| 305 | </example> |
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| 306 | </para> |
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| 307 | |
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| 308 | </sect3> |
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| 309 | </sect2> |
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| 310 | |
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| 311 | <!-- ******************* Section (Level#2) ****************** --> |
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| 312 | <sect2 id="sect.HowToSpecParti.RangeCuts"> |
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| 313 | <title> |
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| 314 | Range Cuts |
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| 315 | </title> |
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| 316 | |
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| 317 | <para> |
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| 318 | To avoid infrared divergence, some electromagnetic processes |
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| 319 | require a threshold below which no secondary will be generated. |
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| 320 | Because of this requirement, gammas, electrons and positrons |
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| 321 | require production thresholds which the user should define. This |
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| 322 | threshold should be defined as a distance, or range cut-off, which |
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| 323 | is internally converted to an energy for individual materials. The |
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| 324 | range threshold should be defined in the initialization phase using |
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| 325 | the <literal>SetCuts()</literal> method of <literal>G4VUserPhysicsList</literal>. |
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| 326 | <xref linkend="sect.CutReg" /> discusses threshold and tracking |
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| 327 | cuts in detail. |
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| 328 | </para> |
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| 329 | |
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| 330 | |
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| 331 | |
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| 332 | <!-- ******************* Section (Level#3) ****************** --> |
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| 333 | <sect3 id="sect.HowToSpecParti.RangeCuts.SetCuts"> |
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| 334 | <title> |
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| 335 | Setting the cuts |
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| 336 | </title> |
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| 337 | |
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| 338 | <para> |
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| 339 | Production threshold values should be defined in <literal>SetCuts()</literal> |
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| 340 | which is a pure virtual method of the <literal>G4VUserPhysicsList</literal> |
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| 341 | class. Construction of particles, materials, and processes should |
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| 342 | precede the invocation of <literal>SetCuts()</literal>. <literal>G4RunManager</literal> |
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| 343 | takes care of this sequence in usual applications. |
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| 344 | </para> |
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| 345 | |
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| 346 | <para> |
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| 347 | The idea of a "unique cut value in range" is one of the |
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| 348 | important features of Geant4 and is used to handle cut values in a |
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| 349 | coherent manner. For most applications, users need to determine |
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| 350 | only one cut value in range, and apply this value to gammas, |
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| 351 | electrons and positrons alike. |
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| 352 | </para> |
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| 353 | |
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| 354 | <para> |
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| 355 | In such a case, the <literal>SetCutsWithDefault()</literal> method may be |
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| 356 | used. It is provided by the <literal>G4VuserPhysicsList</literal> base class, |
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| 357 | which has a <literal>defaultCutValue</literal> member as the default range |
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| 358 | cut-off value. <literal>SetCutsWithDefault()</literal> uses this value. |
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| 359 | </para> |
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| 360 | |
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| 361 | <para> |
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| 362 | It is possible to set different range cut values for gammas, |
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| 363 | electrons and positrons, and also to set different range cut values |
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| 364 | for each geometrical region. In such cases however, one must be |
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| 365 | careful with physics outputs because Geant4 processes (especially |
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| 366 | energy loss) are designed to conform to the "unique cut value in |
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| 367 | range" scheme. |
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| 368 | |
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| 369 | <example id="programlist_HowToSpecParti_3"> |
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| 370 | <title> |
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| 371 | Set cut values by using the default cut value. |
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| 372 | </title> |
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| 373 | <programlisting> |
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| 374 | void ExN04PhysicsList::SetCuts() |
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| 375 | { |
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| 376 | // the G4VUserPhysicsList::SetCutsWithDefault() method sets |
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| 377 | // the default cut value for all particle types |
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| 378 | SetCutsWithDefault(); |
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| 379 | } |
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| 380 | </programlisting> |
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| 381 | </example> |
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| 382 | </para> |
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| 383 | |
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| 384 | <para> |
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| 385 | The <literal>defaultCutValue</literal> is set to 1.0 mm by default. Of |
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| 386 | course, you can set the new default cut value in the constructor of |
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| 387 | your physics list class as shown below. |
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| 388 | |
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| 389 | <example id="programlist_HowToSpecParti_4"> |
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| 390 | <title> |
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| 391 | Set the default cut value. |
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| 392 | </title> |
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| 393 | <programlisting> |
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| 394 | ExN04PhysicsList::ExN04PhysicsList(): G4VUserPhysicsList() |
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| 395 | { |
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| 396 | // default cut value (1.0mm) |
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| 397 | defaultCutValue = 1.0*mm; |
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| 398 | } |
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| 399 | </programlisting> |
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| 400 | </example> |
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| 401 | </para> |
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| 402 | |
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| 403 | <para> |
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| 404 | The <literal>SetDefaultCutValue()</literal> method in |
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| 405 | <literal>G4VUserPhysicsList</literal> may also be used, and the "/run/setCut" |
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| 406 | command may be used to change the default cut value |
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| 407 | interactively. |
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| 408 | </para> |
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| 409 | |
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| 410 | <para> |
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| 411 | WARNING: DO NOT change cut values inside the event loop. Cut |
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| 412 | values may however be changed between runs. |
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| 413 | </para> |
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| 414 | |
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| 415 | <para> |
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| 416 | An example implementation of <literal>SetCuts()</literal> is shown |
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| 417 | below: |
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| 418 | |
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| 419 | <example id="programlist_HowToSpecParti_5"> |
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| 420 | <title> |
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| 421 | Example implementation of the <literal>SetCuts()</literal> method. |
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| 422 | </title> |
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| 423 | <programlisting> |
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| 424 | void ExN03PhysicsList::SetCuts() |
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| 425 | { |
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| 426 | // set cut values for gamma at first and for e- second and next for e+, |
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| 427 | // because some processes for e+/e- need cut values for gamma |
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| 428 | SetCutValue(cutForGamma, "gamma"); |
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| 429 | SetCutValue(cutForElectron, "e-"); |
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| 430 | SetCutValue(cutForElectron, "e+"); |
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| 431 | } |
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| 432 | </programlisting> |
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| 433 | </example> |
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| 434 | </para> |
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| 435 | |
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| 436 | <para> |
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| 437 | Beginning with Geant4 version 5.1, it is now possible to set |
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| 438 | production thresholds for each geometrical region. This new |
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| 439 | functionality is described in <xref linkend="sect.CutReg" />. |
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| 440 | </para> |
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| 441 | |
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| 442 | |
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| 443 | </sect3> |
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| 444 | </sect2> |
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| 445 | </sect1> |
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