$Id: README,v 1.5 2006/05/15 14:43:01 maire Exp $
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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TestEm14
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How to compute cross sections from the direct evaluation of the mean
free path ( see below, item Physics).
How to plot final state of a process.
1- GEOMETRY DEFINITION
It is a single box representing a 'semi infinite' homogeneous medium.
Two parameters define the geometry :
- the material of the box,
- the (full) size of the box.
The default geometry (100 m of water) is constructed in
DetectorConstruction, but the above parameters can be changed
interactively via the commands defined in DetectorMessenger.
2- PHYSICS LIST
The physics list contains the standard electromagnetic processes.
In order not to introduce 'articicial' constraints on the step size, the
multiple scattering is not instanciated, and there is no limitation from
the maximum energy lost per step.
3- AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle starting at the edge
of the box. The type of the particle and its energy are set in
PrimaryGeneratorAction (1 MeV gamma), and can be changed via the G4
build-in commands of ParticleGun class (see the macros provided with
this example).
4- PHYSICS
An event is killed at the first interaction of the incident paticle.
The absorption length, also called mean free path, is computed as
the mean value of the track length of the incident particle.
This is why the medium must be 'infinite' : to be sure that interaction
occurs at any events.
The result is compared with the 'input' data, i.e. with the cross
sections stored in the PhysicsTables and used by Geant4.
The energy spectrum and the angular distribution of the scattered
particle (if any) and of the created secondaries are plotted (see
SteppingAction).
A set of macros defining various run conditions are provided.
The processes are actived/inactived in order to survey the processes
individually.
5- HISTOGRAMS
The test contains 6 built-in 1D histograms, which are managed by the
HistoManager class and its Messenger. The histos can be individually
activated with the command :
/testem/histo/setHisto id nbBins valMin valMax unit
where unit is the desired unit for the histo (MeV or keV, etc..)
(see the macros xxxx.mac).
1 "scattered primary particle: energy spectrum"
2 "scattered primary particle: costheta distribution"
3 "charged secondaries: energy spectrum"
4 "charged secondaries: costheta distribution"
5 "neutral secondaries: energy spectrum"
6 "neutral secondaries: costheta distribution"
See below the note on histogram tools.
One can control the name and the type of the histograms file with
the commands:
/testem/histo/setFileName name (default testem14)
/testem/histo/setFileType name (default hbook)
Note that, by default, histograms are disabled. To activate them,
uncomment the flag G4ANALYSIS_USE in GNUmakefile.
6- VISUALIZATION
The Visualization Manager is set in the main().
The initialisation of the drawing is done via the commands
/vis/... in the macro vis.mac. To get visualisation:
> /control/execute vis.mac
The detector has a default view which is a longitudinal view of the
box.
The tracks are drawn at the end of event, and erased at the end of run.
7- HOW TO START ?
compile and link to generate an executable
% cd geant4/examples/extended/electromagnetic/TestEm14
% gmake
execute TestEm14 in 'batch' mode from macro files :
% TestEm14 compt.mac
execute TestEm14 in 'interactive mode' with visualization :
% TestEm14
Idle> control/execute vis.mac
....
Idle> type your commands
....
Idle> exit
8- USING HISTOGRAMS
By default the histograms are not activated. To activate histograms
the environment variable G4ANALYSIS_USE should be defined. For instance
uncomment the flag G4ANALYSIS_USE in GNUmakefile.
Before compilation of the example it is optimal to clean up old files:
gmake histclean
gmake
To use histograms, at least one of the AIDA implementations should be
available (see http://aida.freehep.org).
8a - PI
A package including AIDA and extended interfaces also using Python is PI,
available from: http://cern.ch/pi
Once installed PI or PI-Lite in a specified local area $MYPY, it is required
to add the installation path to $PATH, i.e. for example, for release 1.2.1 of
PI:
setenv PATH ${PATH}:$MYPI/1.2.1/app/releases/PI/PI_1_2_1/rh73_gcc32/bin
CERN users can use the PATH to the LCG area on AFS.
Before running the example the command should be issued:
eval `aida-config --runtime csh`
8b - OpenScientist
OpenScientist is available at http://OpenScientist.lal.in2p3.fr.
You have to "setup" the OpenScientist AIDA implementation before compiling
(then with G4ANALYSIS_USE set) and running your Geant4 application.
On UNIX you setup, with a csh flavoured shell :
csh> source <<OpenScientist install path>/aida-setup.csh
or with a sh flavoured shell :
sh> . <<OpenScientist install path>/aida-setup.sh
On Windows :
DOS> call <<OpenScientist install path>/aida-setup.bat
You can use various file formats for writing (AIDA-XML, hbook, root).
These formats are readable by the Lab onx interactive program
or the OpenPAW application. See the web pages.
With OpenPAW, on a run.hbook file, one can view the histograms
with something like :
OS> opaw
opaw> h/file 1 run.hbook ( or opaw> h/file 1 run.aida or run.root)
opaw> zone 2 2
opaw> h/plot 1
opaw> h/plot 2
Gabriele Cosmo