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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