[807] | 1 | $Id: README,v 1.6 2006/03/31 14:02:13 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 | ExampleN02 |
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| 9 | ---------- |
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| 10 | |
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| 11 | |
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| 12 | This example simulates a simplified fixe target experiment. |
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| 13 | |
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| 14 | 1- GEOMETRY DEFINITION |
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| 15 | |
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| 16 | The setup consists of a target followed by six chambers of increasing |
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| 17 | transverse size. These chambers are located in a region called Tracker |
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| 18 | region. Their shape are boxes, constructed as parametrised volumes |
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| 19 | (ChamberParametrisation class). |
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| 20 | |
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| 21 | The default geometry is constructed in DetectorConstruction class. |
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| 22 | One can change the material of the target and of the chambers |
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| 23 | interactively via the commands defined in the DetectorMessenger class. |
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| 24 | |
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| 25 | In addition a transverse uniform magnetic field can be applied (see |
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| 26 | N02MagneticField and DetectorMessenger classes). |
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| 27 | |
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| 28 | |
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| 29 | 2- PHYSICS LIST |
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| 30 | |
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| 31 | The particle's type and the physic processes which will be available |
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| 32 | in this example are set in PhysicsList class. |
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| 33 | |
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| 34 | In this example, all the so called 'electromagnetic processes' are |
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| 35 | introduced for gamma, charged leptons, and charged hadrons (see the |
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| 36 | method PhysicsList::ConstructEM()). |
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| 37 | |
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| 38 | An important data member of this class is the defaultCutValue which |
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| 39 | defines the production threshold of secondary particles |
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| 40 | (only Ionisation and Bremsstrahlung processes are concerned by this |
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| 41 | CutValue). |
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| 42 | Notice that the CutValue must be given in unit of length, corresponding |
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| 43 | to the stopping range of the particle. It is automatically converted |
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| 44 | in energy for each material, and a table is printed in the method |
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| 45 | PhysicsList::SetCuts() |
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| 46 | |
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| 47 | In addition the build-in interactive command: |
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| 48 | /process/(in)activate processName |
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| 49 | allows to activate/inactivate the processes one by one. |
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| 50 | |
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| 51 | |
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| 52 | 3- RUNS and EVENTS |
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| 53 | |
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| 54 | The primary kinematic consists of a single particle which hits the |
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| 55 | target perpendicular to the input face. The type of the particle |
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| 56 | and its energy are set in the PrimaryGeneratorAction class, and can |
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| 57 | be changed via the G4 build-in commands of ParticleGun class. |
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| 58 | |
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| 59 | A RUN is a set of events. |
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| 60 | |
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| 61 | The user has control: |
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| 62 | -at Begin and End of each run (class RunAction) |
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| 63 | -at Begin and End of each event (class EventAction) |
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| 64 | -at Begin and End of each track (class TrackingAction, not used here) |
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| 65 | -at End of each step (class SteppingAction) |
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| 66 | |
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| 67 | The class SteppingVerbose prints some informations step per step, |
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| 68 | under the control of the command: /tracking/verbose 1 |
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| 69 | It inherits from G4SteppingVerbose, and has been setup here in order |
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| 70 | to illustrate how to extract informations from the G4 kernel during |
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| 71 | the tracking of a particle. |
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| 72 | |
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| 73 | |
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| 74 | 4- USER' LIMITS |
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| 75 | |
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| 76 | We illustrate how to introduce tracking constraints like maximum step |
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| 77 | length, minimum kinetic energy ..etc.., via G4UserLimits class. |
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| 78 | See DetectorConstruction and PhysicsList. |
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| 79 | |
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| 80 | 5- DETECTOR RESPONSE |
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| 81 | |
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| 82 | A HIT is a record, track per track (even step per step), of all the |
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| 83 | informations needed to simulate and analyse the detector response. |
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| 84 | |
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| 85 | In this example the Tracker chambers are considered as the detector. |
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| 86 | Therefore the chambers are declared 'sensitive detectors' (SD) in |
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| 87 | the DetectorConstruction class. |
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| 88 | |
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| 89 | Then, a Hit is defined as a set of 4 informations per step, inside |
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| 90 | the chambers, namely: |
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| 91 | - the track identifier (an integer), |
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| 92 | - the chamber number, |
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| 93 | - the total energy deposit in this step, |
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| 94 | - the position of the deposit. |
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| 95 | |
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| 96 | A given hit is an instance of the class TrackerHit which is created |
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| 97 | during the tracking of a particle, step by step, in the method |
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| 98 | TrackerSD::ProcessHits(). This hit is inserted in a HitsCollection. |
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| 99 | |
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| 100 | The HitsCollection is printed at the end of event (via the method |
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| 101 | TrackerSD::EndOfEvent()), under the control of the command: /hits/verbose 1 |
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| 102 | |
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| 103 | |
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| 104 | 6- VISUALIZATION |
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| 105 | |
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| 106 | The Visualization Manager is set in the main(). |
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| 107 | The initialisation of the drawing is done via a set of /vis/ commands |
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| 108 | in the macro vis.mac. This macro is automatically read from |
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| 109 | the main when running in interactive mode. |
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| 110 | |
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| 111 | The tracks are automatically drawn at the end of event and erased at |
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| 112 | the beginning of the next run. |
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| 113 | |
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| 114 | The visualization (with OpenGL driver) assumes two things: |
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| 115 | 1- the visualisation & interfaces categories have been compiled |
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| 116 | with the environment variable G4VIS_BUILD_OPENGLX_DRIVER. |
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| 117 | 2- exampleN02.cc has been compiled with G4VIS_USE_OPENGLX. |
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| 118 | |
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| 119 | (The same with DAWNFILE instead of OPENGLX) |
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| 120 | |
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| 121 | |
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| 122 | 7- USER INTERFACES |
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| 123 | |
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| 124 | The default command interface, called G4UIterminal, is done via |
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| 125 | standart cin/G4cout. |
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| 126 | On Linux and Sun-cc on can use a smarter command interface G4UItcsh. |
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| 127 | It is enough to set the environment variable G4UI_USE_TCSH before |
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| 128 | compiling exampleN02.cc |
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| 129 | |
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| 130 | |
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| 131 | 8- HOW TO START ? |
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| 132 | |
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| 133 | - compile and link to generate an executable |
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| 134 | % cd N02 |
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| 135 | % gmake |
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| 136 | |
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| 137 | - execute N02 in 'batch' mode from macro files (without visualization) |
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| 138 | % exampleN02 run1.mac |
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| 139 | |
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| 140 | - execute N02 in 'interactive mode' with visualization |
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| 141 | % exampleN02 |
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| 142 | .... |
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| 143 | Idle> type your commands. For instance: |
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| 144 | Idle> /run/beamOn 10 |
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| 145 | .... |
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| 146 | Idle> /control/execute run2.mac |
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| 147 | .... |
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| 148 | Idle> exit |
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| 149 | |
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| 150 | |
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