1 | <!-- ******************************************************** --> |
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2 | <!-- --> |
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3 | <!-- [History] --> |
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4 | <!-- Created by: Makoto Asai, 14-Apr-2003 --> |
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5 | <!-- Converted to DocBook: Katsuya Amako, Aug-2006 --> |
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6 | <!-- --> |
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7 | <!-- ******************************************************** --> |
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8 | |
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9 | |
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10 | <!-- ******************* Section (Level#1) ****************** --> |
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11 | <sect1 id="sect.CutReg"> |
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12 | <title> |
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13 | Cuts per Region |
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14 | </title> |
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15 | |
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16 | |
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17 | <!-- ******************* Section (Level#2) ****************** --> |
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18 | <sect2 id="sect.CutReg.Gene"> |
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19 | <title> |
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20 | General Concepts |
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21 | </title> |
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22 | |
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23 | <para> |
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24 | Beginning with Geant4 version 5.1, the concept of a region has been |
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25 | defined for use in geometrical descriptions. Details about regions |
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26 | and how to use them are available in |
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27 | <xref linkend="sect.Geom.LogVol.SubReg" />. |
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28 | As an example, suppose a user defines three regions, corresponding to |
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29 | the tracking volume, the calorimeter and the bulk structure of a |
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30 | detector. For performance reasons, the user may not be interested |
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31 | in the detailed development of electromagnetic showers in the |
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32 | insensitive bulk structure, but wishes to maintain the best |
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33 | possible accuracy in the tracking region. In such a use case, |
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34 | Geant4 allows the user to set different production thresholds |
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35 | ("cuts") for each geometrical region. This ability, referred to as |
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36 | "cuts per region", is also a new feature provided by the Geant4 5.1 |
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37 | release. The general concepts of production thresholds were |
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38 | presented in the <xref linkend="sect.ProThres" />. |
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39 | </para> |
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40 | |
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41 | <para> |
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42 | Please note that this new feature is intended only for users |
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43 | who |
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44 | |
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45 | <orderedlist spacing="compact"> |
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46 | <listitem><para> |
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47 | are simulating the most complex geometries, such as an LHC |
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48 | detector, and |
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49 | </para></listitem> |
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50 | <listitem><para> |
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51 | are experienced in simulating electromagnetic showers in |
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52 | matter. |
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53 | </para></listitem> |
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54 | </orderedlist> |
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55 | </para> |
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56 | |
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57 | <para> |
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58 | We strongly recommend that results generated with this new feature |
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59 | be compared with results using the same geometry and uniform |
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60 | production thresholds. Setting completely different cut values for |
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61 | individual regions may break the coherent and comprehensive |
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62 | accuracy of the simulation. Therefore cut values should be |
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63 | carefully optimized, based on a comparison with results obtained |
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64 | using uniform cuts. |
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65 | </para> |
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66 | |
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67 | </sect2> |
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68 | |
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69 | |
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70 | <!-- ******************* Section (Level#2) ****************** --> |
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71 | <sect2 id="sect.CutReg.DefReg"> |
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72 | <title> |
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73 | Default Region |
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74 | </title> |
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75 | |
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76 | <para> |
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77 | The world volume is treated as a region by default. A |
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78 | <emphasis>G4Region</emphasis> object is automatically assigned to the world |
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79 | volume and is referred to as the "default region". The production |
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80 | cuts for this region are the defaults which are defined in the |
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81 | <emphasis>UserPhysicsList</emphasis>. Unless the user defines different cut |
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82 | values for other regions, the cuts in the default region will be |
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83 | used for the entire geometry. |
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84 | </para> |
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85 | |
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86 | <para> |
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87 | Please note that the default region and its default production |
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88 | cuts are created and set automatically by <emphasis>G4RunManager</emphasis>. |
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89 | The user is <emphasis role="bold">not</emphasis> allowed to set a region to |
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90 | the world volume, <emphasis role="bold">nor</emphasis> to assign other |
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91 | production cuts to the default region. |
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92 | </para> |
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93 | |
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94 | </sect2> |
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95 | |
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96 | |
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97 | <!-- ******************* Section (Level#2) ****************** --> |
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98 | <sect2 id="sect.CutReg.Assig"> |
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99 | <title> |
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100 | Assigning Production Cuts to a Region |
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101 | </title> |
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102 | |
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103 | <para> |
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104 | In the <literal>SetCuts()</literal> method of the user's physics list, the |
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105 | user must first define the default cuts. Then a |
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106 | <emphasis>G4ProductionCuts</emphasis> object must be created and initialized with |
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107 | the cut value desired for a given region. This object must in turn |
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108 | be assigned to the region object, which can be accessed by name |
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109 | from the <emphasis>G4RegionStore</emphasis>. An example <literal>SetCuts()</literal> |
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110 | code follows. |
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111 | |
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112 | <example id="programlist_CutReg_1"> |
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113 | <title> |
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114 | <literal>Setting production cuts to a region</literal> |
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115 | </title> |
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116 | |
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117 | <programlisting> |
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118 | void MyPhysicsList::SetCuts() |
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119 | { |
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120 | // default production thresholds for the world volume |
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121 | SetCutsWithDefault(); |
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122 | |
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123 | // Production thresholds for detector regions |
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124 | G4Region* region; |
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125 | G4String regName; |
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126 | G4ProductionCuts* cuts; |
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127 | |
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128 | regName = "tracker"; |
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129 | region = G4RegionStore::GetInstance()->GetRegion(regName); |
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130 | cuts = new G4ProductionCuts; |
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131 | cuts->SetProductionCut(0.01*mm); // same cuts for gamma, e- and e+ |
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132 | region->SetProductionCuts(cuts); |
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133 | |
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134 | regName = "calorimeter"; |
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135 | region = G4RegionStore::GetInstance()->GetRegion(regName); |
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136 | cuts = new G4ProductionCuts; |
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137 | cuts->SetProductionCut(0.01*mm,G4ProductionCuts::GetIndex("gamma")); |
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138 | cuts->SetProductionCut(0.1*mm,G4ProductionCuts::GetIndex("e-")); |
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139 | cuts->SetProductionCut(0.1*mm,G4ProductionCuts::GetIndex("e+")); |
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140 | region->SetProductionCuts(cuts); |
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141 | } |
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142 | </programlisting> |
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143 | </example> |
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144 | </para> |
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145 | |
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146 | |
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147 | </sect2> |
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148 | </sect1> |
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