| 1 | $Id: README,v 1.16 2005/11/22 16:11:04 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 | ExampleN03
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| 9 | ----------
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| 10 |
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| 11 | This example simulates a simple Sampling Calorimeter setup.
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| 12 |
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| 13 | 1- GEOMETRY DEFINITION
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| 14 |
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| 15 | The calorimeter is a box made of a given number of layers. A layer
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| 16 | consists of an absorber plate and of a detection gap. The layer is
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| 17 | replicated.
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| 18 |
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| 19 | Six parameters define the calorimeter :
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| 20 | - the material of the absorber,
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| 21 | - the thickness of an absorber plate,
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| 22 | - the material of the detection gap,
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| 23 | - the thickness of a gap,
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| 24 | - the number of layers,
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| 25 | - the transverse size of the calorimeter (the input face is a square).
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| 26 |
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| 27 | In addition a transverse uniform magnetic field can be applied.
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| 28 |
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| 29 | The default geometry is constructed in DetectorConstruction class,
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| 30 | but all of the above parameters can be modified interactively via
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| 31 | the commands defined in the DetectorMessenger class.
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| 32 |
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| 33 |
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| 34 | |<----layer 0---------->|<----layer 1---------->|<----layer 2---------->|
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| 35 | | | | |
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| 36 | ==========================================================================
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| 37 | || | || | || | ||
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| 38 | || | || | || | ||
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| 39 | || absorber | gap || absorber | gap || absorber | gap ||
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| 40 | || | || | || | ||
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| 41 | || | || | || | ||
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| 42 | beam || | || | || | ||
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| 43 | ======> || | || | || | ||
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| 44 | || | || | || | ||
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| 45 | || | || | || | ||
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| 46 | || | || | || | ||
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| 47 | || | || | || | ||
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| 48 | || | || | || | ||
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| 49 | ==========================================================================
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| 50 |
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| 51 | NB. The thickness of the absorber or of the gap can be set to zero
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| 52 | (but not together), and the number of layers to 1. In this case we
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| 53 | have a unique homogeneous block of matter, which looks like
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| 54 | a bubble chamber rather than a calorimeter ...
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| 55 | (see the macro of commands: newgeom.mac)
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| 56 |
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| 57 | 2- AN EVENT : THE PRIMARY GENERATOR
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| 58 |
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| 59 | The primary kinematic consists of a single particle which hits the
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| 60 | calorimeter perpendicular to the input face. The type of the particle
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| 61 | and its energy are set in the PrimaryGeneratorAction class, and can
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| 62 | be changed via the G4 build-in commands of ParticleGun class (see
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| 63 | the macros provided with this example).
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| 64 |
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| 65 | In addition one can choose randomly the impact point of the incident
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| 66 | particle. The corresponding interactive command is built in
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| 67 | PrimaryGeneratorMessenger class (see run2.mac).
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| 68 |
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| 69 | A RUN is a set of events.
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| 70 |
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| 71 |
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| 72 | 3- VISUALIZATION
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| 73 |
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| 74 | The Visualization Manager is set in the main().
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| 75 | The initialisation of the drawing is done via a set of /vis/ commands
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| 76 | in the macro vis.mac. This macro is automatically read from
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| 77 | the main in case of interactive running mode.
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| 78 |
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| 79 | By default, vis.mac opens a DAWNFILE, suitable for viewing in DAWN,
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| 80 | and an OGLX for OpenGl.
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| 81 | You can switch to other graphics systems by commenting out this line
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| 82 | and instead uncommenting one of the other /vis/open statements, such as
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| 83 | HepRepFile or HepRepXML.
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| 84 |
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| 85 | The DAWNFILE, HepRepFile and HepRepXML drivers are always available
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| 86 | (since they require no external libraries), but the OGLIX driver
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| 87 | requires:
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| 88 | 1- the visualisation & interfaces categories have been compiled
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| 89 | with the environment variable G4VIS_BUILD_OPENGLX_DRIVER.
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| 90 | 2- exampleN03.cc has been compiled with G4VIS_USE_OPENGLX.
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| 91 |
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| 92 | The HepRepXML driver outputs a zip file that can be unzipped into
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| 93 | several individual HepRep files, each viewable in WIRED.
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| 94 |
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| 95 | For more information on visualization, including information on how to
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| 96 | install and run DAWN, OpenGL and WIRED, see the visualization tutorials
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| 97 | on the Geant4 Workshop Tutorial CD available at:
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| 98 | http://geant4.slac.stanford.edu/g4cd/Welcome.html
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| 99 |
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| 100 | The detector has a default view which is a longitudinal view of the
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| 101 | calorimeter.
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| 102 |
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| 103 | The tracks are drawn at the end of event, and erased at the end of run.
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| 104 | Optionaly one can choose to draw all particles, only the charged,
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| 105 | or neutral or none. This command is build in EventActionMessenger class.
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| 106 |
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| 107 | Additional visualization tutorial macros are available in the visTutor
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| 108 | subdirectory. They can be tried as:
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| 109 | % $G4BINDIR/exampleN03
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| 110 | idle > /control/execute visTutor/exN03VisX.mac
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| 111 | For details, see comment lines described in the macro files.
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| 112 | These macros are designed to help your understanding the User's Guide.
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| 113 |
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| 114 |
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| 115 | 4- PHYSICS DEMO
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| 116 |
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| 117 | The particle's type and the physic processes which will be available
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| 118 | in this example are set in PhysicsList class.
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| 119 |
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| 120 | In addition the build-in interactive command:
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| 121 | /process/(in)activate processName
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| 122 | allows to activate/inactivate the processes one by one.
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| 123 | Then one can well visualize the processes one by one, especially
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| 124 | in the bubble chamber setup with a transverse magnetic field.
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| 125 | (see run2.mac and newgeom.mac)
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| 126 |
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| 127 | As a homework try to visualize a gamma conversion alone,
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| 128 | or the effect of the multiple scattering.
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| 129 |
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| 130 | 5- RANDOM NUMBERS HANDLING
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| 131 |
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| 132 | CLHEP provides several random number engines. In this example the Ranecu
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| 133 | engine is choosen at beginning of the main (exampleN03.cc).
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| 134 |
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| 135 | By default, G4RunManager does not save the rndm seed.
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| 136 | To do so the user must set in BeginOfRunAction:
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| 137 | G4RunManager::GetRunManager()->SetRandomNumberStore(true);
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| 138 |
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| 139 | Then the rndm seed is systematically saved at beginning of run
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| 140 | (currentRun.rndm) and beginning of event (currentEvent.rndm)
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| 141 | Therefore, in case of abnormal end, the seed of the last event processed
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| 142 | is available in currentEvent.rndm
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| 143 |
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| 144 | Even in case of normal run processing, the user may wish to preserve the
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| 145 | rndm seed of selected events. At any time in the event, put the
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| 146 | following statement:
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| 147 | if (condition) G4RunManager::GetRunManager()->rndmSaveThisEvent();
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| 148 | currentEvent.rndm will be copied to runXXevntYY.rndm
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| 149 | (see ExN03SteppingAction::UserSteppingAction() )
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| 150 |
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| 151 | To restart a run from a given rndm seed, use the UI command :
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| 152 | /random/resetEngineFrom fileName
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| 153 |
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| 154 | The macro rndmSeed.mac shows how to save and reset the random number
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| 155 | seed between runs, from UI commands.
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| 156 |
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| 157 | 6- USER INTERFACES
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| 158 |
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| 159 | The default command interface, called G4UIterminal, is done via
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| 160 | standart cin/G4cout.
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| 161 | On Linux and Sun-cc on can use a smarter command interface G4UItcsh.
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| 162 | It is enough to set the environment variable G4UI_USE_TCSH
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| 163 |
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| 164 | On can use a Motif driven command interface (called G4UIXm) if:
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| 165 | 1- interfaces category has been compiled with G4UI_BUILD_XM_SESSION
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| 166 | 2- exampleN03.cc has been compiled with G4UI_USE_XM.
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| 167 |
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| 168 |
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| 169 | 7- HOW TO START ?
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| 170 |
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| 171 | - compile and link to generate an executable
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| 172 | % cd N03
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| 173 | % gmake
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| 174 |
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| 175 | - execute N03 in 'batch' mode from macro files
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| 176 | % exampleN03 run1.mac
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| 177 |
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| 178 | - execute N03 in 'interactive mode' with visualization
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| 179 | % exampleN03
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| 180 | ....
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| 181 | Idle> ---> type your commands. For instance:
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| 182 | Idle> /run/beamOn
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| 183 | ....
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| 184 | Idle> /run/beamOn 10
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| 185 | ....
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| 186 | Idle> /control/execute newgeom.mac
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| 187 | ....
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| 188 | Idle> exit
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| 189 |
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| 190 |
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| 191 |
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