Gabriele Cosmo
122 lines
4.4 KiB
Plaintext
122 lines
4.4 KiB
Plaintext
-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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TestEm14
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--------
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How to compute cross sections from the direct evaluation of the mean
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free path ( see below, item Physics).
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How to plot final state of a process.
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1- GEOMETRY DEFINITION
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It is a single box representing a 'semi infinite' homogeneous medium.
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Two parameters define the geometry :
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- the material of the box,
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- the (full) size of the box.
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The default geometry (100 m of water) is constructed in
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DetectorConstruction, but the above parameters can be changed
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interactively via the commands defined in DetectorMessenger.
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2- PHYSICS LIST
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The physics list contains the standard electromagnetic processes.
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In order not to introduce 'artificial' constraints on the step size, the
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multiple scattering is not instanciated, and all processes are
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registered as discrete : there is no continuous energy loss.
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3- AN EVENT : THE PRIMARY GENERATOR
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The primary kinematic consists of a single particle starting at the edge
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of the box. The type of the particle and its energy are set in
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PrimaryGeneratorAction (1 MeV gamma), and can be changed via the G4
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build-in commands of ParticleGun class (see the macros provided with
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this example).
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4- PHYSICS
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An event is killed at the first interaction of the incident paticle.
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The absorption length, also called mean free path, is computed as
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the mean value of the track length of the incident particle.
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This is why the medium must be 'infinite' : to be sure that interaction
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occurs at any events.
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The result is compared with the 'input' data, i.e. with the cross
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sections stored in the PhysicsTables and used by Geant4.
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The energy spectrum and the angular distribution of the scattered
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particle (if any) and of the created secondaries are plotted (see
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SteppingAction).
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A set of macros defining various run conditions are provided.
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The processes are actived/inactived in order to survey the processes
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individually.
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5- HISTOGRAMS
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The test contains 6 built-in 1D histograms, which are managed by the
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HistoManager class and its Messenger. The histos can be individually
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activated with the command :
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/analysis/h1/set id nbBins valMin valMax unit
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where unit is the desired unit for the histo (MeV or keV, etc..)
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(see the macros xxxx.mac).
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1 "scattered primary particle: energy spectrum"
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2 "scattered primary particle: costheta distribution"
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3 "charged secondaries: energy spectrum"
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4 "charged secondaries: costheta distribution"
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5 "neutral secondaries: energy spectrum"
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6 "neutral secondaries: costheta distribution"
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The histograms are managed by the HistoManager class and its Messenger.
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The histos can be individually activated with the command :
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/analysis/h1/set id nbBins valMin valMax unit
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where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
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One can control the name of the histograms file with the command:
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/analysis/setFileName name (default testem14)
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It is possible to choose the format of the histogram file : root (default),
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hbook, xml, csv, by using namespace in HistoManager.hh
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It is also possible to print selected histograms on an ascii file:
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/analysis/h1/setAscii id
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All selected histos will be written on a file name.ascii (default testem14)
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Using hbook format
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------------------
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Need a special treatement : the Cern Library must be installed and the
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environment variable CERNLIB correctly set. Then, *before* compiling,
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activate G4_USE_HBOOK in GNUmakefile and g4hbook.hh in HistoManager.hh
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6- VISUALIZATION
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The Visualization Manager is set in the main().
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The initialisation of the drawing is done via the commands
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/vis/... in the macro vis.mac. To get visualisation:
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> /control/execute vis.mac
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The detector has a default view which is a longitudinal view of the
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box.
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The tracks are drawn at the end of event, and erased at the end of run.
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7- HOW TO START ?
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execute TestEm14 in 'batch' mode from macro files :
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% TestEm14 compt.mac
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execute TestEm14 in 'interactive mode' with visualization :
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% TestEm14
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Idle> control/execute vis.mac
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....
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Idle> type your commands
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....
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Idle> exit
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