$Id: README,v 1.4 2004/09/29 10:37:47 maire Exp $
-------------------------------------------------------------------

     =========================================================
     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
     =========================================================

                            PhotonProcesses
                            ---------------

	This test is devoted to the photon processes: gamma conversion, coherent
	and incoherent scattering, photoelectric effect. It allows to compute
	absorption coefficients and to plot final state. 
	
 1- GEOMETRY DEFINITION
 
 	It is a single box representing a 'semi infinite' homogeneous medium.
 	Two parameters define the geometry :
 	- the material of the box,
	- the (full) size of the box.
 	
 	The default geometry (100 m of water) is constructed in 
	DetectorConstruction, but the above parameters can be changed 
	interactively via the commands defined in DetectorMessenger.
 	
 2- PHYSICS LIST
 
 	The particle list contains only gamma, e+, e-, mu+, mu-.
 	The physics list contains the 'standard' electromagnetic processes. 
 	 
 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
 
	The incident particle is a photon. The event is killed at the first
	interaction of the photon.
	The absorption length is computed as the mean value of the track length
	of the photon.
	The energy spectrum and the angular distribution of the scattered photon
	(if any) and of the secondaries are plotted (see SteppingAction).
 	
 	A set of macros defining various run conditions are provided.
 	The processes are actived/inactived in order to survey the processes 
	individually.

 5- HISTOGRAMS
         
	The test contains 6 built-in 1D histograms, which are managed by the
	HistoManager class and its Messenger. The histos can be individually 
	activated with the command :
	/testem/histo/setHisto id nbBins  valMin valMax unit 
	where unit is the desired unit for the histo (MeV or keV, etc..)
	(see the macros xxxx.mac).
 
	1	"scattered primary particle: energy spectrum"
	2	"scattered primary particle: costheta distribution"
	3	"charged secondaries: energy spectrum"
	4	"charged secondaries: costheta distribution"
	5	"neutral secondaries: energy spectrum"
	6	"neutral secondaries: costheta distribution"			

	See below the note on histogram tools.
	
 	One can control the name of the histograms file with the command:
 	/testem/histo/setFileName  name  (default photonprocesses.aida)
   	
	Note that, by default, histograms are disabled. To activate them, 
	uncomment the flag G4ANALYSIS_USE in GNUmakefile. 	
 	 				
 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/PhotonProcesses
 		% gmake
 		
	execute PhotonProcesses in 'batch' mode from macro files :
 		% PhotonProcesses   compt.mac
 		
	execute PhotonProcesses in 'interactive mode' with visualization :
 		% PhotonProcesses
		Idle> control/execute vis.mac
 		....
 		Idle> type your commands
 		....
 		Idle> exit
 

 8- Using histograms
 ------------------- 

By default the histograms are not activated. To activate histograms
the environment variable G4ANALYSIS_USE should be defined. For instance
uncomment the flag G4ANALYSIS_USE in GNUmakefile.

To use histograms any of implementations of AIDA interfaces should
be available (see http://aida.freehep.org).

A package including AIDA and extended interfaces also using Python
is PI, available from: http://cern.ch/pi .

Once installed PI or PI-Lite in a specified local area $MYPY, it is
required to add the installation path to $PATH, i.e. for example,
for release 1.2.1 of PI:

setenv PATH ${PATH}:$MYPI/1.2.1/app/releases/PI/PI_1_2_1/rh73_gcc32/bin

CERN users can use the PATH to the LCG area on AFS.

Before compilation of the example it is optimal to clean up old 
files:

gmake histclean
gmake

Before running the example the command should be issued:

eval `aida-config --runtime csh`

It is possible to choose the format of the output file with 
histograms using UI command:

/testem/histo/setFileType type

The following types are available: hbook, root, XML.