| Geant4 Cross Reference |
1 2 ========================================================= 3 Geant4 - an Object-Oriented Toolkit for Simulation in HEP 4 ========================================================= 5 6 Hadr03 7 ------ 8 9 How to compute total cross section from the direct evaluation of the 10 mean free path ( see below, item Physics). 11 How to identify nuclear reactions. 12 How to plot energy spectrum of secondary particles. 13 14 1- GEOMETRY DEFINITION 15 16 It is a single box representing a 'semi infinite' homogeneous medium. 17 Two parameters define the geometry : 18 - the material of the box, 19 - the (full) size of the box. 20 21 The default geometry (10 m of molybdenum) is built in DetectorConstruction, 22 but the above parameters can be changed interactively via commands defined 23 in DetectorMessenger. 24 25 2- PHYSICS LIST 26 27 The PhysicsList contains builders for hadronic interactions. 28 Predefined G4 PhysicsConstructors or 'local' PhysicsConstructors can be used 29 (see geant4/source/physics_lists or example runAndEvent/RE04). 30 31 In order not to introduce 'artificial' constraints on the step size, 32 electromagnetic processes are not registered: there is no continuous energy 33 loss. 34 35 Several hadronic physics options are controlled by environment variables. 36 To select them, see Hadr03.cc. 37 38 3- AN EVENT : THE PRIMARY GENERATOR 39 40 The primary kinematic consists of a single particle starting at the edge 41 of the box. The type of the particle and its energy are set in 42 PrimaryGeneratorAction (neutron 1 MeV), and can be changed via the G4 43 build-in commands of ParticleGun class (see the macros provided with 44 this example). 45 46 4- PHYSICS 47 48 An event is killed at the first interaction of the incident particle. 49 The absorption length, also called mean free path, is computed as 50 the mean value of the track length of the incident particle. 51 This is why the medium must be 'infinite' : to be sure that interaction 52 occurs at any events. 53 54 The result is compared with the 'input' value, i.e. with the cross sections 55 given by G4HadronicProcessStore and used by Geant4. 56 57 The list of nuclear reactions that occured is printed. 58 (the number of gamma of deexcitation is not printed). 59 60 Then, comes the total list of generated particles and ions. 61 The energy spectrum of the scattered particle (if any) and of the created 62 secondaries are plotted (see SteppingAction). 63 64 Momentum conservation is checked as : 65 momentum balance = modulus(P_out - P_in) 66 67 A set of macros defining various run conditions are provided. 68 The processes can be actived/inactived in order to survey the processes 69 individually. 70 71 5- HISTOGRAMS 72 73 The test contains 12 built-in 1D histograms, which are managed by 74 G4AnalysisManager and its Messenger. The histos can be individually 75 activated with the command : 76 /analysis/h1/set id nbBins valMin valMax unit 77 where unit is the desired unit for the histo (MeV or keV, etc..) 78 (see the macros xxxx.mac). 79 80 1 "kinetic energy of scattered primary particle" 81 2 "kinetic energy of gamma" 82 3 "kinetic energy of e-" 83 4 "kinetic energy of neutrons" 84 5 "kinetic energy of protons" 85 6 "kinetic energy of deuterons" 86 7 "kinetic energy of alphas" 87 8 "kinetic energy of nuclei" 88 9 "kinetic energy of mesons" 89 10 "kinetic energy of baryons" 90 11 "Q = Ekin out - Ekin in" 91 12 "Pbalance = mag(P_out - P_in)" 92 13 "atomic mass of nuclei" 93 94 The histograms are managed by the HistoManager class and its Messenger. 95 The histos can be individually activated with the command : 96 /analysis/h1/set id nbBins valMin valMax unit 97 where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..) 98 99 One can control the name of the histograms file with the command: 100 /analysis/setFileName name (default Hadr03) 101 102 It is possible to choose the format of the histogram file : root (default), 103 xml, csv, by using namespace in HistoManager.hh 104 105 It is also possible to print selected histograms on an ascii file: 106 /analysis/h1/setAscii id 107 All selected histos will be written on a file name.ascii (default Hadr03) 108 109 6- VISUALIZATION 110 111 The Visualization Manager is set in the main(). 112 The initialisation of the drawing is done via the commands 113 /vis/... in the macro vis.mac. To get visualisation: 114 > /control/execute vis.mac 115 116 The detector has a default view which is a longitudinal view of the box. 117 The tracks are drawn at the end of event, and erased at the end of run. 118 119 7- HOW TO START ? 120 121 Execute Hadr03 in 'batch' mode from macro files : 122 % Hadr03 inelastic.mac 123 124 Execute Hadr03 in 'interactive mode' with visualization : 125 % Hadr03 126 Idle> control/execute vis.mac 127 .... 128 Idle> type your commands 129 .... 130 Idle> exit 131 132 Macros provided in this example: 133 - hadr03.in: macro used in Geant4 testing 134 - Au196.mac: neutron (1 MeV) on Au195 135 - elastic.mac: proton (10 MeV) on Mo100. Elastic collisions alone 136 - fusion.mac: deuteron (400 keV) on tritium 137 - gamma.mac: gamma (10 MeV) on Au196 138 - inelastic.mac: proton (10 MaV) on Mo98. Inelastic interactions alone 139 - ion.mac: Li7 (140 MeV) on Be9 140 - nCapture.mac: neutron (1 eV) on Boron. Capture process alone 141 - nFission.mac: neutron (1 eV) on U235. Fission process alone 142 - neutron.mac: neutron (1 MeV) on Boron 143 144 Macros to be run interactively: 145 - debug.mac: proton (10 MeV) on Boron 146 - vis.mac: To activate visualization