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1 -------------------------------------------------------------------
2
3 =========================================================
4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
5 =========================================================
6
7 TestEm13
8 --------
9
10 How to compute cross sections from the transmition coefficient
11 ( see below, item Physics).
12
13 1- GEOMETRY DEFINITION
14
15 It is a single box representing a layer of finite thickness of
16 homogeneous material.
17 Two parameters define the geometry :
18 - the material of the box,
19 - the (full) size of the box.
20
21 The default geometry (1 cm of water) is constructed in
22 DetectorConstruction, but the above parameters can be changed
23 interactively via the commands defined in DetectorMessenger.
24
25 2- PHYSICS LIST
26
27 The physics list contains the standard electromagnetic processes.
28 In order not to introduce 'artificial' constraints on the step size, the
29 multiple scattering is not instanciated, and all processes are
30 registered as discrete : there is no continuous energy loss.
31
32 3- AN EVENT : THE PRIMARY GENERATOR
33
34 The primary kinematic consists of a single particle starting at the edge
35 of the box. The type of the particle and its energy are set in
36 PrimaryGeneratorAction (1 MeV gamma), and can be changed via the G4
37 build-in commands of ParticleGun class (see the macros provided with
38 this example).
39
40 4- PHYSICS
41
42 An event is killed at the first step of the incident paticle.
43 Either the particle has interacted or is transmitted through the layer.
44 The cross section, also called absorption coefficient, is computed from
45 the rate of unaltered transmitted incident particles.
46
47 The result is compared with the 'input' data, i.e. with the cross
48 sections stored in the PhysicsTables and used by Geant4.
49
50 A set of macros defining various run conditions are provided.
51 The processes are actived/inactived in order to survey the processes
52 individually.
53
54
55 6- VISUALIZATION
56
57 The Visualization Manager is set in the main().
58 The initialisation of the drawing is done via the commands
59 /vis/... in the macro vis.mac. To get visualisation:
60 > /control/execute vis.mac
61
62 The detector has a default view which is a longitudinal view of the
63 box.
64
65 The tracks are drawn at the end of event, and erased at the end of run.
66
67 7- HOW TO START ?
68
69 execute TestEm13 in 'batch' mode from macro files :
70 % TestEm13 compt.mac
71
72 execute TestEm13 in 'interactive mode' with visualization :
73 % TestEm13
74 Idle> control/execute vis.mac
75 ....
76 Idle> type your commands
77 ....
78 Idle> exit
79
80 Macros provided in this example:
81 - anni.mac: e+ (10 MeV) on 5 cm Aluminium
82 - compton.mac: gamma (300 keV) on 1 cm Aluminium
83 - conv.mac: gamma (20 MeV) on 5 mm Lead
84 - electron.mac: e- (100 MeV) on 1 cm Aluminium
85 - gamma.mac: gamma (100 keV) on 1 cm Water
86 - photoelec.mac: gamma (100 keV) on 1 cm Iron
87 - proton.mac: proton (1 GeV) on 1 cm Water
