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1 -------------------------------------------------------------------
2
3 =========================================================
4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
5 =========================================================
6
7 fanoCavity
8 ----------
9
10 This program computes the dose deposited in an ionization chamber by a
11 monoenergetic photon beam.
12 The geometry of the chamber satisfies the conditions of charged particle
13 equilibrium. Hence, under idealized conditions, the ratio of the dose
14 deposited over the beam energy fluence must be equal to the
15 mass_energy_transfer coefficient of the wall material.
16
17 E.Poon and al, Phys. Med. Biol. 50 (2005) 681
18 I.Kawrakow, Med. Phys. 27-3 (2000) 499
19
20 1- GEOMETRY
21
22 The chamber is modelized as a cylinder with a cavity in it.
23
24 6 parameters define the geometry :
25 - the material of the wall of the chamber
26 - the radius of the chamber and the thickness of the wall
27 - the material of the cavity
28 - the radius and the thickness of the cavity
29
30 Wall and cavity must be made of the same material, but with different
31 density
32
33 All above parameters can be redifined via the UI commands built in
34 DetectorMessenger class
35
36 -----------------
37 | |
38 | wall |
39 | ----- |
40 | | | |
41 | | <-+-----+--- cavity
42 ------> | | | |
43 ------> | | | |
44 beam -------------------------------- cylinder axis
45 ------> | | | |
46 ------> | | | |
47 | | | |
48 | | | |
49 | ----- |
50 | |
51 | |
52 -----------------
53
54 2- BEAM
55
56 Monoenergetic incident photon beam is uniformly distribued, perpendicular
57 to the flat end of the chamber. The beam radius can be controled with an
58 UI command built in PrimaryGeneratorMessenger; the default is full wall
59 chamber radius.
60
61 Beam regeneration : after each Compton interaction, the scattered photon is
62 reset to its initial state, energy and direction. Consequently, interaction
63 sites are uniformly distribued within the wall material.
64
65 This modification must be done in the ParticleChange of the final state
66 of the Compton scattering interaction. Therefore, a specific model
67 (MyKleinNishinaCompton) is assigned to the ComptonScattering process in
68 PhysicsList. MyKleinNishinaCompton inherites from G4KleinNishinaCompton;
69 only the function SampleSecondaries() is overwritten.
70
71 3- PURPOSE OF THE PROGRAM
72
73 The program computes the dose deposited in the cavity and the ratio
74 Dose/Beam_energy_fluence. This ratio is compared to the mass_energy_transfer
75 coefficient of the wall material.
76
77 The mass_energy_transfer coefficient needs :
78 - the photon total cross section, which is read from the PhysicsTables
79 by G4EmCalculator (see EndOfRunAction).
80 - the average kinetic energy of charged secondaries generated in the
81 wall during the run.
82
83 The program needs high statistic to reach precision on the computed dose.
84 The UI command /run/printProgress allows to survey the convergence of
85 the kineticEnergy and dose calculations.
86
87 In addition, to increase the program efficiency, the secondary particles
88 which have no chance to reach the cavity are immediately killed (see
89 StackinAction). This feature can be switched off by an UI command (see
90 StackingMessenger).
91
92 The simplest way to study the effect of e- tracking parameters on dose
93 deposition is to use the command /testem/stepMax.
94
95 4- PHYSICS
96
97 The physics lists contains the standard electromagnetic processes, with few
98 modifications listed here.
99
100 - Compton scattering : as explained above, the final state is modified in
101 MyKleinNishinaCompton class.
102
103 In order to make the program more efficient, one can increase the Compton
104 cross section via the function SetCSFactor(factor) and its
105 associated UI command. Default is factor=1000.
106
107 - Bremsstrahlung : Fano conditions imply no energy transfer via
108 bremsstrahlung radiation. Therefore this process is not registered in the
109 physics list. However, it is always possible to include it.
110 See PhysListEmStandard class.
111
112 - Ionisation : In order to have same stopping power in wall and cavity, one
113 must cancel the density correction term in the dedx formula. This is done in
114 a specific MollerBhabha model (MyMollerBhabhaModel) which inherites from
115 G4MollerBhabhaModel.
116
117 To prevent explicit generation of delta-rays, the default production
118 threshold (i.e. cut) is set to 10 km (CSDA condition).
119
120 The finalRange of the step function is set to 10 um, which more on less
121 correspond to a tracking cut in water of about 20 keV. See emOptions.
122 Once again, the above parameters can be controled via UI commands.
123
124 - Multiple scattering : is switched in single Coulomb scattering mode near
125 boundaries. This is selected via EM options in PhysicsList, and can be
126 controled with UI commands.
127
128 - All PhysicsTables are built with 100 bins per decade.
129
130 5- HISTOGRAMS
131
132 fanoCavity has several predefined 1D histograms :
133
134 1 : emission point of e+-
135 2 : energy spectrum of e+-
136 3 : theta distribution of e+-
137 4 : emission point of e+- hitting cavity
138 5 : energy spectrum of e+- when entering in cavity
139 6 : theta distribution of e+- before enter in cavity
140 7 : theta distribution of e+- at first step in cavity
141 8 : track segment of e+- in cavity
142 9 : step size of e+- in wall
143 10 : step size of e+- in cavity
144 11 : energy deposit in cavity per track
145
146 The histograms are managed by G4AnalysisManager class and its messenger.
147 The histos can be individually activated with the command :
148 /analysis/h1/set id nbBins valMin valMax unit
149 where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
150
151 One can control the name of the histograms file with the command:
152 /analysis/setFileName name (default fanoCavity)
153
154 It is possible to choose the format of the histogram file : root (default),
155 hdf5, xml, csv, by changing the default file type in HistoManager.cc
156
157 It is also possible to print selected histograms on an ascii file:
158 /analysis/h1/setAscii id
159 All selected histos will be written on a file name.ascii (default fanocavity)
160
161 6- HOW TO START ?
162
163 - execute fanoCavity in 'batch' mode from macro files
164 % fanoCavity run01.mac
165
166 - execute fanoCavity in 'interactive mode' with visualization
167 % fanoCavity
168 ....
169 Idle> type your commands
170 ....
171 Idle> exit
172
173 Alternative macro file:
174 basic.mac - disabled multiple scattering and fluctuations of energy loss
