| Geant4 Cross Reference |
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2 Geant4 - an Object-Oriented Toolkit f 2 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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4 4
5 WLS 5 WLS
6 ---------- 6 ----------
7 7
8 This application simulates the propagation o << 8 This application simulates the propagation of photons inside a Wave Length
9 Wave Length Shifting (WLS) fiber. << 9 Shifting (WLS) fiber.
10 10
11 11
12 1- Geometry Definition 12 1- Geometry Definition
13 13
14 The default geometry is as follow: 14 The default geometry is as follow:
15 15
16 - A perfect, bare (or clad), PMMA fiber: 0.5mm << 16 - A perfect, bare, PMMA fiber: 0.5mm radius, 2m length at center(0,0,0)
17 center (0,0,0) of the World. << 17 of the World.
18 - A circular MPPC with 0.5mm radius at the +z 18 - A circular MPPC with 0.5mm radius at the +z end of the fiber
19 - World and coupling materials are G4_AIR 19 - World and coupling materials are G4_AIR
20 - Photons will always refracted out to couplin 20 - Photons will always refracted out to coupling material before
21 reaching MPPC 21 reaching MPPC
22 - There are many flexible parameters that the 22 - There are many flexible parameters that the user could specify.
23 They are under the /WLS directory of help. 23 They are under the /WLS directory of help.
24 24
25 25
26 2- Material Choices 26 2- Material Choices
27 27
28 There are several materials that the user ca 28 There are several materials that the user can use for the fiber core,
29 world and coupling. 29 world and coupling.
30 30
31 They are: 31 They are:
32 32
33 - Vacuum (G4_Galactic) 33 - Vacuum (G4_Galactic)
34 - Air (G4_AIR) 34 - Air (G4_AIR)
35 - PMMA, refractive index n = 1.60 << 35 - PMMA, n = 1.60
36 - Pethylene, n = 1.49 36 - Pethylene, n = 1.49
37 - FPethylene, n = 1.42 37 - FPethylene, n = 1.42
38 - Polystyrene, n = 1.60 38 - Polystyrene, n = 1.60
39 - Silicone, n = 1.46 39 - Silicone, n = 1.46
40 40
41 41
42 3- Photon Source 42 3- Photon Source
43 43
44 This program uses the General Particle Sourc 44 This program uses the General Particle Source (G4GeneralParticleSource)
45 provided by Geant4 for generating particles. << 45 provided by GEANT4 for
46 optical photon must be within the range 2.00 << 46 generating photons. The energy of the photon must be within 2.00 eV
>> 47 to 3.47 eV. For detail instruction on how to use the General Particle
>> 48 Source, please visit their home page at:
>> 49
>> 50 http://reat.space.qinetiq.com/gps/
47 51
48 52
49 4- Hit 53 4- Hit
50 54
51 A hit is registered when an optical photon i << 55 A hit is registered when the photon is absorbed on the MPPC surface.
52 surface. Information stored in a hit includ << 56 Information stored in hit includes the local coordinate of the location
53 location the optical photon is absorbed on t << 57 the photon is absorbed on the MPPC, the global coordinate where the
54 where the optical photon left the fiber, the << 58 photon left the fiber and the transit time of the photon.
55 photon, and the energy of the optical photon <<
56 59
57 60
58 5- Stepping Action 61 5- Stepping Action
59 62
60 The stepping action keeps track of the numbe << 63 The stepping action keeps track of the number of bounces a photon has
61 gone through. In order to prevent infinite 64 gone through. In order to prevent infinite loop and extremely skewed
62 rays taking up computing time, there is a li 65 rays taking up computing time, there is a limit of the number of
63 bounces that an optical photon can go throug << 66 bounces that a photon can go through before it is artificially killed.
64 The default limit is 100,000. The user can 67 The default limit is 100,000. The user can set his/her own limit using
65 the /stepping/setBounceLimit command. A val 68 the /stepping/setBounceLimit command. A value of 0 will turn off the
66 limit. All optical photons artificially kil << 69 limit. All photons artificially killed will have murderee flag turned
67 on in their UserTrackInformation. 70 on in their UserTrackInformation.
68 71
69 72
70 6- Visualization 73 6- Visualization
71 74
72 To visualize particle trajectories, simply u << 75 To visualize a photon's trajectory, simply use vis.mac macro in
73 interactive mode or in your own macro. 76 interactive mode or in your own macro.
74 77
75 78
76 7- main() 79 7- main()
77 80
78 - execute wls in 'batch' mode from macro file 81 - execute wls in 'batch' mode from macro files
79 - you can enter an optional integer seed for 82 - you can enter an optional integer seed for batch mode
80 % wls electron.mac (optional: enter a << 83 % wls wls.in (optional: enter an integer seed here)
81 84
82 - wls in 'interactive mode' with visualizatio 85 - wls in 'interactive mode' with visualization
83 % wls 86 % wls
84 .... 87 ....
85 Idle> /control/execute 88 Idle> /control/execute
86 Idle> /run/beamOn 1 89 Idle> /run/beamOn 1
87 .... 90 ....
88 Idle> exit 91 Idle> exit
89 92
90 8- Macros provided 93 8- Macros provided
91 94
92 - electron.mac: Sets up the geometry and conf << 95 - wls.in: sets up the default geometry and provides the commands to change it.
93 Primary particle is a 10 MeV << 96 Primary particle is an optical photon with energy 2.1 eV.
>> 97 - Sr90.mac: Default geometry is used. Primary particle is a strontium ion.
94 - vis.mac: macro for visualization; called au 98 - vis.mac: macro for visualization; called automatically when no macro is
95 given on command line. 99 given on command line.