$Id: README,v 1.6 2007/11/13 12:13:32 maire Exp $ ------------------------------------------------------------------- ========================================================= Geant4 - an Object-Oriented Toolkit for Simulation in HEP ========================================================= TestEm14 -------- How to compute cross sections from the direct evaluation of the mean free path ( see below, item Physics). How to plot final state of a process. 1- GEOMETRY DEFINITION It is a single box representing a 'semi infinite' homogeneous medium. Two parameters define the geometry : - the material of the box, - the (full) size of the box. The default geometry (100 m of water) is constructed in DetectorConstruction, but the above parameters can be changed interactively via the commands defined in DetectorMessenger. 2- PHYSICS LIST The physics list contains the standard electromagnetic processes. In order not to introduce 'artificial' constraints on the step size, the multiple scattering is not instanciated, and there is no limitation from the maximum energy lost per step. 3- AN EVENT : THE PRIMARY GENERATOR The primary kinematic consists of a single particle starting at the edge of the box. The type of the particle and its energy are set in PrimaryGeneratorAction (1 MeV gamma), and can be changed via the G4 build-in commands of ParticleGun class (see the macros provided with this example). 4- PHYSICS An event is killed at the first interaction of the incident paticle. The absorption length, also called mean free path, is computed as the mean value of the track length of the incident particle. This is why the medium must be 'infinite' : to be sure that interaction occurs at any events. The result is compared with the 'input' data, i.e. with the cross sections stored in the PhysicsTables and used by Geant4. The energy spectrum and the angular distribution of the scattered particle (if any) and of the created secondaries are plotted (see SteppingAction). A set of macros defining various run conditions are provided. The processes are actived/inactived in order to survey the processes individually. 5- HISTOGRAMS The test contains 6 built-in 1D histograms, which are managed by the HistoManager class and its Messenger. The histos can be individually activated with the command : /testem/histo/setHisto id nbBins valMin valMax unit where unit is the desired unit for the histo (MeV or keV, etc..) (see the macros xxxx.mac). 1 "scattered primary particle: energy spectrum" 2 "scattered primary particle: costheta distribution" 3 "charged secondaries: energy spectrum" 4 "charged secondaries: costheta distribution" 5 "neutral secondaries: energy spectrum" 6 "neutral secondaries: costheta distribution" See below the note on histogram tools. One can control the name and the type of the histograms file with the commands: /testem/histo/setFileName name (default testem14) /testem/histo/setFileType name (default hbook) It is also possible to print selected histograms on an ascii file: /testem/histo/printHisto id All selected histos will be written on a file name.ascii (default testem14) Note that, by default, histograms are disabled. To activate them, uncomment the flag G4ANALYSIS_USE in GNUmakefile. 6- VISUALIZATION The Visualization Manager is set in the main(). The initialisation of the drawing is done via the commands /vis/... in the macro vis.mac. To get visualisation: > /control/execute vis.mac The detector has a default view which is a longitudinal view of the box. The tracks are drawn at the end of event, and erased at the end of run. 7- HOW TO START ? compile and link to generate an executable % cd geant4/examples/extended/electromagnetic/TestEm14 % gmake execute TestEm14 in 'batch' mode from macro files : % TestEm14 compt.mac execute TestEm14 in 'interactive mode' with visualization : % TestEm14 Idle> control/execute vis.mac .... Idle> type your commands .... Idle> exit 8- USING HISTOGRAMS By default the histograms are not activated. To activate histograms the environment variable G4ANALYSIS_USE should be defined. For instance uncomment the flag G4ANALYSIS_USE in GNUmakefile. Before compilation of the example it is optimal to clean up old files: gmake histclean gmake To use histograms, at least one of the AIDA implementations should be available (see http://aida.freehep.org). 8a - PI A package including AIDA and extended interfaces also using Python is PI, available from: http://cern.ch/pi Once installed PI or PI-Lite in a specified local area $MYPY, it is required to add the installation path to $PATH, i.e. for example, for release 1.2.1 of PI: setenv PATH ${PATH}:$MYPI/1.2.1/app/releases/PI/PI_1_2_1/rh73_gcc32/bin CERN users can use the PATH to the LCG area on AFS. Before running the example the command should be issued: eval `aida-config --runtime csh` 8b - OpenScientist OpenScientist is available at http://OpenScientist.lal.in2p3.fr. You have to "setup" the OpenScientist AIDA implementation before compiling (then with G4ANALYSIS_USE set) and running your Geant4 application. On UNIX you setup, with a csh flavoured shell : csh> source </aida-setup.csh or with a sh flavoured shell : sh> . </aida-setup.sh On Windows : DOS> call </aida-setup.bat You can use various file formats for writing (AIDA-XML, hbook, root). These formats are readable by the Lab onx interactive program or the OpenPAW application. See the web pages. With OpenPAW, on a run.hbook file, one can view the histograms with something like : OS> opaw opaw> h/file 1 run.hbook ( or opaw> h/file 1 run.aida or run.root) opaw> zone 2 2 opaw> h/plot 1 opaw> h/plot 2