Gabriele Cosmo
169 lines
6.0 KiB
Markdown
169 lines
6.0 KiB
Markdown
\page ExampleparticleGun Example particleGun
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History:
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- 10-06-2010 : Makoto Asai - merge into one example
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- 13-05-2010 : Michel Maire - create as three examples
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This example demonstrates 5 ways of the use of G4ParticleGun shooting
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primary particles in different cases. These are
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-# uniform particle direction in a given solid angle
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-# Generate several vertices and particles per event
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-# Show how to sample a tabulated function (eg. energy spectrum)
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-# Divergent beam in an arbitrary direction
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-# Shooting primaries in spherical coordinates with rotation matrix.
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These use cases can be chosen by a UI command
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```
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/gunExample/selectGunAction actionID
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```
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where <i>actionID</i> corresponds to the above cases.
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## Geometry construction
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It is a simple box which represents an 'infinite' homogeneous medium.
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## Physics list
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PhysicsList defines only geantino and transportation process.
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## Primary generator
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There are 5 concrete primary generator action classes
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(PrimaryGeneratorActionN, N=0,1,2,3,4) which can be used as an independent sample
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code.
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PrimaryGeneratorAction is the class which uses and switches between these
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5 concrete action classes. Each concrete generator action shoots geantinoes
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in a distribution decribed below.
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### 0. Uniform particle direction in a given solid angle
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spherical angles (alpha,psi) respective to z axis
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Histograms 5,6 show momentum direction in master frame.
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See: PrimaryGeneratorAction0::GeneratePrimaries()
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### 1. Generate several vertices and particles per event
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- particle 1 : a geantino uniformly randomized on a cylinder surface.
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- particle 2 and 3 : symetric to particle 1.
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In addition, time_zero of each event is randomized.
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See: PrimaryGeneratorAction1::GeneratePrimaries()
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### 2. Show how to sample a tabulated function (energy spectrum)
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Energy is sampled from a tabulated function defined in InitFunction().
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The function is assumed positive, linear per segment, continuous.
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Two sampling methods are illustrated : RejectAccept() and InverseCumul()
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(see Particle Data Group: pdg.lbl.gov --> Monte Carlo techniques)
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Histogram 1 shows generated energy spectrum.
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See: PrimaryGeneratorAction2::GeneratePrimaries()
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### 3. Divergent beam in an arbitrary direction with rotation matrix
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A geantino uniformly randomized around a given direction (theta, phi).
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One wants to limit particle direction uniformly around this direction.
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First, one generates momentum direction in the master frame (eg. World).
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AlphaMax = opening angle around z axis.
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Then one rotates momentum in local frame, using rotateUz() function.
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RotateUz() transforms uz to newUz. It is composition of two simple rotations:
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theta around oy, then phi around oz (non commutative). \n
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See: https://proj-clhep.web.cern.ch/proj-clhep/ \n
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Histograms 5,6 show momentum direction in local frame.
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See: PrimaryGeneratorAction3::GeneratePrimaries()
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### 4. Shooting primaries in spherical coordinates with rotation matrix
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A geantino uniformly randomized within a spherical shell.
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a) Vertex position
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One wishes to shoot uniformly within a spherical shell.
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One works in spherical coordinates. One uses inverse cumulative method with
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analytical formulae. \n
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Histograms 2,3,4 demonstrate uniform distribution of vertex position.
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b) Momentum direction
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One wants to limit particle direction uniformly within (alphaMin, alphaMax).
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First, one generates momentum direction in the master frame (eg. World).
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Then, one rotates momentum in vertex_position frame, using rotateUz() function.
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RotateUz() transforms uz to ur. It is composition of two elementary rotations:
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theta around oy, then phi around oz (non commutative). \n
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See: https://proj-clhep.web.cern.ch/proj-clhep/ \n
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Histograms 5,6 show momentum direction in vertex_position frame.
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See: PrimaryGeneratorAction4::GeneratePrimaries()
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## Visualisation
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Visualization Manager is set in the main().
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Initialisation of the drawing is done via the commands
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`/vis/..`` in the macro vis.mac. This macro is automatically read from the main
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in case of interactive running mode.
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## How to start ?
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- Execute particleGun in 'batch' mode from macro files
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```
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% ./particleGun run1.mac
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```
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- Execute particleGun2 in 'interactive mode' with visualization
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```
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% ./particleGun
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....
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Idle> ---> type your commands. For instance:
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Idle> /gunExample/selectGunAction 1
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Idle> /run/beamOn 10
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....
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Idle> exit
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```
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- Macros provided in this example:
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- run0.mac: see above primaryGenerator, case 0
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- run1.mac: see above primaryGenerator, case 1
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- run2.mac: see above primaryGenerator, case 2
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- run3.mac: see above primaryGenerator, case 3
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- run4.mac: see above primaryGenerator, case 4
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- particleGun.in: macro used in Geant4 testing (similar to run0.mac)
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## Histograms
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particleGun produces several 1D histograms which are saved as
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particleGun.root by default.
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- 1 : energy spectrum dN/dE = f(E)
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- 2 : vertex position: radial distr dN/dv = f(r)
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- 3 : vertex position: cos(theta)
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- 4 : vertex position: phi
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- 5 : particle direction in local frame: cos(alpha)
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- 6 : particle direction in local frame: psi
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Please note that histogram 1 will be filled only if you use
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PrimaryGeneratorAction2, histos 5,6 with PrimaryGeneratorAction0 and 3
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and 2 through 6 will be filled with PrimaryGeneratorAction4.
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The histograms are managed by the HistoManager class and its messenger.
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The histos can be individually activated with the command :
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```
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/analysis/h1/set id nbBins valMin valMax unit
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```
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where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
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One can control the name of the histograms file with the command:
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```
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/analysis/h1/setFileName name (default particleGun)
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```
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It is possible to choose the format of the histogram file : root (default),
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xml, csv by setting default file type in HistoManager::Book().
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It is also possible to print selected histograms on an ascii file:
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```
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/analysis/h1/setAscii id
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```
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All selected histos will be written on a file name.ascii (default gunExample)
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