$Id: README,v 1.4 2006/05/15 14:42:42 maire Exp $
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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TestEm13
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How to compute cross sections from the tramsmition coefficient
( see below, item Physics).
1- GEOMETRY DEFINITION
It is a single box representing a layer of finite thickness of
homogeneous material.
Two parameters define the geometry :
- the material of the box,
- the (full) size of the box.
The default geometry (1 cm 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 step of the incident paticle.
Either the particle has interacted or is transmitted through the layer.
The cross section, also called absorption coefficient, is computed from
the rate of unaltered transmitted incident particles.
The result is compared with the 'input' data, i.e. with the cross
sections stored in the PhysicsTables and used by Geant4.
A set of macros defining various run conditions are provided.
The processes are actived/inactived in order to survey the processes
individually.
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/TestEm13
% gmake
execute TestEm13 in 'batch' mode from macro files :
% TestEm13 compt.mac
execute TestEm13 in 'interactive mode' with visualization :
% TestEm13
Idle> control/execute vis.mac
....
Idle> type your commands
....
Idle> exit
Gabriele Cosmo