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1 -------------------------------------------------------------------
2
3 =========================================================
4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
5 =========================================================
6
7 gammaray_telescope
8 ------------------
9 F. Longo, R. Giannitrapani & G. Santin
10 June 2003
11
12 ---------------------------------------------------------------
13 Acknowledgments to GEANT4 people, in particular to R. Nartallo,
14 A. Pfeiffer, M. G. Pia and G. Cosmo
15 ---------------------------------------------------------------
16
17 GammaRayTel is an example of application of Geant4 in a space
18 environment. It simulates a typical telescope for gamma ray analysis;
19 the detector setup is composed by a tracker made with silicon planes,
20 subdivided in ladders and strips, a CsI calorimeter and an
21 anticoincidence system. In this version, the three detectors are made
22 sensitive but only the hits on the tracker strips are registered and relevant
23 information (energy deposition, position etc.) are dumped to an external
24 ASCII file for subsequent analysis.
25
26 Relevant information from the simulation is processed in the GammarayTelAnalysis
27 class and saved, through the G4AnalysisManager interface, to Histograms and
28 Tuples.
29
30 a) Macros for the visualization of geometry and tracks with
31 OpenGL, VRML and DAWN drivers
32
33 b) Implementation of messengers to change some parameters of
34 the detector geometry, the particle generator and the analysis
35 manager (if present) runtime
36
37 c) Readout geometry mechanism to describe an high number of
38 subdivisions of the planes of the tracker (strips) without
39 affecting in a relevant way the simulation performances
40
41 d) Histogramming facilities are presently provided through the G4AnalysisManager class.
42
43 e) User interfaces via Xmotif or normal terminal provided
44
45
46 1. Setting up the environment variables
47 ---------------------------------------
48
49 - Setup for storing ASCII data
50
51 If you want to store the output data in an ASCII file 'Tracks_x.dat'
52 where x stays for the run number. You should specify the environment
53 variable:
54
55 setenv G4STORE_DATA 1
56
57 - Setup for Visualization
58
59 IMPORTANT: be sure that your Geant4 installation has been done
60 with the proper visualization drivers; for details please see the
61 file geant4/source/visualization/README.
62
63 To use the visualization drivers set the following variables in
64 your local environment:
65
66 setenv G4VIS_USE_OPENGLX 1 # OpenGL visualization
67 setenv G4VIS_USE_DAWNFILE 1 # DAWN file
68 setenv G4VIS_USE_VRMLFILE 1 # VRML file
69 setenv G4VRMLFILE_VIEWER vrmlview # If installed
70
71 - Setup for Xmotif user interface
72
73 setenv G4UI_USE_XM 1
74
75 - Set up for analysis
76
77 To compile the GammaRayTel example with the analysis tools activated,
78 set the following variables
79
80 setenv G4ANALYSIS_USE 1 # Use the analysis tools
81
82 2. Sample run
83 -------------
84
85 To run a sample simulation with gamma tracks interacting with
86 the detector in its standard configuration and without any
87 visualization, execute the following command in the example main
88 directory:
89
90 $G4WORKDIR/bin/$G4SYSTEM/GammaRayTel
91
92 It is possible also to run three different configuration defined in
93 macro1.mac, macro2.mac and macro3.mac for visualization (OpenGL, VRML
94 and DAWN respectively) with the following command
95
96 $G4WORKDIR/bin/$G4SYSTEM/GammaRayTel macroX.mac
97
98 where X can be 1, 2 or 3. Be sure to have the right environment (see
99 the preceding section) and the proper visualization driver enabled in
100 your local G4 installation (see geant4/source/visualization/README for
101 more information).
102
103
104 3. Detector description
105 -----------------------
106
107 The detector is defined in GammaRayTelDetectorConstruction.cc
108 It is composed of a Payload with three main detectors, a Tracker (TKR), a
109 Calorimeter (CAL) and an Anticoincidence system (ACD).
110
111 The standard configuration is made of a TKR of 15 Layers of 2 views made of
112 4 * 4 Si single sided silicon detectors with Lead converter, and a CAL of
113 5 layers of CsI, each made of 2 views of 12 CsI bars orthogonally posed.
114 4 lateral panels and a top layer of plastic scintillator (ACL and ACT)
115 complete the configuration.
116 The Si detectors are composed of two silicon planes subdivided in strips
117 aligned along the X axis in one plane and along the Y axis for the other.
118
119 The following baseline configuration is adopted:
120
121 GEOMETRICAL PARAMETER VALUE
122
123 Converter Thickness 300 micron
124 Silicon Thickness 400 micron
125 Silicon Tile Size XY 9 cm
126 Silicon Pitch 200. micrometer
127 Views Distance 1. mm
128 CAL Bar Thickness 1.5 cm
129 ACD Thickness 1. cm
130
131 It is possible to modify in some way this configuration using the
132 commands defined in GammaRayTelDetectorMessenger.
133 This feature is available in the UI through the commands subtree
134 "/payload/" (see the help command in the UI for more information).
135
136 4. Physics processes
137 --------------------
138
139 This example uses a modular physics list, with a sample of Hadronic processes
140 (see the web page http://cmsdoc.cern.ch/~hpw/GHAD/HomePage/ for more adeguate
141 physics lists), the Standard or the LowEnergy Electromagnetic processes.
142
143 5. Particle Generator
144 ---------------------
145
146 The GammaRayTelParticleGenerationAction and its Messenger let the user define
147 the incident flux of particles, from a specific direction or from an
148 isotropic background. In the first case particles are generated on a spherical
149 surface which diameter is perpendicular to the arrival direction. In the second
150 case the arrival directions are isotropic.
151
152 The user can define also between two spectral options:
153 monochromatic or with a power-law dependence. The particle
154 generator parameters are accessible through the UI tree "/gun/" (use the
155 UI help for more information). We are planning to include, in the next
156 releases of this example, the General Particle Source module of G4.
157
158 6. Hit
159 ------
160
161 In this version the hits from the TKR the CAL and the ACD are generated.
162 Only the hit from the TRK are saved. Each TKR hit contains the following
163 information
164
165 a) ID of the event (this is important for multiple events run)
166 b) Energy deposition of the particle in the strip (keV)
167 c) Number of the strip
168 d) Number of the plane
169 e) Type of the plane (1=X 0=Y)
170 f) Position of the hit (x, y, z) in the reference frame of the payload
171
172 The hit information are saved on an ASCII file named Tracks_N.dat, where
173 N is the progressive ID number associated to the run.
174
175 7. Analysis
176 -----------
177
178 Relevant information from the simulation is processed in the GammarayTelAnalysis
179 class and saved, through the G4AnalysisManager interface, to Histograms and
180 Tuples. The output file is written in ROOT format, but one can easily switch to
181 XML (or Hbook) by changing the appropriate #include in GammarayTelAnalysis.hh
182 No external software is required (apart from the hbook case, in which the CERNLIB
183 must be installed and a FORTRAN compiler must be present)
184
185 Keep in mind that the actual implementation of the analysis tools in GammaRayTel
186 is of a pedagogical nature, so we kept it as simple as possible.
187
188 The actual analysis produces some histograms (see next section) and an ntuple.
189 Both the histograms and the ntuple are saved at the end of the run in the file
190 "gammaraytel.root". Please note that in a multiple run session,
191 the last run always override the root file.
192
193 8. Histogramming
194 ----------------
195
196 The 1D histograms contain the energy deposition in the last X plane of
197 the TKR and the hits distribution along the X planes of the TKR
198 (note again that these histograms have been chosen more for pedagogical
199 motivation than for physical one).
200
201 These histograms are filled and updated at every event and are initialized
202 with each new run; the scale of the histograms is automatically derived from
203 the detector geometry.
204
205 Through a messenger it is possible to set some options with
206 the UI subtree "/analysis/" (use the UI help for more info);
207
208 In this example we only show the use of very basic feature of this new
209 simulation/analysis framework.
210
211 9. Digi
212 -------
213
214 For the TKR also the digits corresponding to the Hits are generated.
215 A digi is generated when the hit energy deposit is greater than a threshold
216 (in this example setted at 120 keV).
217 The TKR digi information are stored on the same file Tracks_N.dat and contain:
218
219 a) ID of the event (this is important for multiple events run)
220 b) Number of the strip
221 c) Number of the plane
222 d) Type of the plane (1=X 0=Y)
223
224 10. Classes Overview
225 --------------------
226
227 This is the overview of the classes defined in this example
228
229 GammaRayTelPrimaryGeneratorAction
230 User action for primaries generator
231
232 GammaRayTelPrimaryGeneratorMessenger
233 Messenger for interactive particle generator
234 parameters modification via the User Interface
235
236 GammaRayTelPhysicsList
237 Determination of modular physics classes
238
239 GammaRayTelDetectorConstruction
240 Geometry and material definitions for the detector
241
242 GammaRayTelDetectorMessenger
243 Messenger for interactive geometry parameters
244 modification via the User Interface
245
246 GammaRayTelAnalysis
247 Analysis manager class (experimental)
248
249 GammaRayTelAnalysisMessenger
250 Messenger for interactive analysis options modification
251 via the User Interface
252
253 GammaRayTelRunAction
254 User run action class
255
256 GammaRayTelEventAction
257 User event action class
258
259 GammaRayTelTrackerHit
260 Description of the hits on the tracker
261
262 GammaRayTelDigi
263 Description of the digi on the tracker
264
265 GammaRayTelDigitizer
266 Description of the digitizer for the tracker
267
268 GammaRayTelTrackerSD
269 Description of the TKR sensitive detector
270
271 GammaRayTelAnticoincidenceHit
272 Description of the hits on the anticoincidence
273
274 GammaRayTelAnticoincidenceSD
275 Description of the ACD sensitive detector
276
277 GammaRayTelCalorimeterHit
278 Description of the hits on the calorimeter
279
280 GammaRayTelCalorimeterSD
281 Description of the CAL sensitive detector
