1 | <!-- ******************************************************** --> |
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2 | <!-- --> |
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3 | <!-- [History] --> |
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4 | <!-- Changed by: Katsuya Amako, 30-Jul-1998 --> |
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5 | <!-- Proof read by: Joe Chuma, 29-Jun-1999 --> |
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6 | <!-- Converted to DocBook: Katsuya Amako, Aug-2006 --> |
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7 | <!-- --> |
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8 | <!-- ******************************************************** --> |
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9 | |
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10 | |
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11 | <!-- ******************* Section (Level#1) ****************** --> |
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12 | <sect1 id="sect.PhysProc"> |
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13 | <title> |
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14 | Physics Processes |
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15 | </title> |
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16 | |
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17 | <para> |
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18 | Physics processes describe how particles interact with a |
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19 | material. Seven major categories of processes are provided by |
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20 | Geant4: |
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21 | |
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22 | <orderedlist spacing="compact"> |
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23 | <listitem><para> |
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24 | <link linkend="sect.PhysProc.EleMag"> |
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25 | electromagnetic |
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26 | </link> |
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27 | , |
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28 | </para></listitem> |
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29 | <listitem><para> |
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30 | <link linkend="sect.PhysProc.Had"> |
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31 | hadronic |
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32 | </link> |
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33 | , |
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34 | </para></listitem> |
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35 | <listitem><para> |
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36 | <link linkend="sect.PhysProc.Decay"> |
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37 | decay |
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38 | </link> |
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39 | , |
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40 | </para></listitem> |
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41 | <listitem><para> |
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42 | <link linkend="sect.PhysProc.PhotoHad"> |
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43 | photolepton-hadron |
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44 | </link> |
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45 | , |
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46 | </para></listitem> |
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47 | <listitem><para> |
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48 | <link linkend="sect.PhysProc.Photo"> |
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49 | optical |
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50 | </link> |
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51 | , |
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52 | </para></listitem> |
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53 | <listitem><para> |
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54 | <link linkend="sect.PhysProc.Param"> |
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55 | parameterization |
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56 | </link> |
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57 | and |
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58 | </para></listitem> |
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59 | <listitem><para> |
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60 | <link linkend="sect.PhysProc.Trans"> |
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61 | transportation |
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62 | </link> |
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63 | . |
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64 | </para></listitem> |
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65 | </orderedlist> |
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66 | </para> |
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67 | |
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68 | <para> |
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69 | The generalization and abstraction of physics processes is a key |
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70 | issue in the design of Geant4. All physics processes are treated in |
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71 | the same manner from the tracking point of view. The Geant4 |
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72 | approach enables anyone to create a process and assign it to a |
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73 | particle type. This openness should allow the creation of processes |
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74 | for novel, domain-specific or customised purposes by individuals or |
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75 | groups of users. |
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76 | </para> |
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77 | |
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78 | <para> |
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79 | Each process has two groups of methods which play an important |
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80 | role in tracking, <literal>GetPhysicalInteractionLength</literal> (GPIL) and |
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81 | <literal>DoIt</literal>. The GPIL method gives the step length from the |
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82 | current space-time point to the next space-time point. It does this |
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83 | by calculating the probability of interaction based on the |
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84 | process's cross section information. At the end of this step the |
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85 | <literal>DoIt</literal> method should be invoked. The <literal>DoIt</literal> method |
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86 | implements the details of the interaction, changing the particle's |
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87 | energy, momentum, direction and position, and producing secondary |
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88 | tracks if required. These changes are recorded as |
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89 | <emphasis>G4VParticleChange</emphasis> objects(see |
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90 | <link linkend="brhead.PhysProc.PrtChng"> |
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91 | Particle Change</link>). |
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92 | </para> |
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93 | |
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94 | <!-- ******* Bridgehead ******* --> |
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95 | <bridgehead renderas='sect4'> |
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96 | G4VProcess |
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97 | </bridgehead> |
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98 | |
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99 | <para> |
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100 | <emphasis>G4VProcess</emphasis> is the base class for all physics processes. |
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101 | Each physics process must implement virtual methods of |
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102 | <emphasis>G4VProcess</emphasis> which describe the interaction (DoIt) and |
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103 | determine when an interaction should occur (GPIL). In order to |
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104 | accommodate various types of interactions <emphasis>G4VProcess</emphasis> |
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105 | provides three <literal>DoIt</literal> methods: |
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106 | |
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107 | <itemizedlist spacing="compact"> |
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108 | <listitem><para> |
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109 | <literal>G4VParticleChange* AlongStepDoIt( const G4Track& track, |
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110 | const G4Step& stepData )</literal> |
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111 | <para> |
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112 | This method is invoked while <emphasis>G4SteppingManager</emphasis> is |
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113 | transporting a particle through one step. The corresponding |
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114 | <literal>AlongStepDoIt</literal> for each defined process is applied for |
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115 | every step regardless of which process produces the minimum step |
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116 | length. Each resulting change to the track information is recorded |
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117 | and accumulated in <emphasis>G4Step</emphasis>. After all processes have been |
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118 | invoked, changes due to <literal>AlongStepDoIt</literal> are applied to |
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119 | <emphasis>G4Track</emphasis>, including the particle relocation and the safety |
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120 | update. Note that after the invocation of <literal>AlongStepDoIt</literal>, |
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121 | the endpoint of the <emphasis>G4Track</emphasis> object is in a new volume if the |
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122 | step was limited by a geometric boundary. In order to obtain |
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123 | information about the old volume, <emphasis>G4Step</emphasis> must be accessed, |
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124 | since it contains information about both endpoints of a step. |
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125 | </para> |
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126 | </para></listitem> |
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127 | <listitem><para> |
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128 | <literal>G4VParticleChange* PostStepDoIt( const G4Track& track, |
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129 | const G4Step& stepData )</literal> |
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130 | <para> |
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131 | This method is invoked at the end point of a step, only if its |
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132 | process has produced the minimum step length, or if the process is |
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133 | forced to occur. <emphasis>G4Track</emphasis> will be updated after each |
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134 | invocation of <literal>PostStepDoIt</literal>, in contrast to the |
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135 | <literal>AlongStepDoIt</literal> method. |
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136 | </para> |
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137 | </para></listitem> |
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138 | <listitem><para> |
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139 | <literal>G4VParticleChange* AtRestDoIt( const G4Track& track, |
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140 | const G4Step& stepData )</literal> |
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141 | <para> |
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142 | This method is invoked only for stopped particles, and only if |
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143 | its process produced the minimum step length or the process is |
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144 | forced to occur. |
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145 | </para> |
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146 | </para></listitem> |
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147 | </itemizedlist> |
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148 | </para> |
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149 | |
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150 | <para> |
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151 | For each of the above <literal>DoIt</literal> methods <emphasis>G4VProcess</emphasis> |
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152 | provides a corresponding pure virtual GPIL method: |
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153 | |
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154 | <itemizedlist spacing="compact"> |
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155 | <listitem><para> |
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156 | <literal>G4double PostStepGetPhysicalInteractionLength( const |
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157 | G4Track& track, G4double previousStepSize, G4ForceCondition* |
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158 | condition )</literal> |
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159 | <para> |
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160 | This method generates the step length allowed by its process. It |
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161 | also provides a flag to force the interaction to occur regardless |
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162 | of its step length. |
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163 | </para> |
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164 | </para></listitem> |
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165 | <listitem><para> |
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166 | <literal>G4double AlongStepGetPhysicalInteractionLength( const |
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167 | G4Track& track, G4double previousStepSize, G4double |
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168 | currentMinimumStep, G4double& proposedSafety, G4GPILSelection* |
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169 | selection )</literal> |
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170 | <para> |
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171 | This method generates the step length allowed by its process. |
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172 | </para> |
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173 | </para></listitem> |
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174 | <listitem><para> |
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175 | <literal>G4double AtRestGetPhysicalInteractionLength( const |
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176 | G4Track& track, G4ForceCondition* condition )</literal> |
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177 | <para> |
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178 | This method generates the step length in time allowed by its |
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179 | process. It also provides a flag to force the interaction to occur |
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180 | regardless of its step length. |
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181 | </para> |
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182 | </para></listitem> |
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183 | </itemizedlist> |
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184 | </para> |
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185 | |
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186 | <para> |
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187 | Other pure virtual methods in <emphasis>G4VProcess</emphasis> follow: |
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188 | |
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189 | <itemizedlist spacing="compact"> |
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190 | <listitem><para> |
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191 | <literal>virtual G4bool IsApplicable(const |
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192 | G4ParticleDefinition&)</literal> |
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193 | <para> |
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194 | returns true if this process object is applicable to the |
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195 | particle type. |
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196 | </para> |
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197 | </para></listitem> |
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198 | <listitem><para> |
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199 | <literal>virtual void PreparePhysicsTable(const |
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200 | G4ParticleDefinition&)</literal> and |
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201 | </para></listitem> |
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202 | <listitem><para> |
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203 | <literal>virtual void BuildPhysicsTable(const |
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204 | G4ParticleDefinition&)</literal> |
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205 | <para> |
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206 | is messaged by the process manager, whenever cross section |
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207 | tables should be prepared and rebuilt due to changing cut-off |
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208 | values. It is not mandatory if the process is not affected by |
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209 | cut-off values. |
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210 | </para> |
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211 | </para></listitem> |
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212 | <listitem><para> |
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213 | <literal>virtual void StartTracking()</literal> and |
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214 | </para></listitem> |
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215 | <listitem><para> |
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216 | <literal>virtual void EndTracking()</literal> |
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217 | <para> |
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218 | are messaged by the tracking manager at the beginning and end of |
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219 | tracking the current track. |
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220 | </para> |
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221 | </para></listitem> |
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222 | </itemizedlist> |
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223 | </para> |
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224 | |
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225 | |
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226 | <!-- ******* Bridgehead ******* --> |
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227 | <bridgehead renderas='sect4'> |
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228 | Other base classes for processes |
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229 | </bridgehead> |
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230 | |
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231 | <para> |
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232 | Specialized processes may be derived from seven additional |
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233 | virtual base classes which are themselves derived from |
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234 | <emphasis>G4VProcess</emphasis>. Three of these classes are used for simple |
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235 | processes: |
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236 | |
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237 | <variablelist> |
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238 | <varlistentry> |
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239 | <term><emphasis>G4VRestProcess</emphasis></term> |
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240 | <listitem> |
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241 | <para> |
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242 | Processes using only the <literal>AtRestDoIt</literal> method. |
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243 | </para> |
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244 | <para> |
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245 | example: neutron capture |
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246 | </para> |
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247 | </listitem> |
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248 | </varlistentry> |
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249 | <varlistentry> |
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250 | <term><emphasis>G4VDiscreteProcess</emphasis></term> |
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251 | <listitem> |
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252 | <para> |
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253 | Processes using only the <literal>PostStepDoIt</literal> method. |
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254 | </para> |
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255 | <para> |
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256 | example: compton scattering, hadron inelastic interaction |
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257 | </para> |
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258 | </listitem> |
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259 | </varlistentry> |
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260 | </variablelist> |
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261 | </para> |
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262 | |
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263 | <para> |
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264 | The other four classes are provided for rather complex |
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265 | processes: |
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266 | |
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267 | <variablelist> |
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268 | <varlistentry> |
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269 | <term><emphasis>G4VContinuousDiscreteProcess</emphasis></term> |
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270 | <listitem> |
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271 | <para> |
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272 | Processes using both <literal>AlongStepDoIt</literal> and |
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273 | <literal>PostStepDoIt</literal> methods. |
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274 | </para> |
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275 | <para> |
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276 | example: transportation, ionisation(energy loss and delta ray) |
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277 | </para> |
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278 | </listitem> |
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279 | </varlistentry> |
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280 | <varlistentry> |
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281 | <term><emphasis>G4VRestDiscreteProcess</emphasis></term> |
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282 | <listitem> |
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283 | <para> |
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284 | Processes using both <literal>AtRestDoIt</literal> and |
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285 | <literal>PostStepDoIt</literal> methods. |
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286 | </para> |
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287 | <para> |
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288 | example: positron annihilation, decay (both in flight and at rest) |
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289 | </para> |
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290 | </listitem> |
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291 | </varlistentry> |
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292 | <varlistentry> |
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293 | <term><emphasis>G4VRestContinuousProcess</emphasis></term> |
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294 | <listitem> |
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295 | <para> |
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296 | Processes using both <literal>AtRestDoIt</literal> and |
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297 | <literal>AlongStepDoIt</literal> methods. |
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298 | </para> |
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299 | </listitem> |
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300 | </varlistentry> |
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301 | <varlistentry> |
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302 | <term><emphasis>G4VRestContinuousDiscreteProcess</emphasis></term> |
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303 | <listitem> |
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304 | <para> |
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305 | Processes using <literal>AtRestDoIt</literal>, |
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306 | <literal>AlongStepDoIt and</literal> PostStepDoIt methods. |
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307 | </para> |
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308 | </listitem> |
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309 | </varlistentry> |
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310 | </variablelist> |
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311 | </para> |
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312 | |
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313 | <!-- ******* Bridgehead ******* --> |
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314 | <bridgehead renderas='sect4' id="brhead.PhysProc.PrtChng"> |
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315 | Particle change |
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316 | </bridgehead> |
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317 | |
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318 | <para> |
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319 | <emphasis>G4VParticleChange</emphasis> and its descendants are used to store |
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320 | the final state information of the track, including secondary |
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321 | tracks, which has been generated by the <literal>DoIt</literal> methods. The |
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322 | instance of <emphasis>G4VParticleChange</emphasis> is the only object whose |
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323 | information is updated by the physics processes, hence it is |
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324 | responsible for updating the step. The stepping manager collects |
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325 | secondary tracks and only sends requests via particle change to |
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326 | update <emphasis>G4Step</emphasis>. |
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327 | </para> |
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328 | |
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329 | <para> |
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330 | <emphasis>G4VParticleChange</emphasis> is introduced as an abstract class. It |
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331 | has a minimal set of methods for updating <emphasis>G4Step</emphasis> and |
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332 | handling secondaries. A physics process can therefore define its |
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333 | own particle change derived from <emphasis>G4VParticleChange</emphasis>. Three |
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334 | pure virtual methods are provided, |
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335 | |
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336 | <itemizedlist spacing="compact"> |
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337 | <listitem><para> |
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338 | <literal>virtual G4Step* UpdateStepForAtRest( G4Step* step)</literal>, |
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339 | </para></listitem> |
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340 | <listitem><para> |
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341 | <literal>virtual G4Step* UpdateStepForAlongStep( G4Step* step )</literal> |
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342 | and |
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343 | </para></listitem> |
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344 | <listitem><para> |
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345 | <literal>virtual G4Step* UpdateStepForPostStep( G4Step* step)</literal>, |
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346 | </para></listitem> |
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347 | </itemizedlist> |
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348 | |
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349 | which correspond to the three <literal>DoIt</literal> methods of |
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350 | <emphasis>G4VProcess</emphasis>. Each derived class should implement these |
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351 | methods. |
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352 | </para> |
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353 | |
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354 | |
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355 | <!-- ******************* Section (Level#2) ****************** --> |
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356 | <sect2 id="sect.PhysProc.EleMag"> |
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357 | <title> |
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358 | Electromagnetic Interactions |
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359 | </title> |
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360 | |
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361 | <para> |
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362 | This section summarizes the electromagnetic (EM) physics processes which |
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363 | are provided with Geant4. Extended information are avalable at EM web |
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364 | <ulink url="http://geant4.web.cern.ch/geant4/collaboration/EMindex.shtml"> |
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365 | <emphasis role="bold">pages</emphasis></ulink>. |
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366 | For details on the implementation of these |
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367 | processes please refer to the |
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368 | <ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/PhysicsReferenceManual/html/PhysicsReferenceManual.html"> |
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369 | <emphasis role="bold">Physics Reference Manual</emphasis></ulink>. |
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370 | </para> |
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371 | |
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372 | <!-- ******************* Section (Level#3) ****************** --> |
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373 | <sect3 id="sect.PhysProc.EleMag.Stand"> |
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374 | <title> |
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375 | "Standard" Electromagnetic Processes |
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376 | </title> |
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377 | |
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378 | <para> |
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379 | The following is a summary of the standard electromagnetic |
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380 | processes available in Geant4. |
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381 | |
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382 | <itemizedlist spacing="compact"> |
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383 | <listitem><para> |
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384 | Photon processes |
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385 | <itemizedlist spacing="compact"> |
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386 | <listitem><para> |
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387 | Compton scattering (class name <emphasis>G4ComptonScattering</emphasis>) |
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388 | </para></listitem> |
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389 | <listitem><para> |
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390 | Gamma conversion (also called pair production, class name |
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391 | <emphasis>G4GammaConversion</emphasis>) |
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392 | </para></listitem> |
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393 | <listitem><para> |
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394 | Photo-electric effect (class name <emphasis>G4PhotoElectricEffect</emphasis>) |
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395 | </para></listitem> |
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396 | <listitem><para> |
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397 | Muon pair production (class name <emphasis>G4GammaConversionToMuons</emphasis>) |
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398 | </para></listitem> |
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399 | </itemizedlist> |
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400 | </para></listitem> |
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401 | <listitem><para> |
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402 | Electron/positron processes |
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403 | <itemizedlist spacing="compact"> |
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404 | <listitem><para> |
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405 | Ionisation and delta ray production (class name |
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406 | <emphasis>G4eIonisation</emphasis>) |
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407 | </para></listitem> |
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408 | <listitem><para> |
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409 | Bremsstrahlung (class name <emphasis>G4eBremsstrahlung</emphasis>) |
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410 | </para></listitem> |
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411 | <listitem><para> |
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412 | Multiple scattering (class name <emphasis>G4eMultipleScattering</emphasis>) |
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413 | </para></listitem> |
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414 | <listitem><para> |
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415 | Positron annihilation into two gammas (class name |
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416 | <emphasis>G4eplusAnnihilation</emphasis>) |
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417 | </para></listitem> |
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418 | <listitem><para> |
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419 | Positron annihilation into two muons (class name |
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420 | <emphasis>G4AnnihiToMuPair</emphasis>) |
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421 | </para></listitem> |
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422 | <listitem><para> |
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423 | Positron annihilation into hadrons (class name |
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424 | <emphasis>G4eeToHadrons</emphasis>) |
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425 | </para></listitem> |
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426 | </itemizedlist> |
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427 | </para></listitem> |
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428 | <listitem><para> |
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429 | Muon processes |
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430 | <itemizedlist spacing="compact"> |
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431 | <listitem><para> |
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432 | Bremsstrahlung (class name <emphasis>G4MuBremsstrahlung</emphasis>) |
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433 | </para></listitem> |
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434 | <listitem><para> |
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435 | Ionisation and delta ray production (class name |
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436 | <emphasis>G4MuIonisation</emphasis>) |
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437 | </para></listitem> |
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438 | <listitem><para> |
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439 | Multiple scattering (class name <emphasis>G4MuMultipleScattering</emphasis>) |
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440 | </para></listitem> |
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441 | <listitem><para> |
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442 | e+e- pair production (class name |
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443 | <emphasis>G4MuPairProduction</emphasis>) |
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444 | </para></listitem> |
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445 | </itemizedlist> |
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446 | </para></listitem> |
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447 | <listitem><para> |
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448 | Hadron/ion processes |
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449 | <itemizedlist spacing="compact"> |
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450 | <listitem><para> |
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451 | Bremsstrahlung (class name <emphasis>G4hBremsstrahlung</emphasis>) |
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452 | </para></listitem> |
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453 | <listitem><para> |
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454 | Ionisation (class name <emphasis>G4hIonisation</emphasis>) |
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455 | </para></listitem> |
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456 | <listitem><para> |
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457 | e+e- pair production (class name <emphasis>G4hPairProduction</emphasis>) |
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458 | </para></listitem> |
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459 | <listitem><para> |
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460 | Ionisation for ions (class name <emphasis>G4ionIonisation</emphasis>) |
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461 | </para></listitem> |
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462 | <listitem><para> |
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463 | Multiple scattering (class name <emphasis>G4hMultipleScattering</emphasis>) |
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464 | </para></listitem> |
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465 | <listitem><para> |
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466 | Ionisation for heavy exotic particles (class name |
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467 | <emphasis>G4hhIonisation</emphasis>) |
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468 | </para></listitem> |
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469 | <listitem><para> |
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470 | Ionisation for classical magnetic monopole (class name |
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471 | <emphasis>G4mplIonisation</emphasis>) |
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472 | </para></listitem> |
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473 | </itemizedlist> |
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474 | </para></listitem> |
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475 | <listitem><para> |
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476 | Coulomb scattering processes |
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477 | <itemizedlist spacing="compact"> |
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478 | <listitem><para> |
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479 | A general process in the sense that the same process/class |
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480 | is used to simulate the multiple scattering of the all charged |
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481 | particles (class name <emphasis>G4MultipleScattering</emphasis>) |
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482 | </para></listitem> |
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483 | <listitem><para> |
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484 | Alternative process for simulation of single Coulomb scattering |
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485 | of all charged particles (class name <emphasis>G4CoulombScattering</emphasis>) |
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486 | </para></listitem> |
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487 | <listitem><para> |
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488 | Alternative process for simulation of single Coulomb scattering |
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489 | of ions (class name <emphasis>G4ScreenedNuclearRecoil</emphasis>) |
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490 | </para></listitem> |
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491 | </itemizedlist> |
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492 | </para></listitem> |
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493 | <listitem><para> |
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494 | Processes for simulation of polarized electron and gamma beams |
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495 | <itemizedlist spacing="compact"> |
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496 | <listitem><para> |
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497 | Compton scattering of circularly polarized gamma beam on |
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498 | polarized target (class name <emphasis>G4PolarizedCompton</emphasis>) |
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499 | </para></listitem> |
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500 | <listitem><para> |
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501 | Pair production induced by circularly polarized gamma beam |
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502 | (class name <emphasis>G4PolarizedGammaConversion</emphasis>) |
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503 | </para></listitem> |
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504 | <listitem><para> |
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505 | Photo-electric effect induced by circularly polarized gamma beam |
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506 | (class name <emphasis>G4PolarizedPhotoElectricEffect</emphasis>) |
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507 | </para></listitem> |
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508 | <listitem><para> |
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509 | Bremsstrahlung of polarized electrons and positrons |
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510 | (class name <emphasis>G4ePolarizedBremsstrahlung</emphasis>) |
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511 | </para></listitem> |
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512 | <listitem><para> |
---|
513 | Ionisation of polarized electron and positron beam |
---|
514 | (class name <emphasis>G4ePolarizedIonisation</emphasis>) |
---|
515 | </para></listitem> |
---|
516 | <listitem><para> |
---|
517 | Annihilation of polarized positrons |
---|
518 | (class name <emphasis>G4eplusPolarizedAnnihilation</emphasis>) |
---|
519 | </para></listitem> |
---|
520 | </itemizedlist> |
---|
521 | </para></listitem> |
---|
522 | <listitem><para> |
---|
523 | Processes for simulation of X-rays and optical protons production by charged particles |
---|
524 | <itemizedlist spacing="compact"> |
---|
525 | <listitem><para> |
---|
526 | Synchrotron radiation (class name <emphasis>G4SynchrotronRadiation</emphasis>) |
---|
527 | </para></listitem> |
---|
528 | <listitem><para> |
---|
529 | Transition radiation |
---|
530 | (class name <emphasis>G4TransitionRadiation</emphasis>) |
---|
531 | </para></listitem> |
---|
532 | <listitem><para> |
---|
533 | Cerenkov radiation |
---|
534 | (class name <emphasis>G4Cerenkov</emphasis>) |
---|
535 | </para></listitem> |
---|
536 | <listitem><para> |
---|
537 | Scintillations |
---|
538 | (class name <emphasis>G4Scintillation</emphasis>) |
---|
539 | </para></listitem> |
---|
540 | </itemizedlist> |
---|
541 | </para></listitem> |
---|
542 | <listitem><para> |
---|
543 | The processes described above use physics model classes, which |
---|
544 | may be combined according to particle energy. It is possible to |
---|
545 | change the energy range over which different models are valid, and |
---|
546 | to apply other models specific to particle type, energy range, and |
---|
547 | G4Region. The following alternative models are available: |
---|
548 | <itemizedlist spacing="compact"> |
---|
549 | <listitem><para> |
---|
550 | Ionisation in thin absorbers (class name <emphasis>G4PAIModel</emphasis>) |
---|
551 | </para></listitem> |
---|
552 | </itemizedlist> |
---|
553 | </para></listitem> |
---|
554 | </itemizedlist> |
---|
555 | </para> |
---|
556 | |
---|
557 | <para> |
---|
558 | It is recommended to use physics constructor classes provided |
---|
559 | with rederence physics lists ($G4INSTALL/source/physics_lists/builders): |
---|
560 | <itemizedlist spacing="compact"> |
---|
561 | <listitem><para> |
---|
562 | default EM physics (class name <emphasis>G4EmStandardPhysics</emphasis>) |
---|
563 | </para></listitem> |
---|
564 | <listitem><para> |
---|
565 | optional EM physics providing similar performance as g4 7.1p01 |
---|
566 | (class name <emphasis>G4EmStandardPhysics_option1</emphasis>) |
---|
567 | </para></listitem> |
---|
568 | <listitem><para> |
---|
569 | Experimental EM physics with enabled "ApplyCuts" option |
---|
570 | (class name <emphasis>G4EmStandardPhysics_option2</emphasis>) |
---|
571 | </para></listitem> |
---|
572 | <listitem><para> |
---|
573 | EM physics for simulation with high accuracy |
---|
574 | (class name <emphasis>G4EmStandardPhysics_option3</emphasis>) |
---|
575 | </para></listitem> |
---|
576 | </itemizedlist> |
---|
577 | Examples of the registration of these physics constructor and |
---|
578 | construction of alternative combinations of options are shown |
---|
579 | in novice and extended examples ($G4INSTALL/examples/extended/electromagnetic). |
---|
580 | Novice and extended electromagnetic examples illustrating the use |
---|
581 | of electromagnetic processes are available as part of the Geant4 |
---|
582 | <ulink url="http://geant4.web.cern.ch/geant4/support/download.shtml"> |
---|
583 | release</ulink>. |
---|
584 | </para> |
---|
585 | |
---|
586 | <para> |
---|
587 | <emphasis role="bold">Options</emphasis> are available for steering the standard |
---|
588 | electromagnetic processes. These options may be invoked either by |
---|
589 | UI commands or by the interface class G4EmProcessOptions. This |
---|
590 | class has the following public methods: |
---|
591 | |
---|
592 | <itemizedlist spacing="compact"> |
---|
593 | <listitem><para> |
---|
594 | SetLossFluctuations(G4bool) |
---|
595 | </para></listitem> |
---|
596 | <listitem><para> |
---|
597 | SetSubCutoff(G4bool, const G4Region* r=0) |
---|
598 | </para></listitem> |
---|
599 | <listitem><para> |
---|
600 | SetIntegral(G4bool) |
---|
601 | </para></listitem> |
---|
602 | <listitem><para> |
---|
603 | SetMinSubRange(G4double) |
---|
604 | </para></listitem> |
---|
605 | <listitem><para> |
---|
606 | SetMinEnergy(G4double) |
---|
607 | </para></listitem> |
---|
608 | <listitem><para> |
---|
609 | SetMaxEnergy(G4double) |
---|
610 | </para></listitem> |
---|
611 | <listitem><para> |
---|
612 | SetMaxEnergyForCSDARange(G4double) |
---|
613 | </para></listitem> |
---|
614 | <listitem><para> |
---|
615 | SetMaxEnergyForMuons(G4double) |
---|
616 | </para></listitem> |
---|
617 | <listitem><para> |
---|
618 | SetDEDXBinning(G4int) |
---|
619 | </para></listitem> |
---|
620 | <listitem><para> |
---|
621 | SetDEDXBinningForCSDARange(G4int) |
---|
622 | </para></listitem> |
---|
623 | <listitem><para> |
---|
624 | SetLambdaBinning(G4int) |
---|
625 | </para></listitem> |
---|
626 | <listitem><para> |
---|
627 | SetStepFunction(G4double, G4double) |
---|
628 | </para></listitem> |
---|
629 | <listitem><para> |
---|
630 | SetRandomStep(G4bool) |
---|
631 | </para></listitem> |
---|
632 | <listitem><para> |
---|
633 | SetApplyCuts(G4bool) |
---|
634 | </para></listitem> |
---|
635 | <listitem><para> |
---|
636 | SetSpline(G4bool) |
---|
637 | </para></listitem> |
---|
638 | <listitem><para> |
---|
639 | SetBuildCSDARange(G4bool) |
---|
640 | </para></listitem> |
---|
641 | <listitem><para> |
---|
642 | SetVerbose(G4int, const G4String name= "all") |
---|
643 | </para></listitem> |
---|
644 | <listitem><para> |
---|
645 | SetLambdaFactor(G4double) |
---|
646 | </para></listitem> |
---|
647 | <listitem><para> |
---|
648 | SetLinearLossLimit(G4double) |
---|
649 | </para></listitem> |
---|
650 | <listitem><para> |
---|
651 | ActivateDeexcitation(G4bool val, const G4Region* r = 0) |
---|
652 | </para></listitem> |
---|
653 | <listitem><para> |
---|
654 | SetMscStepLimitation(G4MscStepLimitType val) |
---|
655 | </para></listitem> |
---|
656 | <listitem><para> |
---|
657 | SetMscLateralDisplacement(G4bool val) |
---|
658 | </para></listitem> |
---|
659 | <listitem><para> |
---|
660 | SetSkin(G4double) |
---|
661 | </para></listitem> |
---|
662 | <listitem><para> |
---|
663 | SetMscRangeFactor(G4double) |
---|
664 | </para></listitem> |
---|
665 | <listitem><para> |
---|
666 | SetMscGeomFactor(G4double) |
---|
667 | </para></listitem> |
---|
668 | <listitem><para> |
---|
669 | SetLPMFlag(G4bool) |
---|
670 | </para></listitem> |
---|
671 | <listitem><para> |
---|
672 | SetBremsstrahlungTh(G4double) |
---|
673 | </para></listitem> |
---|
674 | </itemizedlist> |
---|
675 | </para> |
---|
676 | |
---|
677 | <para> |
---|
678 | The corresponding UI command can be accessed in the UI subdirectory |
---|
679 | "/process/eLoss". The following types of step limitation by multiple scattering |
---|
680 | are available: |
---|
681 | |
---|
682 | <itemizedlist spacing="compact"> |
---|
683 | <listitem><para> |
---|
684 | fSimple - step limitation used in g4 7.1 version (used in QGSP_EMV Physics List) |
---|
685 | </para></listitem> |
---|
686 | <listitem><para> |
---|
687 | fUseSafety - default |
---|
688 | </para></listitem> |
---|
689 | <listitem><para> |
---|
690 | fUseDistanceToBoundary - advance method of step limitation used in EM examples, |
---|
691 | required parameter <emphasis>skin > 0</emphasis>, should be used for |
---|
692 | setup without magnetic field |
---|
693 | </para></listitem> |
---|
694 | </itemizedlist> |
---|
695 | </para> |
---|
696 | |
---|
697 | <para> |
---|
698 | <emphasis role="bold">G4EmCalculator</emphasis> is a class which provides |
---|
699 | access to cross sections and stopping powers. This class can be used |
---|
700 | anywhere in the user code provided the physics list has already been |
---|
701 | initialised (G4State_Idle). G4EmCalculator has "Get" methods which |
---|
702 | can be applied to materials for which physics tables are already |
---|
703 | built, and "Compute" methods which can be applied to any material |
---|
704 | defined in the application or existing in the Geant4 internal |
---|
705 | database. The public methods of this class are: |
---|
706 | |
---|
707 | <itemizedlist spacing="compact"> |
---|
708 | <listitem><para> |
---|
709 | GetDEDX(kinEnergy,particle,material,G4Region region=0) |
---|
710 | </para></listitem> |
---|
711 | <listitem><para> |
---|
712 | GetRangeFromRestrictedDEDX(kinEnergy,particle,material,G4Region* region=0) |
---|
713 | </para></listitem> |
---|
714 | <listitem><para> |
---|
715 | GetCSDARange(kinEnergy,particle,material,G4Region* region=0) |
---|
716 | </para></listitem> |
---|
717 | <listitem><para> |
---|
718 | GetRange(kinEnergy,particle,material,G4Region* region=0) |
---|
719 | </para></listitem> |
---|
720 | <listitem><para> |
---|
721 | GetKinEnergy(range,particle,material,G4Region* region=0) |
---|
722 | </para></listitem> |
---|
723 | <listitem><para> |
---|
724 | GetCrosSectionPerVolume(kinEnergy,particle,material,G4Region* region=0) |
---|
725 | </para></listitem> |
---|
726 | <listitem><para> |
---|
727 | GetMeanFreePath(kinEnergy,particle,material,G4Region* region=0) |
---|
728 | </para></listitem> |
---|
729 | <listitem><para> |
---|
730 | PrintDEDXTable(particle) |
---|
731 | </para></listitem> |
---|
732 | <listitem><para> |
---|
733 | PrintRangeTable(particle) |
---|
734 | </para></listitem> |
---|
735 | <listitem><para> |
---|
736 | PrintInverseRangeTable(particle) |
---|
737 | </para></listitem> |
---|
738 | <listitem><para> |
---|
739 | ComputeDEDX(kinEnergy,particle,process,material,cut=DBL_MAX) |
---|
740 | </para></listitem> |
---|
741 | <listitem><para> |
---|
742 | ComputeElectronicDEDX(kinEnergy,particle,material,cut=DBL_MAX) |
---|
743 | </para></listitem> |
---|
744 | <listitem><para> |
---|
745 | ComputeNuclearDEDX(kinEnergy,particle,material,cut=DBL_MAX) |
---|
746 | </para></listitem> |
---|
747 | <listitem><para> |
---|
748 | ComputeTotalDEDX(kinEnergy,particle,material,cut=DBL_MAX) |
---|
749 | </para></listitem> |
---|
750 | <listitem><para> |
---|
751 | ComputeCrosSectionPerVolume(kinEnergy,particle,process,material,cut=0) |
---|
752 | </para></listitem> |
---|
753 | <listitem><para> |
---|
754 | ComputeCrosSectionPerAtom(kinEnergy,particle,process,Z,A,cut=0) |
---|
755 | </para></listitem> |
---|
756 | <listitem><para> |
---|
757 | ComputeMeanFreePath(kinEnergy,particle,process,material,cut=0) |
---|
758 | </para></listitem> |
---|
759 | <listitem><para> |
---|
760 | ComputeEnergyCutFromRangeCut(range,particle,material) |
---|
761 | </para></listitem> |
---|
762 | <listitem><para> |
---|
763 | FindParticle(const G4String&) |
---|
764 | </para></listitem> |
---|
765 | <listitem><para> |
---|
766 | FindMaterial(const G4String&) |
---|
767 | </para></listitem> |
---|
768 | <listitem><para> |
---|
769 | FindRegion(const G4String&) |
---|
770 | </para></listitem> |
---|
771 | <listitem><para> |
---|
772 | FindCouple(const G4Material*, const G4Region* region=0) |
---|
773 | </para></listitem> |
---|
774 | <listitem><para> |
---|
775 | SetVerbose(G4int) |
---|
776 | </para></listitem> |
---|
777 | </itemizedlist> |
---|
778 | </para> |
---|
779 | |
---|
780 | <para> |
---|
781 | For these interfaces, particles, materials, or processes may be |
---|
782 | pointers or strings with names. |
---|
783 | </para> |
---|
784 | |
---|
785 | </sect3> |
---|
786 | |
---|
787 | |
---|
788 | <!-- ******************* Section (Level#3) ****************** --> |
---|
789 | <sect3 id="sect.PhysProc.EleMag.LowE"> |
---|
790 | <title> |
---|
791 | Low Energy Electromagnetic Processes |
---|
792 | </title> |
---|
793 | |
---|
794 | <para> |
---|
795 | The following is a summary of the Low Energy Electromagnetic |
---|
796 | processes available in Geant4. Further information is available in |
---|
797 | the web |
---|
798 | <ulink url="http://geant4.web.cern.ch/geant4/collaboration/working_groups/LEelectromagnetic/index.shtml">pages |
---|
799 | </ulink> |
---|
800 | of the Geant4 Low Energy Electromagnetic Physics Working Group. |
---|
801 | The physics content of these processes is documented in Geant4 |
---|
802 | <ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/PhysicsReferenceManual/html/PhysicsReferenceManual.html"> |
---|
803 | Physics Reference Manual |
---|
804 | </ulink> |
---|
805 | </para> |
---|
806 | |
---|
807 | <para> |
---|
808 | <itemizedlist spacing="compact"> |
---|
809 | <listitem><para> |
---|
810 | <emphasis role="bold">Photon processes</emphasis> |
---|
811 | <itemizedlist spacing="compact"> |
---|
812 | <listitem><para> |
---|
813 | Compton scattering (class <emphasis>G4LowEnergyCompton</emphasis>) |
---|
814 | </para></listitem> |
---|
815 | <listitem><para> |
---|
816 | Polarized Compton scattering (class |
---|
817 | <emphasis>G4LowEnergyPolarizedCompton</emphasis>) |
---|
818 | </para></listitem> |
---|
819 | <listitem><para> |
---|
820 | Rayleigh scattering (class <emphasis>G4LowEnergyRayleigh</emphasis>) |
---|
821 | </para></listitem> |
---|
822 | <listitem><para> |
---|
823 | Gamma conversion (also called pair production, class |
---|
824 | <emphasis>G4LowEnergyGammaConversion</emphasis>) |
---|
825 | </para></listitem> |
---|
826 | <listitem><para> |
---|
827 | Photo-electric effect (class<emphasis>G4LowEnergyPhotoElectric</emphasis>) |
---|
828 | </para></listitem> |
---|
829 | </itemizedlist> |
---|
830 | </para></listitem> |
---|
831 | <listitem><para> |
---|
832 | <emphasis role="bold">Electron processes</emphasis> |
---|
833 | <itemizedlist spacing="compact"> |
---|
834 | <listitem><para> |
---|
835 | Bremsstrahlung (class <emphasis>G4LowEnergyBremsstrahlung</emphasis>) |
---|
836 | </para></listitem> |
---|
837 | <listitem><para> |
---|
838 | Ionisation and delta ray production (class |
---|
839 | <emphasis>G4LowEnergyIonisation</emphasis>) |
---|
840 | </para></listitem> |
---|
841 | </itemizedlist> |
---|
842 | </para></listitem> |
---|
843 | <listitem><para> |
---|
844 | <emphasis role="bold">Hadron and ion processes</emphasis> |
---|
845 | <itemizedlist spacing="compact"> |
---|
846 | <listitem><para> |
---|
847 | Ionisation and delta ray production (class |
---|
848 | <emphasis>G4hLowEnergyIonisation</emphasis>) |
---|
849 | </para></listitem> |
---|
850 | </itemizedlist> |
---|
851 | </para></listitem> |
---|
852 | </itemizedlist> |
---|
853 | </para> |
---|
854 | |
---|
855 | <para> |
---|
856 | Examples of the registration of physics constructor with low-energy |
---|
857 | electromagnetic processes are shown |
---|
858 | in Geant4 extended examples ($G4INSTALL/examples/extended/electromagnetic). |
---|
859 | <emphasis role="bold">Advanced examples</emphasis> illustrating alternative instantiation |
---|
860 | of these processes. Both are available as part of the Geant4 |
---|
861 | <ulink url="http://geant4.web.cern.ch/geant4/support/download.shtml"> |
---|
862 | release</ulink>. |
---|
863 | </para> |
---|
864 | |
---|
865 | <para> |
---|
866 | To run the Low Energy code for photon and electron |
---|
867 | electromagnetic processes, <emphasis role="bold"> |
---|
868 | <ulink url="http://geant4.web.cern.ch/geant4/support/download.shtml"> |
---|
869 | data files |
---|
870 | </ulink> |
---|
871 | </emphasis> |
---|
872 | need to be copied by the user to his/her code |
---|
873 | repository. These files are distributed together with Geant4. |
---|
874 | The user should set the environment variable |
---|
875 | <emphasis role="bold">G4LEDATA</emphasis> to the |
---|
876 | directory where he/she has copied the files. |
---|
877 | </para> |
---|
878 | |
---|
879 | <para> |
---|
880 | <emphasis role="bold">Options</emphasis> are available for low energy electromagnetic |
---|
881 | processes for hadrons and ions in terms of public member functions |
---|
882 | of the G4hLowEnergyIonisation class: |
---|
883 | |
---|
884 | <itemizedlist spacing="compact"> |
---|
885 | <listitem><para> |
---|
886 | SetHighEnergyForProtonParametrisation(G4double) |
---|
887 | </para></listitem> |
---|
888 | <listitem><para> |
---|
889 | SetLowEnergyForProtonParametrisation(G4double) |
---|
890 | </para></listitem> |
---|
891 | <listitem><para> |
---|
892 | SetHighEnergyForAntiProtonParametrisation(G4double) |
---|
893 | </para></listitem> |
---|
894 | <listitem><para> |
---|
895 | SetLowEnergyForAntiProtonParametrisation(G4double) |
---|
896 | </para></listitem> |
---|
897 | <listitem><para> |
---|
898 | SetElectronicStoppingPowerModel(const G4ParticleDefinition*,const G4String& ) |
---|
899 | </para></listitem> |
---|
900 | <listitem><para> |
---|
901 | SetNuclearStoppingPowerModel(const G4String&) |
---|
902 | </para></listitem> |
---|
903 | <listitem><para> |
---|
904 | SetNuclearStoppingOn() |
---|
905 | </para></listitem> |
---|
906 | <listitem><para> |
---|
907 | SetNuclearStoppingOff() |
---|
908 | </para></listitem> |
---|
909 | <listitem><para> |
---|
910 | SetBarkasOn() |
---|
911 | </para></listitem> |
---|
912 | <listitem><para> |
---|
913 | SetBarkasOff() |
---|
914 | </para></listitem> |
---|
915 | <listitem><para> |
---|
916 | SetFluorescence(const G4bool) |
---|
917 | </para></listitem> |
---|
918 | <listitem><para> |
---|
919 | ActivateAugerElectronProduction(G4bool) |
---|
920 | </para></listitem> |
---|
921 | <listitem><para> |
---|
922 | SetCutForSecondaryPhotons(G4double) |
---|
923 | </para></listitem> |
---|
924 | <listitem><para> |
---|
925 | SetCutForSecondaryElectrons(G4double) |
---|
926 | </para></listitem> |
---|
927 | </itemizedlist> |
---|
928 | </para> |
---|
929 | |
---|
930 | <para> |
---|
931 | <emphasis role="bold">Options</emphasis> are available for low energy electromagnetic |
---|
932 | processes for electrons in the G4LowEnergyIonisation class: |
---|
933 | |
---|
934 | <itemizedlist spacing="compact"> |
---|
935 | <listitem><para> |
---|
936 | ActivateAuger(G4bool) |
---|
937 | </para></listitem> |
---|
938 | <listitem><para> |
---|
939 | SetCutForLowEnSecPhotons(G4double) |
---|
940 | </para></listitem> |
---|
941 | <listitem><para> |
---|
942 | SetCutForLowEnSecElectrons(G4double) |
---|
943 | </para></listitem> |
---|
944 | </itemizedlist> |
---|
945 | </para> |
---|
946 | |
---|
947 | <para> |
---|
948 | <emphasis role="bold">Options</emphasis> are available for low energy electromagnetic |
---|
949 | processes for electrons/positrons in the G4LowEnergyBremsstrahlung |
---|
950 | class, that allow the use of alternative bremsstrahlung angular |
---|
951 | generators: |
---|
952 | |
---|
953 | <itemizedlist spacing="compact"> |
---|
954 | <listitem><para> |
---|
955 | SetAngularGenerator(G4VBremAngularDistribution* distribution); |
---|
956 | </para></listitem> |
---|
957 | <listitem><para> |
---|
958 | SetAngularGenerator(const G4String& name); |
---|
959 | </para></listitem> |
---|
960 | </itemizedlist> |
---|
961 | </para> |
---|
962 | |
---|
963 | <para> |
---|
964 | Currently three angular generators are available: G4ModifiedTsai, |
---|
965 | 2BNGenerator and 2BSGenerator. G4ModifiedTsai is set by default, |
---|
966 | but it can be forced using the string "tsai". 2BNGenerator and |
---|
967 | 2BSGenerator can be set using the strings "2bs" and "2bn". |
---|
968 | Information regarding conditions of use, performance and energy |
---|
969 | limits of different models are available in the |
---|
970 | <ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/PhysicsReferenceManual/html/PhysicsReferenceManual.html"> |
---|
971 | Physics Reference Manual |
---|
972 | </ulink>. |
---|
973 | </para> |
---|
974 | |
---|
975 | <para> |
---|
976 | Other <emphasis role="bold">options</emphasis> G4LowEnergyBremsstrahlung class are: |
---|
977 | |
---|
978 | <itemizedlist spacing="compact"> |
---|
979 | <listitem><para> |
---|
980 | SetCutForLowEnSecPhotons(G4double) |
---|
981 | </para></listitem> |
---|
982 | </itemizedlist> |
---|
983 | </para> |
---|
984 | |
---|
985 | <para> |
---|
986 | <emphasis role="bold">Options</emphasis> can also be set in the G4LowEnergyPhotoElectric |
---|
987 | class, that allow the use of alternative photoelectron angular |
---|
988 | generators: |
---|
989 | |
---|
990 | <itemizedlist spacing="compact"> |
---|
991 | <listitem><para> |
---|
992 | SetAngularGenerator(G4VPhotoElectricAngularDistribution* distribution); |
---|
993 | </para></listitem> |
---|
994 | <listitem><para> |
---|
995 | SetAngularGenerator(const G4String& name); |
---|
996 | </para></listitem> |
---|
997 | <listitem><para> |
---|
998 | |
---|
999 | </para></listitem> |
---|
1000 | <listitem><para> |
---|
1001 | |
---|
1002 | </para></listitem> |
---|
1003 | <listitem><para> |
---|
1004 | |
---|
1005 | </para></listitem> |
---|
1006 | </itemizedlist> |
---|
1007 | </para> |
---|
1008 | |
---|
1009 | <para> |
---|
1010 | Currently three angular generators are available: |
---|
1011 | G4PhotoElectricAngularGeneratorSimple, |
---|
1012 | G4PhotoElectricAngularGeneratorSauterGavrilla and |
---|
1013 | G4PhotoElectricAngularGeneratorPolarized. |
---|
1014 | G4PhotoElectricAngularGeneratorSimple is set by default, but it can |
---|
1015 | be forced using the string "default". |
---|
1016 | G4PhotoElectricAngularGeneratorSauterGavrilla and |
---|
1017 | G4PhotoElectricAngularGeneratorPolarized can be set using the |
---|
1018 | strings "standard" and "polarized". |
---|
1019 | </para> |
---|
1020 | |
---|
1021 | </sect3> |
---|
1022 | |
---|
1023 | <!-- ******************* Section (Level#3) ****************** --> |
---|
1024 | <sect3 id="sect.PhysProc.EleMag.VeryLowE"> |
---|
1025 | <title> |
---|
1026 | Very Low energy Electromagnetic Processes (Geant4-DNA extension) |
---|
1027 | </title> |
---|
1028 | |
---|
1029 | <para> |
---|
1030 | Geant4 low energy electromagnetic Physics processes have been extended down |
---|
1031 | to energies of a few electronVolts suitable for the simulation of radiation |
---|
1032 | effects in liquid water for applications at the cellular and sub-cellular |
---|
1033 | level. These developments take place in the framework of the Geant4-DNA |
---|
1034 | project and are described in the paper |
---|
1035 | <citation> |
---|
1036 | <xref linkend="biblio.chauvie2007" endterm="biblio.chauvie2007.abbrev" /> |
---|
1037 | </citation>. |
---|
1038 | </para> |
---|
1039 | |
---|
1040 | <para> |
---|
1041 | Their implementation in Geant4 is based on the usage of innovative techniques |
---|
1042 | first introduced in Monte Carlo simulation (policy-based class design), to |
---|
1043 | ensure openness to future extension and evolution as well as flexibility of |
---|
1044 | configuration in user applications. In this new design, a generic Geant4-DNA |
---|
1045 | physics process is configured by template specialization in order to acquire |
---|
1046 | physical properties (cross section, final state), using policy classes : |
---|
1047 | a Cross Section policy class and a Final State policy class. |
---|
1048 | </para> |
---|
1049 | |
---|
1050 | <para> |
---|
1051 | These processes apply to electrons, protons, hydrogen, alpha particles and |
---|
1052 | their charge states. |
---|
1053 | </para> |
---|
1054 | |
---|
1055 | <!-- ******* Bridgehead ******* --> |
---|
1056 | <bridgehead renderas='sect4'> |
---|
1057 | Electron processes |
---|
1058 | </bridgehead> |
---|
1059 | <para> |
---|
1060 | <itemizedlist spacing="compact"> |
---|
1061 | <listitem><para> |
---|
1062 | Elastic scattering (two complementary models available depending on energy range, and one alternative model) |
---|
1063 | <itemizedlist spacing="compact"> |
---|
1064 | <listitem><para> |
---|
1065 | - 1) either : cross section policy class names : G4CrossSectionElasticScreenedRutherfordLE (below 200 eV) |
---|
1066 | and G4CrossSectionElasticScreenedRutherfordHE (above 200 eV). Both should be used together. |
---|
1067 | - 2) or : cross section policy class name : G4CrossSectionElasticChampion. |
---|
1068 | </para></listitem> |
---|
1069 | <listitem><para> |
---|
1070 | - 1) either : final state policy class names : G4FinalStateElasticBrennerZaider (corresponding to G4CrossSectionElasticScreenedRutherfordLE) |
---|
1071 | and G4CrossSectionElasticScreenedRutherfordLE (corresponding to G4CrossSectionElasticScreenedRutherfordHE). |
---|
1072 | - 2) or final state policy class name : G4FinalStateElasticChampion (corresponding to G4CrossSectionElasticChampion). |
---|
1073 | </para></listitem> |
---|
1074 | </itemizedlist> |
---|
1075 | </para></listitem> |
---|
1076 | <listitem><para> |
---|
1077 | Excitation (one model) |
---|
1078 | <itemizedlist spacing="compact"> |
---|
1079 | <listitem><para> |
---|
1080 | Cross section policy class name : G4CrossSectionExcitationEmfietzoglou |
---|
1081 | </para></listitem> |
---|
1082 | <listitem><para> |
---|
1083 | Final state policy class name : G4FinalStateExcitationEmfietzoglou |
---|
1084 | </para></listitem> |
---|
1085 | </itemizedlist> |
---|
1086 | </para></listitem> |
---|
1087 | <listitem><para> |
---|
1088 | Ionisation (one model) |
---|
1089 | <itemizedlist spacing="compact"> |
---|
1090 | <listitem><para> |
---|
1091 | Cross section policy class name : G4CrossSectionIonisationBorn |
---|
1092 | </para></listitem> |
---|
1093 | <listitem><para> |
---|
1094 | Final state policy class names : G4FinalStateIonisationBorn |
---|
1095 | </para></listitem> |
---|
1096 | </itemizedlist> |
---|
1097 | </para></listitem> |
---|
1098 | </itemizedlist> |
---|
1099 | </para> |
---|
1100 | |
---|
1101 | <!-- ******* Bridgehead ******* --> |
---|
1102 | <bridgehead renderas='sect4'> |
---|
1103 | Proton processes |
---|
1104 | </bridgehead> |
---|
1105 | <para> |
---|
1106 | <itemizedlist spacing="compact"> |
---|
1107 | <listitem><para> |
---|
1108 | Excitation (two complementary models available depending on energy range) |
---|
1109 | <itemizedlist spacing="compact"> |
---|
1110 | <listitem><para> |
---|
1111 | Cross section policy class name : G4CrossSectionExcitationMillerGreen |
---|
1112 | </para></listitem> |
---|
1113 | <listitem><para> |
---|
1114 | Final state policy class name : G4FinalStateExcitationMillerGreen |
---|
1115 | </para></listitem> |
---|
1116 | <listitem><para> |
---|
1117 | Cross section policy class name : G4CrossSectionExcitationBorn |
---|
1118 | </para></listitem> |
---|
1119 | <listitem><para> |
---|
1120 | Final state policy class name : G4FinalStateExcitationBorn |
---|
1121 | </para></listitem> |
---|
1122 | </itemizedlist> |
---|
1123 | </para></listitem> |
---|
1124 | <listitem><para> |
---|
1125 | Ionisation (two complementary models available depending on energy range) |
---|
1126 | <itemizedlist spacing="compact"> |
---|
1127 | <listitem><para> |
---|
1128 | Cross section policy class name : G4CrossSectionIonisationRudd |
---|
1129 | </para></listitem> |
---|
1130 | <listitem><para> |
---|
1131 | Final state policy class name : G4FinalStateIonisationRudd |
---|
1132 | </para></listitem> |
---|
1133 | <listitem><para> |
---|
1134 | Cross section policy class name : G4CrossSectionIonisationBorn |
---|
1135 | </para></listitem> |
---|
1136 | <listitem><para> |
---|
1137 | Final state policy class name : G4FinalStateIonisationBorn |
---|
1138 | </para></listitem> |
---|
1139 | </itemizedlist> |
---|
1140 | </para></listitem> |
---|
1141 | <listitem><para> |
---|
1142 | Charge decrease (one model) |
---|
1143 | <itemizedlist spacing="compact"> |
---|
1144 | <listitem><para> |
---|
1145 | Cross section policy class name : G4CrossSectionChargeDecrease |
---|
1146 | </para></listitem> |
---|
1147 | <listitem><para> |
---|
1148 | Final state policy class name : G4FinalStateChargeDecrease |
---|
1149 | </para></listitem> |
---|
1150 | </itemizedlist> |
---|
1151 | </para></listitem> |
---|
1152 | </itemizedlist> |
---|
1153 | </para> |
---|
1154 | |
---|
1155 | <!-- ******* Bridgehead ******* --> |
---|
1156 | <bridgehead renderas='sect4'> |
---|
1157 | Hydrogen processes |
---|
1158 | </bridgehead> |
---|
1159 | <para> |
---|
1160 | <itemizedlist spacing="compact"> |
---|
1161 | <listitem><para> |
---|
1162 | Ionisation (one model) |
---|
1163 | <itemizedlist spacing="compact"> |
---|
1164 | <listitem><para> |
---|
1165 | Cross section policy class name : G4CrossSectionIonisationRudd |
---|
1166 | </para></listitem> |
---|
1167 | <listitem><para> |
---|
1168 | Final state policy class name : G4FinalStateIonisationRudd |
---|
1169 | </para></listitem> |
---|
1170 | </itemizedlist> |
---|
1171 | </para></listitem> |
---|
1172 | <listitem><para> |
---|
1173 | Charge increase (one model) |
---|
1174 | <itemizedlist spacing="compact"> |
---|
1175 | <listitem><para> |
---|
1176 | Cross section policy class name : G4CrossSectionChargeIncrease |
---|
1177 | </para></listitem> |
---|
1178 | <listitem><para> |
---|
1179 | Final state policy class name : G4FinalStateChargeIncrease |
---|
1180 | </para></listitem> |
---|
1181 | </itemizedlist> |
---|
1182 | </para></listitem> |
---|
1183 | </itemizedlist> |
---|
1184 | </para> |
---|
1185 | |
---|
1186 | <!-- ******* Bridgehead ******* --> |
---|
1187 | <bridgehead renderas='sect4'> |
---|
1188 | Helium (neutral) processes |
---|
1189 | </bridgehead> |
---|
1190 | <para> |
---|
1191 | <itemizedlist spacing="compact"> |
---|
1192 | <listitem><para> |
---|
1193 | Excitation (one model) |
---|
1194 | <itemizedlist spacing="compact"> |
---|
1195 | <listitem><para> |
---|
1196 | Cross section policy class name : G4CrossSectionExcitationMillerGreen |
---|
1197 | </para></listitem> |
---|
1198 | <listitem><para> |
---|
1199 | Final state policy class name : G4FinalStateExcitationMillerGreen |
---|
1200 | </para></listitem> |
---|
1201 | </itemizedlist> |
---|
1202 | </para></listitem> |
---|
1203 | <listitem><para> |
---|
1204 | Ionisation (one model) |
---|
1205 | <itemizedlist spacing="compact"> |
---|
1206 | <listitem><para> |
---|
1207 | Cross section policy class name : G4CrossSectionIonisationRudd |
---|
1208 | </para></listitem> |
---|
1209 | <listitem><para> |
---|
1210 | Final state policy class name : G4FinalStateIonisationRudd |
---|
1211 | </para></listitem> |
---|
1212 | </itemizedlist> |
---|
1213 | </para></listitem> |
---|
1214 | <listitem><para> |
---|
1215 | Charge increase (one model) |
---|
1216 | <itemizedlist spacing="compact"> |
---|
1217 | <listitem><para> |
---|
1218 | Cross section policy class name : G4CrossSectionChargeIncrease |
---|
1219 | </para></listitem> |
---|
1220 | <listitem><para> |
---|
1221 | Final state policy class name : G4FinalStateChargeIncrease |
---|
1222 | </para></listitem> |
---|
1223 | </itemizedlist> |
---|
1224 | </para></listitem> |
---|
1225 | </itemizedlist> |
---|
1226 | </para> |
---|
1227 | |
---|
1228 | <!-- ******* Bridgehead ******* --> |
---|
1229 | <bridgehead renderas='sect4'> |
---|
1230 | Helium+ (ionized once) processes |
---|
1231 | </bridgehead> |
---|
1232 | <para> |
---|
1233 | <itemizedlist spacing="compact"> |
---|
1234 | <listitem><para> |
---|
1235 | Excitation (one model) |
---|
1236 | <itemizedlist spacing="compact"> |
---|
1237 | <listitem><para> |
---|
1238 | Cross section policy class name : G4CrossSectionExcitationMillerGreen |
---|
1239 | </para></listitem> |
---|
1240 | <listitem><para> |
---|
1241 | Final state policy class name : G4FinalStateExcitationMillerGreen |
---|
1242 | </para></listitem> |
---|
1243 | </itemizedlist> |
---|
1244 | </para></listitem> |
---|
1245 | <listitem><para> |
---|
1246 | Ionisation (one model) |
---|
1247 | <itemizedlist spacing="compact"> |
---|
1248 | <listitem><para> |
---|
1249 | Cross section policy class name : G4CrossSectionIonisationRudd |
---|
1250 | </para></listitem> |
---|
1251 | <listitem><para> |
---|
1252 | Final state policy class name : G4FinalStateIonisationRudd |
---|
1253 | </para></listitem> |
---|
1254 | </itemizedlist> |
---|
1255 | </para></listitem> |
---|
1256 | <listitem><para> |
---|
1257 | Charge increase (one model) |
---|
1258 | <itemizedlist spacing="compact"> |
---|
1259 | <listitem><para> |
---|
1260 | Cross section policy class name : G4CrossSectionChargeIncrease |
---|
1261 | </para></listitem> |
---|
1262 | <listitem><para> |
---|
1263 | Final state policy class name : G4FinalStateChargeIncrease |
---|
1264 | </para></listitem> |
---|
1265 | </itemizedlist> |
---|
1266 | </para></listitem> |
---|
1267 | <listitem><para> |
---|
1268 | Charge decrease (one model) |
---|
1269 | <itemizedlist spacing="compact"> |
---|
1270 | <listitem><para> |
---|
1271 | Cross section policy class name : G4CrossSectionChargeDecrease |
---|
1272 | </para></listitem> |
---|
1273 | <listitem><para> |
---|
1274 | Final state policy class name : G4FinalStateChargeDecrease |
---|
1275 | </para></listitem> |
---|
1276 | </itemizedlist> |
---|
1277 | </para></listitem> |
---|
1278 | </itemizedlist> |
---|
1279 | </para> |
---|
1280 | |
---|
1281 | <!-- ******* Bridgehead ******* --> |
---|
1282 | <bridgehead renderas='sect4'> |
---|
1283 | Helium++ (ionised twice) processes |
---|
1284 | </bridgehead> |
---|
1285 | <para> |
---|
1286 | <itemizedlist spacing="compact"> |
---|
1287 | <listitem><para> |
---|
1288 | Excitation (one model) |
---|
1289 | <itemizedlist spacing="compact"> |
---|
1290 | <listitem><para> |
---|
1291 | Cross section policy class name : G4CrossSectionExcitationMillerGreen |
---|
1292 | </para></listitem> |
---|
1293 | <listitem><para> |
---|
1294 | Final state policy class name : G4FinalStateExcitationMillerGreen |
---|
1295 | </para></listitem> |
---|
1296 | </itemizedlist> |
---|
1297 | </para></listitem> |
---|
1298 | <listitem><para> |
---|
1299 | Ionisation (one model) |
---|
1300 | <itemizedlist spacing="compact"> |
---|
1301 | <listitem><para> |
---|
1302 | Cross section policy class name : G4CrossSectionIonisationRudd |
---|
1303 | </para></listitem> |
---|
1304 | <listitem><para> |
---|
1305 | Final state policy class name : G4FinalStateIonisationRudd |
---|
1306 | </para></listitem> |
---|
1307 | </itemizedlist> |
---|
1308 | </para></listitem> |
---|
1309 | <listitem><para> |
---|
1310 | Charge decrease (one model) |
---|
1311 | <itemizedlist spacing="compact"> |
---|
1312 | <listitem><para> |
---|
1313 | Cross section policy class name : G4CrossSectionChargeDecrease |
---|
1314 | </para></listitem> |
---|
1315 | <listitem><para> |
---|
1316 | Final state policy class name : G4FinalStateChargeDecrease |
---|
1317 | </para></listitem> |
---|
1318 | </itemizedlist> |
---|
1319 | </para></listitem> |
---|
1320 | </itemizedlist> |
---|
1321 | </para> |
---|
1322 | |
---|
1323 | <para> |
---|
1324 | An example of the registration of these processes in a physics list is given here below : |
---|
1325 | |
---|
1326 | <informalexample> |
---|
1327 | <programlisting> |
---|
1328 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
---|
1329 | |
---|
1330 | // Geant4 DNA header files |
---|
1331 | |
---|
1332 | #include "G4DNAGenericIonsManager.hh" |
---|
1333 | #include "G4FinalStateProduct.hh" |
---|
1334 | #include "G4DNAProcess.hh" |
---|
1335 | |
---|
1336 | #include "G4CrossSectionExcitationEmfietzoglou.hh" |
---|
1337 | #include "G4FinalStateExcitationEmfietzoglou.hh" |
---|
1338 | |
---|
1339 | #include "G4CrossSectionElasticScreenedRutherfordLE.hh" |
---|
1340 | #include "G4FinalStateElasticBrennerZaider.hh" |
---|
1341 | |
---|
1342 | #include "G4CrossSectionElasticScreenedRutherfordHE.hh" |
---|
1343 | #include "G4FinalStateElasticScreenedRutherford.hh" |
---|
1344 | |
---|
1345 | #include "G4CrossSectionElasticChampion.hh" |
---|
1346 | #include "G4FinalStateElasticChampion.hh" |
---|
1347 | |
---|
1348 | #include "G4CrossSectionExcitationBorn.hh" |
---|
1349 | #include "G4FinalStateExcitationBorn.hh" |
---|
1350 | |
---|
1351 | #include "G4CrossSectionIonisationBorn.hh" |
---|
1352 | #include "G4FinalStateIonisationBorn.hh" |
---|
1353 | |
---|
1354 | #include "G4CrossSectionIonisationRudd.hh" |
---|
1355 | #include "G4FinalStateIonisationRudd.hh" |
---|
1356 | |
---|
1357 | #include "G4CrossSectionExcitationMillerGreen.hh" |
---|
1358 | #include "G4FinalStateExcitationMillerGreen.hh" |
---|
1359 | |
---|
1360 | #include "G4CrossSectionChargeDecrease.hh" |
---|
1361 | #include "G4FinalStateChargeDecrease.hh" |
---|
1362 | |
---|
1363 | #include "G4CrossSectionChargeIncrease.hh" |
---|
1364 | #include "G4FinalStateChargeIncrease.hh" |
---|
1365 | |
---|
1366 | // Processes definition |
---|
1367 | |
---|
1368 | typedef G4DNAProcess<G4CrossSectionElasticScreenedRutherfordLE,G4FinalStateElasticBrennerZaider> |
---|
1369 | ElasticScreenedRutherfordLE; |
---|
1370 | typedef G4DNAProcess<G4CrossSectionElasticScreenedRutherfordHE,G4FinalStateElasticScreenedRutherford> |
---|
1371 | ElasticScreenedRutherfordHE; |
---|
1372 | typedef G4DNAProcess<G4CrossSectionElasticChampion,G4FinalStateElasticChampion> |
---|
1373 | ElasticChampion; |
---|
1374 | typedef G4DNAProcess<G4CrossSectionExcitationEmfietzoglou,G4FinalStateExcitationEmfietzoglou> |
---|
1375 | ExcitationEmfietzoglou; |
---|
1376 | typedef G4DNAProcess<G4CrossSectionExcitationBorn,G4FinalStateExcitationBorn> |
---|
1377 | ExcitationBorn; |
---|
1378 | typedef G4DNAProcess<G4CrossSectionIonisationBorn,G4FinalStateIonisationBorn> |
---|
1379 | IonisationBorn; |
---|
1380 | typedef G4DNAProcess<G4CrossSectionIonisationRudd,G4FinalStateIonisationRudd> |
---|
1381 | IonisationRudd; |
---|
1382 | typedef G4DNAProcess<G4CrossSectionExcitationMillerGreen,G4FinalStateExcitationMillerGreen> |
---|
1383 | ExcitationMillerGreen; |
---|
1384 | typedef G4DNAProcess<G4CrossSectionChargeDecrease,G4FinalStateChargeDecrease> |
---|
1385 | ChargeDecrease; |
---|
1386 | typedef G4DNAProcess<G4CrossSectionChargeIncrease,G4FinalStateChargeIncrease> |
---|
1387 | ChargeIncrease; |
---|
1388 | |
---|
1389 | // Processes registration |
---|
1390 | |
---|
1391 | void MicrodosimetryPhysicsList::ConstructEM() |
---|
1392 | { |
---|
1393 | theParticleIterator->reset(); |
---|
1394 | |
---|
1395 | while( (*theParticleIterator)() ){ |
---|
1396 | |
---|
1397 | G4ParticleDefinition* particle = theParticleIterator->value(); |
---|
1398 | G4ProcessManager* processManager = particle->GetProcessManager(); |
---|
1399 | G4String particleName = particle->GetParticleName(); |
---|
1400 | |
---|
1401 | if (particleName == "e-") { |
---|
1402 | processManager->AddDiscreteProcess(new ExcitationEmfietzoglou("ExcitationEmfietzoglou")); |
---|
1403 | |
---|
1404 | // The two following elastic scattering models should be registered together |
---|
1405 | processManager->AddDiscreteProcess(new ElasticScreenedRutherfordLE("ElasticScreenedRutherfordLE")); |
---|
1406 | processManager->AddDiscreteProcess(new ElasticScreenedRutherfordHE("ElasticScreenedRutherfordHE")); |
---|
1407 | |
---|
1408 | // The following process is commented here because it is ALTERNATIVE to ElasticScreenedRutherfordLE and ElasticScreenedRutherfordHE |
---|
1409 | // It should NOT be registered simultaneously with ElasticScreenedRutherfordLE and ElasticScreenedRutherfordHE |
---|
1410 | // processManager->AddDiscreteProcess(new ElasticChampion("ElasticChampion")); |
---|
1411 | |
---|
1412 | processManager->AddDiscreteProcess(new IonisationBorn("IonisationBorn")); |
---|
1413 | |
---|
1414 | } else if ( particleName == "proton" ) { |
---|
1415 | processManager->AddDiscreteProcess(new ExcitationMillerGreen("ExcitationMillerGreen")); |
---|
1416 | processManager->AddDiscreteProcess(new ExcitationBorn("ExcitationBorn")); |
---|
1417 | processManager->AddDiscreteProcess(new IonisationRudd("IonisationRudd")); |
---|
1418 | processManager->AddDiscreteProcess(new IonisationBorn("IonisationBorn")); |
---|
1419 | processManager->AddDiscreteProcess(new ChargeDecrease("ChargeDecrease")); |
---|
1420 | |
---|
1421 | } else if ( particleName == "hydrogen" ) { |
---|
1422 | processManager->AddDiscreteProcess(new IonisationRudd("IonisationRudd")); |
---|
1423 | processManager->AddDiscreteProcess(new ChargeIncrease("ChargeIncrease")); |
---|
1424 | |
---|
1425 | } else if ( particleName == "alpha" ) { |
---|
1426 | processManager->AddDiscreteProcess(new ExcitationMillerGreen("ExcitationMillerGreen")); |
---|
1427 | processManager->AddDiscreteProcess(new IonisationRudd("IonisationRudd")); |
---|
1428 | processManager->AddDiscreteProcess(new ChargeDecrease("ChargeDecrease")); |
---|
1429 | |
---|
1430 | } else if ( particleName == "alpha+" ) { |
---|
1431 | processManager->AddDiscreteProcess(new ExcitationMillerGreen("ExcitationMillerGreen")); |
---|
1432 | processManager->AddDiscreteProcess(new IonisationRudd("IonisationRudd")); |
---|
1433 | processManager->AddDiscreteProcess(new ChargeDecrease("ChargeDecrease")); |
---|
1434 | processManager->AddDiscreteProcess(new ChargeIncrease("ChargeIncrease")); |
---|
1435 | |
---|
1436 | } else if ( particleName == "helium" ) { |
---|
1437 | processManager->AddDiscreteProcess(new ExcitationMillerGreen("ExcitationMillerGreen")); |
---|
1438 | processManager->AddDiscreteProcess(new IonisationRudd("IonisationRudd")); |
---|
1439 | processManager->AddDiscreteProcess(new ChargeIncrease("ChargeIncrease")); |
---|
1440 | } |
---|
1441 | |
---|
1442 | } |
---|
1443 | } |
---|
1444 | |
---|
1445 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
---|
1446 | </programlisting> |
---|
1447 | </informalexample> |
---|
1448 | </para> |
---|
1449 | |
---|
1450 | <para> |
---|
1451 | Note that in the above example, "alpha" particles are helium atoms ionised |
---|
1452 | twice and "helium" particles are neutral helium atoms. The definition of |
---|
1453 | particles in the physics list may be for example implemented as follows : |
---|
1454 | |
---|
1455 | <informalexample> |
---|
1456 | <programlisting> |
---|
1457 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
---|
1458 | |
---|
1459 | #include "G4DNAGenericIonsManager.hh" |
---|
1460 | |
---|
1461 | void MicrodosimetryPhysicsList::ConstructBaryons() |
---|
1462 | { |
---|
1463 | // construct baryons --- |
---|
1464 | |
---|
1465 | // Geant4 DNA particles |
---|
1466 | |
---|
1467 | G4DNAGenericIonsManager * genericIonsManager; |
---|
1468 | genericIonsManager=G4DNAGenericIonsManager::Instance(); |
---|
1469 | genericIonsManager->GetIon("alpha++"); |
---|
1470 | genericIonsManager->GetIon("alpha+"); |
---|
1471 | genericIonsManager->GetIon("helium"); |
---|
1472 | genericIonsManager->GetIon("hydrogen"); |
---|
1473 | |
---|
1474 | } |
---|
1475 | |
---|
1476 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
---|
1477 | </programlisting> |
---|
1478 | </informalexample> |
---|
1479 | </para> |
---|
1480 | |
---|
1481 | <para> |
---|
1482 | To run the Geant4 DNA extension, data files need to be copied by the user to |
---|
1483 | his/her code repository. These files are distributed together with the Geant4 release. |
---|
1484 | </para> |
---|
1485 | |
---|
1486 | <para> |
---|
1487 | The user should set the environment variable G4LEDATA to the directory where |
---|
1488 | he/she has copied the files. |
---|
1489 | </para> |
---|
1490 | |
---|
1491 | </sect3> |
---|
1492 | </sect2> |
---|
1493 | |
---|
1494 | |
---|
1495 | <!-- ******************* Section (Level#2) ****************** --> |
---|
1496 | <sect2 id="sect.PhysProc.Had"> |
---|
1497 | <title> |
---|
1498 | Hadronic Interactions |
---|
1499 | </title> |
---|
1500 | |
---|
1501 | <para> |
---|
1502 | This section briefly introduces the hadronic physics processes |
---|
1503 | installed in Geant4. For details of the implementation of hadronic |
---|
1504 | interactions available in Geant4, please refer to the |
---|
1505 | <ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/PhysicsReferenceManual/html/PhysicsReferenceManual.html"> |
---|
1506 | <emphasis role="bold">Physics Reference Manual</emphasis></ulink>. |
---|
1507 | </para> |
---|
1508 | |
---|
1509 | <!-- ******************* Section (Level#3) ****************** --> |
---|
1510 | <sect3 id="sect.PhysProc.Had.TreatCross"> |
---|
1511 | <title> |
---|
1512 | Treatment of Cross Sections |
---|
1513 | </title> |
---|
1514 | |
---|
1515 | <!-- ******* Bridgehead ******* --> |
---|
1516 | <bridgehead renderas='sect4'> |
---|
1517 | Cross section data sets |
---|
1518 | </bridgehead> |
---|
1519 | |
---|
1520 | <para> |
---|
1521 | Each hadronic process object (derived from |
---|
1522 | <emphasis>G4HadronicProcess</emphasis>) may have one or more cross section data |
---|
1523 | sets associated with it. The term "data set" is meant, in a broad |
---|
1524 | sense, to be an object that encapsulates methods and data for |
---|
1525 | calculating total cross sections for a given process. The methods |
---|
1526 | and data may take many forms, from a simple equation using a few |
---|
1527 | hard-wired numbers to a sophisticated parameterisation using large |
---|
1528 | data tables. Cross section data sets are derived from the abstract |
---|
1529 | class <emphasis>G4VCrossSectionDataSet</emphasis>, and are required to implement |
---|
1530 | the following methods: |
---|
1531 | |
---|
1532 | <informalexample> |
---|
1533 | <programlisting> |
---|
1534 | G4bool IsApplicable( const G4DynamicParticle*, const G4Element* ) |
---|
1535 | </programlisting> |
---|
1536 | </informalexample> |
---|
1537 | </para> |
---|
1538 | |
---|
1539 | <para> |
---|
1540 | This method must return <literal>True</literal> if the data set is able to |
---|
1541 | calculate a total cross section for the given particle and |
---|
1542 | material, and <literal>False</literal> otherwise. |
---|
1543 | |
---|
1544 | <informalexample> |
---|
1545 | <programlisting> |
---|
1546 | G4double GetCrossSection( const G4DynamicParticle*, const G4Element* ) |
---|
1547 | </programlisting> |
---|
1548 | </informalexample> |
---|
1549 | </para> |
---|
1550 | |
---|
1551 | <para> |
---|
1552 | This method, which will be invoked only if <literal>True</literal> was |
---|
1553 | returned by <literal>IsApplicable</literal>, must return a cross section, in |
---|
1554 | Geant4 default units, for the given particle and material. |
---|
1555 | |
---|
1556 | <informalexample> |
---|
1557 | <programlisting> |
---|
1558 | void BuildPhysicsTable( const G4ParticleDefinition& ) |
---|
1559 | </programlisting> |
---|
1560 | </informalexample> |
---|
1561 | </para> |
---|
1562 | |
---|
1563 | <para> |
---|
1564 | This method may be invoked to request the data set to recalculate |
---|
1565 | its internal database or otherwise reset its state after a change |
---|
1566 | in the cuts or other parameters of the given particle type. |
---|
1567 | |
---|
1568 | |
---|
1569 | <informalexample> |
---|
1570 | <programlisting> |
---|
1571 | void DumpPhysicsTable( const G4ParticleDefinition& ) = 0 |
---|
1572 | </programlisting> |
---|
1573 | </informalexample> |
---|
1574 | </para> |
---|
1575 | |
---|
1576 | <para> |
---|
1577 | This method may be invoked to request the data set to print its |
---|
1578 | internal database and/or other state information, for the given |
---|
1579 | particle type, to the standard output stream. |
---|
1580 | </para> |
---|
1581 | |
---|
1582 | <!-- ******* Bridgehead ******* --> |
---|
1583 | <bridgehead renderas='sect4'> |
---|
1584 | Cross section data store |
---|
1585 | </bridgehead> |
---|
1586 | |
---|
1587 | <para> |
---|
1588 | Cross section data sets are used by the process for the |
---|
1589 | calculation of the physical interaction length. A given cross |
---|
1590 | section data set may only apply to a certain energy range, or may |
---|
1591 | only be able to calculate cross sections for a particular type of |
---|
1592 | particle. The class <emphasis>G4CrossSectionDataStore</emphasis> has been |
---|
1593 | provided to allow the user to specify, if desired, a series of data |
---|
1594 | sets for a process, and to arrange the priority of data sets so |
---|
1595 | that the appropriate one is used for a given energy range, |
---|
1596 | particle, and material. It implements the following public |
---|
1597 | methods: |
---|
1598 | |
---|
1599 | <informalexample> |
---|
1600 | <programlisting> |
---|
1601 | G4CrossSectionDataStore() |
---|
1602 | |
---|
1603 | ~G4CrossSectionDataStore() |
---|
1604 | </programlisting> |
---|
1605 | </informalexample> |
---|
1606 | |
---|
1607 | and |
---|
1608 | |
---|
1609 | <informalexample> |
---|
1610 | <programlisting> |
---|
1611 | G4double GetCrossSection( const G4DynamicParticle*, const G4Element* ) |
---|
1612 | </programlisting> |
---|
1613 | </informalexample> |
---|
1614 | </para> |
---|
1615 | |
---|
1616 | <para> |
---|
1617 | For a given particle and material, this method returns a cross |
---|
1618 | section value provided by one of the collection of cross section |
---|
1619 | data sets listed in the data store object. If there are no known |
---|
1620 | data sets, a <literal>G4Exception</literal> is thrown and <literal>DBL_MIN</literal> is |
---|
1621 | returned. Otherwise, each data set in the list is queried, in |
---|
1622 | reverse list order, by invoking its <literal>IsApplicable</literal> method |
---|
1623 | for the given particle and material. The first data set object that |
---|
1624 | responds positively will then be asked to return a cross section |
---|
1625 | value via its <literal>GetCrossSection</literal> method. If no data set |
---|
1626 | responds positively, a <literal>G4Exception</literal> is thrown and |
---|
1627 | <literal>DBL_MIN</literal> is returned. |
---|
1628 | </para> |
---|
1629 | |
---|
1630 | <para> |
---|
1631 | <informalexample> |
---|
1632 | <programlisting> |
---|
1633 | void AddDataSet( G4VCrossSectionDataSet* aDataSet ) |
---|
1634 | </programlisting> |
---|
1635 | </informalexample> |
---|
1636 | |
---|
1637 | This method adds the given cross section data set to the end of the |
---|
1638 | list of data sets in the data store. For the evaluation of cross |
---|
1639 | sections, the list has a LIFO (Last In First Out) priority, meaning |
---|
1640 | that data sets added later to the list will have priority over |
---|
1641 | those added earlier to the list. Another way of saying this, is |
---|
1642 | that the data store, when given a <literal>GetCrossSection</literal> request, |
---|
1643 | does the <literal>IsApplicable</literal> queries in the reverse list order, |
---|
1644 | starting with the last data set in the list and proceeding to the |
---|
1645 | first, and the first data set that responds positively is used to |
---|
1646 | calculate the cross section. |
---|
1647 | </para> |
---|
1648 | |
---|
1649 | <para> |
---|
1650 | <informalexample> |
---|
1651 | <programlisting> |
---|
1652 | void BuildPhysicsTable( const G4ParticleDefinition& aParticleType ) |
---|
1653 | </programlisting> |
---|
1654 | </informalexample> |
---|
1655 | |
---|
1656 | This method may be invoked to indicate to the data store that there |
---|
1657 | has been a change in the cuts or other parameters of the given |
---|
1658 | particle type. In response, the data store will invoke the |
---|
1659 | <literal>BuildPhysicsTable</literal> of each of its data sets. |
---|
1660 | </para> |
---|
1661 | |
---|
1662 | <para> |
---|
1663 | <informalexample> |
---|
1664 | <programlisting> |
---|
1665 | void DumpPhysicsTable( const G4ParticleDefinition& ) |
---|
1666 | </programlisting> |
---|
1667 | </informalexample> |
---|
1668 | |
---|
1669 | This method may be used to request the data store to invoke the |
---|
1670 | <literal>DumpPhysicsTable</literal> method of each of its data sets. |
---|
1671 | </para> |
---|
1672 | |
---|
1673 | <!-- ******* Bridgehead ******* --> |
---|
1674 | <bridgehead renderas='sect4'> |
---|
1675 | Default cross sections |
---|
1676 | </bridgehead> |
---|
1677 | |
---|
1678 | <para> |
---|
1679 | The defaults for total cross section data and calculations have |
---|
1680 | been encapsulated in the singleton class |
---|
1681 | <emphasis>G4HadronCrossSections</emphasis>. Each hadronic process: |
---|
1682 | <emphasis>G4HadronInelasticProcess</emphasis>, |
---|
1683 | <emphasis>G4HadronElasticProcess</emphasis>, |
---|
1684 | <emphasis>G4HadronFissionProcess</emphasis>, |
---|
1685 | and <emphasis>G4HadronCaptureProcess</emphasis>, |
---|
1686 | comes already equipped with a cross section data store and a |
---|
1687 | default cross section data set. The data set objects are really |
---|
1688 | just shells that invoke the singleton <emphasis>G4HadronCrossSections</emphasis> |
---|
1689 | to do the real work of calculating cross sections. |
---|
1690 | </para> |
---|
1691 | |
---|
1692 | <para> |
---|
1693 | The default cross sections can be overridden in whole or in part |
---|
1694 | by the user. To this end, the base class <emphasis>G4HadronicProcess</emphasis> |
---|
1695 | has a ``get'' method: |
---|
1696 | |
---|
1697 | <informalexample> |
---|
1698 | <programlisting> |
---|
1699 | G4CrossSectionDataStore* GetCrossSectionDataStore() |
---|
1700 | </programlisting> |
---|
1701 | </informalexample> |
---|
1702 | |
---|
1703 | which gives public access to the data store for each process. The |
---|
1704 | user's cross section data sets can be added to the data store |
---|
1705 | according to the following framework: |
---|
1706 | |
---|
1707 | <informalexample> |
---|
1708 | <programlisting> |
---|
1709 | G4Hadron...Process aProcess(...) |
---|
1710 | |
---|
1711 | MyCrossSectionDataSet myDataSet(...) |
---|
1712 | |
---|
1713 | aProcess.GetCrossSectionDataStore()->AddDataSet( &MyDataSet ) |
---|
1714 | </programlisting> |
---|
1715 | </informalexample> |
---|
1716 | </para> |
---|
1717 | |
---|
1718 | <para> |
---|
1719 | The added data set will override the default cross section data |
---|
1720 | whenever so indicated by its <literal>IsApplicable</literal> method. |
---|
1721 | </para> |
---|
1722 | |
---|
1723 | <para> |
---|
1724 | In addition to the ``get'' method, <emphasis>G4HadronicProcess</emphasis> also |
---|
1725 | has the method |
---|
1726 | |
---|
1727 | <informalexample> |
---|
1728 | <programlisting> |
---|
1729 | void SetCrossSectionDataStore( G4CrossSectionDataStore* ) |
---|
1730 | </programlisting> |
---|
1731 | </informalexample> |
---|
1732 | |
---|
1733 | which allows the user to completely replace the default data |
---|
1734 | store with a new data store. |
---|
1735 | </para> |
---|
1736 | |
---|
1737 | <para> |
---|
1738 | It should be noted that a process does not send any information |
---|
1739 | about itself to its associated data store (and hence data set) |
---|
1740 | objects. Thus, each data set is assumed to be formulated to |
---|
1741 | calculate cross sections for one and only one type of process. Of |
---|
1742 | course, this does not prevent different data sets from sharing |
---|
1743 | common data and/or calculation methods, as in the case of the |
---|
1744 | <emphasis>G4HadronCrossSections</emphasis> class mentioned above. Indeed, |
---|
1745 | <emphasis>G4VCrossSectionDataSet</emphasis> specifies only the abstract interface |
---|
1746 | between physics processes and their data sets, and leaves the user |
---|
1747 | free to implement whatever sort of underlying structure is |
---|
1748 | appropriate. |
---|
1749 | </para> |
---|
1750 | |
---|
1751 | <para> |
---|
1752 | The current implementation of the data set |
---|
1753 | <emphasis>G4HadronCrossSections</emphasis> reuses the total cross-sections for |
---|
1754 | inelastic and elastic scattering, radiative capture and fission as |
---|
1755 | used with <emphasis role="bold">GHEISHA</emphasis> to provide cross-sections |
---|
1756 | for calculation |
---|
1757 | of the respective mean free paths of a given particle in a given |
---|
1758 | material. |
---|
1759 | </para> |
---|
1760 | |
---|
1761 | <!-- ******* Bridgehead ******* --> |
---|
1762 | <bridgehead renderas='sect4'> |
---|
1763 | Cross-sections for low energy neutron transport |
---|
1764 | </bridgehead> |
---|
1765 | |
---|
1766 | <para> |
---|
1767 | The cross section data for low energy neutron transport are |
---|
1768 | organized in a set of files that are read in by the corresponding |
---|
1769 | data set classes at time zero. Hereby the file system is used, in |
---|
1770 | order to allow highly granular access to the data. The ``root'' |
---|
1771 | directory of the cross-section directory structure is accessed |
---|
1772 | through an environment variable, <literal>NeutronHPCrossSections</literal>, |
---|
1773 | which is to be set by the user. The classes accessing the total |
---|
1774 | cross-sections of the individual processes, i.e., the cross-section |
---|
1775 | data set classes for low energy neutron transport, are |
---|
1776 | <emphasis>G4NeutronHPElasticData</emphasis>, |
---|
1777 | <emphasis>G4NeutronHPCaptureData</emphasis>, |
---|
1778 | <emphasis>G4NeutronHPFissionData</emphasis>, |
---|
1779 | and <emphasis>G4NeutronHPInelasticData</emphasis>. |
---|
1780 | </para> |
---|
1781 | |
---|
1782 | <para> |
---|
1783 | For detailed descriptions of the low energy neutron total |
---|
1784 | cross-sections, they may be registered by the user as described |
---|
1785 | above with the data stores of the corresponding processes for |
---|
1786 | neutron interactions. |
---|
1787 | </para> |
---|
1788 | |
---|
1789 | <para> |
---|
1790 | It should be noted that using these total cross section classes |
---|
1791 | does not require that the neutron_hp models also be used. It is up |
---|
1792 | to the user to decide whethee this is desirable or not for his |
---|
1793 | particular problem. |
---|
1794 | </para> |
---|
1795 | |
---|
1796 | </sect3> |
---|
1797 | |
---|
1798 | <!-- ******************* Section (Level#3) ****************** --> |
---|
1799 | <sect3 id="sect.PhysProc.Had.AtRest"> |
---|
1800 | <title> |
---|
1801 | Hadrons at Rest |
---|
1802 | </title> |
---|
1803 | |
---|
1804 | <!-- ******* Bridgehead ******* --> |
---|
1805 | <bridgehead renderas='sect4'> |
---|
1806 | List of implemented "Hadron at Rest" processes |
---|
1807 | </bridgehead> |
---|
1808 | |
---|
1809 | <para> |
---|
1810 | The following process classes have been implemented: |
---|
1811 | |
---|
1812 | <itemizedlist spacing="compact"> |
---|
1813 | <listitem><para> |
---|
1814 | pi- absorption (class name <emphasis>G4PionMinusAbsorptionAtRest</emphasis> |
---|
1815 | or <emphasis>G4PiMinusAbsorptionAtRest</emphasis>) |
---|
1816 | </para></listitem> |
---|
1817 | <listitem><para> |
---|
1818 | kaon- absorption (class name <emphasis>G4KaonMinusAbsorptionAtRest</emphasis> |
---|
1819 | or <emphasis>G4KaonMinusAbsorption</emphasis>) |
---|
1820 | </para></listitem> |
---|
1821 | <listitem><para> |
---|
1822 | neutron capture (class name <emphasis>G4NeutronCaptureAtRest</emphasis>) |
---|
1823 | </para></listitem> |
---|
1824 | <listitem><para> |
---|
1825 | anti-proton annihilation (class name |
---|
1826 | <emphasis>G4AntiProtonAnnihilationAtRest</emphasis>) |
---|
1827 | </para></listitem> |
---|
1828 | <listitem><para> |
---|
1829 | anti-neutron annihilation (class name |
---|
1830 | <emphasis>G4AntiNeutronAnnihilationAtRest</emphasis>) |
---|
1831 | </para></listitem> |
---|
1832 | <listitem><para> |
---|
1833 | mu- capture (class name <emphasis>G4MuonMinusCaptureAtRest</emphasis>) |
---|
1834 | </para></listitem> |
---|
1835 | <listitem><para> |
---|
1836 | alternative CHIPS model for any negativly charged particle |
---|
1837 | (class name <emphasis>G4QCaptureAtRest</emphasis>) |
---|
1838 | </para></listitem> |
---|
1839 | </itemizedlist> |
---|
1840 | </para> |
---|
1841 | |
---|
1842 | <para> |
---|
1843 | Obviously the last process does not, strictly speaking, deal with a |
---|
1844 | ``hadron at rest''. It does, nonetheless, share common features |
---|
1845 | with the others in the above list because of the implementation |
---|
1846 | model chosen. The differences between the alternative |
---|
1847 | implementation for kaon and pion absorption concern the fast part |
---|
1848 | of the emitted particle spectrum. G4PiMinusAbsorptionAtRest, and |
---|
1849 | G4KaonMinusAbsorptionAtRest focus especially on a good description |
---|
1850 | of this part of the spectrum. |
---|
1851 | </para> |
---|
1852 | |
---|
1853 | <!-- ******* Bridgehead ******* --> |
---|
1854 | <bridgehead renderas='sect4'> |
---|
1855 | Implementation Interface to Geant4 |
---|
1856 | </bridgehead> |
---|
1857 | |
---|
1858 | <para> |
---|
1859 | All of these classes are derived from the abstract class |
---|
1860 | <emphasis>G4VRestProcess</emphasis>. In addition to the constructor and |
---|
1861 | destructor methods, the following public methods of the abstract |
---|
1862 | class have been implemented for each of the above six |
---|
1863 | processes: |
---|
1864 | |
---|
1865 | <itemizedlist spacing="compact"> |
---|
1866 | <listitem><para> |
---|
1867 | <para> |
---|
1868 | <literal>AtRestGetPhysicalInteractionLength( const G4Track&, |
---|
1869 | G4ForceCondition* )</literal> |
---|
1870 | </para> |
---|
1871 | <para> |
---|
1872 | This method returns the time taken before the interaction actually |
---|
1873 | occurs. In all processes listed above, except for muon capture, a |
---|
1874 | value of zero is returned. For the muon capture process the muon |
---|
1875 | capture lifetime is returned. |
---|
1876 | </para> |
---|
1877 | </para></listitem> |
---|
1878 | <listitem><para> |
---|
1879 | <para> |
---|
1880 | <literal>AtRestDoIt( const G4Track&, const G4Step&)</literal> |
---|
1881 | </para> |
---|
1882 | <para> |
---|
1883 | This method generates the secondary particles produced by the |
---|
1884 | process. |
---|
1885 | </para> |
---|
1886 | </para></listitem> |
---|
1887 | <listitem><para> |
---|
1888 | <para> |
---|
1889 | <literal>IsApplicable( const G4ParticleDefinition& )</literal> |
---|
1890 | </para> |
---|
1891 | <para> |
---|
1892 | This method returns the result of a check to see if the process is |
---|
1893 | possible for a given particle. |
---|
1894 | </para> |
---|
1895 | </para></listitem> |
---|
1896 | </itemizedlist> |
---|
1897 | </para> |
---|
1898 | |
---|
1899 | |
---|
1900 | <!-- ******* Bridgehead ******* --> |
---|
1901 | <bridgehead renderas='sect4'> |
---|
1902 | Example of how to use a hadron at rest process |
---|
1903 | </bridgehead> |
---|
1904 | |
---|
1905 | <para> |
---|
1906 | Including a ``hadron at rest'' process for a particle, a pi- for |
---|
1907 | example, into the Geant4 system is straightforward and can be done |
---|
1908 | in the following way: |
---|
1909 | |
---|
1910 | <itemizedlist spacing="compact"> |
---|
1911 | <listitem><para> |
---|
1912 | create a process: |
---|
1913 | <informalexample> |
---|
1914 | <programlisting> |
---|
1915 | theProcess = new G4PionMinusAbsorptionAtRest(); |
---|
1916 | </programlisting> |
---|
1917 | </informalexample> |
---|
1918 | </para></listitem> |
---|
1919 | <listitem><para> |
---|
1920 | register the process with the particle's process manager: |
---|
1921 | <informalexample> |
---|
1922 | <programlisting> |
---|
1923 | theParticleDef = G4PionMinus::PionMinus(); |
---|
1924 | G4ProcessManager* pman = theParticleDef->GetProcessManager(); |
---|
1925 | pman->AddRestProcess( theProcess ); |
---|
1926 | </programlisting> |
---|
1927 | </informalexample> |
---|
1928 | </para></listitem> |
---|
1929 | </itemizedlist> |
---|
1930 | </para> |
---|
1931 | |
---|
1932 | </sect3> |
---|
1933 | |
---|
1934 | <!-- ******************* Section (Level#3) ****************** --> |
---|
1935 | <sect3 id="sect.PhysProc.Had.Flight"> |
---|
1936 | <title> |
---|
1937 | Hadrons in Flight |
---|
1938 | </title> |
---|
1939 | |
---|
1940 | <!-- ******* Bridgehead ******* --> |
---|
1941 | <bridgehead renderas='sect4'> |
---|
1942 | What processes do you need? |
---|
1943 | </bridgehead> |
---|
1944 | |
---|
1945 | <para> |
---|
1946 | For hadrons in motion, there are four physics process classes. |
---|
1947 | <xref linkend="table.PhysProc_1" /> shows each process and the |
---|
1948 | particles for which it is relevant. |
---|
1949 | |
---|
1950 | <table id="table.PhysProc_1"> |
---|
1951 | <title> |
---|
1952 | Hadronic processes and relevant particles. |
---|
1953 | </title> |
---|
1954 | |
---|
1955 | <tgroup cols="2"> |
---|
1956 | <tbody> |
---|
1957 | <row> |
---|
1958 | <entry> |
---|
1959 | <emphasis>G4HadronElasticProcess</emphasis> |
---|
1960 | </entry> |
---|
1961 | <entry> |
---|
1962 | pi+, pi-, K<superscript>+</superscript>, |
---|
1963 | K<superscript>0</superscript><subscript>S</subscript>, |
---|
1964 | K<superscript>0</superscript><subscript>L</subscript>, |
---|
1965 | K<superscript>-</superscript>, |
---|
1966 | p, p-bar, n, n-bar, lambda, lambda-bar, |
---|
1967 | Sigma<superscript>+</superscript>, Sigma<superscript>-</superscript>, |
---|
1968 | Sigma<superscript>+</superscript>-bar, |
---|
1969 | Sigma<superscript>-</superscript>-bar, |
---|
1970 | Xi<superscript>0</superscript>, Xi<superscript>-</superscript>, |
---|
1971 | Xi<superscript>0</superscript>-bar, Xi<superscript>-</superscript>-bar |
---|
1972 | </entry> |
---|
1973 | </row> |
---|
1974 | <row> |
---|
1975 | <entry> |
---|
1976 | <emphasis>G4HadronInelasticProcess</emphasis> |
---|
1977 | </entry> |
---|
1978 | <entry> |
---|
1979 | pi+, pi-, K<superscript>+</superscript>, |
---|
1980 | K<superscript>0</superscript><subscript>S</subscript>, |
---|
1981 | K<superscript>0</superscript><subscript>L</subscript>, |
---|
1982 | K<superscript>-</superscript>, |
---|
1983 | p, p-bar, n, n-bar, lambda, lambda-bar, |
---|
1984 | Sigma<superscript>+</superscript>, Sigma<superscript>-</superscript>, |
---|
1985 | Sigma<superscript>+</superscript>-bar, |
---|
1986 | Sigma<superscript>-</superscript>-bar, Xi<superscript>0</superscript>, |
---|
1987 | Xi<superscript>-</superscript>, Xi<superscript>0</superscript>-bar, |
---|
1988 | Xi<superscript>-</superscript>-bar |
---|
1989 | </entry> |
---|
1990 | </row> |
---|
1991 | <row> |
---|
1992 | <entry> |
---|
1993 | <emphasis>G4HadronFissionProcess</emphasis> |
---|
1994 | </entry> |
---|
1995 | <entry> |
---|
1996 | all |
---|
1997 | </entry> |
---|
1998 | </row> |
---|
1999 | <row> |
---|
2000 | <entry> |
---|
2001 | <emphasis>G4CaptureProcess</emphasis> |
---|
2002 | </entry> |
---|
2003 | <entry> |
---|
2004 | n, n-bar |
---|
2005 | </entry> |
---|
2006 | </row> |
---|
2007 | </tbody> |
---|
2008 | </tgroup> |
---|
2009 | </table> |
---|
2010 | </para> |
---|
2011 | |
---|
2012 | <!-- ******* Bridgehead ******* --> |
---|
2013 | <bridgehead renderas='sect4'> |
---|
2014 | How to register Models |
---|
2015 | </bridgehead> |
---|
2016 | |
---|
2017 | <para> |
---|
2018 | To register an inelastic process model for a particle, a proton |
---|
2019 | for example, first get the pointer to the particle's process |
---|
2020 | manager: |
---|
2021 | |
---|
2022 | <informalexample> |
---|
2023 | <programlisting> |
---|
2024 | G4ParticleDefinition *theProton = G4Proton::ProtonDefinition(); |
---|
2025 | G4ProcessManager *theProtonProcMan = theProton->GetProcessManager(); |
---|
2026 | </programlisting> |
---|
2027 | </informalexample> |
---|
2028 | </para> |
---|
2029 | |
---|
2030 | <para> |
---|
2031 | Create an instance of the particle's inelastic process: |
---|
2032 | |
---|
2033 | <informalexample> |
---|
2034 | <programlisting> |
---|
2035 | G4ProtonInelasticProcess *theProtonIEProc = new G4ProtonInelasticProcess(); |
---|
2036 | </programlisting> |
---|
2037 | </informalexample> |
---|
2038 | </para> |
---|
2039 | |
---|
2040 | <para> |
---|
2041 | Create an instance of the model which determines the secondaries |
---|
2042 | produced in the interaction, and calculates the momenta of the |
---|
2043 | particles: |
---|
2044 | |
---|
2045 | <informalexample> |
---|
2046 | <programlisting> |
---|
2047 | G4LEProtonInelastic *theProtonIE = new G4LEProtonInelastic(); |
---|
2048 | </programlisting> |
---|
2049 | </informalexample> |
---|
2050 | </para> |
---|
2051 | |
---|
2052 | <para> |
---|
2053 | Register the model with the particle's inelastic process: |
---|
2054 | |
---|
2055 | <informalexample> |
---|
2056 | <programlisting> |
---|
2057 | theProtonIEProc->RegisterMe( theProtonIE ); |
---|
2058 | </programlisting> |
---|
2059 | </informalexample> |
---|
2060 | </para> |
---|
2061 | |
---|
2062 | <para> |
---|
2063 | Finally, add the particle's inelastic process to the list of |
---|
2064 | discrete processes: |
---|
2065 | |
---|
2066 | <informalexample> |
---|
2067 | <programlisting> |
---|
2068 | theProtonProcMan->AddDiscreteProcess( theProtonIEProc ); |
---|
2069 | </programlisting> |
---|
2070 | </informalexample> |
---|
2071 | </para> |
---|
2072 | |
---|
2073 | <para> |
---|
2074 | The particle's inelastic process class, |
---|
2075 | <emphasis>G4ProtonInelasticProcess</emphasis> in the example above, derives from |
---|
2076 | the <emphasis>G4HadronicInelasticProcess</emphasis> class, and simply defines the |
---|
2077 | process name and calls the <emphasis>G4HadronicInelasticProcess</emphasis> |
---|
2078 | constructor. All of the specific particle inelastic processes |
---|
2079 | derive from the <emphasis>G4HadronicInelasticProcess</emphasis> class, which |
---|
2080 | calls the <literal>PostStepDoIt</literal> function, which returns the |
---|
2081 | particle change object from the <emphasis>G4HadronicProcess</emphasis> function |
---|
2082 | <literal>GeneralPostStepDoIt</literal>. This class also gets the mean free |
---|
2083 | path, builds the physics table, and gets the microscopic cross |
---|
2084 | section. The <emphasis>G4HadronicInelasticProcess</emphasis> class derives from |
---|
2085 | the <emphasis>G4HadronicProcess</emphasis> class, which is the top level hadronic |
---|
2086 | process class. The <emphasis>G4HadronicProcess</emphasis> class derives from the |
---|
2087 | <emphasis>G4VDiscreteProcess</emphasis> class. The inelastic, elastic, capture, |
---|
2088 | and fission processes derive from the <emphasis>G4HadronicProcess</emphasis> |
---|
2089 | class. This pure virtual class also provides the energy range |
---|
2090 | manager object and the <literal>RegisterMe</literal> access function. |
---|
2091 | </para> |
---|
2092 | |
---|
2093 | <para> |
---|
2094 | A sample case for the proton's inelastic interaction model class |
---|
2095 | is shown in <xref linkend="programlist_PhysProc_3" />, where |
---|
2096 | <literal>G4LEProtonInelastic.hh</literal> is the name of the include |
---|
2097 | file: |
---|
2098 | |
---|
2099 | <example id="programlist_PhysProc_3"> |
---|
2100 | <title> |
---|
2101 | An example of a proton inelastic interaction model class. |
---|
2102 | </title> |
---|
2103 | |
---|
2104 | <programlisting> |
---|
2105 | ----------------------------- include file ------------------------------------------ |
---|
2106 | |
---|
2107 | #include "G4InelasticInteraction.hh" |
---|
2108 | class G4LEProtonInelastic : public G4InelasticInteraction |
---|
2109 | { |
---|
2110 | public: |
---|
2111 | G4LEProtonInelastic() : G4InelasticInteraction() |
---|
2112 | { |
---|
2113 | SetMinEnergy( 0.0 ); |
---|
2114 | SetMaxEnergy( 25.*GeV ); |
---|
2115 | } |
---|
2116 | ~G4LEProtonInelastic() { } |
---|
2117 | G4ParticleChange *ApplyYourself( const G4Track &aTrack, |
---|
2118 | G4Nucleus &targetNucleus ); |
---|
2119 | private: |
---|
2120 | void CascadeAndCalculateMomenta( required arguments ); |
---|
2121 | }; |
---|
2122 | |
---|
2123 | ----------------------------- source file ------------------------------------------ |
---|
2124 | |
---|
2125 | #include "G4LEProtonInelastic.hh" |
---|
2126 | G4ParticleChange * |
---|
2127 | G4LEProton Inelastic::ApplyYourself( const G4Track &aTrack, |
---|
2128 | G4Nucleus &targetNucleus ) |
---|
2129 | { |
---|
2130 | theParticleChange.Initialize( aTrack ); |
---|
2131 | const G4DynamicParticle *incidentParticle = aTrack.GetDynamicParticle(); |
---|
2132 | // create the target particle |
---|
2133 | G4DynamicParticle *targetParticle = targetNucleus.ReturnTargetParticle(); |
---|
2134 | CascadeAndCalculateMomenta( required arguments ) |
---|
2135 | { ... } |
---|
2136 | return &theParticleChange; |
---|
2137 | } |
---|
2138 | </programlisting> |
---|
2139 | </example> |
---|
2140 | </para> |
---|
2141 | |
---|
2142 | <para> |
---|
2143 | The <literal>CascadeAndCalculateMomenta</literal> function is the bulk of |
---|
2144 | the model and is to be provided by the model's creator. It should |
---|
2145 | determine what secondary particles are produced in the interaction, |
---|
2146 | calculate the momenta for all the particles, and put this |
---|
2147 | information into the <emphasis>ParticleChange</emphasis> object which is |
---|
2148 | returned. |
---|
2149 | </para> |
---|
2150 | |
---|
2151 | <para> |
---|
2152 | The <emphasis>G4LEProtonInelastic</emphasis> class derives from the |
---|
2153 | <emphasis>G4InelasticInteraction</emphasis> class, which is an abstract base |
---|
2154 | class since the pure virtual function <literal>ApplyYourself</literal> is not |
---|
2155 | defined there. <emphasis>G4InelasticInteraction</emphasis> itself derives from |
---|
2156 | the <emphasis>G4HadronicInteraction</emphasis> abstract base class. This class is |
---|
2157 | the base class for all the model classes. It sorts out the energy |
---|
2158 | range for the models and provides class utilities. The |
---|
2159 | <emphasis>G4HadronicInteraction</emphasis> class provides the |
---|
2160 | <literal>Set/GetMinEnergy</literal> and the <literal>Set/GetMaxEnergy</literal> |
---|
2161 | functions which determine the minimum and maximum energy range for |
---|
2162 | the model. An energy range can be set for a specific element, a |
---|
2163 | specific material, or for general applicability: |
---|
2164 | |
---|
2165 | <informalexample> |
---|
2166 | <programlisting> |
---|
2167 | void SetMinEnergy( G4double anEnergy, G4Element *anElement ) |
---|
2168 | void SetMinEnergy( G4double anEnergy, G4Material *aMaterial ) |
---|
2169 | void SetMinEnergy( const G4double anEnergy ) |
---|
2170 | void SetMaxEnergy( G4double anEnergy, G4Element *anElement ) |
---|
2171 | void SetMaxEnergy( G4double anEnergy, G4Material *aMaterial ) |
---|
2172 | void SetMaxEnergy( const G4double anEnergy ) |
---|
2173 | </programlisting> |
---|
2174 | </informalexample> |
---|
2175 | </para> |
---|
2176 | |
---|
2177 | <!-- ******* Bridgehead ******* --> |
---|
2178 | <bridgehead renderas='sect4'> |
---|
2179 | Which models are there, and what are the defaults |
---|
2180 | </bridgehead> |
---|
2181 | |
---|
2182 | <para> |
---|
2183 | In Geant4, any model can be run together with any other model |
---|
2184 | without the need for the implementation of a special interface, or |
---|
2185 | batch suite, and the ranges of applicability for the different |
---|
2186 | models can be steered at initialisation time. This way, highly |
---|
2187 | specialised models (valid only for one material and particle, and |
---|
2188 | applicable only in a very restricted energy range) can be used in |
---|
2189 | the same application, together with more general code, in a |
---|
2190 | coherent fashion. |
---|
2191 | </para> |
---|
2192 | |
---|
2193 | <para> |
---|
2194 | Each model has an intrinsic range of applicability, and the |
---|
2195 | model chosen for a simulation depends very much on the use-case. |
---|
2196 | Consequently, there are no ``defaults''. However, physics lists are |
---|
2197 | provided which specify sets of models for various purposes. |
---|
2198 | </para> |
---|
2199 | |
---|
2200 | <para> |
---|
2201 | Three types of hadronic shower models have been implemented: |
---|
2202 | parametrisation driven models, data driven models, and theory |
---|
2203 | driven models. |
---|
2204 | |
---|
2205 | <itemizedlist spacing="compact"> |
---|
2206 | <listitem><para> |
---|
2207 | Parametrisation driven models are used for all processes |
---|
2208 | pertaining to particles coming to rest, and interacting with the |
---|
2209 | nucleus. For particles in flight, two sets of models exist for |
---|
2210 | inelastic scattering; low energy, and high energy models. Both sets |
---|
2211 | are based originally on the <emphasis role="bold">GHEISHA</emphasis> |
---|
2212 | package of Geant3.21, |
---|
2213 | and the original approaches to primary interaction, nuclear |
---|
2214 | excitation, intra-nuclear cascade and evaporation is kept. The |
---|
2215 | models are located in the sub-directories |
---|
2216 | <literal>hadronics/models/low_energy</literal> and |
---|
2217 | <literal>hadronics/models/high_energy</literal>. The low energy models are |
---|
2218 | targeted towards energies below 20 GeV; the high energy models |
---|
2219 | cover the energy range from 20 GeV to O(TeV). Fission, capture and |
---|
2220 | coherent elastic scattering are also modeled through parametrised |
---|
2221 | models. |
---|
2222 | </para></listitem> |
---|
2223 | <listitem><para> |
---|
2224 | Data driven models are available for the transport of low |
---|
2225 | energy neutrons in matter in sub-directory |
---|
2226 | <literal>hadronics/models/neutron_hp</literal>. The modeling is based |
---|
2227 | on the data formats of <emphasis role="bold">ENDF/B-VI</emphasis>, |
---|
2228 | and all distributions of this standard data format are implemented. |
---|
2229 | The data sets used are selected from data libraries that conform to |
---|
2230 | these standard formats. The file system is used in order to allow granular |
---|
2231 | access to, and flexibility in, the use of the cross sections for different |
---|
2232 | isotopes, and channels. The energy coverage of these models is from |
---|
2233 | thermal energies to 20 MeV. |
---|
2234 | </para></listitem> |
---|
2235 | <listitem><para> |
---|
2236 | Theory driven models are available for inelastic scattering in |
---|
2237 | a first implementation, covering the full energy range of LHC |
---|
2238 | experiments. They are located in sub-directory |
---|
2239 | <literal>hadronics/models/generator</literal>. The current philosophy |
---|
2240 | implies the usage of parton string models at high energies, of |
---|
2241 | intra-nuclear transport models at intermediate energies, and of |
---|
2242 | statistical break-up models for de-excitation. |
---|
2243 | </para></listitem> |
---|
2244 | </itemizedlist> |
---|
2245 | </para> |
---|
2246 | |
---|
2247 | </sect3> |
---|
2248 | </sect2> |
---|
2249 | |
---|
2250 | <!-- ******************* Section (Level#2) ****************** --> |
---|
2251 | <sect2 id="sect.PhysProc.Decay"> |
---|
2252 | <title> |
---|
2253 | Particle Decay Process |
---|
2254 | </title> |
---|
2255 | |
---|
2256 | <para> |
---|
2257 | This section briefly introduces decay processes installed in |
---|
2258 | Geant4. For details of the implementation of particle decays, |
---|
2259 | please refer to the |
---|
2260 | <ulink url="http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/PhysicsReferenceManual/html/PhysicsReferenceManual.html"> |
---|
2261 | <emphasis role="bold">Physics Reference Manual</emphasis></ulink>. |
---|
2262 | </para> |
---|
2263 | |
---|
2264 | <!-- ******************* Section (Level#3) ****************** --> |
---|
2265 | <sect3 id="sect.PhysProc.Decay.Class"> |
---|
2266 | <title> |
---|
2267 | Particle Decay Class |
---|
2268 | </title> |
---|
2269 | |
---|
2270 | <para> |
---|
2271 | Geant4 provides a <emphasis>G4Decay</emphasis> class for both ``at rest'' and |
---|
2272 | ``in flight'' particle decays. <emphasis>G4Decay</emphasis> can be applied to all |
---|
2273 | particles except: |
---|
2274 | |
---|
2275 | <variablelist> |
---|
2276 | <varlistentry> |
---|
2277 | <term> |
---|
2278 | massless particles, i.e., |
---|
2279 | </term> |
---|
2280 | <listitem> |
---|
2281 | <literal>G4ParticleDefinition::thePDGMass <= 0</literal> |
---|
2282 | </listitem> |
---|
2283 | </varlistentry> |
---|
2284 | <varlistentry> |
---|
2285 | <term> |
---|
2286 | particles with ``negative'' life time, i.e., |
---|
2287 | </term> |
---|
2288 | <listitem> |
---|
2289 | <literal>G4ParticleDefinition::thePDGLifeTime < 0</literal> |
---|
2290 | </listitem> |
---|
2291 | </varlistentry> |
---|
2292 | <varlistentry> |
---|
2293 | <term> |
---|
2294 | shortlived particles, i.e., |
---|
2295 | </term> |
---|
2296 | <listitem> |
---|
2297 | <literal>G4ParticleDefinition::fShortLivedFlag = True</literal> |
---|
2298 | </listitem> |
---|
2299 | </varlistentry> |
---|
2300 | </variablelist> |
---|
2301 | </para> |
---|
2302 | |
---|
2303 | <para> |
---|
2304 | Decay for some particles may be switched on or off by using |
---|
2305 | <literal>G4ParticleDefinition::SetPDGStable()</literal> as well as |
---|
2306 | <literal>ActivateProcess()</literal> and <literal>InActivateProcess()</literal> |
---|
2307 | methods of <emphasis>G4ProcessManager</emphasis>. |
---|
2308 | </para> |
---|
2309 | |
---|
2310 | <para> |
---|
2311 | <emphasis>G4Decay</emphasis> proposes the step length (or step time for |
---|
2312 | <literal>AtRest</literal>) according to the lifetime of the particle unless |
---|
2313 | <literal>PreAssignedDecayProperTime</literal> is defined in |
---|
2314 | <emphasis>G4DynamicParticle</emphasis>. |
---|
2315 | </para> |
---|
2316 | |
---|
2317 | <para> |
---|
2318 | The <emphasis>G4Decay</emphasis> class itself does not define decay modes of |
---|
2319 | the particle. Geant4 provides two ways of doing this: |
---|
2320 | |
---|
2321 | <itemizedlist spacing="compact"> |
---|
2322 | <listitem><para> |
---|
2323 | using <emphasis>G4DecayChannel</emphasis> in <emphasis>G4DecayTable</emphasis>, |
---|
2324 | and |
---|
2325 | </para></listitem> |
---|
2326 | <listitem><para> |
---|
2327 | using <literal>thePreAssignedDecayProducts</literal> of |
---|
2328 | <emphasis>G4DynamicParticle</emphasis> |
---|
2329 | </para></listitem> |
---|
2330 | </itemizedlist> |
---|
2331 | </para> |
---|
2332 | |
---|
2333 | <para> |
---|
2334 | The <emphasis>G4Decay</emphasis> class calculates the |
---|
2335 | <literal>PhysicalInteractionLength</literal> and boosts decay products |
---|
2336 | created by <emphasis>G4VDecayChannel</emphasis> or event generators. See below |
---|
2337 | for information on the determination of the decay modes. |
---|
2338 | </para> |
---|
2339 | |
---|
2340 | <para> |
---|
2341 | An object of <emphasis>G4Decay</emphasis> can be shared by particles. |
---|
2342 | Registration of the decay process to particles in the |
---|
2343 | <literal>ConstructPhysics</literal> method of <emphasis>PhysicsList</emphasis> |
---|
2344 | (see <xref linkend="sect.HowToSpecPhysProc.SpecPhysProc" />) |
---|
2345 | is shown in <xref linkend="programlist_PhysProc_4" />. |
---|
2346 | |
---|
2347 | <example id="programlist_PhysProc_4"> |
---|
2348 | <title> |
---|
2349 | Registration of the decay process to particles in the |
---|
2350 | <literal>ConstructPhysics</literal> method of <emphasis>PhysicsList</emphasis>. |
---|
2351 | </title> |
---|
2352 | |
---|
2353 | <programlisting> |
---|
2354 | #include "G4Decay.hh" |
---|
2355 | void ExN02PhysicsList::ConstructGeneral() |
---|
2356 | { |
---|
2357 | // Add Decay Process |
---|
2358 | G4Decay* theDecayProcess = new G4Decay(); |
---|
2359 | theParticleIterator->reset(); |
---|
2360 | while( (*theParticleIterator)() ){ |
---|
2361 | G4ParticleDefinition* particle = theParticleIterator->value(); |
---|
2362 | G4ProcessManager* pmanager = particle->GetProcessManager(); |
---|
2363 | if (theDecayProcess->IsApplicable(*particle)) { |
---|
2364 | pmanager ->AddProcess(theDecayProcess); |
---|
2365 | // set ordering for PostStepDoIt and AtRestDoIt |
---|
2366 | pmanager ->SetProcessOrdering(theDecayProcess, idxPostStep); |
---|
2367 | pmanager ->SetProcessOrdering(theDecayProcess, idxAtRest); |
---|
2368 | } |
---|
2369 | } |
---|
2370 | } |
---|
2371 | </programlisting> |
---|
2372 | </example> |
---|
2373 | </para> |
---|
2374 | |
---|
2375 | </sect3> |
---|
2376 | |
---|
2377 | <!-- ******************* Section (Level#3) ****************** --> |
---|
2378 | <sect3 id="sect.PhysProc.Decay.Table"> |
---|
2379 | <title> |
---|
2380 | Decay Table |
---|
2381 | </title> |
---|
2382 | |
---|
2383 | <para> |
---|
2384 | Each particle has its <emphasis>G4DecayTable</emphasis>, which stores information |
---|
2385 | on the decay modes of the particle. Each decay mode, with its |
---|
2386 | branching ratio, corresponds to an object of various ``decay |
---|
2387 | channel'' classes derived from <emphasis>G4VDecayChannel</emphasis>. Default |
---|
2388 | decay modes are created in the constructors of particle classes. |
---|
2389 | For example, the decay table of the neutral pion has |
---|
2390 | <emphasis>G4PhaseSpaceDecayChannel</emphasis> and |
---|
2391 | <emphasis>G4DalitzDecayChannel</emphasis> as follows: |
---|
2392 | |
---|
2393 | <informalexample> |
---|
2394 | <programlisting> |
---|
2395 | // create a decay channel |
---|
2396 | G4VDecayChannel* mode; |
---|
2397 | // pi0 -> gamma + gamma |
---|
2398 | mode = new G4PhaseSpaceDecayChannel("pi0",0.988,2,"gamma","gamma"); |
---|
2399 | table->Insert(mode); |
---|
2400 | // pi0 -> gamma + e+ + e- |
---|
2401 | mode = new G4DalitzDecayChannel("pi0",0.012,"e-","e+"); |
---|
2402 | table->Insert(mode); |
---|
2403 | </programlisting> |
---|
2404 | </informalexample> |
---|
2405 | </para> |
---|
2406 | |
---|
2407 | <para> |
---|
2408 | Decay modes and branching ratios defined in Geant4 are listed in |
---|
2409 | <xref linkend="sect.Parti.Def" />. |
---|
2410 | </para> |
---|
2411 | |
---|
2412 | </sect3> |
---|
2413 | |
---|
2414 | <!-- ******************* Section (Level#3) ****************** --> |
---|
2415 | <sect3 id="sect.PhysProc.Decay.PreAssgn"> |
---|
2416 | <title> |
---|
2417 | Pre-assigned Decay Modes by Event Generators |
---|
2418 | </title> |
---|
2419 | |
---|
2420 | <para> |
---|
2421 | Decays of heavy flavor particles such as B mesons are very complex, |
---|
2422 | with many varieties of decay modes and decay mechanisms. There are |
---|
2423 | many models for heavy particle decay provided by various event |
---|
2424 | generators and it is impossible to define all the decay modes of |
---|
2425 | heavy particles by using <emphasis>G4VDecayChannel</emphasis>. In other words, |
---|
2426 | decays of heavy particles cannot be defined by the Geant4 decay |
---|
2427 | process, but should be defined by event generators or other |
---|
2428 | external packages. Geant4 provides two ways to do this: |
---|
2429 | <literal>pre-assigned decay mode</literal> and <literal>external decayer</literal>. |
---|
2430 | </para> |
---|
2431 | |
---|
2432 | <para> |
---|
2433 | In the latter approach, the class <emphasis>G4VExtDecayer</emphasis> is used |
---|
2434 | for the interface to an external package which defines decay modes |
---|
2435 | for a particle. If an instance of <emphasis>G4VExtDecayer</emphasis> is attached |
---|
2436 | to <emphasis>G4Decay</emphasis>, daughter particles will be generated by the |
---|
2437 | external decay handler. |
---|
2438 | </para> |
---|
2439 | |
---|
2440 | <para> |
---|
2441 | In the former case, decays of heavy particles are simulated by |
---|
2442 | an event generator and the primary event contains the decay |
---|
2443 | information. <emphasis>G4VPrimaryGenerator</emphasis> automatically attaches any |
---|
2444 | daughter particles to the parent particle as the |
---|
2445 | PreAssignedDecayProducts member of <emphasis>G4DynamicParticle</emphasis>. |
---|
2446 | <emphasis>G4Decay</emphasis> adopts these pre-assigned daughter particles instead |
---|
2447 | of asking <emphasis>G4VDecayChannel</emphasis> to generate decay products. |
---|
2448 | </para> |
---|
2449 | |
---|
2450 | <para> |
---|
2451 | In addition, the user may assign a <literal>pre-assigned</literal> decay |
---|
2452 | time for a specific track in its rest frame (i.e. decay time is |
---|
2453 | defined in the proper time) by using the |
---|
2454 | <emphasis>G4PrimaryParticle::SetProperTime()</emphasis> method. |
---|
2455 | <emphasis>G4VPrimaryGenerator</emphasis> sets the PreAssignedDecayProperTime |
---|
2456 | member of <emphasis>G4DynamicParticle</emphasis>. <emphasis>G4Decay</emphasis> |
---|
2457 | uses this decay time instead of the life time of the particle type. |
---|
2458 | </para> |
---|
2459 | |
---|
2460 | </sect3> |
---|
2461 | </sect2> |
---|
2462 | |
---|
2463 | |
---|
2464 | <!-- ******************* Section (Level#2) ****************** --> |
---|
2465 | <sect2 id="sect.PhysProc.PhotoHad"> |
---|
2466 | <title> |
---|
2467 | Photolepton-hadron Processes |
---|
2468 | </title> |
---|
2469 | |
---|
2470 | <para> |
---|
2471 | To be delivered. |
---|
2472 | </para> |
---|
2473 | |
---|
2474 | </sect2> |
---|
2475 | |
---|
2476 | |
---|
2477 | <!-- ******************* Section (Level#2) ****************** --> |
---|
2478 | <sect2 id="sect.PhysProc.Photo"> |
---|
2479 | <title> |
---|
2480 | Optical Photon Processes |
---|
2481 | </title> |
---|
2482 | |
---|
2483 | <para> |
---|
2484 | A photon is considered to be <emphasis>optical</emphasis> when its wavelength |
---|
2485 | is much greater than the typical atomic spacing. In GEANT4 optical |
---|
2486 | photons are treated as a class of particle distinct from their |
---|
2487 | higher energy <emphasis>gamma</emphasis> cousins. This implementation allows the |
---|
2488 | wave-like properties of electromagnetic radiation to be |
---|
2489 | incorporated into the optical photon process. Because this |
---|
2490 | theoretical description breaks down at higher energies, there is no |
---|
2491 | smooth transition as a function of energy between the optical |
---|
2492 | photon and gamma particle classes. |
---|
2493 | </para> |
---|
2494 | |
---|
2495 | <para> |
---|
2496 | For the simulation of optical photons to work correctly in |
---|
2497 | GEANT4, they must be imputed a linear polarization. This is unlike |
---|
2498 | most other particles in GEANT4 but is automatically and correctly |
---|
2499 | done for optical photons that are generated as secondaries by |
---|
2500 | existing processes in GEANT4. Not so, if the user wishes to start |
---|
2501 | optical photons as primary particles. In this case, the user must |
---|
2502 | set the linear polarization using particle gun methods, the General |
---|
2503 | Particle Source, or his/her PrimaryGeneratorAction. For an |
---|
2504 | unpolarized source, the linear polarization should be sampled |
---|
2505 | randomly for each new primary photon. |
---|
2506 | </para> |
---|
2507 | |
---|
2508 | <para> |
---|
2509 | The GEANT4 catalogue of processes at optical wavelengths |
---|
2510 | includes refraction and reflection at medium boundaries, bulk |
---|
2511 | absorption and Rayleigh scattering. Processes which produce optical |
---|
2512 | photons include the Cerenkov effect, transition radiation and |
---|
2513 | scintillation. Optical photons are generated in GEANT4 without |
---|
2514 | energy conservation and their energy must therefore not be tallied |
---|
2515 | as part of the energy balance of an event. |
---|
2516 | </para> |
---|
2517 | |
---|
2518 | <para> |
---|
2519 | The optical properties of the medium which are key to the |
---|
2520 | implementation of these types of processes are stored as entries in |
---|
2521 | a <literal>G4MaterialPropertiesTable</literal> which is linked to the |
---|
2522 | <literal>G4Material</literal> in question. These properties may be constants |
---|
2523 | or they may be expressed as a function of the photon's wavelength. |
---|
2524 | This table is a private data member of the <literal>G4Material</literal> |
---|
2525 | class. The <literal>G4MaterialPropertiesTable</literal> is implemented as a |
---|
2526 | hash directory, in which each entry consists of a <emphasis>value</emphasis> and |
---|
2527 | a <emphasis>key</emphasis>. The key is used to quickly and efficiently retrieve |
---|
2528 | the corresponding value. All values in the dictionary are either |
---|
2529 | instantiations of <literal>G4double</literal> or the class |
---|
2530 | <literal>G4MaterialPropertyVector</literal>, and all keys are of type |
---|
2531 | <literal>G4String</literal>. |
---|
2532 | </para> |
---|
2533 | |
---|
2534 | <para> |
---|
2535 | A <literal>G4MaterialPropertyVector</literal> is composed of |
---|
2536 | instantiations of the class <literal>G4MPVEntry</literal>. The |
---|
2537 | <literal>G4MPVEntry</literal> is a pair of numbers, which in the case of an |
---|
2538 | optical property, are the photon momentum and corresponding |
---|
2539 | property value. The <literal>G4MaterialPropertyVector</literal> is |
---|
2540 | implemented as a <literal>G4std::vector</literal>, with the sorting operation |
---|
2541 | defined as |
---|
2542 | MPVEntry<subscript>1</subscript> < MPVEntry<subscript>2</subscript> == |
---|
2543 | photon_momentum<subscript>1</subscript> < photon_momentum<subscript>2</subscript>. |
---|
2544 | This results in all <literal>G4MaterialPropertyVector</literal>s being sorted in |
---|
2545 | ascending order of photon momenta. It is possible for the user to |
---|
2546 | add as many material (optical) properties to the material as he |
---|
2547 | wishes using the methods supplied by the |
---|
2548 | <literal>G4MaterialPropertiesTable</literal> class. An example of this is |
---|
2549 | shown in <xref linkend="programlist_PhysProc_5" />. |
---|
2550 | |
---|
2551 | <example id="programlist_PhysProc_5"> |
---|
2552 | <title> |
---|
2553 | Optical properties added to a <literal>G4MaterialPropertiesTable</literal> |
---|
2554 | and linked to a <literal>G4Material</literal> |
---|
2555 | </title> |
---|
2556 | |
---|
2557 | <programlisting> |
---|
2558 | const G4int NUMENTRIES = 32; |
---|
2559 | |
---|
2560 | G4double ppckov[NUMENTRIES] = {2.034*eV, ......, 4.136*eV}; |
---|
2561 | G4double rindex[NUMENTRIES] = {1.3435, ......, 1.3608}; |
---|
2562 | G4double absorption[NUMENTRIES] = {344.8*cm, ......, 1450.0*cm]; |
---|
2563 | |
---|
2564 | G4MaterialPropertiesTable *MPT = new G4MaterialPropertiesTable(); |
---|
2565 | |
---|
2566 | MPT -> AddConstProperty("SCINTILLATIONYIELD",100./MeV); |
---|
2567 | |
---|
2568 | MPT -> AddProperty("RINDEX",ppckov,rindex,NUMENTRIES}; |
---|
2569 | MPT -> AddProperty("ABSLENGTH",ppckov,absorption,NUMENTRIES}; |
---|
2570 | |
---|
2571 | scintillator -> SetMaterialPropertiesTable(MPT); |
---|
2572 | </programlisting> |
---|
2573 | </example> |
---|
2574 | </para> |
---|
2575 | |
---|
2576 | |
---|
2577 | <!-- ******************* Section (Level#3) ****************** --> |
---|
2578 | <sect3 id="sect.PhysProc.Photo.Cerenkov"> |
---|
2579 | <title> |
---|
2580 | Generation of Photons in |
---|
2581 | <literal>processes/electromagnetic/xrays</literal> - Cerenkov Effect |
---|
2582 | </title> |
---|
2583 | |
---|
2584 | <para> |
---|
2585 | The radiation of Cerenkov light occurs when a charged particle |
---|
2586 | moves through a dispersive medium faster than the group velocity of |
---|
2587 | light in that medium. Photons are emitted on the surface of a cone, |
---|
2588 | whose opening angle with respect to the particle's instantaneous |
---|
2589 | direction decreases as the particle slows down. At the same time, |
---|
2590 | the frequency of the photons emitted increases, and the number |
---|
2591 | produced decreases. When the particle velocity drops below the |
---|
2592 | local speed of light, the radiation ceases and the emission cone |
---|
2593 | angle collapses to zero. The photons produced by this process have |
---|
2594 | an inherent polarization perpendicular to the cone's surface at |
---|
2595 | production. |
---|
2596 | </para> |
---|
2597 | |
---|
2598 | <para> |
---|
2599 | The flux, spectrum, polarization and emission of Cerenkov |
---|
2600 | radiation in the <literal>AlongStepDoIt</literal> method of the class |
---|
2601 | <literal>G4Cerenkov</literal> follow well-known formulae, with two inherent |
---|
2602 | computational limitations. The first arises from step-wise |
---|
2603 | simulation, and the second comes from the requirement that |
---|
2604 | numerical integration calculate the average number of Cerenkov |
---|
2605 | photons per step. The process makes use of a |
---|
2606 | <literal>G4PhysicsTable</literal> which contains incremental integrals to |
---|
2607 | expedite this calculation. |
---|
2608 | </para> |
---|
2609 | |
---|
2610 | <para> |
---|
2611 | The time and position of Cerenkov photon emission are calculated |
---|
2612 | from quantities known at the beginning of a charged particle's |
---|
2613 | step. The step is assumed to be rectilinear even in the presence of |
---|
2614 | a magnetic field. The user may limit the step size by specifying a |
---|
2615 | maximum (average) number of Cerenkov photons created during the |
---|
2616 | step, using the <literal>SetMaxNumPhotonsPerStep(const G4int |
---|
2617 | NumPhotons)</literal> method. The actual number generated will |
---|
2618 | necessarily be different due to the Poissonian nature of the |
---|
2619 | production. In the present implementation, the production density |
---|
2620 | of photons is distributed evenly along the particle's track |
---|
2621 | segment, even if the particle has slowed significantly during the |
---|
2622 | step. |
---|
2623 | </para> |
---|
2624 | |
---|
2625 | <para> |
---|
2626 | The frequently very large number of secondaries produced in a |
---|
2627 | single step (about 300/cm in water), compelled the idea in |
---|
2628 | GEANT3.21 of suspending the primary particle until all its progeny |
---|
2629 | have been tracked. Despite the fact that GEANT4 employs dynamic |
---|
2630 | memory allocation and thus does not suffer from the limitations of |
---|
2631 | GEANT3.21 with its fixed large initial ZEBRA store, GEANT4 |
---|
2632 | nevertheless provides for an analogous functionality with the |
---|
2633 | public method <literal>SetTrackSecondariesFirst</literal>. An example of the |
---|
2634 | registration of the Cerenkov process is given in |
---|
2635 | <xref linkend="programlist_PhysProc_6" />. |
---|
2636 | |
---|
2637 | <example id="programlist_PhysProc_6"> |
---|
2638 | <title> |
---|
2639 | Registration of the Cerenkov process in <literal>PhysicsList</literal>. |
---|
2640 | </title> |
---|
2641 | |
---|
2642 | <programlisting> |
---|
2643 | #include "G4Cerenkov.hh" |
---|
2644 | |
---|
2645 | void ExptPhysicsList::ConstructOp(){ |
---|
2646 | |
---|
2647 | G4Cerenkov* theCerenkovProcess = new G4Cerenkov("Cerenkov"); |
---|
2648 | |
---|
2649 | G4int MaxNumPhotons = 300; |
---|
2650 | |
---|
2651 | theCerenkovProcess->SetTrackSecondariesFirst(true); |
---|
2652 | theCerenkovProcess->SetMaxNumPhotonsPerStep(MaxNumPhotons); |
---|
2653 | |
---|
2654 | theParticleIterator->reset(); |
---|
2655 | while( (*theParticleIterator)() ){ |
---|
2656 | G4ParticleDefinition* particle = theParticleIterator->value(); |
---|
2657 | G4ProcessManager* pmanager = particle->GetProcessManager(); |
---|
2658 | G4String particleName = particle->GetParticleName(); |
---|
2659 | if (theCerenkovProcess->IsApplicable(*particle)) { |
---|
2660 | pmanager->AddContinuousProcess(theCerenkovProcess); |
---|
2661 | } |
---|
2662 | } |
---|
2663 | } |
---|
2664 | </programlisting> |
---|
2665 | </example> |
---|
2666 | </para> |
---|
2667 | |
---|
2668 | </sect3> |
---|
2669 | |
---|
2670 | |
---|
2671 | <!-- ******************* Section (Level#3) ****************** --> |
---|
2672 | <sect3 id="sect.PhysProc.Photo.Scinti"> |
---|
2673 | <title> |
---|
2674 | Generation of Photons in |
---|
2675 | <literal>processes/electromagnetic/xrays</literal> - Scintillation |
---|
2676 | </title> |
---|
2677 | |
---|
2678 | <para> |
---|
2679 | Every scintillating material has a characteristic light yield, |
---|
2680 | <literal>SCINTILLATIONYIELD</literal>, and an intrinsic resolution, |
---|
2681 | <literal>RESOLUTIONSCALE</literal>, which generally broadens the statistical |
---|
2682 | distribution of generated photons. A wider intrinsic resolution is |
---|
2683 | due to impurities which are typical for doped crystals like NaI(Tl) |
---|
2684 | and CsI(Tl). On the other hand, the intrinsic resolution can also |
---|
2685 | be narrower when the Fano factor plays a role. The actual number of |
---|
2686 | emitted photons during a step fluctuates around the mean number of |
---|
2687 | photons with a width given by |
---|
2688 | <literal>ResolutionScale*sqrt(MeanNumberOfPhotons)</literal>. The average |
---|
2689 | light yield, <literal>MeanNumberOfPhotons</literal>, has a linear dependence |
---|
2690 | on the local energy deposition, but it may be different for minimum |
---|
2691 | ionizing and non-minimum ionizing particles. |
---|
2692 | </para> |
---|
2693 | |
---|
2694 | <para> |
---|
2695 | A scintillator is also characterized by its photon emission |
---|
2696 | spectrum and by the exponential decay of its time spectrum. In |
---|
2697 | GEANT4 the scintillator can have a fast and a slow component. The |
---|
2698 | relative strength of the fast component as a fraction of total |
---|
2699 | scintillation yield is given by the <literal>YIELDRATIO</literal>. |
---|
2700 | Scintillation may be simulated by specifying these empirical |
---|
2701 | parameters for each material. It is sufficient to specify in the |
---|
2702 | user's <literal>DetectorConstruction</literal> class a relative spectral |
---|
2703 | distribution as a function of photon energy for the scintillating |
---|
2704 | material. An example of this is shown in |
---|
2705 | <xref linkend="programlist_PhysProc_7" /> |
---|
2706 | |
---|
2707 | <example id="programlist_PhysProc_7"> |
---|
2708 | <title> |
---|
2709 | Specification of scintillation properties in |
---|
2710 | <literal>DetectorConstruction</literal>. |
---|
2711 | </title> |
---|
2712 | <programlisting> |
---|
2713 | const G4int NUMENTRIES = 9; |
---|
2714 | G4double Scnt_PP[NUMENTRIES] = { 6.6*eV, 6.7*eV, 6.8*eV, 6.9*eV, |
---|
2715 | 7.0*eV, 7.1*eV, 7.2*eV, 7.3*eV, 7.4*eV }; |
---|
2716 | |
---|
2717 | G4double Scnt_FAST[NUMENTRIES] = { 0.000134, 0.004432, 0.053991, 0.241971, |
---|
2718 | 0.398942, 0.000134, 0.004432, 0.053991, |
---|
2719 | 0.241971 }; |
---|
2720 | G4double Scnt_SLOW[NUMENTRIES] = { 0.000010, 0.000020, 0.000030, 0.004000, |
---|
2721 | 0.008000, 0.005000, 0.020000, 0.001000, |
---|
2722 | 0.000010 }; |
---|
2723 | |
---|
2724 | G4Material* Scnt; |
---|
2725 | G4MaterialPropertiesTable* Scnt_MPT = new G4MaterialPropertiesTable(); |
---|
2726 | |
---|
2727 | Scnt_MPT->AddProperty("FASTCOMPONENT", Scnt_PP, Scnt_FAST, NUMENTRIES); |
---|
2728 | Scnt_MPT->AddProperty("SLOWCOMPONENT", Scnt_PP, Scnt_SLOW, NUMENTRIES); |
---|
2729 | |
---|
2730 | Scnt_MPT->AddConstProperty("SCINTILLATIONYIELD", 5000./MeV); |
---|
2731 | Scnt_MPT->AddConstProperty("RESOLUTIONSCALE", 2.0); |
---|
2732 | Scnt_MPT->AddConstProperty("FASTTIMECONSTANT", 1.*ns); |
---|
2733 | Scnt_MPT->AddConstProperty("SLOWTIMECONSTANT", 10.*ns); |
---|
2734 | Scnt_MPT->AddConstProperty("YIELDRATIO", 0.8); |
---|
2735 | |
---|
2736 | Scnt->SetMaterialPropertiesTable(Scnt_MPT); |
---|
2737 | </programlisting> |
---|
2738 | </example> |
---|
2739 | </para> |
---|
2740 | |
---|
2741 | <para> |
---|
2742 | In cases where the scintillation yield of a scintillator depends |
---|
2743 | on the particle type, different scintillation processes may be |
---|
2744 | defined for them. How this yield scales to the one specified for |
---|
2745 | the material is expressed with the |
---|
2746 | <literal>ScintillationYieldFactor</literal> in the user's |
---|
2747 | <literal>PhysicsList</literal> as shown in |
---|
2748 | <xref linkend="programlist_PhysProc_8" />. |
---|
2749 | In those cases where the fast to slow excitation ratio changes with particle |
---|
2750 | type, the method <literal>SetScintillationExcitationRatio</literal> can be |
---|
2751 | called for each scintillation process (see the advanced |
---|
2752 | underground_physics example). This overwrites the |
---|
2753 | <literal>YieldRatio</literal> obtained from the |
---|
2754 | <literal>G4MaterialPropertiesTable</literal>. |
---|
2755 | |
---|
2756 | <example id="programlist_PhysProc_8"> |
---|
2757 | <title> |
---|
2758 | Implementation of the scintillation process in |
---|
2759 | <literal>PhysicsList</literal>. |
---|
2760 | </title> |
---|
2761 | |
---|
2762 | <programlisting> |
---|
2763 | G4Scintillation* theMuonScintProcess = new G4Scintillation("Scintillation"); |
---|
2764 | |
---|
2765 | theMuonScintProcess->SetTrackSecondariesFirst(true); |
---|
2766 | theMuonScintProcess->SetScintillationYieldFactor(0.8); |
---|
2767 | |
---|
2768 | theParticleIterator->reset(); |
---|
2769 | while( (*theParticleIterator)() ){ |
---|
2770 | G4ParticleDefinition* particle = theParticleIterator->value(); |
---|
2771 | G4ProcessManager* pmanager = particle->GetProcessManager(); |
---|
2772 | G4String particleName = particle->GetParticleName(); |
---|
2773 | if (theMuonScintProcess->IsApplicable(*particle)) { |
---|
2774 | if (particleName == "mu+") { |
---|
2775 | pmanager->AddProcess(theMuonScintProcess); |
---|
2776 | pmanager->SetProcessOrderingToLast(theMuonScintProcess, idxAtRest); |
---|
2777 | pmanager->SetProcessOrderingToLast(theMuonScintProcess, idxPostStep); |
---|
2778 | } |
---|
2779 | } |
---|
2780 | } |
---|
2781 | </programlisting> |
---|
2782 | </example> |
---|
2783 | </para> |
---|
2784 | |
---|
2785 | <para> |
---|
2786 | A Gaussian-distributed number of photons is generated according |
---|
2787 | to the energy lost during the step. A resolution scale of 1.0 |
---|
2788 | produces a statistical fluctuation around the average yield set |
---|
2789 | with <literal>AddConstProperty("SCINTILLATIONYIELD")</literal>, while values |
---|
2790 | > 1 broaden the fluctuation. A value of zero produces no |
---|
2791 | fluctuation. Each photon's frequency is sampled from the empirical |
---|
2792 | spectrum. The photons originate evenly along the track segment and |
---|
2793 | are emitted uniformly into 4π with a random linear polarization |
---|
2794 | and at times characteristic for the scintillation component. |
---|
2795 | </para> |
---|
2796 | |
---|
2797 | </sect3> |
---|
2798 | |
---|
2799 | <!-- ******************* Section (Level#3) ****************** --> |
---|
2800 | <sect3 id="sect.PhysProc.Photo.WaveShift"> |
---|
2801 | <title> |
---|
2802 | Generation of Photons in |
---|
2803 | <literal>processes/optical</literal> - Wavelength Shifting |
---|
2804 | </title> |
---|
2805 | |
---|
2806 | <para> |
---|
2807 | Wavelength Shifting (WLS) fibers are used in many high-energy |
---|
2808 | particle physics experiments. They absorb light at one wavelength |
---|
2809 | and re-emit light at a different wavelength and are used for |
---|
2810 | several reasons. For one, they tend to decrease the self-absorption |
---|
2811 | of the detector so that as much light reaches the PMTs as possible. |
---|
2812 | WLS fibers are also used to match the emission spectrum of the |
---|
2813 | detector with the input spectrum of the PMT. |
---|
2814 | </para> |
---|
2815 | |
---|
2816 | <para> |
---|
2817 | A WLS material is characterized by its photon absorption and |
---|
2818 | photon emission spectrum and by a possible time delay between the |
---|
2819 | absorption and re-emission of the photon. Wavelength Shifting may |
---|
2820 | be simulated by specifying these empirical parameters for each WLS |
---|
2821 | material in the simulation. It is sufficient to specify in the |
---|
2822 | user's <literal>DetectorConstruction</literal> class a relative spectral |
---|
2823 | distribution as a function of photon energy for the WLS material. |
---|
2824 | WLSABSLENGTH is the absorption length of the material as a function |
---|
2825 | of the photon's momentum. WLSCOMPONENT is the relative emission |
---|
2826 | spectrum of the material as a function of the photon's momentum, |
---|
2827 | and WLSTIMECONSTANT accounts for any time delay which may occur |
---|
2828 | between absorption and re-emission of the photon. An example is |
---|
2829 | shown in <xref linkend="programlist_PhysProc_9" />. |
---|
2830 | |
---|
2831 | <example id="programlist_PhysProc_9"> |
---|
2832 | <title> |
---|
2833 | Specification of WLS properties in <literal>DetectorConstruction</literal>. |
---|
2834 | </title> |
---|
2835 | |
---|
2836 | <programlisting> |
---|
2837 | const G4int nEntries = 9; |
---|
2838 | |
---|
2839 | G4double PhotonEnergy[nEntries] = { 6.6*eV, 6.7*eV, 6.8*eV, 6.9*eV, |
---|
2840 | 7.0*eV, 7.1*eV, 7.2*eV, 7.3*eV, 7.4*eV }; |
---|
2841 | |
---|
2842 | G4double RIndexFiber[nEntries] = |
---|
2843 | { 1.60, 1.60, 1.60, 1.60, 1.60, 1.60, 1.60, 1.60, 1.60 }; |
---|
2844 | G4double AbsFiber[nEntries] = |
---|
2845 | {0.1*mm,0.2*mm,0.3*mm,0.4*cm,1.0*cm,10*cm,1.0*m,10.0*m,10.0*m}; |
---|
2846 | G4double EmissionFiber[nEntries] = |
---|
2847 | {0.0, 0.0, 0.0, 0.1, 0.5, 1.0, 5.0, 10.0, 10.0 }; |
---|
2848 | |
---|
2849 | G4Material* WLSFiber; |
---|
2850 | G4MaterialPropertiesTable* MPTFiber = new G4MaterialPropertiesTable(); |
---|
2851 | |
---|
2852 | MPTFiber->AddProperty("RINDEX",PhotonEnergy,RIndexFiber,nEntries); |
---|
2853 | MPTFiber->AddProperty("WLSABSLENGTH",PhotonEnergy,AbsFiber,nEntries); |
---|
2854 | MPTFiber->AddProperty("WLSCOMPONENT",PhotonEnergy,EmissionFiber,nEntries); |
---|
2855 | MPTFiber->AddConstProperty("WLSTIMECONSTANT", 0.5*ns); |
---|
2856 | |
---|
2857 | WLSFiber->SetMaterialPropertiesTable(MPTFiber); |
---|
2858 | </programlisting> |
---|
2859 | </example> |
---|
2860 | </para> |
---|
2861 | |
---|
2862 | <para> |
---|
2863 | The process is defined in the PhysicsList in the usual way. The |
---|
2864 | process class name is G4OpWLS. It should be instantiated with |
---|
2865 | theWLSProcess = new G4OpWLS("OpWLS") and attached to the process |
---|
2866 | manager of the optical photon as a DiscreteProcess. The way the |
---|
2867 | WLSTIMECONSTANT is used depends on the time profile method chosen |
---|
2868 | by the user. If in the PhysicsList |
---|
2869 | theWLSProcess->UseTimeGenerator("exponential") option is set, |
---|
2870 | the time delay between absorption and re-emission of the photon is |
---|
2871 | sampled from an exponential distribution, with the decay term equal |
---|
2872 | to WLSTIMECONSTANT. If, on the other hand, |
---|
2873 | theWLSProcess->UseTimeGenerator("delta") is chosen, the time |
---|
2874 | delay is a delta function and equal to WLSTIMECONSTANT. The default |
---|
2875 | is "delta" in case the G4OpWLS::UseTimeGenerator(const G4String |
---|
2876 | name) method is not used. |
---|
2877 | </para> |
---|
2878 | |
---|
2879 | </sect3> |
---|
2880 | |
---|
2881 | |
---|
2882 | <!-- ******************* Section (Level#3) ****************** --> |
---|
2883 | <sect3 id="sect.PhysProc.Photo.Track"> |
---|
2884 | <title> |
---|
2885 | Tracking of Photons in <literal>processes/optical</literal> |
---|
2886 | </title> |
---|
2887 | |
---|
2888 | <!-- ******* Bridgehead ******* --> |
---|
2889 | <bridgehead renderas='sect4'> |
---|
2890 | Absorption |
---|
2891 | </bridgehead> |
---|
2892 | |
---|
2893 | <para> |
---|
2894 | The implementation of optical photon bulk absorption, |
---|
2895 | <literal>G4OpAbsorption</literal>, is trivial in that the process merely |
---|
2896 | kills the particle. The procedure requires the user to fill the |
---|
2897 | relevant <literal>G4MaterialPropertiesTable</literal> with empirical data for |
---|
2898 | the absorption length, using <literal>ABSLENGTH</literal> as the property key |
---|
2899 | in the public method <literal>AddProperty</literal>. The absorption length is |
---|
2900 | the average distance traveled by a photon before being absorpted by |
---|
2901 | the medium; i.e. it is the mean free path returned by the |
---|
2902 | <literal>GetMeanFreePath</literal> method. |
---|
2903 | </para> |
---|
2904 | |
---|
2905 | <!-- ******* Bridgehead ******* --> |
---|
2906 | <bridgehead renderas='sect4'> |
---|
2907 | Rayleigh Scattering |
---|
2908 | </bridgehead> |
---|
2909 | |
---|
2910 | <para> |
---|
2911 | The differential cross section in Rayleigh scattering, |
---|
2912 | σ/ω, is proportional |
---|
2913 | to cos<superscript>2</superscript>(&thetas;), |
---|
2914 | where &thetas; is the polar of the new polarization vector with |
---|
2915 | respect to the old polarization vector. The <literal>G4OpRayleigh</literal> |
---|
2916 | scattering process samples this angle accordingly and then |
---|
2917 | calculates the scattered photon's new direction by requiring that |
---|
2918 | it be perpendicular to the photon's new polarization in such a way |
---|
2919 | that the final direction, initial and final polarizations are all |
---|
2920 | in one plane. This process thus depends on the particle's |
---|
2921 | polarization (spin). The photon's polarization is a data member of |
---|
2922 | the <literal>G4DynamicParticle</literal> class. |
---|
2923 | </para> |
---|
2924 | |
---|
2925 | <para> |
---|
2926 | A photon which is not assigned a polarization at production, |
---|
2927 | either via the <literal>SetPolarization</literal> method of the |
---|
2928 | <literal>G4PrimaryParticle</literal> class, or indirectly with the |
---|
2929 | <literal>SetParticlePolarization</literal> method of the |
---|
2930 | <literal>G4ParticleGun</literal> class, may not be Rayleigh scattered. |
---|
2931 | Optical photons produced by the <literal>G4Cerenkov</literal> process have |
---|
2932 | inherently a polarization perpendicular to the cone's surface at |
---|
2933 | production. Scintillation photons have a random linear polarization |
---|
2934 | perpendicular to their direction. |
---|
2935 | </para> |
---|
2936 | |
---|
2937 | <para> |
---|
2938 | The process requires a <literal>G4MaterialPropertiesTable</literal> to be |
---|
2939 | filled by the user with Rayleigh scattering length data. The |
---|
2940 | Rayleigh scattering attenuation length is the average distance |
---|
2941 | traveled by a photon before it is Rayleigh scattered in the medium |
---|
2942 | and it is the distance returned by the <literal>GetMeanFreePath</literal> |
---|
2943 | method. The <literal>G4OpRayleigh</literal> class provides a |
---|
2944 | <literal>RayleighAttenuationLengthGenerator</literal> method which calculates |
---|
2945 | the attenuation coefficient of a medium following the |
---|
2946 | Einstein-Smoluchowski formula whose derivation requires the use of |
---|
2947 | statistical mechanics, includes temperature, and depends on the |
---|
2948 | isothermal compressibility of the medium. This generator is |
---|
2949 | convenient when the Rayleigh attenuation length is not known from |
---|
2950 | measurement but may be calculated from first principles using the |
---|
2951 | above material constants. For a medium named <emphasis>Water</emphasis> and no |
---|
2952 | Rayleigh scattering attenutation length specified by the user, the |
---|
2953 | program automatically calls the |
---|
2954 | <literal>RayleighAttenuationLengthGenerator</literal> |
---|
2955 | which calculates it for 10 degrees Celsius liquid water. |
---|
2956 | </para> |
---|
2957 | |
---|
2958 | <!-- ******* Bridgehead ******* --> |
---|
2959 | <bridgehead renderas='sect4'> |
---|
2960 | Boundary Process |
---|
2961 | </bridgehead> |
---|
2962 | |
---|
2963 | <para> |
---|
2964 | Reference: E. Hecht and A. Zajac, Optics |
---|
2965 | <citation> |
---|
2966 | <xref linkend="biblio.hecht1974" endterm="biblio.hecht1974.abbrev" /> |
---|
2967 | </citation> |
---|
2968 | </para> |
---|
2969 | |
---|
2970 | <para> |
---|
2971 | For the simple case of a perfectly smooth interface between two |
---|
2972 | dielectric materials, all the user needs to provide are the |
---|
2973 | refractive indices of the two materials stored in their respective |
---|
2974 | <literal>G4MaterialPropertiesTable</literal>. In all other cases, the optical |
---|
2975 | boundary process design relies on the concept of <emphasis>surfaces</emphasis>. |
---|
2976 | The information is split into two classes. One class in the |
---|
2977 | material category keeps information about the physical properties |
---|
2978 | of the surface itself, and a second class in the geometry category |
---|
2979 | holds pointers to the relevant physical and logical volumes |
---|
2980 | involved and has an association to the physical class. Surface |
---|
2981 | objects of the second type are stored in a related table and can be |
---|
2982 | retrieved by either specifying the two ordered pairs of physical |
---|
2983 | volumes touching at the surface, or by the logical volume entirely |
---|
2984 | surrounded by this surface. The former is called a <emphasis>border |
---|
2985 | surface</emphasis> while the latter is referred to as the <emphasis>skin |
---|
2986 | surface</emphasis>. This second type of surface is useful in situations |
---|
2987 | where a volume is coded with a reflector and is placed into many |
---|
2988 | different mother volumes. A limitation is that the skin surface can |
---|
2989 | only have one and the same optical property for all of the enclosed |
---|
2990 | volume's sides. The border surface is an ordered pair of physical |
---|
2991 | volumes, so in principle, the user can choose different optical |
---|
2992 | properties for photons arriving from the reverse side of the same |
---|
2993 | interface. For the optical boundary process to use a border |
---|
2994 | surface, the two volumes must have been positioned with |
---|
2995 | <literal>G4PVPlacement</literal>. The ordered combination can exist at many |
---|
2996 | places in the simulation. When the surface concept is not needed, |
---|
2997 | and a perfectly smooth surface exists beteen two dielectic |
---|
2998 | materials, the only relevant property is the index of refraction, a |
---|
2999 | quantity stored with the material, and no restriction exists on how |
---|
3000 | the volumes were positioned. |
---|
3001 | </para> |
---|
3002 | |
---|
3003 | <para> |
---|
3004 | The physical surface object also specifies which model the |
---|
3005 | boundary process should use to simulate interactions with that |
---|
3006 | surface. In addition, the physical surface can have a material |
---|
3007 | property table all its own. The usage of this table allows all |
---|
3008 | specular constants to be wavelength dependent. In case the surface |
---|
3009 | is painted or wrapped (but not a cladding), the table may include |
---|
3010 | the thin layer's index of refraction. This allows the simulation of |
---|
3011 | boundary effects at the intersection between the medium and the |
---|
3012 | surface layer, as well as the Lambertian reflection at the far side |
---|
3013 | of the thin layer. This occurs within the process itself and does |
---|
3014 | not invoke the <literal>G4Navigator</literal>. Combinations of surface finish |
---|
3015 | properties, such as <emphasis>polished</emphasis> or |
---|
3016 | <emphasis>ground</emphasis> and <emphasis>front |
---|
3017 | painted</emphasis> or <emphasis>back painted</emphasis>, enumerate the different |
---|
3018 | situations which can be simulated. |
---|
3019 | </para> |
---|
3020 | |
---|
3021 | <para> |
---|
3022 | When a photon arrives at a medium boundary its behavior depends |
---|
3023 | on the nature of the two materials that join at that boundary. |
---|
3024 | Medium boundaries may be formed between two dielectric materials or |
---|
3025 | a dielectric and a metal. In the case of two dielectric materials, |
---|
3026 | the photon can undergo total internal reflection, refraction or |
---|
3027 | reflection, depending on the photon's wavelength, angle of |
---|
3028 | incidence, and the refractive indices on both sides of the |
---|
3029 | boundary. Furthermore, reflection and transmission probabilites are |
---|
3030 | sensitive to the state of linear polarization. In the case of an |
---|
3031 | interface between a dielectric and a metal, the photon can be |
---|
3032 | absorbed by the metal or reflected back into the dielectric. If the |
---|
3033 | photon is absorbed it can be detected according to the |
---|
3034 | photoelectron efficiency of the metal. |
---|
3035 | </para> |
---|
3036 | |
---|
3037 | <para> |
---|
3038 | As expressed in Maxwell's equations, Fresnel reflection and |
---|
3039 | refraction are intertwined through their relative probabilities of |
---|
3040 | occurrence. Therefore neither of these processes, nor total |
---|
3041 | internal reflection, are viewed as individual processes deserving |
---|
3042 | separate class implementation. Nonetheless, an attempt was made to |
---|
3043 | adhere to the abstraction of having independent processes by |
---|
3044 | splitting the code into different methods where practicable. |
---|
3045 | </para> |
---|
3046 | |
---|
3047 | <para> |
---|
3048 | One implementation of the <literal>G4OpBoundaryProcess</literal> class |
---|
3049 | employs the |
---|
3050 | <ulink url="http://geant4.slac.stanford.edu/UsersWorkshop/G4Lectures/Peter/moisan.ps"> |
---|
3051 | UNIFIED model</ulink> |
---|
3052 | [A. Levin and C. Moisan, A More Physical Approach |
---|
3053 | to Model the Surface Treatment of Scintillation Counters and its |
---|
3054 | Implementation into DETECT, TRIUMF Preprint TRI-PP-96-64, Oct. |
---|
3055 | 1996] of the DETECT program [G.F. Knoll, T.F. Knoll and T.M. |
---|
3056 | Henderson, Light Collection Scintillation Detector Composites for |
---|
3057 | Neutron Detection, IEEE Trans. Nucl. Sci., 35 (1988) 872.]. It |
---|
3058 | applies to dielectric-dielectric interfaces and tries to provide a |
---|
3059 | realistic simulation, which deals with all aspects of surface |
---|
3060 | finish and reflector coating. The surface may be assumed as smooth |
---|
3061 | and covered with a metallized coating representing a specular |
---|
3062 | reflector with given reflection coefficient, or painted with a |
---|
3063 | diffuse reflecting material where Lambertian reflection occurs. The |
---|
3064 | surfaces may or may not be in optical contact with another |
---|
3065 | component and most importantly, one may consider a surface to be |
---|
3066 | made up of micro-facets with normal vectors that follow given |
---|
3067 | distributions around the nominal normal for the volume at the |
---|
3068 | impact point. For very rough surfaces, it is possible for the |
---|
3069 | photon to inversely aim at the same surface again after reflection |
---|
3070 | of refraction and so multiple interactions with the boundary are |
---|
3071 | possible within the process itself and without the need for |
---|
3072 | relocation by <literal>G4Navigator</literal>. |
---|
3073 | </para> |
---|
3074 | |
---|
3075 | <para> |
---|
3076 | The UNIFIED model provides for a range of different reflection |
---|
3077 | mechanisms. The specular lobe constant represents the reflection |
---|
3078 | probability about the normal of a micro facet. The specular spike |
---|
3079 | constant, in turn, illustrates the probability of reflection about |
---|
3080 | the average surface normal. The diffuse lobe constant is for the |
---|
3081 | probability of internal Lambertian reflection, and finally the |
---|
3082 | back-scatter spike constant is for the case of several reflections |
---|
3083 | within a deep groove with the ultimate result of exact |
---|
3084 | back-scattering. The four probabilities must add up to one, with |
---|
3085 | the diffuse lobe constant being implicit. The reader may consult |
---|
3086 | the reference for a thorough description of the model. |
---|
3087 | |
---|
3088 | <example id="programlist_PhysProc_10"> |
---|
3089 | <title> |
---|
3090 | Dielectric-dielectric surface properties |
---|
3091 | defined via the <emphasis>G4OpticalSurface</emphasis>. |
---|
3092 | </title> |
---|
3093 | |
---|
3094 | <programlisting> |
---|
3095 | G4VPhysicalVolume* volume1; |
---|
3096 | G4VPhysicalVolume* volume2; |
---|
3097 | |
---|
3098 | G4OpticalSurface* OpSurface = new G4OpticalSurface("name"); |
---|
3099 | |
---|
3100 | G4LogicalBorderSurface* Surface = new |
---|
3101 | G4LogicalBorderSurface("name",volume1,volume2,OpSurface); |
---|
3102 | |
---|
3103 | G4double sigma_alpha = 0.1; |
---|
3104 | |
---|
3105 | OpSurface -> SetType(dielectric_dielectric); |
---|
3106 | OpSurface -> SetModel(unified); |
---|
3107 | OpSurface -> SetFinish(groundbackpainted); |
---|
3108 | OpSurface -> SetSigmaAlpha(sigma_alpha); |
---|
3109 | |
---|
3110 | const G4int NUM = 2; |
---|
3111 | |
---|
3112 | G4double pp[NUM] = {2.038*eV, 4.144*eV}; |
---|
3113 | G4double specularlobe[NUM] = {0.3, 0.3}; |
---|
3114 | G4double specularspike[NUM] = {0.2, 0.2}; |
---|
3115 | G4double backscatter[NUM] = {0.1, 0.1}; |
---|
3116 | G4double rindex[NUM] = {1.35, 1.40}; |
---|
3117 | G4double reflectivity[NUM] = {0.3, 0.5}; |
---|
3118 | G4double efficiency[NUM] = {0.8, 0.1}; |
---|
3119 | |
---|
3120 | G4MaterialPropertiesTable* SMPT = new G4MaterialPropertiesTable(); |
---|
3121 | |
---|
3122 | SMPT -> AddProperty("RINDEX",pp,rindex,NUM); |
---|
3123 | SMPT -> AddProperty("SPECULARLOBECONSTANT",pp,specularlobe,NUM); |
---|
3124 | SMPT -> AddProperty("SPECULARSPIKECONSTANT",pp,specularspike,NUM); |
---|
3125 | SMPT -> AddProperty("BACKSCATTERCONSTANT",pp,backscatter,NUM); |
---|
3126 | SMPT -> AddProperty("REFLECTIVITY",pp,reflectivity,NUM); |
---|
3127 | SMPT -> AddProperty("EFFICIENCY",pp,efficiency,NUM); |
---|
3128 | |
---|
3129 | OpSurface -> SetMaterialPropertiesTable(SMPT); |
---|
3130 | </programlisting> |
---|
3131 | </example> |
---|
3132 | </para> |
---|
3133 | |
---|
3134 | <para> |
---|
3135 | The original |
---|
3136 | <ulink url="http://wwwasdoc.web.cern.ch/wwwasdoc/geant_html3/node231.html"> |
---|
3137 | GEANT3.21 implementation</ulink> of this process is also available via |
---|
3138 | the GLISUR methods flag. [GEANT Detector Description and Simulation |
---|
3139 | Tool, Application Software Group, Computing and Networks Division, |
---|
3140 | CERN, PHYS260-6 tp 260-7.]. |
---|
3141 | |
---|
3142 | <example id="programlist_PhysProc_11"> |
---|
3143 | <title> |
---|
3144 | Dielectric metal surface properties defined via the |
---|
3145 | <emphasis>G4OpticalSurface</emphasis>. |
---|
3146 | </title> |
---|
3147 | |
---|
3148 | <programlisting> |
---|
3149 | G4LogicalVolume* volume_log; |
---|
3150 | |
---|
3151 | G4OpticalSurface* OpSurface = new G4OpticalSurface("name"); |
---|
3152 | |
---|
3153 | G4LogicalSkinSurface* Surface = new |
---|
3154 | G4LogicalSkinSurface("name",volume_log,OpSurface); |
---|
3155 | |
---|
3156 | OpSurface -> SetType(dielectric_metal); |
---|
3157 | OpSurface -> SetFinish(ground); |
---|
3158 | OpSurface -> SetModel(glisur); |
---|
3159 | |
---|
3160 | G4double polish = 0.8; |
---|
3161 | |
---|
3162 | G4MaterialPropertiesTable *OpSurfaceProperty = new G4MaterialPropertiesTable(); |
---|
3163 | |
---|
3164 | OpSurfaceProperty -> AddProperty("REFLECTIVITY",pp,reflectivity,NUM); |
---|
3165 | OpSurfaceProperty -> AddProperty("EFFICIENCY",pp,efficiency,NUM); |
---|
3166 | |
---|
3167 | OpSurface -> SetMaterialPropertiesTable(OpSurfaceProperty); |
---|
3168 | </programlisting> |
---|
3169 | </example> |
---|
3170 | </para> |
---|
3171 | |
---|
3172 | <para> |
---|
3173 | The reflectivity off a metal surface can also be calculated by way of a complex |
---|
3174 | index of refraction. Instead of storing the REFLECTIVITY directly, the user |
---|
3175 | stores the real part (REALRINDEX) and the imaginary part (IMAGINARYRINDEX) as |
---|
3176 | a function of photon energy separately in the G4MaterialPropertyTable. Geant4 |
---|
3177 | then |
---|
3178 | <ulink url="./AllResources/TrackingAndPhysics/physicsProcessOptical.src/GetReflectivity.pdf"> |
---|
3179 | calculates the reflectivity |
---|
3180 | </ulink> |
---|
3181 | depending on the incident angle, photon energy, degree of TE and TM |
---|
3182 | polarization, and this complex refractive index. |
---|
3183 | </para> |
---|
3184 | |
---|
3185 | <para> |
---|
3186 | The program defaults to the GLISUR model and <emphasis>polished</emphasis> |
---|
3187 | surface finish when no specific model and surface finish is |
---|
3188 | specified by the user. In the case of a dielectric-metal interface, |
---|
3189 | or when the GLISUR model is specified, the only surface finish |
---|
3190 | options available are <emphasis>polished</emphasis> or <emphasis>ground</emphasis>. For |
---|
3191 | dielectric-metal surfaces, the <literal>G4OpBoundaryProcess</literal> also |
---|
3192 | defaults to unit reflectivity and zero detection efficiency. In |
---|
3193 | cases where the user specifies the UNIFIED model, but does not |
---|
3194 | otherwise specify the model reflection probability constants, the |
---|
3195 | default becomes Lambertian reflection. |
---|
3196 | </para> |
---|
3197 | |
---|
3198 | </sect3> |
---|
3199 | </sect2> |
---|
3200 | |
---|
3201 | |
---|
3202 | <!-- ******************* Section (Level#2) ****************** --> |
---|
3203 | <sect2 id="sect.PhysProc.Param"> |
---|
3204 | <title> |
---|
3205 | Parameterization |
---|
3206 | </title> |
---|
3207 | |
---|
3208 | <para> |
---|
3209 | In this section we describe how to use the parameterization or |
---|
3210 | "fast simulation" facilities of GEANT4. Examples are provided in |
---|
3211 | the <emphasis role="bold">examples/novice/N05 directory</emphasis>. |
---|
3212 | </para> |
---|
3213 | |
---|
3214 | |
---|
3215 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3216 | <sect3 id="sect.PhysProc.Param.Gene"> |
---|
3217 | <title> |
---|
3218 | Generalities: |
---|
3219 | </title> |
---|
3220 | |
---|
3221 | <para> |
---|
3222 | The Geant4 parameterization facilities allow you to shortcut the |
---|
3223 | detailed tracking in a given volume and for given particle types in |
---|
3224 | order for you to provide your own implementation of the physics and |
---|
3225 | of the detector response. |
---|
3226 | </para> |
---|
3227 | |
---|
3228 | <para> |
---|
3229 | Parameterisations are bound to a |
---|
3230 | <emphasis role="bold"><literal>G4Region</literal></emphasis> |
---|
3231 | object, which, in the case of fast simulation is also called an |
---|
3232 | <emphasis role="bold">envelope</emphasis>. Prior to release 8.0, |
---|
3233 | parameterisations were bound |
---|
3234 | to a <literal>G4LogicalVolume</literal>, the root of a volume hierarchy. |
---|
3235 | These root volumes are now attributes of the <literal>G4Region</literal>. |
---|
3236 | Envelopes often correspond to the volumes of sub-detectors: |
---|
3237 | electromagnetic calorimeters, tracking chambers, etc. With GEANT4 |
---|
3238 | it is also possible to define envelopes by overlaying a parallel or |
---|
3239 | "ghost" geometry as discussed in <xref linkend="sect.PhysProc.Param.Ghost" />. |
---|
3240 | </para> |
---|
3241 | |
---|
3242 | <para> |
---|
3243 | In GEANT4, parameterisations have three main features. You must |
---|
3244 | specify: |
---|
3245 | |
---|
3246 | <itemizedlist spacing="compact"> |
---|
3247 | <listitem><para> |
---|
3248 | the particle types for which your parameterisation is valid; |
---|
3249 | </para></listitem> |
---|
3250 | <listitem><para> |
---|
3251 | the dynamics conditions for which your parameterisation is |
---|
3252 | valid and must be triggered; |
---|
3253 | </para></listitem> |
---|
3254 | <listitem><para> |
---|
3255 | the parameterisation itself: where the primary will be killed |
---|
3256 | or moved, whether or not to create it or create secondaries, etc., |
---|
3257 | and where the detector response will be computed. |
---|
3258 | </para></listitem> |
---|
3259 | </itemizedlist> |
---|
3260 | </para> |
---|
3261 | |
---|
3262 | <para> |
---|
3263 | GEANT4 will message your parameterisation code for each step |
---|
3264 | starting in any root G4LogicalVolume (including daughters. |
---|
3265 | sub-daughters, etc. of this volume) of the <literal>G4Region</literal>. |
---|
3266 | It will proceed by first asking the available parameterisations for |
---|
3267 | the current particle type if one of them (and only one) wants to |
---|
3268 | issue a trigger. If so it will invoke its parameterisation. In this |
---|
3269 | case, the tracking |
---|
3270 | <emphasis role="bold"><emphasis>will not apply physics</emphasis></emphasis> |
---|
3271 | to the particle in the step. Instead, the UserSteppingAction will be |
---|
3272 | invoked. |
---|
3273 | </para> |
---|
3274 | |
---|
3275 | <para> |
---|
3276 | Parameterisations look like a "user stepping action" but are more |
---|
3277 | advanced because: |
---|
3278 | |
---|
3279 | <itemizedlist spacing="compact"> |
---|
3280 | <listitem><para> |
---|
3281 | parameterisation code is messaged only in the |
---|
3282 | <literal>G4Region</literal> to which it is bound; |
---|
3283 | </para></listitem> |
---|
3284 | <listitem><para> |
---|
3285 | parameterisation code is messaged anywhere in the |
---|
3286 | <literal>G4Region</literal>, that is, any volume in which the track is |
---|
3287 | located; |
---|
3288 | </para></listitem> |
---|
3289 | <listitem><para> |
---|
3290 | GEANT4 will provide information to your parameterisation code |
---|
3291 | about the current root volume of the <literal>G4Region</literal> |
---|
3292 | in which the track is travelling. |
---|
3293 | </para></listitem> |
---|
3294 | </itemizedlist> |
---|
3295 | </para> |
---|
3296 | |
---|
3297 | </sect3> |
---|
3298 | |
---|
3299 | |
---|
3300 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3301 | <sect3 id="sect.PhysProc.Param.OvComp"> |
---|
3302 | <title> |
---|
3303 | Overview of Parameterisation Components |
---|
3304 | </title> |
---|
3305 | |
---|
3306 | <para> |
---|
3307 | The GEANT4 components which allow the implementation and control |
---|
3308 | of parameterisations are: |
---|
3309 | |
---|
3310 | <variablelist> |
---|
3311 | <varlistentry> |
---|
3312 | <term> |
---|
3313 | <literal><emphasis role="bold">G4VFastSimulationModel</emphasis></literal> |
---|
3314 | </term> |
---|
3315 | <listitem><para> |
---|
3316 | This is the abstract class for the implementation of parameterisations. |
---|
3317 | You must inherit from it to implement your concrete parameterisation model. |
---|
3318 | </para></listitem> |
---|
3319 | </varlistentry> |
---|
3320 | <varlistentry> |
---|
3321 | <term> |
---|
3322 | <literal><emphasis role="bold">G4FastSimulationManager</emphasis></literal> |
---|
3323 | </term> |
---|
3324 | <listitem><para> |
---|
3325 | The G4VFastSimulationModel objects are attached to the |
---|
3326 | <literal>G4Region</literal> through a G4FastSimulationManager. |
---|
3327 | This object will manage the list of models and will message them at |
---|
3328 | tracking time. |
---|
3329 | </para></listitem> |
---|
3330 | </varlistentry> |
---|
3331 | <varlistentry> |
---|
3332 | <term> |
---|
3333 | <literal><emphasis role="bold">G4Region/Envelope</emphasis></literal> |
---|
3334 | </term> |
---|
3335 | <listitem><para> |
---|
3336 | As mentioned before, an envelope in GEANT4 is a |
---|
3337 | <literal><emphasis role="bold">G4Region</emphasis></literal>. |
---|
3338 | The parameterisation is bound to the <literal>G4Region</literal> by |
---|
3339 | setting a <literal>G4FastSimulationManager</literal> pointer to it. |
---|
3340 | </para> |
---|
3341 | <para> |
---|
3342 | The figure below shows how the <literal>G4VFastSimulationModel</literal> |
---|
3343 | and <literal>G4FastSimulationManager</literal> objects are bound to the |
---|
3344 | <literal>G4Region</literal>. Then for all root G4LogicalVolume's held by |
---|
3345 | the G4Region, the fast simulation code is active. |
---|
3346 | |
---|
3347 | <mediaobject> |
---|
3348 | <imageobject role="fo"> |
---|
3349 | <imagedata fileref="./AllResources/TrackingAndPhysics/physicsProcessPARAM.src/ComponentsWithRegion.jpg" |
---|
3350 | format="JPG" contentwidth="7.0cm" align="center" /> |
---|
3351 | </imageobject> |
---|
3352 | <imageobject role="html"> |
---|
3353 | <imagedata fileref="./AllResources/TrackingAndPhysics/physicsProcessPARAM.src/ComponentsWithRegion.jpg" |
---|
3354 | format="JPG" align="center" /> |
---|
3355 | </imageobject> |
---|
3356 | <caption> |
---|
3357 | </caption> |
---|
3358 | </mediaobject> |
---|
3359 | |
---|
3360 | </para></listitem> |
---|
3361 | </varlistentry> |
---|
3362 | <varlistentry> |
---|
3363 | <term> |
---|
3364 | <literal><emphasis role="bold">G4FastSimulationManagerProcess</emphasis></literal> |
---|
3365 | </term> |
---|
3366 | <listitem><para> |
---|
3367 | This is a <literal>G4VProcess</literal>. It provides the interface |
---|
3368 | between the tracking and the parameterisation. It must be set in the |
---|
3369 | process list of the particles you want to parameterise. |
---|
3370 | </para></listitem> |
---|
3371 | </varlistentry> |
---|
3372 | <varlistentry> |
---|
3373 | <term> |
---|
3374 | <literal><emphasis role="bold">G4GlobalFastSimulationManager</emphasis></literal> |
---|
3375 | </term> |
---|
3376 | <listitem><para> |
---|
3377 | This a singleton class which provides the management of the |
---|
3378 | <literal>G4FastSimulationManager</literal> objects and some ghost |
---|
3379 | facilities. |
---|
3380 | </para></listitem> |
---|
3381 | </varlistentry> |
---|
3382 | </variablelist> |
---|
3383 | </para> |
---|
3384 | |
---|
3385 | </sect3> |
---|
3386 | |
---|
3387 | |
---|
3388 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3389 | <sect3 id="sect.PhysProc.Param.FastSimModel"> |
---|
3390 | <title> |
---|
3391 | The <literal>G4VFastSimulationModel</literal> Abstract Class |
---|
3392 | </title> |
---|
3393 | |
---|
3394 | <!-- ******* Bridgehead ******* --> |
---|
3395 | <bridgehead renderas='sect4'> |
---|
3396 | Constructors: |
---|
3397 | </bridgehead> |
---|
3398 | |
---|
3399 | <para> |
---|
3400 | The <literal>G4VFastSimulationModel</literal> class has two constructors. |
---|
3401 | The second one allows you to get started quickly: |
---|
3402 | |
---|
3403 | <variablelist> |
---|
3404 | <varlistentry> |
---|
3405 | <term> |
---|
3406 | <emphasis role="bold"><literal>G4VFastSimulationModel( |
---|
3407 | const G4String& aName)</literal></emphasis>: |
---|
3408 | </term> |
---|
3409 | <listitem><para> |
---|
3410 | Here <literal>aName</literal> identifies the parameterisation model. |
---|
3411 | </para></listitem> |
---|
3412 | </varlistentry> |
---|
3413 | <varlistentry> |
---|
3414 | <term> |
---|
3415 | <emphasis role="bold"><literal>G4VFastSimulationModel(const G4String& |
---|
3416 | aName, G4Region*, G4bool IsUnique=false):</literal></emphasis> |
---|
3417 | </term> |
---|
3418 | <listitem><para> |
---|
3419 | In addition to the model name, this constructor accepts a G4Region pointer. |
---|
3420 | The needed G4FastSimulationManager object is constructed if necessary, |
---|
3421 | passing to it the G4Region pointer and the boolean value. If it |
---|
3422 | already exists, the model is simply added to this manager. Note |
---|
3423 | that the <emphasis>G4VFastSimulationModel object will not keep track of |
---|
3424 | the G4Region passed in the constructor</emphasis>. |
---|
3425 | The boolean argument is there for optimization purposes: if you |
---|
3426 | know that the G4Region has a unique root G4LogicalVolume, uniquely |
---|
3427 | placed, you can set the boolean value to "true". |
---|
3428 | </para></listitem> |
---|
3429 | </varlistentry> |
---|
3430 | </variablelist> |
---|
3431 | </para> |
---|
3432 | |
---|
3433 | <!-- ******* Bridgehead ******* --> |
---|
3434 | <bridgehead renderas='sect4'> |
---|
3435 | Virtual methods: |
---|
3436 | </bridgehead> |
---|
3437 | |
---|
3438 | <para> |
---|
3439 | The G4VFastSimulationModel has three pure virtual methods which |
---|
3440 | must be overriden in your concrete class: |
---|
3441 | |
---|
3442 | <variablelist> |
---|
3443 | <varlistentry> |
---|
3444 | <term> |
---|
3445 | <emphasis role="bold"><literal>G4VFastSimulationModel( |
---|
3446 | <emphasis>const G4String& aName</emphasis>):</literal></emphasis> |
---|
3447 | </term> |
---|
3448 | <listitem><para> |
---|
3449 | Here aName identifies the parameterisation model. |
---|
3450 | </para></listitem> |
---|
3451 | </varlistentry> |
---|
3452 | <varlistentry> |
---|
3453 | <term> |
---|
3454 | <emphasis role="bold"><literal>G4bool ModelTrigger( |
---|
3455 | <emphasis>const G4FastTrack&</emphasis>):</literal></emphasis> |
---|
3456 | </term> |
---|
3457 | <listitem><para> |
---|
3458 | You must return "true" when the dynamic conditions to trigger your |
---|
3459 | parameterisation are fulfilled. |
---|
3460 | G4FastTrack provides access to the current G4Track, gives simple |
---|
3461 | access to the current root G4LogicalVolume related features (its |
---|
3462 | G4VSolid, and G4AffineTransform references between the global and |
---|
3463 | the root G4LogicalVolume local coordinates systems) and simple |
---|
3464 | access to the position and momentum expressed in the root |
---|
3465 | G4LogicalVolume coordinate system. Using these quantities and the |
---|
3466 | G4VSolid methods, you can for example easily check how far you are |
---|
3467 | from the root G4LogicalVolume boundary. |
---|
3468 | </para></listitem> |
---|
3469 | </varlistentry> |
---|
3470 | <varlistentry> |
---|
3471 | <term> |
---|
3472 | <emphasis role="bold"><literal>G4bool IsApplicable( |
---|
3473 | <emphasis>const G4ParticleDefinition&</emphasis>):</literal></emphasis> |
---|
3474 | </term> |
---|
3475 | <listitem><para> |
---|
3476 | In your implementation, you must return "true" when your model is |
---|
3477 | applicable to the G4ParticleDefinition passed to this method. The |
---|
3478 | G4ParticleDefinition provides all intrinsic particle information |
---|
3479 | (mass, charge, spin, name ...). |
---|
3480 | </para> |
---|
3481 | <para> |
---|
3482 | If you want to implement a model which is valid only for certain |
---|
3483 | particle types, it is recommended for efficiency that you use the |
---|
3484 | static pointer of the corresponding particle classes. |
---|
3485 | </para> |
---|
3486 | <para> |
---|
3487 | As an example, in a model valid for <emphasis>gamma</emphasis>s only, |
---|
3488 | the IsApplicable() method should take the form: |
---|
3489 | |
---|
3490 | <informalexample> |
---|
3491 | <programlisting> |
---|
3492 | #include "G4Gamma.hh" |
---|
3493 | |
---|
3494 | G4bool MyGammaModel::IsApplicable(const G4ParticleDefinition& partDef) |
---|
3495 | { |
---|
3496 | return &partDef == G4Gamma::GammaDefinition(); |
---|
3497 | } |
---|
3498 | </programlisting> |
---|
3499 | </informalexample> |
---|
3500 | </para></listitem> |
---|
3501 | </varlistentry> |
---|
3502 | <varlistentry> |
---|
3503 | <term> |
---|
3504 | <emphasis role="bold"><literal>G4bool ModelTrigger( |
---|
3505 | <emphasis>const G4FastTrack&</emphasis>):</literal></emphasis> |
---|
3506 | </term> |
---|
3507 | <listitem><para> |
---|
3508 | You must return "true" when the dynamic conditions to trigger your |
---|
3509 | parameterisation are fulfilled. |
---|
3510 | The G4FastTrack provides access to the current G4Track, gives |
---|
3511 | simple access to envelope related features (G4LogicalVolume, |
---|
3512 | G4VSolid, and G4AffineTransform references between the global and |
---|
3513 | the envelope local coordinates systems) and simple access to the |
---|
3514 | position and momentum expressed in the envelope coordinate system. |
---|
3515 | Using these quantities and the G4VSolid methods, you can for |
---|
3516 | example easily check how far you are from the envelope boundary. |
---|
3517 | </para></listitem> |
---|
3518 | </varlistentry> |
---|
3519 | <varlistentry> |
---|
3520 | <term> |
---|
3521 | <emphasis role="bold"><literal>void DoIt( |
---|
3522 | <emphasis>const G4FastTrack&, G4FastStep&</emphasis>):</literal></emphasis> |
---|
3523 | </term> |
---|
3524 | <listitem><para> |
---|
3525 | The details of your parameterisation will be implemented in this method. |
---|
3526 | The G4FastTrack reference provides the input information, and the final |
---|
3527 | state of the particles after parameterisation must be returned |
---|
3528 | through the G4FastStep reference. Tracking for the final state |
---|
3529 | particles is requested after your parameterisation has been invoked. |
---|
3530 | </para></listitem> |
---|
3531 | </varlistentry> |
---|
3532 | </variablelist> |
---|
3533 | </para> |
---|
3534 | |
---|
3535 | </sect3> |
---|
3536 | |
---|
3537 | |
---|
3538 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3539 | <sect3 id="sect.PhysProc.Param.FastSimMan"> |
---|
3540 | <title> |
---|
3541 | The <literal>G4FastSimulationManager</literal> Class: |
---|
3542 | </title> |
---|
3543 | |
---|
3544 | <para> |
---|
3545 | G4FastSimulationManager functionnalities regarding the use of ghost |
---|
3546 | volumes are explained in <xref linkend="sect.PhysProc.Param.Ghost" />. |
---|
3547 | </para> |
---|
3548 | |
---|
3549 | <!-- ******* Bridgehead ******* --> |
---|
3550 | <bridgehead renderas='sect4'> |
---|
3551 | Constructor: |
---|
3552 | </bridgehead> |
---|
3553 | |
---|
3554 | <para> |
---|
3555 | <variablelist> |
---|
3556 | <varlistentry> |
---|
3557 | <term> |
---|
3558 | <literal><emphasis role="bold">G4FastSimulationManager( |
---|
3559 | <emphasis>G4Region *anEnvelope, G4bool IsUnique=false</emphasis>): |
---|
3560 | </emphasis></literal> |
---|
3561 | </term> |
---|
3562 | <listitem><para> |
---|
3563 | This is the only constructor. You specify the G4Region by providing |
---|
3564 | its pointer. The G4FastSimulationManager object will bind itself |
---|
3565 | to this G4Region. If you know that this G4Region has a single root |
---|
3566 | G4LogicalVolume, placed only once, you can set the IsUnique boolean |
---|
3567 | to "true" to allow some optimization. |
---|
3568 | </para> |
---|
3569 | <para> |
---|
3570 | Note that if you choose to use the G4VFastSimulationModel(const |
---|
3571 | G4String&, G4Region*, G4bool) constructor for your model, the |
---|
3572 | G4FastSimulationManager will be constructed using the given |
---|
3573 | G4Region* and G4bool values of the model constructor. |
---|
3574 | </para></listitem> |
---|
3575 | </varlistentry> |
---|
3576 | </variablelist> |
---|
3577 | </para> |
---|
3578 | |
---|
3579 | <!-- ******* Bridgehead ******* --> |
---|
3580 | <bridgehead renderas='sect4'> |
---|
3581 | G4VFastSimulationModel object management: |
---|
3582 | </bridgehead> |
---|
3583 | |
---|
3584 | <para> |
---|
3585 | The following two methods provide the usual management |
---|
3586 | functions. |
---|
3587 | |
---|
3588 | <itemizedlist spacing="compact"> |
---|
3589 | <listitem><para> |
---|
3590 | <literal><emphasis role="bold">void AddFastSimulationModel( |
---|
3591 | G4VFastSimulationModel*)</emphasis></literal> |
---|
3592 | </para></listitem> |
---|
3593 | <listitem><para> |
---|
3594 | <literal><emphasis role="bold">RemoveFastSimulationModel( |
---|
3595 | G4VFastSimulationModel*)</emphasis></literal> |
---|
3596 | </para></listitem> |
---|
3597 | </itemizedlist> |
---|
3598 | </para> |
---|
3599 | |
---|
3600 | <!-- ******* Bridgehead ******* --> |
---|
3601 | <bridgehead renderas='sect4'> |
---|
3602 | Interface with the G4FastSimulationManagerProcess: |
---|
3603 | </bridgehead> |
---|
3604 | |
---|
3605 | <para> |
---|
3606 | This is described in the User's Guide for Toolkit Developers |
---|
3607 | ( |
---|
3608 | <!-- !!! xref linkend=""/ or ulink url="" --> |
---|
3609 | section 3.9.6 |
---|
3610 | <!-- !! /ulink (remove this tag for xref) --> |
---|
3611 | ) |
---|
3612 | </para> |
---|
3613 | |
---|
3614 | </sect3> |
---|
3615 | |
---|
3616 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3617 | <sect3 id="sect.PhysProc.Param.FastSimManProc"> |
---|
3618 | <title> |
---|
3619 | The <literal>G4FastSimulationManagerProcess</literal> Class |
---|
3620 | </title> |
---|
3621 | |
---|
3622 | <para> |
---|
3623 | This G4VProcess serves as an interface between the tracking and the |
---|
3624 | parameterisation. At tracking time, it collaborates with the |
---|
3625 | G4FastSimulationManager of the current volume, if any, to allow the |
---|
3626 | models to trigger. If no manager exists or if no model issues a |
---|
3627 | trigger, the tracking goes on normally. |
---|
3628 | </para> |
---|
3629 | |
---|
3630 | <para> |
---|
3631 | <emphasis>In the present implementation, you must set this process in |
---|
3632 | the G4ProcessManager of the particles you parameterise to enable |
---|
3633 | your parameterisation.</emphasis> |
---|
3634 | </para> |
---|
3635 | |
---|
3636 | <para> |
---|
3637 | The processes ordering is: |
---|
3638 | |
---|
3639 | <informalexample> |
---|
3640 | <programlisting> |
---|
3641 | [n-3] ... |
---|
3642 | [n-2] Multiple Scattering |
---|
3643 | [n-1] G4FastSimulationManagerProcess |
---|
3644 | [ n ] G4Transportation |
---|
3645 | </programlisting> |
---|
3646 | </informalexample> |
---|
3647 | </para> |
---|
3648 | |
---|
3649 | <para> |
---|
3650 | This ordering is important if you use ghost geometries, since the |
---|
3651 | G4FastSimulationManagerProcess will provide navigation in the ghost |
---|
3652 | world to limit the step on ghost boundaries. |
---|
3653 | </para> |
---|
3654 | |
---|
3655 | <para> |
---|
3656 | The G4FastSimulationManager must be added to the process list of a |
---|
3657 | particle as a continuous and discrete process if you use ghost |
---|
3658 | geometries for this particle. You can add it as a discrete process |
---|
3659 | if you don't use ghosts. |
---|
3660 | </para> |
---|
3661 | |
---|
3662 | <para> |
---|
3663 | The following code registers the G4FastSimulationManagerProcess |
---|
3664 | with all the particles as a discrete and continuous process: |
---|
3665 | |
---|
3666 | <informalexample> |
---|
3667 | <programlisting> |
---|
3668 | void MyPhysicsList::addParameterisation() |
---|
3669 | { |
---|
3670 | G4FastSimulationManagerProcess* |
---|
3671 | theFastSimulationManagerProcess = new G4FastSimulationManagerProcess(); |
---|
3672 | theParticleIterator->reset(); |
---|
3673 | while( (*theParticleIterator)() ) |
---|
3674 | { |
---|
3675 | G4ParticleDefinition* particle = theParticleIterator->value(); |
---|
3676 | G4ProcessManager* pmanager = particle->GetProcessManager(); |
---|
3677 | pmanager->AddProcess(theFastSimulationManagerProcess, -1, 0, 0); |
---|
3678 | } |
---|
3679 | } |
---|
3680 | </programlisting> |
---|
3681 | </informalexample> |
---|
3682 | </para> |
---|
3683 | |
---|
3684 | </sect3> |
---|
3685 | |
---|
3686 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3687 | <sect3 id="sect.PhysProc.Param.FastSimManSing"> |
---|
3688 | <title> |
---|
3689 | The <literal>G4GlobalFastSimulationManager</literal> Singleton Class |
---|
3690 | </title> |
---|
3691 | |
---|
3692 | <para> |
---|
3693 | This class is a singleton which can be accessed as follows: |
---|
3694 | |
---|
3695 | <informalexample> |
---|
3696 | <programlisting> |
---|
3697 | #include "G4GlobalFastSimulationManager.hh" |
---|
3698 | ... |
---|
3699 | ... |
---|
3700 | G4GlobalFastSimulationManager* globalFSM; |
---|
3701 | globalFSM = G4GlobalFastSimulationManager::getGlobalFastSimulationManager(); |
---|
3702 | ... |
---|
3703 | ... |
---|
3704 | </programlisting> |
---|
3705 | </informalexample> |
---|
3706 | </para> |
---|
3707 | |
---|
3708 | <para> |
---|
3709 | Presently, you will mainly need to use the |
---|
3710 | GlobalFastSimulationManager if you use ghost geometries. |
---|
3711 | </para> |
---|
3712 | |
---|
3713 | </sect3> |
---|
3714 | |
---|
3715 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3716 | <sect3 id="sect.PhysProc.Param.Ghost"> |
---|
3717 | <title> |
---|
3718 | Parameterisation Using Ghost Geometries |
---|
3719 | </title> |
---|
3720 | |
---|
3721 | <para> |
---|
3722 | In some cases, volumes of the tracking geometry do not allow |
---|
3723 | envelopes to be defined. This may be the case with a geometry |
---|
3724 | coming from a CAD system. Since such a geometry is flat, a parallel |
---|
3725 | geometry must be used to define the envelopes. |
---|
3726 | </para> |
---|
3727 | |
---|
3728 | <para> |
---|
3729 | Another interesting case involves defining an envelope which groups |
---|
3730 | the electromagnetic and hadronic calorimeters of a detector into |
---|
3731 | one volume. This may be useful when parameterizing the interaction |
---|
3732 | of charged pions. You will very likely not want electrons to see |
---|
3733 | this envelope, which means that ghost geometries have to be |
---|
3734 | organized by particle flavours. |
---|
3735 | </para> |
---|
3736 | |
---|
3737 | <para> |
---|
3738 | Using ghost geometries implies some more overhead in the |
---|
3739 | parameterisation mechanism for the particles sensitive to ghosts, |
---|
3740 | since navigation is provided in the ghost geometry by the |
---|
3741 | G4FastSimulationManagerProcess. Usually, however, only a few |
---|
3742 | volumes will be placed in this ghost world, so that the geometry |
---|
3743 | computations will remain rather cheap. |
---|
3744 | </para> |
---|
3745 | |
---|
3746 | <para> |
---|
3747 | In the existing implementation (temporary implementation with |
---|
3748 | G4Region but before parallel geometry implementation), you may only |
---|
3749 | consider ghost G4Regions with just one root G4LogicalVolume. The |
---|
3750 | G4GlobalFastSimulationManager provides the construction of the |
---|
3751 | ghost geometry by making first an empty "clone" of the world for |
---|
3752 | tracking provided by the construct() method of your |
---|
3753 | G4VUserDetectorConstruction concrete class. You provide the |
---|
3754 | placement of the G4Region root G4LogicalVolume relative to the |
---|
3755 | ghost world coordinates in the G4FastSimulationManager objects. A |
---|
3756 | ghost G4Region is recognized by the fact that its associated |
---|
3757 | G4FastSimulationManager retains a non-empty list of placements. |
---|
3758 | </para> |
---|
3759 | |
---|
3760 | <para> |
---|
3761 | The G4GlobalFastSimulationManager will then use both those |
---|
3762 | placements and the IsApplicable() methods of the models attached to |
---|
3763 | the G4FastSimulationManager objects to build the flavour-dependant |
---|
3764 | ghost geometries. |
---|
3765 | </para> |
---|
3766 | |
---|
3767 | <para> |
---|
3768 | Then at the beginning of the tracking of a particle, the |
---|
3769 | appropriate ghost world, if any, will be selected. |
---|
3770 | </para> |
---|
3771 | |
---|
3772 | <para> |
---|
3773 | The steps required to build one ghost G4Region are: |
---|
3774 | |
---|
3775 | <orderedlist spacing="compact"> |
---|
3776 | <listitem><para> |
---|
3777 | built the ghost G4Region : myGhostRegion; |
---|
3778 | </para></listitem> |
---|
3779 | <listitem><para> |
---|
3780 | build the root G4LogicalVolume: myGhostLogical, set it to |
---|
3781 | myGhostRegion; |
---|
3782 | </para></listitem> |
---|
3783 | <listitem><para> |
---|
3784 | build a G4FastSimulationManager object, myGhostFSManager, |
---|
3785 | giving myGhostRegion as argument of the constructor; |
---|
3786 | </para></listitem> |
---|
3787 | <listitem><para> |
---|
3788 | <para> |
---|
3789 | give to the G4FastSimulationManager the placement of the |
---|
3790 | myGhostLogical, by invoking for the G4FastSimulationManager method: |
---|
3791 | <informalexample> |
---|
3792 | <programlisting> |
---|
3793 | AddGhostPlacement(G4RotationMatrix*, const G4ThreeVector&); |
---|
3794 | </programlisting> |
---|
3795 | </informalexample> |
---|
3796 | or: |
---|
3797 | <informalexample> |
---|
3798 | <programlisting> |
---|
3799 | AddGhostPlacement(G4Transform3D*); |
---|
3800 | </programlisting> |
---|
3801 | </informalexample> |
---|
3802 | |
---|
3803 | where the rotation matrix and translation vector of the 3-D |
---|
3804 | transformation describe the placement relative to the ghost world |
---|
3805 | coordinates. |
---|
3806 | </para> |
---|
3807 | </para></listitem> |
---|
3808 | <listitem><para> |
---|
3809 | build your G4VFastSimulationModel objects and add them to the |
---|
3810 | myGhostFSManager. |
---|
3811 | <emphasis>The IsApplicable() methods of your models will be used by the |
---|
3812 | G4GlobalFastSimulationManager to build the ghost geometries |
---|
3813 | corresponding to a given particle type.</emphasis> |
---|
3814 | </para></listitem> |
---|
3815 | <listitem><para> |
---|
3816 | <para> |
---|
3817 | Invoke the G4GlobalFastSimulationManager method: |
---|
3818 | |
---|
3819 | <informalexample> |
---|
3820 | <programlisting> |
---|
3821 | G4GlobalFastSimulationManager::getGlobalFastSimulationManager()-> |
---|
3822 | |
---|
3823 | CloseFastSimulation(); |
---|
3824 | </programlisting> |
---|
3825 | </informalexample> |
---|
3826 | </para> |
---|
3827 | </para></listitem> |
---|
3828 | </orderedlist> |
---|
3829 | </para> |
---|
3830 | |
---|
3831 | <para> |
---|
3832 | This last call will cause the G4GlobalFastSimulationManager to |
---|
3833 | build the flavour-dependent ghost geometries. This call must be |
---|
3834 | done before the RunManager closes the geometry. (It is foreseen |
---|
3835 | that the run manager in the future will invoke the |
---|
3836 | CloseFastSimulation() to synchronize properly with the closing of |
---|
3837 | the geometry). |
---|
3838 | </para> |
---|
3839 | |
---|
3840 | <para> |
---|
3841 | Visualization facilities are provided for ghosts geometries. After |
---|
3842 | the CloseFastSimulation() invocation, it is possible to ask for the |
---|
3843 | drawing of ghosts in an interactive session. The basic commands |
---|
3844 | are: |
---|
3845 | |
---|
3846 | <itemizedlist spacing="compact"> |
---|
3847 | <listitem><para> |
---|
3848 | <para> |
---|
3849 | /vis/draw/Ghosts particle_name |
---|
3850 | </para> |
---|
3851 | <para> |
---|
3852 | which makes the drawing of the ghost geometry associated with the |
---|
3853 | particle specified by name in the command line. |
---|
3854 | </para> |
---|
3855 | </para></listitem> |
---|
3856 | <listitem><para> |
---|
3857 | /vis/draw/Ghosts |
---|
3858 | <para> |
---|
3859 | which draws all the ghost geometries. |
---|
3860 | </para> |
---|
3861 | </para></listitem> |
---|
3862 | </itemizedlist> |
---|
3863 | </para> |
---|
3864 | |
---|
3865 | </sect3> |
---|
3866 | |
---|
3867 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3868 | <sect3 id="sect.PhysProc.Param.GFlash"> |
---|
3869 | <title> |
---|
3870 | Gflash Parameterization |
---|
3871 | </title> |
---|
3872 | |
---|
3873 | <para> |
---|
3874 | This section describes how to use the Gflash library. Gflash is a |
---|
3875 | concrete parameterization which is based on the equations and |
---|
3876 | parameters of the original Gflash package from H1(hep-ex/0001020, |
---|
3877 | Grindhammer & Peters, see physics manual) and uses the "fast |
---|
3878 | simulation" facilities of GEANT4 described above. Briefly, whenever |
---|
3879 | a e-/e+ particle enters the calorimeter, it is parameterized if it |
---|
3880 | has a minimum energy and the shower is expected to be contained in |
---|
3881 | the calorimeter (or " parameterization envelope"). If this is |
---|
3882 | fulfilled the particle is killed, as well as all secondaries, and |
---|
3883 | the energy is deposited according to the Gflash equations. An |
---|
3884 | example, provided in |
---|
3885 | <emphasis role="bold">examples/extended/parametrisation/gflash/</emphasis>, |
---|
3886 | shows how to interface Gflash to your application. The simulation time is |
---|
3887 | measured, so the user can immediately see the speed increase |
---|
3888 | resulting from the use of Gflash. |
---|
3889 | </para> |
---|
3890 | |
---|
3891 | </sect3> |
---|
3892 | |
---|
3893 | <!-- ******************* Section (Level#3) ****************** --> |
---|
3894 | <sect3 id="sect.PhysProc.Param.UsingGFlash"> |
---|
3895 | <title> |
---|
3896 | Using the Gflash Parameterisation |
---|
3897 | </title> |
---|
3898 | |
---|
3899 | <para> |
---|
3900 | To use Gflash "out of the box" the following steps are necessary: |
---|
3901 | |
---|
3902 | <itemizedlist spacing="compact"> |
---|
3903 | <listitem><para> |
---|
3904 | The user must add the fast simulation process to his process |
---|
3905 | manager: |
---|
3906 | |
---|
3907 | <informalexample> |
---|
3908 | <programlisting> |
---|
3909 | void MyPhysicsList::addParameterisation() |
---|
3910 | { |
---|
3911 | G4FastSimulationManagerProcess* |
---|
3912 | theFastSimulationManagerProcess = new G4FastSimulationManagerProcess(); |
---|
3913 | theParticleIterator->reset(); |
---|
3914 | while( (*theParticleIterator)() ) |
---|
3915 | { |
---|
3916 | G4ParticleDefinition* particle = theParticleIterator->value(); |
---|
3917 | G4ProcessManager* pmanager = particle->GetProcessManager(); |
---|
3918 | pmanager->AddProcess(theFastSimulationManagerProcess, -1, 0, 0); |
---|
3919 | } |
---|
3920 | } |
---|
3921 | </programlisting> |
---|
3922 | </informalexample> |
---|
3923 | </para></listitem> |
---|
3924 | <listitem><para> |
---|
3925 | <para> |
---|
3926 | The envelope in which the parameterization should be performed |
---|
3927 | must be specified (below: G4Region m_calo_region) and the |
---|
3928 | GFlashShowerModel must be assigned to this region. Furthermore, the |
---|
3929 | classes GFlashParticleBounds (which provides thresholds for the |
---|
3930 | parameterization like minimal energy etc.), GflashHitMaker(a helper |
---|
3931 | class to generate hits in the sensitive detector) and |
---|
3932 | GFlashHomoShowerParamterisation (which does the computations) must |
---|
3933 | be constructed (by the user at the moment) and assigned to the |
---|
3934 | GFlashShowerModel. Please note that at the moment only homogeneous |
---|
3935 | calorimeters are supported. |
---|
3936 | </para> |
---|
3937 | <para> |
---|
3938 | <informalexample> |
---|
3939 | <programlisting> |
---|
3940 | m_theFastShowerModel = new GFlashShowerModel("fastShowerModel",m_calo_region); |
---|
3941 | m_theParametrisation = new GFlashHomoShowerParamterisation(matManager->getMaterial(mat)); |
---|
3942 | m_theParticleBounds = new GFlashParticleBounds(); |
---|
3943 | m_theHMaker = new GFlashHitMaker(); |
---|
3944 | m_theFastShowerModel->SetParametrisation(*m_theParametrisation); |
---|
3945 | m_theFastShowerModel->SetParticleBounds(*m_theParticleBounds) ; |
---|
3946 | m_theFastShowerModel->SetHitMaker(*m_theHMaker); |
---|
3947 | </programlisting> |
---|
3948 | </informalexample> |
---|
3949 | </para> |
---|
3950 | <para> |
---|
3951 | The user must also set the material of the calorimeter, since the |
---|
3952 | computation depends on the material. |
---|
3953 | </para> |
---|
3954 | </para></listitem> |
---|
3955 | <listitem><para> |
---|
3956 | <para> |
---|
3957 | It is mandatory to use G4VGFlashSensitiveDetector as |
---|
3958 | (additional) base class for the sensitive detector. |
---|
3959 | </para> |
---|
3960 | <para> |
---|
3961 | <informalexample> |
---|
3962 | <programlisting> |
---|
3963 | class ExGflashSensitiveDetector: public G4VSensitiveDetector ,public G4VGFlashSensitiveDetector |
---|
3964 | </programlisting> |
---|
3965 | </informalexample> |
---|
3966 | </para> |
---|
3967 | <para> |
---|
3968 | Here it is necessary to implement a separate interface, where the |
---|
3969 | GFlash spots are processed. |
---|
3970 | </para> |
---|
3971 | <para> |
---|
3972 | <informalexample> |
---|
3973 | <programlisting> |
---|
3974 | (ProcessHits(G4GFlashSpot*aSpot ,G4TouchableHistory* ROhist)) |
---|
3975 | </programlisting> |
---|
3976 | </informalexample> |
---|
3977 | </para> |
---|
3978 | <para> |
---|
3979 | A separate interface is used, because the Gflash spots naturally |
---|
3980 | contain less information than the full simulation. |
---|
3981 | </para> |
---|
3982 | </para></listitem> |
---|
3983 | </itemizedlist> |
---|
3984 | </para> |
---|
3985 | |
---|
3986 | <para> |
---|
3987 | Since the parameters in the Gflash package are taken from fits to |
---|
3988 | full simulations with Geant3, some retuning might be necessary for |
---|
3989 | good agreement with Geant4 showers. For experiment-specific |
---|
3990 | geometries some retuning might be necessary anyway. The tuning is |
---|
3991 | quite complicated since there are many parameters (some correlated) |
---|
3992 | and cannot be described here (see again hep-ex/0001020). For brave |
---|
3993 | users the Gflash framework already forsees the possibility of |
---|
3994 | passing a class with the (users) |
---|
3995 | parameters,<emphasis role="bold">GVFlashHomoShowerTuning</emphasis>, |
---|
3996 | to the GFlashHomoShowerParamterisation constructor. |
---|
3997 | The default parameters are the original Gflash parameters: |
---|
3998 | |
---|
3999 | <informalexample> |
---|
4000 | <programlisting> |
---|
4001 | GFlashHomoShowerParameterisation(G4Material * aMat, GVFlashHomoShowerTuning * aPar = 0); |
---|
4002 | </programlisting> |
---|
4003 | </informalexample> |
---|
4004 | </para> |
---|
4005 | |
---|
4006 | <para> |
---|
4007 | Now there is also a preliminary implemenation of a parameterization |
---|
4008 | for sampling calorimeters. |
---|
4009 | </para> |
---|
4010 | |
---|
4011 | <para> |
---|
4012 | The user must specify the active and passive material, as well as |
---|
4013 | the thickness of the active and passive layer. |
---|
4014 | </para> |
---|
4015 | |
---|
4016 | <para> |
---|
4017 | The sampling structure of the calorimeter is taken into account by |
---|
4018 | using an "effective medium" to compute the shower shape. |
---|
4019 | </para> |
---|
4020 | |
---|
4021 | <para> |
---|
4022 | All material properties needed are calculated automatically. If |
---|
4023 | tuning is required, the user can pass his own parameter set in |
---|
4024 | the class |
---|
4025 | <emphasis role="bold">GFlashSamplingShowerTuning</emphasis>. |
---|
4026 | Here the user can also set his calorimeter resolution. |
---|
4027 | </para> |
---|
4028 | |
---|
4029 | <para> |
---|
4030 | All in all the constructor looks the following: |
---|
4031 | |
---|
4032 | <informalexample> |
---|
4033 | <programlisting> |
---|
4034 | GFlashSamplingShowerParamterisation(G4Material * Mat1, G4Material * Mat2,G4double d1,G4double d2, |
---|
4035 | GVFlashSamplingShowerTuning * aPar = 0); |
---|
4036 | </programlisting> |
---|
4037 | </informalexample> |
---|
4038 | </para> |
---|
4039 | |
---|
4040 | <para> |
---|
4041 | An implementation of some tools that should help the user to tune |
---|
4042 | the parameterization is forseen. |
---|
4043 | </para> |
---|
4044 | |
---|
4045 | </sect3> |
---|
4046 | </sect2> |
---|
4047 | |
---|
4048 | |
---|
4049 | <!-- ******************* Section (Level#2) ****************** --> |
---|
4050 | <sect2 id="sect.PhysProc.Trans"> |
---|
4051 | <title> |
---|
4052 | Transportation Process |
---|
4053 | </title> |
---|
4054 | |
---|
4055 | <para> |
---|
4056 | To be delivered by J. Apostolakis (<email>John.Apostolakis@cern.ch</email>). |
---|
4057 | </para> |
---|
4058 | |
---|
4059 | |
---|
4060 | </sect2> |
---|
4061 | </sect1> |
---|