$Id: README,v 1.8 2001/11/27 11:10:31 maire Exp $
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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ExampleN03
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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 an absorber plate and of a detection gap. The layer is
replicated.
Six parameters define the calorimeter :
- the material of the absorber,
- the thickness of an absorber plate,
- the material of the detection gap,
- the thickness of a gap,
- the number of layers,
- 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 thickness of the absorber or of the gap can be set to zero
(but not together), and the number of layers 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- 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.
3- DETECTOR RESPONSE
A HIT is a record, event per event and volume per volume, of all the
informations needed to simulate and analyse the detector response.
In this example a CalorHit is defined as a set of 4 informations per
layer :
- the total energy deposit in the absorber plate,
- the total tracklength of all charged particles in the absorber plate,
- the total energy deposit in the detection gap,
- the total tracklength of all charged particles in the detection gap.
Therefore both the absorber and the detection gap are declared
'sensitive detector' (SD), which means they can contribute to the hit.
At the end of a run, from the CalorHitsCollection, one can study the
calorimeter performances such as :
- shower profile,
- calorimeter resolution,
- pi/e ratio ...
4- VISUALIZATION
The Visualization Manager is set in the main().
The initialisation of the drawing is done via a set of /vis/ commands
in the macro vis.mac. This macro is automatically read from
the main in case of interactive running mode.
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,
or neutral or none. This command is build in EventActionMessenger class.
NB 1: the visualization (with OpenGL driver) assumes two things:
1- the visualisation & interfaces categories have been compiled
with the environment variable G4VIS_BUILD_OPENGLX_DRIVER.
2- exampleN03.cc has been compiled with G4VIS_USE_OPENGLX.
NB 2: the visualization (with DAWNFILE driver) assumes two things:
1- the visualisation & interfaces categories have been compiled
with the environment variable G4VIS_BUILD_DAWNFILE_DRIVER.
2- exampleN03.cc has been compiled with G4VIS_USE_DAWNFILE.
NN 3: The macros "visTutor/exN03VisX.mac" are tutorial macros for
visualization. They can be tried as:
% $G4BINDIR/exampleN03
idle > /control/execute visTutor/exN03VisX.mac
For details, see comment lines described in the macro files.
These macros are designed to help your understanding the
User's Guide.
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 the build-in interactive command:
/process/(in)activate processName
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.
6- USER INTERFACES
The default command interface, called G4UIterminal, is done via
standart cin/G4cout.
On Linux and Sun-cc on can use a smarter command interface G4UItcsh.
It is enough to set the environment variable G4UI_USE_TCSH
On can use a Motif driven command interface (called G4UIXm) if:
1- interfaces category has been compiled with G4UI_BUILD_XM_SESSION
2- exampleN03.cc has been compiled with G4UI_USE_XM.
7- HOW TO START ?
- compile and link to generate an executable
% cd N03
% gmake
- execute N03 in 'batch' mode from macro files
% exampleN03 run1.mac
- execute N03 in 'interactive mode' with visualization
% exampleN03
....
Idle> type your commands. For instance:
Idle> /control/execute newgeom.mac
....
Idle> exit
Gabriele Cosmo