| 1 | $Id: README,v 1.4 2006/05/15 14:42:42 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 | TestEm13 |
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| 9 | -------- |
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| 10 | |
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| 11 | How to compute cross sections from the tramsmition coefficient |
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| 12 | ( see below, item Physics). |
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| 13 | |
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| 14 | 1- GEOMETRY DEFINITION |
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| 15 | |
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| 16 | It is a single box representing a layer of finite thickness of |
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| 17 | homogeneous material. |
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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 (1 cm 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 'articicial' constraints on the step size, the |
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| 30 | multiple scattering is not instanciated, and there is no limitation from |
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| 31 | the maximum energy lost per step. |
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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 step of the incident paticle. |
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| 44 | Either the particle has interacted or is transmitted through the layer. |
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| 45 | The cross section, also called absorption coefficient, is computed from |
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| 46 | the rate of unaltered transmitted incident particles. |
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| 47 | |
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| 48 | The result is compared with the 'input' data, i.e. with the cross |
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| 49 | sections stored in the PhysicsTables and used by Geant4. |
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| 50 | |
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| 51 | A set of macros defining various run conditions are provided. |
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| 52 | The processes are actived/inactived in order to survey the processes |
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| 53 | individually. |
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| 54 | |
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| 55 | |
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| 56 | 6- VISUALIZATION |
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| 57 | |
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| 58 | The Visualization Manager is set in the main(). |
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| 59 | The initialisation of the drawing is done via the commands |
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| 60 | /vis/... in the macro vis.mac. To get visualisation: |
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| 61 | > /control/execute vis.mac |
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| 62 | |
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| 63 | The detector has a default view which is a longitudinal view of the |
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| 64 | box. |
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| 65 | |
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| 66 | The tracks are drawn at the end of event, and erased at the end of run. |
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| 67 | |
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| 68 | 7- HOW TO START ? |
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| 69 | |
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| 70 | compile and link to generate an executable |
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| 71 | % cd geant4/examples/extended/electromagnetic/TestEm13 |
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| 72 | % gmake |
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| 73 | |
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| 74 | execute TestEm13 in 'batch' mode from macro files : |
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| 75 | % TestEm13 compt.mac |
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| 76 | |
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| 77 | execute TestEm13 in 'interactive mode' with visualization : |
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| 78 | % TestEm13 |
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| 79 | Idle> control/execute vis.mac |
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| 80 | .... |
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| 81 | Idle> type your commands |
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| 82 | .... |
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| 83 | Idle> exit |
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| 84 | |
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