geant4

                   Extended Example for G4GeneralParticleSource (GPS)
                   -------------------------------------------------- 

  exgps is created to demonstrate the usage of G4GeneralParticleSource
  for generating  primary particle according to user defined distributions.
  These range from simple monocromatic point source to complicated mutiple
  sources with various biasing schemes. 
  
  http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides
        /ForApplicationDeveloper/html/ch02s07.html
   
   
  1 - GEOMETRY

  Simple geometry consists of a "Vacuum" world and, in it, two other components:
    - An alunimium box : 20 x 20 x 20 cm in size, cerntered at the origin.
    - A SiO2 sphere (radius 5 cm) is placed at the centre of the aluminium box.

  2 - PHYSICS

  Tranportation process only for all particles.

  3 - EVENT

  The event generator is the G4GeneralParticleSource (GPS). The instantiation of
  G4GeneralParticleSource is same as that for G4ParticleGun. 
  See the exGPSPrimaryGeneratorAction.cc file for details.  
  
  4 - VISUALIZATION
 
  Visualisation of the geometry and the tracks is possible with many of the 
  G4 visualisation packages.
  An example of displaying the geometry and tracks using OGL is given in the 
  macro vis.mac.  

  5 - HISTOGRAMS

  This example implements an histo manager which creates histograms and
  ntuples using Geant4 analysis tools.
     
  The output file contains 6 histograms and one ntuple:

  histo1D 1: energy spectrum.
  histo1D 2: vertex: radial distribution dN/dv.
  histo1D 3: angular distribution: cos(theta).
  histo1D 4: angular distribution: phi.      
  histo2D 1: vertex position in the X-Y plane.
  histo2D 2: vertex position in the X-Z plane.
  histo2D 3: vertex position in the Y-Z plane.
  histo2D 4: angular distribution: phi-cos(theta).
  histo2D 5: angular distribution: of phi-theta.
 
  In the ntuple the following data are recorded for each incident particle:  

  Particle ID
  Incident Position (x,y,z);
  Incident Angle (theta,phi);
  Particle weight;
	
  The histograms are managed by G4AnalysisManager 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 exgps)
   
  It is possible to choose the format of the histogram file : root (default),
  xml, csv, by using namespace in HistoManager.hh 
	

  6 - GETTING STARTED
 
  - execute exgps in 'batch' mode from macro files
	% exgps   exgps.in
 		
  - execute exgps in 'interactive mode' with visualization
	% exgps
	....
	Idle> type your commands
	....
	Idle> exit

 7 - FURTHER EXAMPLES of MACRO FILES

 There are a number of mac files in the ./macros subdirectory, to show the 
 various features of GPS. 
 Please see README file there for further informations.