This program computes the dose deposited in an ionization chamber by an extended (one dimensional) monoenergetic electron source. The geometry of the chamber satisfies the conditions of charged particle equilibrium. Hence, under idealized conditions, the ratio of the dose deposited over the beam energy fluence must be equal to 1. This variante of the Fano cavity test make use of an reciprocity theorem.

J.Sempau and P.Andreo, Phys. Med. Biol. 51 (2006) 3533

GEOMETRY

The chamber is modelized as a cylinder with a cavity in it.

5 parameters define the geometry :

the radius of the chamber (must be big)
the material of the wall
the thickness of the wall
the material of the cavity
the thickness of the cavity

Wall and cavity must be made of the same material, but with different density. Radius must be bigger than range of electrons in cavity.

All above parameters can be redifined via the UI commands built in DetectorMessenger class.

                        _________________
     radius (infinite)  |     |   |     |
                        |     |   |     |
                        |     |   |     |
                        |     |   |     |
                        |     | <-+-----+--- cavity
                        |     |   |     |
                        |     |   |     |
                 ---------------------------- cylinder axis = e- source
                        |     |   |     |
                        |     |   |     |
                        |     |   |     |
                        |wall |   |wall |
                        |     |   |     |
                        |     |   |     |
                        |     |   |     |
                        -----------------

BEAM

Monoenergetic (E0) incident electron source is uniformly distribued along cylinder axis, within wall and cavity, with constant lineic density per mass: I. An effective wall thickness is defined from the range of e- at energy E0.

Beam_energy_fluence is E0*I

PURPOSE OF THE PROGRAM

The program computes the dose deposited in the cavity and the ratio Dose/Beam_energy_fluence. This ratio must be 1.

The program needs high statistic to reach precision on the computed dose. The UI command /run/printProgress allows to survey the convergence of the dose calculation.

The simplest way to study the effect of e- tracking parameters on dose deposition is to use the command /testem/stepMax.

PHYSICS

The physics list contains the standard electromagnetic processes, with few modifications listed here.

Bremsstrahlung : Fano conditions imply no energy transfer via bremsstrahlung radiation. Therefore this process is not registered in the physics list. However, it is always possible to include it. See PhysListEm classes.
Ionization : In order to have same stopping power in wall and cavity, one must cancel the density correction term in the dedx formula. This is done in a specific MollerBhabha model (MyMollerBhabhaModel) which inherites from G4MollerBhabhaModel.

To prevent explicit generation of delta-rays, the default production threshold (i.e. cut) is set to 10 km (CSDA condition).

The finalRange of the step function is set to 10 um, which more on less correspond to a tracking cut in water of about 20 keV. See emOptions. Once again, the above parameters can be controled via UI commands.
Multiple scattering : is switched in single Coulomb scattering mode near boundaries. This is selected via EM options in PhysicsList, and can be controled with UI commands.
All PhysicsTables are built with 100 bins per decade.

HISTOGRAMS

fanoCavity2 has several predefined 1D histograms :

1 : emission point of e+-
2 : energy spectrum of e+-
3 : theta distribution of e+-
4 : emission point of e+- hitting cavity
5 : energy spectrum of e+- when entering in cavity
6 : theta distribution of e+- before enter in cavity
7 : theta distribution of e+- at first step in cavity
8 : track segment of e+- in cavity
9 : step size of e+- in wall
10 : step size of e+- in cavity
11 : energy deposit in cavity per track

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 fanocavity2)

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 fanocavity2)

HOW TO START ?

Execute fanoCavity2 in 'batch' mode from macro files
```
% fanoCavity2   run01.mac
```

Execute fanoCavity2 in 'interactive mode' with visualization

% fanoCavity2
....
Idle> type your commands
....
Idle> exit