$Id: README,v 1.3 2007/01/18 09:07:20 hbu Exp $
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     =========================================================
     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
     =========================================================

                            TestEm16
                            --------
      Simulate synchrotron radiation
	
 1- GEOMETRY DEFINITION

     The geometry consists of a single block of a homogenous material.

     Two parameters define the geometry :
 	- the material of the box,
	- the (full) size of the box.
     The default is 500 m of vacuum.

     A transverse uniform magnetic field can be applied.

     The default geometry is constructed in DetectorConstruction class,
     but all of the above parameters can be changed interactively via
     the commands defined in the DetectorMessenger class.

 2- PHYSICS LIST

     The particle list is the one of novice/exampleN03 and TestEm6
     with in addition synchrotron radiation.
     To make the synchrotron radiation easily visible, a very low
     pressure "vaccuum" and a magnetic field of by default 1 Tesla
     in z-direction is used.

 3- AN EVENT : THE PRIMARY GENERATOR

     The primary kinematic consists of a single particle which hits the
     block perpendicular to the input face. The type of the particle
     and its energy are set in the PrimaryGeneratorAction class, and can
     changed via the G4 build-in commands of ParticleGun class (see
     the macros provided with this example).
     The default is an positron of 10 GeV.
     	
     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- VISUALIZATION

     The Visualization Manager is set in the main().
     The initialisation of the drawing is done via the command
     > /control/execute vis.mac
     > /run/beamOn 1

     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.
     Optionaly one can choose to draw all particles, only the charged one,
     or none. This command is defined in EventActionMessenger class.

 5- PHYSICS DEMO

     The particle's type and the physic processes which will be available
     in this example are set in PhysicsList class.

     In addition a build-in interactive command (/process/inactivate proname)
     allows to activate/inactivate the processes one by one.

     The threshold for producing secondaries can be changed.
     eg: /run/particle/setCut 100 micrometer
         /run/initialize
	
     To visualize the Synchrotron radiation :
	 /control/execute vis.mac
		  	
 6- HOW TO START ?

     - compile and link to generate an executable
	% cd geant4/examples/extended/electromagnetic/TestEm16
 	% make

     - execute Test  in 'batch' mode from macro files
 	% TestEm16    run01.mac

     - execute Test  in 'interactive mode' with visualization
 	% TestEm16
 		....
 	Idle> type your commands
 		....
 	Idle> exit

 7 - TRACKING : stepMax and setMaxStepLength

  In order to control the accuracy of the deposition, the user can limit
  'by hand' the maximum  step size stepMax of charged particles.

  The maximum tracking step length for computing of magnetic field lines
  is by default set to 1 km.
  Synchrotron radiation in very weak magnetic fields of the order of 1 Gauss
  may require longer pathlength.
  This can be achieved with using setMaxStepLength like
  /testem/tracking/setMaxStepLength 100 km

8- HISTOGRAMS

  TestEm16 produces 3 histograms which illustrate synchrotron radiation.
  The photon energy spectrum (photons / energy bin) and the power spectrum
  (photon spectrum weighted with the photon energy) and a histogram
  of the path length between photon radiation is produced.

  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.

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

  By default the histograms are saved as testem16.hbook
  It is possible to choose the format of the histogram file (hbook, root, XML)
  and the binning using /testem/histo/ command, see run01.mac