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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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                                 HADR01

            A.Bagulya, I.Gudowska, V.Ivanchenko, N.Starkov
                       CERN, Geneva, Switzerland
            Karolinska Institute & Hospital, Stockholm, Sweden
               Lebedev Physical Institute, Moscow, Russia


This example application is based on the application IION developed for
simulation of proton or ion beam interaction with a water target. Different 
aspects of beam target interaction are demonstrating in the example including 
logitudinal profile of energy deposition, spectra of secondary  particles,
spectra of particles leaving the target. The results are presenting in a form
of average numbers and histograms. 


                           GEOMETRY

The Target volume is a cilinder placed inside Check cilindrical volume. The 
Check volume is placed inside the World volume. The radius and the length of
the Check volume are 1 mm larger than the radiaus and the length of the Target.
The material of the Check volume is the same as the World material.  The World
volume has the sizes 10 mm larger than that of the Target volume.  Any naterial
from the Geant4 database can be defined. The default World  material is
G4Galactic and the default  Target material is aluminum. The Target is
subdivided on number of equal slices. Follwoing UI commands are available to
modify the geometry:

/testhadr/TargetMat     G4_Pb
/testhadr/WorldMat      G4_AIR
/testhadr/TargetRadius  10 mm
/testhadr/TargetLength  20 cm
/testhadr/NumberDivZ    200

If geometry was changed between two runs, then the follwoing command need to
be executed:

/testhadr/Update

Beam direction coinsides with the target axis and is Z axis in the global
coordinate system. The beam starts 5 mm in front of the target. G4ParticleGun
is used as a primary generator. The energy and the type of the beam can be
defined via standard UI commands

/gun/energy   15 GeV
/gun/particle proton

Default beam position is -(targetHalfLength + 5*mm) and direction along Z axis.
Beam position and direction can be changed by gun UI commands:

/gun/position  1 10 3 mm
/gun/direction 1 0 0

however, position command is active only if before it the flag is set

/testhadr/DefaultBeamPosition false   
 
                           SCORING

The scoring is performed with the help of UserStackingAction class and two
sensitive detector  classes: one associated with a target slice, another with
the Check volume. Each secondary particle is scored by the StackingAction.  In
the StackingAction it is also possible to kill all or one type of secondary 
particles 

/testhadr/Kill             neutron
/testhadr/KillAllSecondaries  

To control running the following options are available:

/testhadr/PrintModulo      100
/testhadr/DebugEvent       977

The last command selects an events, for which "/tracking/verbose 2" level
of printout is established.


                           PHYSICS

PhysicsList of the application uses components, which are distributed with
Geant4 in /geant4/physics_lists subdirectory. So, before compiling hadro01 it
is necessary to compile physics_lists

The choice of the physics is provided by the UI command:

/testhadr/Physics     QGSP

The command 

/testhadr/Physics     PHYSLIST

allows allows to download a physics configuration defined by an environment
variable PHYSLIST. 

To see the list of available configurations one can use

/testhadr/ListPhysics

The cuts for electromagnetic phsyics can be established via

/testhadr/CutsAll       1 mm
/testhadr/CutsGamma   0.1 mm
/testhadr/CutsEl      0.2 mm
/testhadr/CutsPos     0.3 mm


                          VISUALISATION

For interactive mode G4 visualization options and variables should be
defined, then the example should be recompiled:

gmake visclean
gmake

The vis.mac file can be used an example of visualization. The following command can 
be used:

/testhadr/DrawTracks  charged
/testhadr/DrawTracks  charged+n
/testhadr/DrawTracks  neutral
/testhadr/DrawTracks  all


                          HISTOGRAMS

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 $PI_DIR, it is
required to add the installation path to $PATH, i.e. for example,
for release 1.2.1 of PI:

setenv PATH ${PATH}:$PI_DIR/1.3.12/app/releases/PI/PI_1_3_12/slc3_gcc323/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
setenv G4ANALYSIS_USE 1
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:

/testhadr/HistoName   name
/testhadr/HistoType   type
/testhadr/HistoOption "uncompress"

The following types are available: hbook, root, aida. They will be 
stored in the file "name.hbook", "name.root", or "name.aida". 
If the environment variable HISTODIR is defined, files are stored in this 
subdirectory.

To show the contence of a histogram ID=i the commands may be applied:

/testhadr/HistoPrint  i

All histograms are normalised to the number of events.