Gabriele Cosmo
175 lines
7.9 KiB
Plaintext
175 lines
7.9 KiB
Plaintext
|
|
=========================================================
|
|
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
|
|
=========================================================
|
|
|
|
electronScattering2
|
|
------------------
|
|
|
|
Electron scattering benchmark variant 2 (Joseph Perl)
|
|
|
|
The two examples, electronScattering and electronScattering2 demonstrate how two alternate
|
|
approaches can be taken to simulating the same electron scattering benchmark experiment.
|
|
|
|
ElectronScattering2 simulates the experiment with a minimum of user code, whereas the other
|
|
version of this example shows how to do more of the work directly as the user.
|
|
In ElectronScattering2:
|
|
Primary generation relies on the G4GeneralParticleSource.
|
|
Material definitions are taken from the NIST database.
|
|
Visualization uses the standard G4VisExective.
|
|
Scoring is handled by the ready-made Geant4 scorer, G4PSCellFlux.
|
|
|
|
Both electronScattering and electronScattering2 simulate a precision electron scattering benchmark
|
|
experiment performed at NRCC Canada and published as:
|
|
"Measurement of multiple scattering of 13 and 20 MeV electrons by thin foils,"
|
|
by C. K. Ross, M. R. McEwen, A. F. McDonald, C. D. Cojocaru and B. A. Faddegon,
|
|
Med. Phys. Volume 35, Issue 9, pp. 4121-4131 (September 2008), DOI: 10.1118/1.2968095
|
|
|
|
The experiment represents the most accurate benchmark of its type.
|
|
|
|
A schematic of the experimental setup is shown in NRCC_electron_scat.pdf
|
|
|
|
The experimental data was itself published, as document number E-MPHYA6-35-034809 at http://www.aip.org/pubservs/epaps.html
|
|
|
|
The testing of three Monte Carlo simulation codes against this experimental benchmark has been
|
|
published as:
|
|
"The accuracy of EGSnrc, Geant4 and PENELOPE Monte Carlo systems for the simulation of electron
|
|
scatter in external beam radiotherapy,"
|
|
by Bruce A Faddegon, Iwan Kawrakow, Yuri Kubyshin, Joseph Perl, Josep Sempau and Laszlo Urban,
|
|
Phys. Med. Biol. 54 (2009) 6151Ð6163, DOI:10.1088/0031-9155/54/20/008
|
|
|
|
This present example, electronScattering2, was the Geant4 code used for this publication.
|
|
|
|
|
|
1- GEOMETRY DEFINITION
|
|
|
|
The geometry is described in the enclosed documument: NRCC_electron_scat.pdf
|
|
- A "World" volume contains an Exit Window, Primary Foil, Monitor Chamber and Helium Bag.
|
|
- The Helium Bag contains a Gas volume, which in turn contains 2 aluminium Rings
|
|
- A scoring cylinder is defined near the end of the World.
|
|
|
|
The default geometry is constructed in the DetectorConstruction class.
|
|
The parameters of the Primary Foil (material and thickness) are defined from macro commands.
|
|
|
|
|
|
2- PHYSICS LIST
|
|
|
|
Physics lists are based on modular design. Several modules are instantiated:
|
|
1. Transportation
|
|
2. EM physics
|
|
3. Decays
|
|
4. StepMax - for step limitation
|
|
|
|
EM physics builders are from the G4 kernel physics_lists subdirectory.
|
|
- "emstandard_opt0" recommended standard EM physics for LHC
|
|
- "emstandard_opt1" best CPU performance standard physics for LHC
|
|
- "emstandard_opt2" similar fast simulation
|
|
- "emstandard_opt3" best standard EM options - analog to "local" above
|
|
- "emstandard_opt4" best current advanced EM options standard + lowenergy
|
|
- "emstandardSS" standard EM physics and single scattering model
|
|
- "emstandardWVI" standard EM physics and WentzelVI multiple scattering
|
|
- "emstandardGS" standard EM physics and Goudsmit-Saunderson multiple scatt.
|
|
- "emlivermore" low-energy EM physics using Livermore data
|
|
- "empenelope" low-energy EM physics implementing Penelope models
|
|
- "emlowenergy" low-energy EM physics implementing experimental
|
|
low-energy models
|
|
|
|
Physics lists and options can be (re)set with UI commands
|
|
|
|
Note that options set through G4EmProcessOptions are global, eg for all particle types.
|
|
In G4 builders, it is shown how to set options per particle type.
|
|
|
|
|
|
3- PRIMARY GENERATOR
|
|
|
|
All of the work of the primary event generation is deferred to the G4GeneralParticleSource.
|
|
The specific characteristics of the source are configured from the macro file, using
|
|
/gps commands.
|
|
Energy is set to either 13 or 20 MeV.
|
|
Particle type is set to electron.
|
|
Direction is set exactly orthogonal to the scattering foil.
|
|
Source type is set to beam.
|
|
Spatial distribution of the beam is set as a circle gassian sigma_r of 0.042 cm
|
|
|
|
|
|
4- VISUALIZATION
|
|
|
|
Visualization is controlled by the standard G4VisExecutive.
|
|
The standard set of visualization options is supported.
|
|
Example macros use HepRepFile.
|
|
|
|
|
|
5- SCORING
|
|
|
|
All of the work of the scoring is done by the standard Geant4 scorers, G4PSCellFlux and G4PSPopulation.
|
|
Flux and population are scored in concentric rings at the scoring surface.
|
|
Flux is corrected for ring area just before output (as PSCellFlux assumes the area is the complete
|
|
area of the face of the cylinder, not the area of the one ring).
|
|
|
|
Because the geometry may need to be updated after various /primfoil commands,
|
|
ElectronBenchmarkDetector is written in such a way that the sensitive detector can have its scorer ring
|
|
logical volume updated after geometry changes. After any geometry change, ConstructSDandField is again
|
|
called, setting the sensitive detector to use the logical volume of the updated scorer ring.
|
|
The same sensitive detector is reused, but the manner in which the sensitive detector pointer
|
|
is stored for this reuse is complicated by the fact that this example may be run in multi-threaded mode
|
|
(in which each worker thread has its own sensitive detector).
|
|
We therefore store the sensitive detector pointer in a G4Cache rather than in a direct pointer.
|
|
|
|
|
|
6- MACROS
|
|
|
|
Macros are provided for all of the 37 different combinations of scattering foils and beam energies
|
|
that were used in the actual experiment.
|
|
Separate directories of these macros are provided for the different EM Physics options, Opt0, 1, 2 and 3.
|
|
|
|
|
|
7- HOW TO START
|
|
|
|
- execute electornScattering2 in 'batch' mode from macro files:
|
|
% electronScattering2 <macro_file> <starting_seed> <output_file>
|
|
|
|
- for example, to run the Al1_13MeV case with physics option 2 and a starting random seed of 1:
|
|
% electronScattering2 macros/Opt2/Al1_13MeV.mac 1 output/Opt2/Al1_13MeV_1
|
|
|
|
- if macro_file is not specfied, the job starts and then just waits for interactive commands
|
|
|
|
- if starting_seed is not specified, it defaults to 1.
|
|
Precision benchmark studies often involve running multiple long batch jobs and then combining the results.
|
|
If you plan to combine more than one job with the same primary foil and energy, be sure to use different
|
|
random seeds for each of the jobs.
|
|
|
|
- if output_file is not specified, it defaults to output.csv in the current directory
|
|
|
|
- to simplify batch submission of large numbers of jobs, a shell script is given called run.csh.
|
|
The above submission could be done, for example, by:
|
|
run.csh Opt2/Al1_13MeV 1
|
|
|
|
- to run a basic visualization job, producing output to a HepRep file, use vis.mac, as in:
|
|
% electronScattering2
|
|
then:
|
|
PreInit> /control/execute macros/vis.mac
|
|
|
|
|
|
8- OUTPUT
|
|
|
|
Results are given as comma-separated values (csv) files.
|
|
The first column gives the CellFlux for all particles.
|
|
The second column gives the CellFlux counting only electrons.
|
|
The third column gives the population for all particles.
|
|
The fourth column gives the population counting only electrons.
|
|
|
|
|
|
9 - MULTITHREADING
|
|
|
|
This example supports multi-threading.
|
|
To run in multi-threaded mode, build your Geant4 with the cmake option:
|
|
-DGEANT4_BUILD_MULTITHREADED=ON
|
|
and then set the desired number of threads by inserting the /run/numberOfThreads command
|
|
into your macro file just before /run/initialize, as in:
|
|
/run/numberOfThreads 8
|
|
You may also find the output more readable if you use the following command to make output from
|
|
each thread be collected together:
|
|
/control/cout/useBuffer
|
|
The visualization macro, /macros/vis.mac demonstrates use of the above two commands.
|
|
Output from the multiple worker threads is merged by the Merge method at the end of ElectronRun.cc
|