$Id: README,v 1.18 2004/06/23 11:30:39 maire Exp $
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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TestEm3
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This example simulates a simple Sampling Calorimeter setup.
1- GEOMETRY DEFINITION
The calorimeter is a box made of a given number of layers.
A layer consists of a sequence of various absorbers (maximum 10).
The layer is replicated.
Parameters defining the calorimeter :
- the number of layers,
- the number of absorbers within a layer,
- the material of the absorbers,
- the thickness of the absorbers,
- the transverse size of the calorimeter (the input face is a square).
In addition a transverse uniform magnetic field can be applied.
The default geometry is constructed in DetectorConstruction class,
but all of the above parameters can be modified interactively via
the commands defined in the DetectorMessenger class.
NB. The number of absorbers and the number of layers can be set to 1.
In this case we have a unique homogeneous block of matter,
which looks like a bubble chamber rather than a calorimeter ...
(see the macro of commands: newgeom.mac)
2- PHYSICS LISTS
Physics Lists are subdivided on 4 following modules:
1. "particles" - particle definitions
2. "general" - decays and transportation
3. "standard" (alternative) - standard EM physics
4. "model" (alternative) - standard EM physics using model approach
Notice that there is an example of definition of a static ion : IonC12
(see PhysListParticle.cc) and an example of use : ionC12.mac
3- AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle which hits the
calorimeter perpendicular to the input face. The type of the particle
and its energy are set in the PrimaryGeneratorAction class, and can
be changed via the G4 build-in commands of ParticleGun class (see
the macros provided with this example).
In addition one can choose randomly the impact point of the incident
particle. The corresponding interactive command is built in
PrimaryGeneratorMessenger class.
A RUN is a set of events.
4- 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. In interactive session:
PreInit or Idle > /control/execute vis.mac
The detector has a default view which is a longitudinal view of the
calorimeter.
The tracks are drawn at the end of event, and erased at the end of run.
Optionaly one can choose to draw all particles, only the charged one,
or none. This command is defined in EventActionMessenger class.
5- PHYSICS DEMO
The particle's type and the physic processes which will be available
in this example are set in PhysicsList class.
In addition a build-in interactive command (/process/inactivate proname)
allows to activate/inactivate the processes one by one.
Then one can well visualize the processes one by one, especially
in the bubble chamber setup with a transverse magnetic field.
As a homework try to visualize a gamma conversion alone,
or the effect of the multiple scattering.
Notice that one can control the maximum step size at tracking time,
via G4UserLimit class and the command /tracking/stepMax
(see DetectorConstruction and DetectorMessenger classes)
6- HOW TO START ?
- compile and link to generate an executable
% cd TestEm3
% gmake
- execute TestEm3 in 'batch' mode from macro files
% TestEm3 run01.mac
- execute TestEm3 in 'interactive mode' with visualization
% TestEm3
....
Idle> type your commands. For instance:
Idle> /control/execute run01.mac
....
Idle> exit
7- HISTOGRAMS
Testem3 produces histograms :
histo 1 : energy deposit in absorber 0
histo 2 : energy deposit in absorber 1
...etc...........
One can control the binning of the histo with the command:
/testem/histo/setHisto idAbsor nbin Emin Emax unit
...etc...........
where unit is the desired energy unit for that histo (see TestEm3.in).
One can control the name of the histograms file with the command:
/testem/histo/setFileName name (default testem3.paw)
Note that, by default, histograms are disabled. To activate them, uncomment
the flag G4ANALYSIS_USE in GNUmakefile.
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.
To use histograms any of implementations of AIDA interfaces should
be available (see http://aida.freehep.org).
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 compilation of the example it is optimal to clean up old
files:
gmake histclean
gmake
Before running the example the command should be issued:
eval `aida-config --runtime csh`
It is possible to choose the format of the output file with
histograms using UI command:
/testem/histo/setFileType type
The following types are available: hbook, root, xml.
Gabriele Cosmo