| 1 | $Id: README,v 1.9 2010/04/02 13:22:02 maire Exp $ |
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| 2 | ------------------------------------------------------------------- |
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| 3 | |
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| 4 | ========================================================= |
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| 5 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
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| 6 | ========================================================= |
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| 7 | |
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| 8 | TestEm14 |
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| 9 | -------- |
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| 10 | |
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| 11 | How to compute cross sections from the direct evaluation of the mean |
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| 12 | free path ( see below, item Physics). |
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| 13 | How to plot final state of a process. |
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| 14 | |
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| 15 | 1- GEOMETRY DEFINITION |
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| 16 | |
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| 17 | It is a single box representing a 'semi infinite' homogeneous medium. |
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| 18 | Two parameters define the geometry : |
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| 19 | - the material of the box, |
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| 20 | - the (full) size of the box. |
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| 21 | |
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| 22 | The default geometry (100 m of water) is constructed in |
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| 23 | DetectorConstruction, but the above parameters can be changed |
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| 24 | interactively via the commands defined in DetectorMessenger. |
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| 25 | |
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| 26 | 2- PHYSICS LIST |
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| 27 | |
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| 28 | The physics list contains the standard electromagnetic processes. |
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| 29 | In order not to introduce 'artificial' constraints on the step size, the |
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| 30 | multiple scattering is not instanciated, and all processes are |
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| 31 | registered as discrete : there is no continuous energy loss. |
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| 32 | |
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| 33 | 3- AN EVENT : THE PRIMARY GENERATOR |
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| 34 | |
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| 35 | The primary kinematic consists of a single particle starting at the edge |
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| 36 | of the box. The type of the particle and its energy are set in |
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| 37 | PrimaryGeneratorAction (1 MeV gamma), and can be changed via the G4 |
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| 38 | build-in commands of ParticleGun class (see the macros provided with |
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| 39 | this example). |
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| 40 | |
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| 41 | 4- PHYSICS |
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| 42 | |
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| 43 | An event is killed at the first interaction of the incident paticle. |
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| 44 | The absorption length, also called mean free path, is computed as |
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| 45 | the mean value of the track length of the incident particle. |
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| 46 | This is why the medium must be 'infinite' : to be sure that interaction |
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| 47 | occurs at any events. |
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| 48 | |
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| 49 | The result is compared with the 'input' data, i.e. with the cross |
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| 50 | sections stored in the PhysicsTables and used by Geant4. |
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| 51 | |
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| 52 | The energy spectrum and the angular distribution of the scattered |
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| 53 | particle (if any) and of the created secondaries are plotted (see |
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| 54 | SteppingAction). |
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| 55 | |
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| 56 | A set of macros defining various run conditions are provided. |
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| 57 | The processes are actived/inactived in order to survey the processes |
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| 58 | individually. |
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| 59 | |
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| 60 | 5- HISTOGRAMS |
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| 61 | |
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| 62 | The test contains 6 built-in 1D histograms, which are managed by the |
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| 63 | HistoManager class and its Messenger. The histos can be individually |
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| 64 | activated with the command : |
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| 65 | /testem/histo/setHisto id nbBins valMin valMax unit |
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| 66 | where unit is the desired unit for the histo (MeV or keV, etc..) |
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| 67 | (see the macros xxxx.mac). |
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| 68 | |
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| 69 | 1 "scattered primary particle: energy spectrum" |
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| 70 | 2 "scattered primary particle: costheta distribution" |
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| 71 | 3 "charged secondaries: energy spectrum" |
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| 72 | 4 "charged secondaries: costheta distribution" |
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| 73 | 5 "neutral secondaries: energy spectrum" |
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| 74 | 6 "neutral secondaries: costheta distribution" |
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| 75 | |
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| 76 | See below the note on histogram tools. |
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| 77 | |
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| 78 | One can control the name and the type of the histograms file with |
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| 79 | the commands: |
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| 80 | /testem/histo/setFileName name (default testem14) |
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| 81 | /testem/histo/setFileType name (default root) |
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| 82 | |
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| 83 | It is also possible to print selected histograms on an ascii file: |
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| 84 | /testem/histo/printHisto id |
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| 85 | All selected histos will be written on a file name.ascii |
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| 86 | (default testem14) |
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| 87 | |
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| 88 | Note that, by default, histograms are disabled. To activate them, |
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| 89 | uncomment the flag G4ANALYSIS_USE in GNUmakefile. |
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| 90 | |
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| 91 | 6- VISUALIZATION |
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| 92 | |
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| 93 | The Visualization Manager is set in the main(). |
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| 94 | The initialisation of the drawing is done via the commands |
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| 95 | /vis/... in the macro vis.mac. To get visualisation: |
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| 96 | > /control/execute vis.mac |
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| 97 | |
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| 98 | The detector has a default view which is a longitudinal view of the |
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| 99 | box. |
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| 100 | |
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| 101 | The tracks are drawn at the end of event, and erased at the end of run. |
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| 102 | |
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| 103 | 7- HOW TO START ? |
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| 104 | |
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| 105 | compile and link to generate an executable |
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| 106 | % cd geant4/examples/extended/electromagnetic/TestEm14 |
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| 107 | % gmake |
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| 108 | |
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| 109 | execute TestEm14 in 'batch' mode from macro files : |
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| 110 | % TestEm14 compt.mac |
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| 111 | |
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| 112 | execute TestEm14 in 'interactive mode' with visualization : |
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| 113 | % TestEm14 |
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| 114 | Idle> control/execute vis.mac |
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| 115 | .... |
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| 116 | Idle> type your commands |
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| 117 | .... |
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| 118 | Idle> exit |
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| 119 | |
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| 120 | |
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| 121 | 8- USING HISTOGRAMS |
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| 122 | |
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| 123 | By default the histograms are not activated. To activate histograms |
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| 124 | the environment variable G4ANALYSIS_USE should be defined. For instance |
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| 125 | uncomment the flag G4ANALYSIS_USE in GNUmakefile. |
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| 126 | |
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| 127 | Before compilation of the example it is optimal to clean up old files: |
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| 128 | gmake histclean |
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| 129 | gmake |
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| 130 | |
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| 131 | To use histograms, at least one of the AIDA implementations should be |
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| 132 | available. See InstallAida.txt |
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| 133 | |
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