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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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Hadr07
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Survey energy deposition and particle's flux from an hadronic cascade.
Use PhysicsConstructor objects rather than predefined G4 PhysicsLists.
Show how to plot a depth dose profile in a rectangular box.
1- MATERIALS AND GEOMETRY DEFINITION
The geometry consists of a stack of one or several blocks of homogenous
material, called absorbers.
A minimum of 4 parameters define the geometry :
- the number of absorbers (NbOfAbsor)
- the material of each absorber,
- the thickness of each absorber,
- the tranverse dimension of the stack (sizeYZ)
In addition a transverse uniform magnetic field can be applied.
eg: /globalField/setValue 0 0 5 tesla
The absorber is surrounded by a World volume (vacuum)
A function, and its associated UI command, allows to build a material
directly from a single isotope.
The default geometry is built in DetectorConstruction, but the above parameters
can be changed interactively via commands defined in DetectorMessenger.
To be identified by the ThermalScattering module, the elements composing a
material must have a specific name (see G4ParticleHPThermalScatteringNames.cc)
Examples of such materials are build in Hadr06/src/DetectorConstruction.
2- PHYSICS LIST
"Full" set of physics processes are registered, but via PhysicsConstructor
objects rather than complete pre-defined G4 physics lists. This alternative
way gives more freedom to register physics.
Physics constructors are either constructors provided in Geant4 (with G4 prefix)
or 'local'. They include : HadronElastic, HadronInelastic, IonsInelastic, GammaNuclear,
RadioactiveDecay and Electomagnetic.
(see geant4/source/physics_lists/constructors)
HadronElasticPhysicsHP include a model for thermalized neutrons, under the control of a command
defined in NeutronHPMesseger.
GammmaNuclearPhysics is a subset of G4BertiniElectroNuclearBuilder.
ElectromagneticPhysics is a simplified version of G4EmStandardPhysics.
In perticular, no step constraint is imposed for energy loss mechanism (ionisation and brems).
This is enough when spatial distribution of deposited energy do not need
to be accurate (see param->SetStepFunction(1., 1*mm)).
Several hadronic physics options are controlled by environment variables.
To trigger them, an envHadronic.csh has been added in this example.
One must select the options wished, and do
source envHadronic.csh (or sh)
3- AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle starting at the
left face of the box. 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 G4ParticleGun 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- PHYSICS
The program computes the energy deposited in each absorber,
and the flux of particles emerging in the world.
Processes invoked and particles generated are listed.
5- HISTOGRAMS
The test has several built-in 1D histograms, which are managed by
G4AnalysisManager and its Messenger. The histos can be individually
activated with the command :
/analysis/h1/set id nbBins valMin valMax unit
where unit is the desired unit for the histo (MeV or keV, etc..)
(see the macros xxxx.mac).
1 "total energy deposited in absorber 1
2 "total energy deposited in absorber 2
...........................................
9 "total energy deposited in absorber 9
10 "Edep (MeV/mm) profile along absorbers"
One can control the name of the histograms file with the command:
/analysis/setFileName name (default Hadr07)
It is possible to choose the format of the histogram file : root (default),
xml, csv, by using namespace in HistoManager.hh
It is also possible to print selected histograms on an ascii file:
/analysis/h1/setAscii id
All selected histos will be written on a file name.ascii (default Hadr07)
6- TRACKING and STEP MAX
Hadr07 computes the distribution of energy deposited along the trajectory of
the incident particle : the so-called longitudinal energy profile,
or depth dose distribution (histogram 10).
The energy deposited (edep) is randomly distribued along the step (see
SteppingAction).
In order to control the accuracy of the deposition, the maximum step size
of charged particles is computed automatically from the binning of
histogram 10.
As an example, this limitation is implemented as a 'full' process :
see StepMax class and its Messenger. The 'StepMax process' is registered
in the Physics List, via a physicsConstructor object (a builder).
StepMax is evaluated in the StepMax process.
A boolean UI command allows to deactivate this mechanism.
Another UI command allows to define directly a stepMax value.
7- 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 tracks are drawn at the end of event, and erased at the end of run.
gamma green
neutron yellow
negative particles (e-, ...) red
positive particles (e+, ions, ...) blue
8- HOW TO START ?
Execute Hadr07 in 'batch' mode from macro files :
% Hadr07 run1.mac
Execute Hadr07 in 'interactive mode' with visualization :
% Hadr07
Idle> control/execute vis.mac
....
Idle> type your commands
....
Idle> exit
Gabriele Cosmo