$Id: README 69174 2013-04-21 20:38:15Z maire $
=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
NeutronSource
-------------
NeutronSource is an example of neutrons production. It illustrates the cooperative work
of nuclear reactions and radioactive decay processes.
It survey energy deposition and particle's flux.
It uses PhysicsConstructor objects.
1- MATERIALS AND GEOMETRY DEFINITION
The geometry is a cylinder (absorber) of an homogenous material (default : Beryllium oxide).
This absorber is within a container (default : stainless-steel).
Five parameters define the geometry :
- the material of the absorber
- the radius and length of the absorber
- the material of the container
- the thickness of the container
The default geometry is built in DetectorConstruction, but the above
parameters can be changed interactively via commands defined in DetectorMessenger.
The container is surrounded by a World volume (air)
A function, and its associated UI command, allows to build a material
directly from a single isotope.
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 DetectorConstruction of Hadr04,06,07.
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.
PhysicsConstructors are either predefined G4 PhysicsConstructors or 'local'.
They include : HadronElastic (including neutronHP), HadronInelastic,
IonsInelastic, GammaNuclear physics, RadioactiveDecay and Electromagnetic physics.
(see geant4/source/physics_lists/constructors)
ElectromagneticPhysics is a variante of EmStandard. 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 is a single particle uniformly shooted within the absorber.
The type of the particle and its energy are set in PrimaryGeneratorAction (Am241, at rest),
and can be changed via the G4 build-in commands of ParticleGun class
(see the macros provided with this example).
4- PHYSICS
The program computes and plots energy deposited in the interaction volume
(absorber + container) and the flux of particles leaving this volume.
Processes invoked and particles generated during hadronic cascade are listed.
5- HISTOGRAMS
The test contains 13 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 deposit"
2 "dummy"
3 "total kinetic energy flow"
4 "gamma flux (dN/dE) at exit"
5 "e+- flux (dN/dE) at exit"
6 "neutrons flux (dN/dE) at exit"
7 "protons flux (dN/dE) at exit"
8 "deuterons flux (dN/dE) at exit"
9 "alphas flux (dN/dE) at exit"
10 "all others ions flux (dN/dE) at exit"
11 "all others baryons flux (dN/dE) at exit"
12 "all others mesons flux (dN/dE) at exit"
13 "all others leptons flux (dN/dE) at exit"
The histograms are managed by the HistoManager class 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, deg or mrad, etc..)
One can control the name of the histograms file with the command:
/analysis/setFileName name (default NeutronSource)
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 NeutronSource)
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 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
7- HOW TO START ?
Execute NeutronSource in 'batch' mode from macro files :
% NeutronSource run1.mac
Execute NeutronSource in 'interactive mode' with visualization :
% NeutronSource
Idle> control/execute vis.mac
....
Idle> type your commands
....
Idle> exit
Gabriele Cosmo