[904] | 1 | <!-- ******************************************************** --> |
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| 2 | <!-- Docbook Version: For Toolkit Developers Guide --> |
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| 3 | <!-- ******************************************************** --> |
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| 4 | |
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| 5 | <!-- ******************* Section (Level#1) ****************** --> |
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| 6 | <sect1 id="sect.ExtdFuncHadPhys"> |
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| 7 | <title> |
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| 8 | Hadronic Physics |
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| 9 | </title> |
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| 10 | |
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| 11 | <!-- |
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| 12 | This is a verbatim of a paper published in a refereed journal. |
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| 13 | A suggestion by one of the documentation referees to re-write |
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| 14 | completely seems quite inappropriate. |
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| 15 | --> |
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| 16 | |
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| 17 | <!-- ******************* Section (Level#2) ****************** --> |
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| 18 | <sect2 id="sect.ExtdFuncHadPhys.Intro"> |
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| 19 | <title> |
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| 20 | Introduction |
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| 21 | </title> |
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| 22 | |
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| 23 | <para> |
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| 24 | Optimal exploitation of hadronic final |
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| 25 | states played a key role in successes of all recent collider experiment in HEP, |
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| 26 | and the ability to use hadronic final states will continue to be one of the |
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| 27 | decisive issues during the analysis phase of the LHC experiments. |
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| 28 | Monte Carlo programs like Geant4 facilitate the use of |
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| 29 | hadronic final states, and have been developed for many years. |
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| 30 | </para> |
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| 31 | |
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| 32 | <para> |
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| 33 | We give an overview of the Object Oriented frameworks for hadronic generators |
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| 34 | in Geant4, and illustrate the physics models underlying hadronic shower |
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| 35 | simulation on examples, including the three basic types of modeling; |
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| 36 | data-driven, parametrisation-driven, and theory-driven modeling, and their |
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| 37 | possible realisations in the Object Oriented component system of Geant4. |
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| 38 | We put particular focus on the level of extendibility that can and has been |
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| 39 | achieved by our Russian dolls approach to Object Oriented design, and the |
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| 40 | role and importance of the frameworks in a component system. |
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| 41 | </para> |
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| 42 | |
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| 43 | </sect2> |
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| 44 | |
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| 45 | <!-- ******************* Section (Level#2) ****************** --> |
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| 46 | <sect2 id="sect.ExtdFuncHadPhys.PrncCnsd"> |
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| 47 | <title> |
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| 48 | Principal Considerations |
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| 49 | </title> |
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| 50 | |
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| 51 | <para> |
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| 52 | The purpose of this section is to explain the implementation frameworks used |
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| 53 | in and provided by Geant4 for hadronic shower simulation as in the 1.1 |
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| 54 | release of the program. The implementation frameworks follow the Russian dolls |
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| 55 | approach to implementation framework design. |
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| 56 | A top-level, very abstracting implementation framework provides the basic |
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| 57 | interface to the other Geant4 categories, and fulfils the most general |
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| 58 | use-case for hadronic shower simulation. It is refined for more specific |
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| 59 | use-cases by implementing a hierarchy of implementation frameworks, each level |
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| 60 | implementing the common logic of a particular use-case package in a concrete |
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| 61 | implementation of the interface specification of one framework level above, |
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| 62 | this way refining the granularity of abstraction and delegation. This defines |
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| 63 | the Russian dolls architectural pattern. |
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| 64 | Abstract classes are used as the delegation mechanism |
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| 65 | |
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| 66 | <footnote> |
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| 67 | <para> |
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| 68 | The same can be achieved with template specialisations |
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| 69 | with slightly improved CPU performance but at the cost of significantly more |
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| 70 | complex designs and, with present compilers, significantly reduced |
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| 71 | portability. |
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| 72 | </para> |
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| 73 | </footnote> |
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| 74 | . |
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| 75 | </para> |
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| 76 | |
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| 77 | <para> |
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| 78 | All framework functional requirements were obtained through use-case analysis. |
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| 79 | In the following we present for each framework level the compressed use-cases, |
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| 80 | requirements, designs including the flexibility provided, and illustrate the |
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| 81 | framework functionality with examples. All design patterns cited are to |
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| 82 | be read as defined in |
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| 83 | <citation><xref linkend="biblio.Gamma1995" endterm="biblio.Gamma1995.abbrev" /></citation>. |
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| 84 | </para> |
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| 85 | |
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| 86 | </sect2> |
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| 87 | |
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| 88 | <!-- ******************* Section (Level#2) ****************** --> |
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| 89 | <sect2 id="sect.ExtdFuncHadPhys.L1_Proc"> |
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| 90 | <title> |
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| 91 | Level 1 Framework - processes |
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| 92 | </title> |
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| 93 | |
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| 94 | <para> |
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| 95 | There are two principal use-cases of the level 1 framework. A user will |
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| 96 | want to choose the processes used for his particular simulation run, and a |
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| 97 | physicist will want to write code for processes of his own and use these |
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| 98 | together with the rest of the system in a seamless manner. |
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| 99 | </para> |
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| 100 | |
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| 101 | <!-- ******* Bridgehead ******* --> |
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| 102 | <bridgehead renderas='sect4'> |
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| 103 | Requirements |
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| 104 | </bridgehead> |
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| 105 | |
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| 106 | <para> |
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| 107 | <orderedlist spacing="compact"> |
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| 108 | <listitem><para> |
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| 109 | Provide a standard interface to be used by process implementations. |
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| 110 | </para></listitem> |
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| 111 | <listitem><para> |
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| 112 | Provide registration mechanisms for processes. |
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| 113 | </para></listitem> |
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| 114 | </orderedlist> |
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| 115 | </para> |
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| 116 | |
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| 117 | <!-- ******* Bridgehead ******* --> |
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| 118 | <bridgehead renderas='sect4'> |
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| 119 | Design and interfaces |
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| 120 | </bridgehead> |
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| 121 | |
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| 122 | <para> |
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| 123 | Both requirements are implemented in a sub-set of the tracking-physics |
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| 124 | interface in Geant4}. The class diagram is shown in |
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| 125 | <xref linkend="fig.ExtdFuncHadPhys_1" />. |
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| 126 | |
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| 127 | <figure id="fig.ExtdFuncHadPhys_1"> |
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| 128 | <title> |
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| 129 | Level 1 implementation framework of the hadronic category of GEANT4. |
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| 130 | </title> |
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| 131 | <mediaobject> |
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| 132 | <imageobject role="fo"> |
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[921] | 133 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level1.jpg" |
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[1208] | 134 | format="JPG" contentwidth="10.0cm" align="center" /> |
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[904] | 135 | </imageobject> |
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| 136 | <imageobject role="html"> |
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[921] | 137 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level1.jpg" |
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[1208] | 138 | format="JPG" contentwidth="120%" align="center" /> |
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[904] | 139 | </imageobject> |
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| 140 | </mediaobject> |
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| 141 | </figure> |
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| 142 | </para> |
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| 143 | |
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| 144 | <para> |
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| 145 | All processes have a common base-class <literal>G4VProcess</literal>, |
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| 146 | from which a set of specialised classes are derived. Three of them are |
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| 147 | used as base classes for hadronic processes for particles at rest |
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| 148 | (<literal>G4VRestProcess</literal>), for interactions in flight |
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| 149 | (<literal>G4VDiscreteProcess</literal>), and for processes like |
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| 150 | radioactive decay where the same implementation can represent both these |
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| 151 | extreme cases (<literal>G4VRestDiscrete-Process</literal>). |
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| 152 | </para> |
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| 153 | |
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| 154 | <para> |
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| 155 | Each of these classes declares two types of methods; one for calculating the |
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| 156 | time to interaction or the physical interaction length, allowing tracking to |
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| 157 | request the information necessary to decide on the process responsible for |
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| 158 | final state production, and one to compute the final state. These are pure |
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| 159 | virtual methods, and have to be implemented in each individual derived class, |
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| 160 | as enforced by the compiler. |
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| 161 | </para> |
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| 162 | |
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| 163 | |
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| 164 | <!-- ******* Bridgehead ******* --> |
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| 165 | <bridgehead renderas='sect4'> |
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| 166 | Framework functionality |
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| 167 | </bridgehead> |
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| 168 | |
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| 169 | <para> |
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| 170 | The functionality provided is through the use of process base-class pointers |
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| 171 | in the tracking-physics interface, and the |
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| 172 | <literal>G4Process-Manager</literal>. |
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| 173 | All functionality is implemented in abstract, and registration of derived process |
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| 174 | classes with the <literal>G4Process-Manager</literal> of an individual particle |
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| 175 | allows for arbitrary combination of both Geant4 provided processes, and |
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| 176 | user-implemented processes. This registration mechanism is a modification on a |
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| 177 | Chain of Responsibility. It is outside the scope of the current paper, and its |
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| 178 | description is available from |
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| 179 | <ulink url="http://geant4.web.cern.ch/geant4/support/userdocuments.shtml"> |
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| 180 | G4Manual</ulink>. |
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| 181 | </para> |
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| 182 | |
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| 183 | </sect2> |
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| 184 | |
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| 185 | <!-- ******************* Section (Level#2) ****************** --> |
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| 186 | <sect2 id="sect.ExtdFuncHadPhys.L2F_CrssSctMdl"> |
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| 187 | <title> |
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| 188 | Level 2 Framework - Cross Sections and Models |
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| 189 | </title> |
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| 190 | |
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| 191 | <para> |
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| 192 | At the next level of abstraction, only processes that occur for particles |
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| 193 | in flight are considered. For these, it is easily observed that the sources |
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| 194 | of cross sections and final state production are rarely the same. Also, |
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| 195 | different sources will come with different restrictions. The principal |
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| 196 | use-cases of the framework are addressing these commonalities. A user might |
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| 197 | want to combine different cross sections and final state or isotope production |
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| 198 | models as provided by Geant4, and a physicist might |
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| 199 | want to implement his own model for particular situation, and add cross-section |
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| 200 | data sets that are relevant for his particular analysis to the system in a |
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| 201 | seamless manner. |
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| 202 | </para> |
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| 203 | |
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| 204 | <!-- ******* Bridgehead ******* --> |
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| 205 | <bridgehead renderas='sect4'> |
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| 206 | Requirements |
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| 207 | </bridgehead> |
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| 208 | |
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| 209 | <para> |
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| 210 | <orderedlist spacing="compact"> |
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| 211 | <listitem><para> |
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| 212 | Flexible choice of inclusive scattering cross-sections. |
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| 213 | </para></listitem> |
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| 214 | <listitem><para> |
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| 215 | Ability to use different data-sets for different parts of |
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| 216 | the simulation, depending on the conditions at the point of interaction. |
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| 217 | </para></listitem> |
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| 218 | <listitem><para> |
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| 219 | Ability to add user-defined data-sets in a seamless manner. |
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| 220 | </para></listitem> |
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| 221 | <listitem><para> |
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| 222 | Flexible, unconstrained choice of final state production models. |
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| 223 | </para></listitem> |
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| 224 | <listitem><para> |
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| 225 | Ability to use different final state production codes |
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| 226 | for different parts of the simulation, depending on the conditions at the |
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| 227 | point of interaction. |
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| 228 | </para></listitem> |
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| 229 | <listitem><para> |
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| 230 | Ability to add user-defined final state production models in |
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| 231 | a seamless manner. |
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| 232 | </para></listitem> |
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| 233 | <listitem><para> |
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| 234 | Flexible choice of isotope production models, to run in |
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| 235 | parasitic mode to any kind of transport models. |
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| 236 | </para></listitem> |
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| 237 | <listitem><para> |
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| 238 | Ability to use different isotope production codes |
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| 239 | for different parts of the simulation, depending on the conditions at the |
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| 240 | point of interaction. |
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| 241 | </para></listitem> |
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| 242 | <listitem><para> |
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| 243 | Ability to add user-defined isotope production models in a seamless manner. |
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| 244 | </para></listitem> |
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| 245 | </orderedlist> |
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| 246 | </para> |
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| 247 | |
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| 248 | |
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| 249 | <!-- ******* Bridgehead ******* --> |
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| 250 | <bridgehead renderas='sect4'> |
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| 251 | Design and interfaces |
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| 252 | </bridgehead> |
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| 253 | |
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| 254 | <para> |
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| 255 | The above requirements are implemented in three framework components, one |
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| 256 | for cross-sections, final state production, and isotope production each. |
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| 257 | The class diagrams are shown in |
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| 258 | <xref linkend="fig.ExtdFuncHadPhys_2" /> |
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| 259 | for the cross-section aspects, |
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| 260 | <xref linkend="fig.ExtdFuncHadPhys_3" /> |
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| 261 | for the final state production aspects, and figure |
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| 262 | <xref linkend="fig.ExtdFuncHadPhys_4" /> |
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| 263 | for the isotope production aspects. |
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| 264 | |
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| 265 | <figure id="fig.ExtdFuncHadPhys_2"> |
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| 266 | <title> |
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| 267 | Level 2 implementation framework of the hadronic category of Geant4; |
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| 268 | cross-section aspect. |
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| 269 | </title> |
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| 270 | <mediaobject> |
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| 271 | <imageobject role="fo"> |
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[921] | 272 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level2_1.jpg" |
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[1208] | 273 | format="JPG" contentwidth="10.0cm" align="center" /> |
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[904] | 274 | </imageobject> |
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| 275 | <imageobject role="html"> |
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[921] | 276 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level2_1.jpg" |
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[1208] | 277 | format="JPG" contentwidth="120%" align="center" /> |
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[904] | 278 | </imageobject> |
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| 279 | </mediaobject> |
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| 280 | </figure> |
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| 281 | |
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| 282 | <figure id="fig.ExtdFuncHadPhys_3"> |
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| 283 | <title> |
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| 284 | Level 2 implementation framework of the hadronic category of Geant4; |
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| 285 | final state production aspect. |
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| 286 | </title> |
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| 287 | <mediaobject> |
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| 288 | <imageobject role="fo"> |
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[921] | 289 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level2_2.jpg" |
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[1208] | 290 | format="JPG" contentwidth="10.0cm" align="center" /> |
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[904] | 291 | </imageobject> |
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| 292 | <imageobject role="html"> |
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[921] | 293 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level2_2.jpg" |
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[1208] | 294 | format="JPG" contentwidth="120%" align="center" /> |
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[904] | 295 | </imageobject> |
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| 296 | </mediaobject> |
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| 297 | </figure> |
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| 298 | |
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| 299 | <figure id="fig.ExtdFuncHadPhys_4"> |
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| 300 | <title> |
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| 301 | Level 2 implementation framework of the hadronic category of Geant4; |
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| 302 | isotope production aspect |
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| 303 | </title> |
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| 304 | <mediaobject> |
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| 305 | <imageobject role="fo"> |
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[921] | 306 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level2_3.jpg" |
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[1208] | 307 | format="JPG" contentwidth="10.0cm" align="center" /> |
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[904] | 308 | </imageobject> |
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| 309 | <imageobject role="html"> |
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[921] | 310 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level2_3.jpg" |
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[1208] | 311 | format="JPG" contentwidth="120%" align="center" /> |
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[904] | 312 | </imageobject> |
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| 313 | </mediaobject> |
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| 314 | </figure> |
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| 315 | </para> |
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| 316 | |
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| 317 | <para> |
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| 318 | The three parts are integrated in the <literal>G4Hadronic-Process</literal> |
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| 319 | class, that serves as base-class for all hadronic processes of particles in flight. |
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| 320 | </para> |
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| 321 | |
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| 322 | |
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| 323 | <!-- ******* Bridgehead ******* --> |
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| 324 | <bridgehead renderas='sect4'> |
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| 325 | Cross-sections |
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| 326 | </bridgehead> |
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| 327 | |
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| 328 | <para> |
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| 329 | Each hadronic process is derived from <literal>G4Hadronic-Process}</literal>, |
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| 330 | which holds a list of ``cross section data sets''. |
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| 331 | The term ``data set'' is |
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| 332 | representing an object that encapsulates methods and data for calculating |
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| 333 | total cross sections for a given process in a certain range of validity. |
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| 334 | The implementations may take any form. It can be a simple equation as well as |
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| 335 | sophisticated parameterisations, or evaluated data. |
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| 336 | All cross section data set classes are derived from the abstract class |
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| 337 | <literal>G4VCrossSection-DataSet}</literal>, which declares methods that allow |
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| 338 | the process inquire, about the applicability of an individual data-set through |
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| 339 | <literal>IsApplicable(const G4DynamicParticle*, const G4Element*)</literal>, |
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| 340 | and to delegate the calculation of the actual cross-section value through |
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| 341 | <literal>GetCrossSection(const G4DynamicParticle*, const G4Element*)</literal>. |
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| 342 | </para> |
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| 343 | |
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| 344 | <!-- ******* Bridgehead ******* --> |
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| 345 | <bridgehead renderas='sect4'> |
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| 346 | Final state production |
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| 347 | </bridgehead> |
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| 348 | |
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| 349 | <para> |
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| 350 | The <literal>G4HadronicInteraction</literal> base class is provided for final state |
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| 351 | generation. It declares a minimal interface of only one pure virtual method: |
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| 352 | <literal>G4VParticleChange* ApplyYourself(const G4Track &, G4Nucleus &)}. |
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| 353 | </literal> |
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| 354 | |
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| 355 | <literal>G4HadronicProcess</literal> provides a registry for final state |
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| 356 | production models inheriting from <literal>G4Hadronic-Interaction</literal>. |
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| 357 | Again, final state production model is meant in very general terms. This can |
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| 358 | be an implementation of a quark gluon string model |
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| 359 | <citation><xref linkend="biblio.QGSM" endterm="biblio.QGSM.abbrev"/></citation>, |
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| 360 | a sampling code for ENDF/B data formats |
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| 361 | <citation><xref linkend="biblio.ENDFForm" endterm="biblio.ENDFForm.abbrev"/></citation>, |
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| 362 | or a parametrisation describing only |
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| 363 | neutron elastic scattering off Silicon up to 300~MeV. |
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| 364 | </para> |
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| 365 | |
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| 366 | <!-- ******* Bridgehead ******* --> |
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| 367 | <bridgehead renderas='sect4'> |
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| 368 | Isotope production |
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| 369 | </bridgehead> |
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| 370 | |
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| 371 | <para> |
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| 372 | For isotope production, a base class (<literal>G4VIsotope-Production</literal>) |
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| 373 | is provided. It declares a method |
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| 374 | <literal>G4IsoResult * GetIsotope(const G4Track &, const G4Nucleus &)</literal> |
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| 375 | that calculates and returns the isotope production information. Any concrete |
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| 376 | isotope production model will inherit from this class, and implement the |
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| 377 | method. Again, the modeling possibilities are not limited, and the |
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| 378 | implementation of concrete production models is not restricted in any way. |
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| 379 | By convention, the <literal>GetIsotope</literal> method returns NULL, if the model |
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| 380 | is not applicable for the current projectile target combination. |
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| 381 | </para> |
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| 382 | |
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| 383 | <!-- ******* Bridgehead ******* --> |
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| 384 | <bridgehead renderas='sect3'> |
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| 385 | Framework functionality: |
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| 386 | </bridgehead> |
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| 387 | |
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| 388 | <para> |
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| 389 | </para> |
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| 390 | |
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| 391 | <!-- ******* Bridgehead ******* --> |
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| 392 | <bridgehead renderas='sect4'> |
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| 393 | Cross Sections |
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| 394 | </bridgehead> |
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| 395 | |
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| 396 | <para> |
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| 397 | <literal>G4HadronicProcess</literal> provides registering possibilities |
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| 398 | for data sets. A default is provided covering all possible |
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| 399 | conditions to some approximation. The process stores and retrieves |
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| 400 | the data sets through a data store that acts like a FILO stack |
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| 401 | (a Chain of Responsibility with a |
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| 402 | First In Last Out decision strategy). This allows the user to map out |
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| 403 | the entire parameter space by overlaying cross section data sets to optimise |
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| 404 | the overall result. Examples are the cross sections for low energy neutron |
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| 405 | transport. If these are registered last by the user, they will be used |
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| 406 | whenever low energy neutrons are encountered. In all other conditions the |
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| 407 | system falls back on the default, or data sets with earlier registration dates. |
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| 408 | The fact that the registration is done through abstract base classes with no |
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| 409 | side-effects allows the user to implement and use his own cross sections. |
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| 410 | Examples are special reaction cross sections of |
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| 411 | κ<superscript>0</superscript>-nuclear interactions |
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| 412 | that might be used for ε/ε' analysis at LHC to control the |
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| 413 | systematic error. |
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| 414 | </para> |
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| 415 | |
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| 416 | <!-- ******* Bridgehead ******* --> |
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| 417 | <bridgehead renderas='sect4'> |
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| 418 | Final state production |
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| 419 | </bridgehead> |
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| 420 | |
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| 421 | <para> |
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| 422 | The <literal>G4HadronicProcess</literal> class provides a |
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| 423 | registration service for classes deriving from |
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| 424 | <literal>G4Hadronic-Interaction</literal>, and delegates final state |
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| 425 | production to the applicable model. |
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| 426 | <literal>G4Hadronic-Interaction</literal>provides the functionality needed |
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| 427 | to define and enforce the applicability of a particular model. |
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| 428 | Models inheriting from <literal>G4Hadronic-Interaction</literal> |
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| 429 | can be restricted in applicability in projectile |
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| 430 | type and energy, and can be activated/deactivated for individual materials and |
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| 431 | elements. This allows a user to use final state production models in |
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| 432 | arbitrary combinations, and to write his own models for |
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| 433 | final state production. The design is a variant of a Chain of Responsibility. |
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| 434 | An example would be the likely CMS scenario - the combination of low energy |
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| 435 | neutron transport with a quantum molecular dynamics |
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| 436 | <citation><xref linkend="biblio.QMD" endterm="biblio.QMD.abbrev"/></citation>, |
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| 437 | invariant phase space decay |
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| 438 | <citation><xref linkend="biblio.CHIPS" endterm="biblio.CHIPS.abbrev"/></citation>, |
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| 439 | and fast parametrised models for calorimeter materials, with user defined |
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| 440 | modeling of interactions of spallation nucleons with the most abundant |
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| 441 | tracker and calorimeter materials. |
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| 442 | </para> |
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| 443 | |
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| 444 | <!-- ******* Bridgehead ******* --> |
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| 445 | <bridgehead renderas='sect4'> |
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| 446 | Isotope production |
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| 447 | </bridgehead> |
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| 448 | |
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| 449 | <para> |
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| 450 | The <literal>G4HadronicProcess</literal> by default calculates the isotope production |
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| 451 | information from the final state given by the transport model. In addition, it |
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| 452 | provides a registering mechanism for isotope production models that run in |
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| 453 | parasitic mode to the transport models and inherit from |
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| 454 | <literal>G4VIsotope-Production</literal>. The registering mechanism behaves like a FILO |
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| 455 | stack, again based on Chain of Responsibility. The models will be asked for |
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| 456 | isotope production information in inverse order of registration. The first |
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| 457 | model that returns a non-NULL value will be applied. In addition, the |
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| 458 | <literal>G4Hadronic-Process</literal> provides the basic infrastructure for accessing and |
---|
| 459 | steering of isotope-production information. It allows to enable and disable |
---|
| 460 | the calculation of isotope production information globally, or for individual |
---|
| 461 | processes, and to retrieve the isotope production information through the |
---|
| 462 | <literal>G4IsoParticleChange * GetIsotopeProductionInfo()}</literal> |
---|
| 463 | method at the end of each step. The <literal>G4HadronicProcess</literal> is a finite state |
---|
| 464 | machine that will ensure the <literal>GetIsotope-ProductionInfo</literal> returns a |
---|
| 465 | non-zero value only at the first call after isotope production occurred. An |
---|
| 466 | example of the use of this functionality is the study of activation of a |
---|
| 467 | Germanium detector in a high precision, low background experiment. |
---|
| 468 | </para> |
---|
| 469 | |
---|
| 470 | </sect2> |
---|
| 471 | |
---|
| 472 | |
---|
| 473 | <!-- ******************* Section (Level#2) ****************** --> |
---|
| 474 | <sect2 id="sect.ExtdFuncHadPhys.L3F_ThrtMdl"> |
---|
| 475 | <title> |
---|
| 476 | Level 3 Framework - Theoretical Models |
---|
| 477 | </title> |
---|
| 478 | |
---|
| 479 | <para> |
---|
| 480 | <figure id="fig.ExtdFuncHadPhys_5"> |
---|
| 481 | <title> |
---|
| 482 | Level 3 implementation framework of the hadronic category of Geant4; |
---|
| 483 | theoretical model aspect. |
---|
| 484 | </title> |
---|
| 485 | <mediaobject> |
---|
| 486 | <imageobject role="fo"> |
---|
[921] | 487 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level3_1.jpg" |
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[1208] | 488 | format="JPG" contentwidth="10.0cm" align="center" /> |
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[904] | 489 | </imageobject> |
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| 490 | <imageobject role="html"> |
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[921] | 491 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level3_1.jpg" |
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[1208] | 492 | format="JPG" contentwidth="120%" align="center" /> |
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[904] | 493 | </imageobject> |
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| 494 | </mediaobject> |
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| 495 | </figure> |
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| 496 | |
---|
| 497 | Geant4 provides at present one implementation framework for theory |
---|
| 498 | driven models. The main use-case is that of a user wishing to use theoretical |
---|
| 499 | models in general, and to use various intra-nuclear transport or pre-compound |
---|
| 500 | models together with models simulating the initial interactions at very high |
---|
| 501 | energies. |
---|
| 502 | </para> |
---|
| 503 | |
---|
| 504 | <!-- ******* Bridgehead ******* --> |
---|
| 505 | <bridgehead renderas='sect4'> |
---|
| 506 | Requirements |
---|
| 507 | </bridgehead> |
---|
| 508 | |
---|
| 509 | <para> |
---|
| 510 | <orderedlist spacing="compact"> |
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| 511 | <listitem><para> |
---|
| 512 | Allow to use or adapt any string-parton or parton transport |
---|
| 513 | <citation><xref linkend="biblio.VNI" endterm="biblio.VNI.abbrev"/></citation>, |
---|
| 514 | </para></listitem> |
---|
| 515 | <listitem><para> |
---|
| 516 | Allow to adapt event generators, ex. |
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| 517 | <citation><xref linkend="biblio.PYTHIA7" endterm="biblio.PYTHIA7.abbrev"/></citation>, |
---|
| 518 | state production in shower simulation. |
---|
| 519 | </para></listitem> |
---|
| 520 | <listitem><para> |
---|
| 521 | Allow for combination of the above with any intra-nuclear transport (INT). |
---|
| 522 | </para></listitem> |
---|
| 523 | <listitem><para> |
---|
| 524 | Allow stand-alone use of intra-nuclear transport. |
---|
| 525 | </para></listitem> |
---|
| 526 | <listitem><para> |
---|
| 527 | Allow for combination of the above with any pre-compound model. |
---|
| 528 | </para></listitem> |
---|
| 529 | <listitem><para> |
---|
| 530 | Allow stand-alone use of any pre-compound model. |
---|
| 531 | </para></listitem> |
---|
| 532 | <listitem><para> |
---|
| 533 | Allow for use of any evaporation code. |
---|
| 534 | </para></listitem> |
---|
| 535 | <listitem><para> |
---|
| 536 | Allow for seamless integration of user defined components for any of the above. |
---|
| 537 | </para></listitem> |
---|
| 538 | </orderedlist> |
---|
| 539 | </para> |
---|
| 540 | |
---|
| 541 | <!-- ******* Bridgehead ******* --> |
---|
| 542 | <bridgehead renderas='sect4'> |
---|
| 543 | Design and interfaces |
---|
| 544 | </bridgehead> |
---|
| 545 | |
---|
| 546 | <para> |
---|
| 547 | To provide the above flexibility, the following abstract base classes have been |
---|
| 548 | implemented: |
---|
| 549 | |
---|
| 550 | <itemizedlist spacing="compact"> |
---|
| 551 | <listitem><para> |
---|
| 552 | <literal>G4VHighEnergyGenerator</literal> |
---|
| 553 | </para></listitem> |
---|
| 554 | <listitem><para> |
---|
| 555 | <literal>G4VIntranuclearTransportModel</literal> |
---|
| 556 | </para></listitem> |
---|
| 557 | <listitem><para> |
---|
| 558 | <literal>G4VPreCompoundModel</literal> |
---|
| 559 | </para></listitem> |
---|
| 560 | <listitem><para> |
---|
| 561 | <literal>G4VExcitationHandler</literal> |
---|
| 562 | </para></listitem> |
---|
| 563 | </itemizedlist> |
---|
| 564 | </para> |
---|
| 565 | |
---|
| 566 | <para> |
---|
| 567 | In addition, the class <literal>G4TheoFS-Generator</literal> is provided to orchestrate |
---|
| 568 | interactions between these classes. The class diagram is shown in |
---|
| 569 | <xref linkend="fig.ExtdFuncHadPhys_5" />. |
---|
| 570 | </para> |
---|
| 571 | |
---|
| 572 | <para> |
---|
| 573 | <literal>G4VHighEnergy-Generator</literal> serves as base class for parton transport or |
---|
| 574 | parton string models, and for Adapters to event generators. This class |
---|
| 575 | declares two methods, <literal>Scatter</literal>, and |
---|
| 576 | <literal>GetWoundedNucleus</literal>. |
---|
| 577 | </para> |
---|
| 578 | |
---|
| 579 | <para> |
---|
| 580 | The base class for INT inherits from <literal>G4Hadronic-Interaction</literal>, |
---|
| 581 | making any concrete implementation usable as a stand-alone model. In doing so, it |
---|
| 582 | re-declares the <literal>ApplyYourself</literal> interface of |
---|
| 583 | <literal>G4Hadronic-Interaction</literal>, |
---|
| 584 | and adds a second interface, <literal>Propagate</literal>, for further propagation |
---|
| 585 | after high energy interactions. <literal>Propagate</literal> takes as arguments a |
---|
| 586 | three-dimensional model of a wounded nucleus, and a set of secondaries with |
---|
| 587 | energies and positions. |
---|
| 588 | </para> |
---|
| 589 | |
---|
| 590 | <para> |
---|
| 591 | The base class for pre-equilibrium decay models, <literal>G4VPre-CompoundModel</literal>, |
---|
| 592 | inherits from <literal>G4Hadronic-Interaction</literal>, again making any concrete |
---|
| 593 | implementation usable as stand-alone model. It adds a pure virtual |
---|
| 594 | <literal>DeExcite</literal> method for further evolution of the system when |
---|
| 595 | intra-nuclear transport assumptions break down. |
---|
| 596 | <literal>DeExcite</literal> takes a <literal>G4Fragment</literal>, |
---|
| 597 | the Geant4 representation of an excited nucleus, as argument. |
---|
| 598 | </para> |
---|
| 599 | |
---|
| 600 | <para> |
---|
| 601 | The base class for evaporation phases, <literal>G4VExcitation-Handler</literal>, |
---|
| 602 | declares an abstract method, <literal>BreakItUP()</literal>, for compound decay. |
---|
| 603 | </para> |
---|
| 604 | |
---|
| 605 | |
---|
| 606 | <!-- ******* Bridgehead ******* --> |
---|
| 607 | <bridgehead renderas='sect4'> |
---|
| 608 | Framework functionality |
---|
| 609 | </bridgehead> |
---|
| 610 | |
---|
| 611 | <para> |
---|
| 612 | The <literal>G4TheoFSGenerator</literal> class inherits from |
---|
| 613 | <literal>G4Hadronic-Interaction</literal>, |
---|
| 614 | and hence can be registered as a model for final state production with a |
---|
| 615 | hadronic process. It allows a concrete implementation of |
---|
| 616 | <literal>G4VIntranuclear-TransportModel</literal> and |
---|
| 617 | <literal>G4VHighEnergy-Generator</literal> to be |
---|
| 618 | registered, and delegates initial interactions, and intra-nuclear transport |
---|
| 619 | of the corresponding secondaries to the respective classes. The design is a |
---|
| 620 | complex variant of a Strategy. The most spectacular application of this |
---|
| 621 | pattern is the use of parton-string models for string excitation, quark |
---|
| 622 | molecular dynamics for correlated string decay, and quantum molecular dynamics |
---|
| 623 | for transport, a combination which promises to result in a coherent |
---|
| 624 | description of quark gluon plasma in high energy nucleus-nucleus interactions. |
---|
| 625 | </para> |
---|
| 626 | |
---|
| 627 | <para> |
---|
| 628 | The class <literal>G4VIntranuclearTransportModel</literal> provides |
---|
| 629 | registering mechanisms for concrete implementations of |
---|
| 630 | <literal>G4VPreCompound-Model</literal>, and provides |
---|
| 631 | concrete intra-nuclear transports with the possibility of delegating |
---|
| 632 | pre-compound decay to these models. |
---|
| 633 | </para> |
---|
| 634 | |
---|
| 635 | <para> |
---|
| 636 | <literal>G4VPreCompoundModel</literal> provides a registering mechanism |
---|
| 637 | for compound decay through the |
---|
| 638 | <literal>G4VExcitation-Handler</literal> interface, and provides concrete |
---|
| 639 | implementations with the possibility of delegating the decay of a compound |
---|
| 640 | nucleus. |
---|
| 641 | </para> |
---|
| 642 | |
---|
| 643 | <para> |
---|
| 644 | The concrete scenario of <literal>G4TheoFS-Generator</literal> using a |
---|
| 645 | dual parton model |
---|
| 646 | and a classical cascade, which in turn uses an exciton pre-compound model that |
---|
| 647 | delegates to an evaporation phase, would be the following: |
---|
| 648 | <literal>G4TheoFS-Generator</literal> receives the conditions of the interaction; |
---|
| 649 | a primary particle and a nucleus. It asks the dual parton model to perform the |
---|
| 650 | initial scatterings, and return the final state, along with the by then |
---|
| 651 | damaged nucleus. The nucleus records all information on the damage sustained. |
---|
| 652 | <literal>G4TheoFS-Generator</literal> forwards all information to the classical cascade, |
---|
| 653 | that propagates the particles in the already damaged nucleus, keeping track of |
---|
| 654 | interactions, further damage to the nucleus, etc.. Once the cascade assumptions |
---|
| 655 | break down, the cascade will collect the information of the current state of |
---|
| 656 | the hadronic system, like excitation energy and number of excited particles, |
---|
| 657 | and interpret it as a pre-compound system. It delegates the decay of this to |
---|
| 658 | the exciton model. The exciton model will take the information provided, and |
---|
| 659 | calculate |
---|
| 660 | transitions and emissions, until the number of excitons in the system equals |
---|
| 661 | the mean number of excitons expected in equilibrium for the current excitation |
---|
| 662 | energy. Then it hands over to the |
---|
| 663 | evaporation phase. The evaporation phase decays the residual nucleus, and the Chain of |
---|
| 664 | Command rolls back to <literal>G4TheoFS-Generator</literal>, accumulating the |
---|
| 665 | information produced in the various levels of delegation. |
---|
| 666 | </para> |
---|
| 667 | |
---|
| 668 | </sect2> |
---|
| 669 | |
---|
| 670 | <!-- ******************* Section (Level#2) ****************** --> |
---|
| 671 | <sect2 id="sect.ExtdFuncHadPhys.L4F_StgPartIntNuc"> |
---|
| 672 | <title> |
---|
| 673 | Level 4 Frameworks - String Parton Models and Intra-Nuclear Cascade |
---|
| 674 | </title> |
---|
| 675 | |
---|
| 676 | <para> |
---|
| 677 | <figure id="fig.ExtdFuncHadPhys_6"> |
---|
| 678 | <title> |
---|
| 679 | Level 4 implementation framework of the hadronic category of Geant4; |
---|
| 680 | parton string aspect. |
---|
| 681 | </title> |
---|
| 682 | <mediaobject> |
---|
| 683 | <imageobject role="fo"> |
---|
[921] | 684 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level4_1.jpg" |
---|
[1208] | 685 | format="JPG" contentwidth="10.0cm" align="center" /> |
---|
[904] | 686 | </imageobject> |
---|
| 687 | <imageobject role="html"> |
---|
[921] | 688 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level4_1.jpg" |
---|
[1208] | 689 | format="JPG" contentwidth="120%" align="center" /> |
---|
[904] | 690 | </imageobject> |
---|
| 691 | </mediaobject> |
---|
| 692 | </figure> |
---|
| 693 | |
---|
| 694 | <figure id="fig.ExtdFuncHadPhys_7"> |
---|
| 695 | <title> |
---|
| 696 | Level 4 implementation framework of the hadronic category of Geant4; |
---|
| 697 | intra-nuclear transport aspect. |
---|
| 698 | </title> |
---|
| 699 | <mediaobject> |
---|
| 700 | <imageobject role="fo"> |
---|
[921] | 701 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level4_2.jpg" |
---|
[1208] | 702 | format="JPG" contentwidth="10.0cm" align="center" /> |
---|
[904] | 703 | </imageobject> |
---|
| 704 | <imageobject role="html"> |
---|
[921] | 705 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level4_2.jpg" |
---|
[1208] | 706 | format="JPG" contentwidth="120%" align="center" /> |
---|
[904] | 707 | </imageobject> |
---|
| 708 | </mediaobject> |
---|
| 709 | </figure> |
---|
| 710 | </para> |
---|
| 711 | |
---|
| 712 | <para> |
---|
| 713 | The use-cases of this level are related to commonalities and detailed choices |
---|
| 714 | in string-parton models and cascade models. They are use-cases of an expert |
---|
| 715 | user wishing to alter details of a model, or a theoretical physicist, wishing |
---|
| 716 | to study details of a particular model. |
---|
| 717 | </para> |
---|
| 718 | |
---|
| 719 | <!-- ******* Bridgehead ******* --> |
---|
| 720 | <bridgehead renderas='sect4'> |
---|
| 721 | Requirements |
---|
| 722 | </bridgehead> |
---|
| 723 | |
---|
| 724 | <para> |
---|
| 725 | <orderedlist spacing="compact"> |
---|
| 726 | <listitem><para> |
---|
| 727 | Allow to select string decay algorithm |
---|
| 728 | </para></listitem> |
---|
| 729 | <listitem><para> |
---|
| 730 | Allow to select string excitation. |
---|
| 731 | </para></listitem> |
---|
| 732 | <listitem><para> |
---|
| 733 | Allow the selection of concrete implementations of three-dimensional |
---|
| 734 | models of the nucleus |
---|
| 735 | </para></listitem> |
---|
| 736 | <listitem><para> |
---|
| 737 | Allow the selection of concrete implementations of final state and |
---|
| 738 | cross sections in intra-nuclear scattering. |
---|
| 739 | </para></listitem> |
---|
| 740 | </orderedlist> |
---|
| 741 | </para> |
---|
| 742 | |
---|
| 743 | <!-- ******* Bridgehead ******* --> |
---|
| 744 | <bridgehead renderas='sect4'> |
---|
| 745 | Design and interfaces |
---|
| 746 | </bridgehead> |
---|
| 747 | |
---|
| 748 | <para> |
---|
| 749 | To fulfil the requirements on string models, two abstract classes are provided, |
---|
| 750 | the <literal>G4VParton-StringModel</literal> and the |
---|
| 751 | <literal>G4VString-Fragmentation</literal>. |
---|
| 752 | The base class for parton string models, <literal>G4VParton-StringModel</literal>, |
---|
| 753 | declares the <literal>GetStrings()</literal> pure virtual method. |
---|
| 754 | <literal>G4VString-Fragmentation</literal>, the pure abstract base class for string |
---|
| 755 | fragmentation, declares the interface for string fragmentation. |
---|
| 756 | </para> |
---|
| 757 | |
---|
| 758 | <para> |
---|
| 759 | To fulfill the requirements on intra-nuclear transport, two abstract classes |
---|
| 760 | are provided, <literal>G4V3DNucleus</literal>, and <literal>G4VScatterer</literal>. |
---|
| 761 | At this point in time, the usage of these intra-nuclear transport related classes |
---|
| 762 | by concrete codes is not enforced by designs, as the details of the |
---|
| 763 | cascade loop are still model dependent, and more experience has to be gathered to achieve |
---|
| 764 | standardisation. It is within the responsibility of the implementers of concrete |
---|
| 765 | intra-nuclear transport |
---|
| 766 | codes to use the abstract interfaces as defined in these classes. |
---|
| 767 | </para> |
---|
| 768 | |
---|
| 769 | <para> |
---|
| 770 | The class diagram is shown in |
---|
| 771 | <xref linkend="fig.ExtdFuncHadPhys_6" /> |
---|
| 772 | for the string parton model aspects, and in |
---|
| 773 | <xref linkend="fig.ExtdFuncHadPhys_7" /> |
---|
| 774 | for the intra-nuclear transport. |
---|
| 775 | </para> |
---|
| 776 | |
---|
| 777 | |
---|
| 778 | <!-- ******* Bridgehead ******* --> |
---|
| 779 | <bridgehead renderas='sect4'> |
---|
| 780 | Framework functionality |
---|
| 781 | </bridgehead> |
---|
| 782 | |
---|
| 783 | <para> |
---|
| 784 | Again variants of Strategy, Bridge and Chain of Responsibility are used. |
---|
| 785 | <literal>G4VParton-StringModel</literal> implements the initialisation of a |
---|
| 786 | three-dimensional model of a nucleus, and the logic of scattering. It |
---|
| 787 | delegates secondary production to string fragmentation through a |
---|
| 788 | <literal>G4VString-Fragmentation</literal> pointer. It provides a registering service for |
---|
| 789 | the concrete string fragmentation, and delegates the string excitation to |
---|
| 790 | derived classes. Selection of string excitation is through selection of |
---|
| 791 | derived class. Selection of string fragmentation is through registration. |
---|
| 792 | </para> |
---|
| 793 | |
---|
| 794 | </sect2> |
---|
| 795 | |
---|
| 796 | <!-- ******************* Section (Level#2) ****************** --> |
---|
| 797 | <sect2 id="sect.ExtdFuncHadPhys.L5F_StrgDeExc"> |
---|
| 798 | <title> |
---|
| 799 | Level 5 Framework - String De-excitation} |
---|
| 800 | </title> |
---|
| 801 | |
---|
| 802 | <para> |
---|
| 803 | <figure id="fig.ExtdFuncHadPhys_8"> |
---|
| 804 | <title> |
---|
| 805 | Level 5 implementation framework of the hadronic category of Geant4; |
---|
| 806 | string fragmentation aspect. |
---|
| 807 | </title> |
---|
| 808 | <mediaobject> |
---|
| 809 | <imageobject role="fo"> |
---|
[921] | 810 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level5_1.jpg" |
---|
[1208] | 811 | format="JPG" contentwidth="10.0cm" align="center" /> |
---|
[904] | 812 | </imageobject> |
---|
| 813 | <imageobject role="html"> |
---|
[921] | 814 | <imagedata fileref="./AllResources/GuideToExtendFunctionality/HadronicPhysics/Level5_1.jpg" |
---|
[1208] | 815 | format="JPG" contentwidth="120%" align="center" /> |
---|
[904] | 816 | </imageobject> |
---|
| 817 | </mediaobject> |
---|
| 818 | </figure> |
---|
| 819 | </para> |
---|
| 820 | |
---|
| 821 | <para> |
---|
| 822 | The use-case of this level is that of a user or theoretical physicist wishing |
---|
| 823 | to understand the systematic effects involved in combining various |
---|
| 824 | fragmentation functions with individual types of string fragmentation. Note |
---|
| 825 | that this framework level is meeting the current state of the art, making |
---|
| 826 | extensions and changes of interfaces in subsequent releases likely. |
---|
| 827 | </para> |
---|
| 828 | |
---|
| 829 | <!-- ******* Bridgehead ******* --> |
---|
| 830 | <bridgehead renderas='sect4'> |
---|
| 831 | Requirements |
---|
| 832 | </bridgehead> |
---|
| 833 | |
---|
| 834 | <para> |
---|
| 835 | <orderedlist spacing="compact"> |
---|
| 836 | <listitem><para> |
---|
| 837 | Allow the selection of fragmentation function. |
---|
| 838 | </para></listitem> |
---|
| 839 | </orderedlist> |
---|
| 840 | </para> |
---|
| 841 | |
---|
| 842 | <!-- ******* Bridgehead ******* --> |
---|
| 843 | <bridgehead renderas='sect4'> |
---|
| 844 | Design and interfaces |
---|
| 845 | </bridgehead> |
---|
| 846 | |
---|
| 847 | <para> |
---|
| 848 | A base class for fragmentation functions, |
---|
| 849 | <literal>G4VFragmentation-Function}</literal>, is |
---|
| 850 | provided. It declares the <literal>GetLightConeZ()</literal> interface. |
---|
| 851 | </para> |
---|
| 852 | |
---|
| 853 | <!-- ******* Bridgehead ******* --> |
---|
| 854 | <bridgehead renderas='sect4'> |
---|
| 855 | Framework functionality |
---|
| 856 | </bridgehead> |
---|
| 857 | |
---|
| 858 | <para> |
---|
| 859 | The design is a basic Strategy. The class diagram is shown in |
---|
| 860 | <xref linkend="fig.ExtdFuncHadPhys_8" />. |
---|
| 861 | At this point in time, the usage of the |
---|
| 862 | <literal>G4VFragmentation-Function</literal> is not enforced by design, |
---|
| 863 | but made available from the |
---|
| 864 | <literal>G4VString-Fragmentation</literal> to an implementer of a concrete string |
---|
| 865 | decay. <literal>G4VString-Fragmentation</literal> provides a registering |
---|
| 866 | mechanism for the |
---|
| 867 | concrete fragmentation function. It delegates the calculation of |
---|
| 868 | z<subscript>f</subscript> of the |
---|
| 869 | hadron to split of the string to the concrete implementation. Standardisation |
---|
| 870 | in this area is expected. |
---|
| 871 | </para> |
---|
| 872 | |
---|
| 873 | </sect2> |
---|
[1208] | 874 | </sect1> |
---|