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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">5.3. |
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9 | Particles |
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10 | </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch05s02.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><th width="60%" align="center">Chapter 5. |
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11 | Tracking and Physics |
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12 | </th><td width="20%" align="right"> <a accesskey="n" href="ch05s04.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.Parti"></a>5.3. |
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13 | Particles |
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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.Parti.Basic"></a>5.3.1. |
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15 | Basic concepts |
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16 | </h3></div></div></div><p> |
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17 | There are three levels of classes to describe particles in Geant4. |
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18 | |
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19 | </p><div class="variablelist"><dl><dt><span class="term"> |
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20 | <span class="emphasis"><em>G4ParticleDefinition</em></span> |
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21 | </span></dt><dd> |
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22 | defines a particle |
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23 | </dd><dt><span class="term"> |
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24 | <span class="emphasis"><em>G4DynamicParticle</em></span> |
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25 | </span></dt><dd> |
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26 | describes a particle interacting with materials |
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27 | </dd><dt><span class="term"> |
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28 | <span class="emphasis"><em>G4Track</em></span> |
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29 | </span></dt><dd> |
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30 | describes a particle traveling in space and time |
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31 | </dd></dl></div><p> |
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32 | </p><p> |
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33 | <span class="emphasis"><em>G4ParticleDefinition</em></span> aggregates information to |
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34 | characterize a particle's properties, such as name, mass, spin, |
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35 | life time, and decay modes. <span class="emphasis"><em>G4DynamicParticle</em></span> aggregates |
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36 | information to describe the dynamics of particles, such as energy, |
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37 | momentum, polarization, and proper time, as well as ``particle |
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38 | definition'' information. <span class="emphasis"><em>G4Track</em></span> includes all information |
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39 | necessary for tracking in a detector simulation, such as time, |
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40 | position, and step, as well as ``dynamic particle'' |
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41 | information. |
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42 | </p><p> |
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43 | <span class="emphasis"><em>G4Track</em></span> has all the information necessary for tracking in |
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44 | Geant4. It includes position, time, and step, as well as |
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45 | kinematics. Details of <span class="emphasis"><em>G4Track</em></span> will be described in |
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46 | <a href="ch05.html#sect.Track" title="5.1. |
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47 | Tracking |
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48 | ">Section 5.1</a>. |
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49 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Parti.Def"></a>5.3.2. |
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50 | Definition of a particle |
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51 | </h3></div></div></div><p> |
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52 | There are a large number of elementary particles and nuclei. Geant4 |
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53 | provides the <span class="emphasis"><em>G4ParticleDefinition</em></span> class to represent |
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54 | particles, and various particles, such as the electron, proton, and |
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55 | gamma have their own classes derived from |
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56 | <span class="emphasis"><em>G4ParticleDefinition</em></span>. |
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57 | </p><p> |
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58 | We do not need to make a class in Geant4 for every kind of |
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59 | particle in the world. There are more than 100 types of particles |
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60 | defined in Geant4 by default. Which particles should be included, |
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61 | and how to implement them, is determined according to the following |
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62 | criteria. (Of course, the user can define any particles he wants. |
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63 | Please see the <span class="bold"><strong>User's Guide: For ToolKit |
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64 | Developers</strong></span>). |
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65 | </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.Parti.Def.PartiList"></a>5.3.2.1. |
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66 | Particle List in Geant4 |
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67 | </h4></div></div></div><p> |
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68 | This list includes all particles in Geant4 and you can see |
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69 | properties of particles such as |
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70 | |
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71 | </p><div class="itemizedlist"><ul type="disc" compact><li><p> |
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72 | PDG encoding |
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73 | </p></li><li><p> |
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74 | mass and width |
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75 | </p></li><li><p> |
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76 | electric charge |
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77 | </p></li><li><p> |
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78 | spin, isospin and parity |
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79 | </p></li><li><p> |
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80 | magnetic moment |
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81 | </p></li><li><p> |
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82 | quark contents |
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83 | </p></li><li><p> |
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84 | life time and decay modes |
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85 | </p></li></ul></div><p> |
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86 | </p><p> |
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87 | Here is a list of particles in Geant4. This list is generated |
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88 | automatically by using Geant4 functionality, so listed values are |
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89 | same as those in your Geant4 application (as far as you do not |
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90 | change source codes). |
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91 | </p><h5><a name="id470604"></a> |
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92 | Categories |
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93 | </h5><p> |
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94 | </p><div class="itemizedlist"><ul type="disc" compact><li><p> |
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95 | <a href="./AllResources/TrackingAndPhysics/particleList.src/quarks/index.html" target="_top"> |
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96 | gluon / quarks / di-quarks |
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97 | </a> |
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98 | </p></li><li><p> |
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99 | <a href="./AllResources/TrackingAndPhysics/particleList.src/leptons/index.html" target="_top"> |
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100 | leptons |
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101 | </a> |
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102 | </p></li><li><p> |
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103 | <a href="./AllResources/TrackingAndPhysics/particleList.src/mesons/index.html" target="_top"> |
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104 | mesons |
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105 | </a> |
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106 | </p></li><li><p> |
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107 | <a href="./AllResources/TrackingAndPhysics/particleList.src/baryons/index.html" target="_top"> |
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108 | baryons |
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109 | </a> |
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110 | </p></li><li><p> |
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111 | <a href="./AllResources/TrackingAndPhysics/particleList.src/ions/index.html" target="_top"> |
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112 | ions |
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113 | </a> |
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114 | </p></li><li><p> |
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115 | <a href="./AllResources/TrackingAndPhysics/particleList.src/others/index.html" target="_top"> |
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116 | others |
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117 | </a> |
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118 | </p></li></ul></div><p> |
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119 | </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.Parti.Def.Classif"></a>5.3.2.2. |
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120 | Classification of particles |
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121 | </h4></div></div></div><p> |
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122 | </p><div class="orderedlist"><ol type="1" compact><li><p> |
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123 | </p><p> |
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124 | elementary particles which should be tracked in Geant4 volumes |
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125 | </p><p> |
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126 | </p><p> |
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127 | All particles that can fly a finite length and interact with |
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128 | materials in detectors are included in this category. In addition, |
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129 | some particles with a very short lifetime are included |
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130 | for user's convenience. |
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131 | |
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132 | </p><div class="orderedlist"><ol type="a" compact><li><p> |
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133 | stable particles |
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134 | </p><p> |
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135 | Stable means that the particle can not decay, or has a very small |
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136 | possibility to decay in detectors, e.g., gamma, electron, proton, |
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137 | and neutron. |
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138 | </p><p> |
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139 | </p></li><li><p> |
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140 | long life (>10<sup>-14</sup>sec) particles |
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141 | </p><p> |
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142 | Particles which may travel a finite length, e.g., muon, charged |
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143 | pions. |
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144 | </p><p> |
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145 | </p></li><li><p> |
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146 | short life particles that decay immediately in Geant4 |
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147 | </p><p> |
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148 | For example, pi<sup>0</sup>, eta |
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149 | </p><p> |
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150 | </p></li><li><p> |
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151 | K<sup>0</sup> system |
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152 | </p><p> |
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153 | K<sup>0</sup> "decays" immediately into |
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154 | K<sup>0</sup><sub>S</sub> |
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155 | or K<sup>0</sup><sub>L</sub>, and then |
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156 | K<sup>0</sup><sub>S</sub>/ |
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157 | K<sup>0</sup><sub>L</sub> decays |
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158 | according to its life time and decay modes. |
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159 | </p><p> |
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160 | </p></li><li><p> |
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161 | optical photon |
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162 | </p><p> |
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163 | Gamma and optical photon are distinguished in the simulation |
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164 | view, though both are the same particle (photons with different |
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165 | energies). For example, optical photon is used for Cerenkov light |
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166 | and scintillation light. |
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167 | </p><p> |
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168 | </p></li><li><p> |
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169 | geantino/charged geantino |
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170 | </p><p> |
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171 | Geantino and charged geantino are virtual particles for |
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172 | simulation which do not interact with materials and undertake |
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173 | transportation processes only. |
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174 | </p><p> |
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175 | </p></li></ol></div><p> |
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176 | </p><p> |
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177 | </p></li><li><p> |
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178 | nuclei |
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179 | </p><p> |
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180 | Any kinds of nucleus can be used in Geant4, such as alpha(He-4), |
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181 | uranium-238 and excited states of carbon-14. In addition, |
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182 | Geant4 provides hyper-nuclei. Nuclei in Geant4 are |
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183 | divided into two groups from the viewpoint of implementation. |
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184 | </p><div class="orderedlist"><ol type="a" compact><li><p> |
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185 | light nuclei |
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186 | </p><p> |
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187 | Light nuclei frequently used in simulation, e.g., alpha, deuteron, |
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188 | He3, triton. |
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189 | </p><p> |
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190 | </p></li><li><p> |
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191 | heavy nuclei (including hyper-nuclei) |
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192 | </p><p> |
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193 | Nuclei other than those defined in the previous category. |
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194 | </p><p> |
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195 | </p></li></ol></div><p> |
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196 | |
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197 | Note that G4ParticleDefinition represents nucleus state and |
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198 | G4DynamicParticle represents atomic state with some nucleus. Both |
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199 | alpha particle with charge of +2e and helium atom with no charge |
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200 | aggregates the same "particle definition" of G4Alpha, but different |
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201 | G4DynamicParticle objects should be assigned to them. (Details can |
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202 | be found below) |
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203 | </p><p> |
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204 | </p></li><li><p> |
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205 | short-lived particles |
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206 | </p><p> |
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207 | Particles with very short life time decay immediately and are never |
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208 | tracked in the detector geometry. These particles are usually used |
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209 | only inside physics processes to implement some models of |
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210 | interactions. <span class="emphasis"><em>G4VShortLivedParticle</em></span> is provided as |
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211 | the base class for these particles. All classes related to particles in |
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212 | this category can be found in <code class="literal">shortlived</code> sub-directory |
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213 | under the <code class="literal">particles</code> directory. |
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214 | |
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215 | </p><div class="orderedlist"><ol type="a" compact><li><p> |
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216 | quarks/di-quarks |
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217 | </p><p> |
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218 | For example, all 6 quarks. |
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219 | </p><p> |
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220 | </p></li><li><p> |
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221 | gluon |
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222 | </p></li><li><p> |
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223 | baryon excited states with very short life |
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224 | </p><p> |
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225 | For example, spin 3/2 baryons and anti-baryons |
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226 | </p><p> |
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227 | </p></li><li><p> |
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228 | meson excited states with very short life |
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229 | </p><p> |
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230 | For example, spin 1 vector bosons |
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231 | </p><p> |
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232 | </p></li></ol></div><p> |
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233 | </p><p> |
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234 | </p></li></ol></div><p> |
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235 | </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.Parti.Def.Imple"></a>5.3.2.3. |
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236 | Implementation of particles |
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237 | </h4></div></div></div><p> |
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238 | <span class="emphasis"><em>Single object created in the initialization :</em></span> |
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239 | Categories a, b-1 |
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240 | </p><p> |
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241 | These particles are frequently used for tracking in |
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242 | Geant4. An individual class is defined for each particle in these |
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243 | categories. The object in each class is unique. |
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244 | The user can get pointers to these objects by using static methods |
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245 | in their own classes. The unique object for each class is created |
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246 | when its static method is called in the ``initialization phase''. |
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247 | </p><p> |
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248 | <span class="emphasis"><em>On-the-fly creation:</em></span> Category b-2 |
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249 | </p><p> |
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250 | Ions will travel in a detector geometry and should |
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251 | be tracked, however, the number of ions which may be used for |
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252 | hadronic processes is so huge that ions are dynamically |
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253 | created by requests from processes (and users). |
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254 | Each ion corresponds to one object of the <span class="emphasis"><em>G4Ions</em></span> |
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255 | class. |
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256 | <span class="emphasis"><em>G4IonTable</em></span> class is a dictionary for ions. |
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257 | <code class="literal">G4ParticleTable::GetIon()</code> method invokes |
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258 | <code class="literal">G4IonTable::GetIon()</code> method to create ions |
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259 | on the fly. |
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260 | </p><p> |
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261 | Users can register a <span class="emphasis"><em>G4IsotopeTable</em></span> to the |
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262 | <span class="emphasis"><em>G4IonTable</em></span>. <span class="emphasis"><em>G4IsotopeTable</em></span> |
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263 | describes properties of ions (exited energy, decay modes, life time |
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264 | and magnetic moments), which are used to create ions. |
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265 | </p><p> |
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266 | <span class="emphasis"><em>Dynamic creation by processes:</em></span> Category c |
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267 | </p><p> |
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268 | Particle types in this category are are not created |
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269 | by default, but will only be created by request from processes or |
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270 | directly by users. Each shortlived particle corresponds to one |
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271 | object of a class derived from <span class="emphasis"><em>G4VshortLivedParticle</em></span>, |
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272 | and it will be created dynamically during the ``initialization |
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273 | phase''. |
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274 | </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="sect.Parti.Def.G4Parti"></a>5.3.2.4. |
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275 | G4ParticleDefinition |
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276 | </h4></div></div></div><p> |
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277 | The <span class="emphasis"><em>G4ParticleDefinition</em></span> class has ``read-only'' properties |
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278 | to characterize individual particles, such as name, mass, charge, |
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279 | spin, and so on. These properties are set during initialization of |
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280 | each particle. Methods to get these properties are listed in |
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281 | <a href="ch05s03.html#table.Parti_1" title="Table 5.2. |
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282 | Methods to get particle properties. |
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283 | ">Table 5.2</a>. |
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284 | |
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285 | </p><div class="table"><a name="table.Parti_1"></a><div class="table-contents"><table summary=" |
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286 | Methods to get particle properties. |
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287 | " border="1"><colgroup><col><col></colgroup><tbody><tr><td> |
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288 | <code class="literal">G4String GetParticleName()</code> |
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289 | </td><td> |
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290 | particle name |
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291 | </td></tr><tr><td> |
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292 | <code class="literal">G4double GetPDGMass()</code> |
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293 | </td><td> |
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294 | mass |
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295 | </td></tr><tr><td> |
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296 | <code class="literal">G4double GetPDGWidth()</code> |
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297 | </td><td> |
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298 | decay width |
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299 | </td></tr><tr><td> |
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300 | <code class="literal">G4double GetPDGCharge()</code> |
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301 | </td><td> |
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302 | electric charge |
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303 | </td></tr><tr><td> |
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304 | <code class="literal">G4double GetPDGSpin()</code> |
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305 | </td><td> |
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306 | spin |
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307 | </td></tr><tr><td> |
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308 | <code class="literal">G4double GetPDGMagneticMoment()</code> |
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309 | </td><td> |
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310 | magnetic moment (0: not defined or no magnetic moment) |
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311 | </td></tr><tr><td> |
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312 | <code class="literal">G4int GetPDGiParity()</code> |
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313 | </td><td> |
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314 | parity (0:not defined) |
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315 | </td></tr><tr><td> |
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316 | <code class="literal">G4int GetPDGiConjugation()</code> |
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317 | </td><td> |
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318 | charge conjugation (0:not defined) |
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319 | </td></tr><tr><td> |
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320 | <code class="literal">G4double GetPDGIsospin()</code> |
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321 | </td><td> |
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322 | iso-spin |
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323 | </td></tr><tr><td> |
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324 | <code class="literal">G4double GetPDGIsospin3()</code> |
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325 | </td><td> |
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326 | 3<sup>rd</sup>-component of iso-spin |
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327 | </td></tr><tr><td> |
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328 | <code class="literal">G4int GetPDGiGParity()</code> |
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329 | </td><td> |
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330 | G-parity (0:not defined) |
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331 | </td></tr><tr><td> |
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332 | <code class="literal">G4String GetParticleType()</code> |
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333 | </td><td> |
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334 | particle type |
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335 | </td></tr><tr><td> |
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336 | <code class="literal">G4String GetParticleSubType()</code> |
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337 | </td><td> |
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338 | particle sub-type |
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339 | </td></tr><tr><td> |
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340 | <code class="literal">G4int GetLeptonNumber()</code> |
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341 | </td><td> |
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342 | lepton number |
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343 | </td></tr><tr><td> |
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344 | <code class="literal">G4int GetBaryonNumber()</code> |
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345 | </td><td> |
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346 | baryon number |
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347 | </td></tr><tr><td> |
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348 | <code class="literal">G4int GetPDGEncoding()</code> |
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349 | </td><td> |
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350 | particle encoding number by PDG |
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351 | </td></tr><tr><td> |
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352 | <code class="literal">G4int GetAntiPDGEncoding()</code> |
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353 | </td><td> |
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354 | encoding for anti-particle of this particle |
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355 | </td></tr></tbody></table></div><p class="title"><b>Table 5.2. |
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356 | Methods to get particle properties. |
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357 | </b></p></div><p><br class="table-break"> |
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358 | </p><p> |
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359 | <a href="ch05s03.html#table.Parti_2" title="Table 5.3. |
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360 | Methods to get particle decay modes and life time. |
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361 | ">Table 5.3</a> shows the methods of |
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362 | <span class="emphasis"><em>G4ParticleDefinition</em></span> for |
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363 | getting information about decay modes and the life time of the |
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364 | particle. |
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365 | |
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366 | </p><div class="table"><a name="table.Parti_2"></a><div class="table-contents"><table summary=" |
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367 | Methods to get particle decay modes and life time. |
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368 | " border="1"><colgroup><col><col></colgroup><tbody><tr><td> |
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369 | <code class="literal">G4bool GetPDGStable()</code> |
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370 | </td><td> |
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371 | stable flag |
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372 | </td></tr><tr><td> |
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373 | <code class="literal">G4double GetPDGLifeTime()</code> |
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374 | </td><td> |
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375 | life time |
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376 | </td></tr><tr><td> |
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377 | <code class="literal">G4DecayTable* GetDecayTable()</code> |
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378 | </td><td> |
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379 | decay table |
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380 | </td></tr></tbody></table></div><p class="title"><b>Table 5.3. |
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381 | Methods to get particle decay modes and life time. |
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382 | </b></p></div><p><br class="table-break"> |
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383 | </p><p> |
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384 | Users can modify these properties, though the other properties |
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385 | listed above can not be change without rebuilding the |
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386 | libraries. |
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387 | </p><p> |
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388 | Each particle has its own <span class="emphasis"><em>G4ProcessManger</em></span> |
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389 | object that manages a list of processes applicable to the |
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390 | particle.(see <a href="ch02s05.html#sect.HowToSpecPhysProc.ManagingProc" title="2.5.2. |
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391 | Managing Processes |
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392 | ">Section 2.5.2</a> ) |
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393 | </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Parti.Dynam"></a>5.3.3. |
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394 | Dynamic particle |
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395 | </h3></div></div></div><p> |
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396 | The <span class="emphasis"><em>G4DynamicParticle</em></span> class has kinematics information for |
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397 | the particle and is used for describing the dynamics of physics |
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398 | processes. The properties in <span class="emphasis"><em>G4DynamicParticle</em></span> are listed in |
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399 | <a href="ch05s03.html#table.Parti_4" title="Table 5.4. |
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400 | Methods to set/get cut off values. |
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401 | ">Table 5.4</a>. |
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402 | |
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403 | </p><div class="table"><a name="table.Parti_4"></a><div class="table-contents"><table summary=" |
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404 | Methods to set/get cut off values. |
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405 | " border="1"><colgroup><col><col></colgroup><tbody><tr><td> |
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406 | <code class="literal">G4double theDynamicalMass</code> |
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407 | </td><td> |
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408 | dynamical mass |
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409 | </td></tr><tr><td> |
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410 | <code class="literal">G4ThreeVector theMomentumDirection</code> |
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411 | </td><td> |
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412 | normalized momentum vector |
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413 | </td></tr><tr><td> |
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414 | <code class="literal">G4ParticleDefinition* theParticleDefinition</code> |
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415 | </td><td> |
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416 | definition of particle |
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417 | </td></tr><tr><td> |
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418 | <code class="literal">G4double theDynamicalSpin</code> |
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419 | </td><td> |
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420 | dynamical spin |
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421 | (i.e. total angular momentum as a ion/atom ) |
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422 | </td></tr><tr><td> |
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423 | <code class="literal">G4ThreeVector thePolarization</code> |
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424 | </td><td> |
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425 | polarization vector |
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426 | </td></tr><tr><td> |
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427 | <code class="literal">G4double theMagneticMoment</code> |
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428 | </td><td> |
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429 | dynamical magnetic moment |
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430 | (i.e. total magnetic moment as a ion/atom ) |
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431 | </td></tr><tr><td> |
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432 | <code class="literal">G4double theKineticEnergy</code> |
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433 | </td><td> |
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434 | kinetic energy |
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435 | </td></tr><tr><td> |
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436 | <code class="literal">G4double theProperTime</code> |
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437 | </td><td> |
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438 | proper time |
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439 | </td></tr><tr><td> |
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440 | <code class="literal">G4double theDynamicalCharge</code> |
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441 | </td><td> |
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442 | dynamical electric charge |
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443 | (i.e. total electric charge as a ion/atom ) |
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444 | </td></tr><tr><td> |
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445 | <code class="literal">G4ElectronOccupancy* theElectronOccupancy</code> |
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446 | </td><td> |
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447 | electron orbits for ions |
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448 | </td></tr></tbody></table></div><p class="title"><b>Table 5.4. |
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449 | Methods to set/get cut off values. |
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450 | </b></p></div><p><br class="table-break"> |
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451 | </p><p> |
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452 | Here, the dynamical mass is defined as the mass for the dynamic |
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453 | particle. For most cases, it is same as the mass defined in |
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454 | <span class="emphasis"><em>G4ParticleDefinition</em></span> class ( i.e. mass value given by |
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455 | <code class="literal">GetPDGMass()</code> method). However, there are two |
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456 | exceptions. |
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457 | |
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458 | </p><div class="itemizedlist"><ul type="disc" compact><li><p> |
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459 | resonance particle |
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460 | </p></li><li><p> |
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461 | ions |
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462 | </p></li></ul></div><p> |
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463 | </p><p> |
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464 | Resonance particles have large mass width and the total energy of |
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465 | decay products at the center of mass system can be different event |
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466 | by event. |
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467 | </p><p> |
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468 | As for ions, <span class="emphasis"><em>G4ParticleDefintion</em></span> defines a nucleus and |
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469 | <span class="emphasis"><em>G4DynamicParticle</em></span> defines an atom. |
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470 | <span class="emphasis"><em>G4ElectronOccupancy</em></span> describes state of orbital electrons. |
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471 | So, the dynamic mass can be different from the PDG mass by the mass |
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472 | of electrons (and their binding energy). In addition, the dynamical |
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473 | charge, spin and magnetic moment are those of the atom/ion |
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474 | (i.e. including nucleus and orbit electrons). |
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475 | </p><p> |
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476 | Decay products of heavy flavor particles are given in many event |
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477 | generators. In such cases, <span class="emphasis"><em>G4VPrimaryGenerator</em></span> sets this |
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478 | information in <code class="literal">*thePreAssignedDecayProducts</code>. In addition, |
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479 | decay time of the particle can be set arbitrarily time by using |
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480 | <code class="literal">PreAssignedDecayProperTime</code>. |
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481 | </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch05s02.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><td width="20%" align="center"><a accesskey="u" href="ch05.html"><img src="AllResources/IconsGIF/up.gif" alt="Up"></a></td><td width="40%" align="right"> <a accesskey="n" href="ch05s04.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr><tr><td width="40%" align="left" valign="top">5.2. |
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482 | Physics Processes |
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483 | </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"> 5.4. |
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484 | Production Threshold versus Tracking Cut |
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485 | </td></tr></table></div></body></html> |
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