How to compute cross sections from the direct evaluation of the mean free path ( see below, PHYSICS).
How to plot final state of a process.

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.

PHYSICS LIST

The physics list contains the standard electromagnetic processes. In order not to introduce 'artificial' constraints on the step size, the multiple scattering is not instanciated, and all processes are registered as discrete : there is no continuous energy loss.

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 G4ParticleGun class (see the macros provided with this example).

PHYSICS

An event is killed at the first interaction of the incident paticle. The absorption length, also called mean free path, is computed as the mean value of the track length of the incident particle. This is why the medium must be 'infinite' : to be sure that interaction occurs at any events.

The result is compared with the 'input' data, i.e. with the cross sections stored in the PhysicsTables and used by Geant4.

The energy spectrum and the angular distribution of the scattered particle (if any) and of the created 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.

HISTOGRAMS

The test contains 6 built-in 1D histograms, which are managed by the HistoManager class and its messenger, HistoMessenger. 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 : "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"

The histograms are managed by the HistoManager class and its messenger, HistoMessenger 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 testem14)

It is possible to choose the format of the histogram file : root (default), hdf5, xml, csv, by changing the default file type in HistoManager.cc

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 testem14)

VISUALIZATION

The Visualization Manager is set in the main () (see TestEm14.cc). 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.

HOW TO START ?

Execute TestEm14 in 'batch' mode from macro files :
```
% TestEm14   compt.mac
```

Execute TestEm14 in 'interactive mode' with visualization :

% TestEm14
Idle> control/execute vis.mac
....
Idle> type your commands
....
Idle> exit