g4simple

Perhaps the simplest fully-featured G4 application.

Based on one-file simulation by Jason Detwiler.

Installation:

Compile geant4 with GDML support (and optionally HDF5 support), then in your terminal, enter:

source (g4install_path)/share/(g4version)/geant4make/geant4make.sh

(or source (g4install_path)/share/(g4version)/geant4make/geant4make.csh)

make

May 2021: G4 deprecated geant4make-based installation for cmake. As a result, visualizations don't work with this method of installation. Worse yet, Geant4's installation instructions are incomplete and I have not yet been able to get cmake to work with HDF5 support. I'll update the instructions here once I figure it out. --Jason

Physics List:

uses Geant4's named physics lists, set them using macro commands (see example run.mac)

Generator:

uses Geant4's GPS. Set it up using macro commands (see example run.mac).

Geometry:

uses GDML (see example run.mac). Can use materials from Geant4's NIST Material Database (note: the GDML parser will complain that the materials have not been defined, but Geant4 will still run without error). Also supports Geant4's text file geometry scheme.

Output:

uses Geant4's analysis manager (root, hdf5, xml, csv), with several configurable options for output format, sensitive volumes (including regex-based pattern matching / replacement), etc. (see example run.mac). Records event/track/step numbers, PIDs (see also the python package particle), positions, energies, etc.

Other macro commands

see the example run.mac, or run g4simple and type "help" and choose the g4simple option. Note: more commands become available after setting a physics list.

Visualization

uses available options in your G4 build (see example vis.mac).

Postprocessing

you will want to postprocess the output to apply e.g. detector response. See example code that runs on the output of run.mac.

Ouput parameters:

Output parameter values are in Geant4 internal units:

• Length in mm
• Time in ns
• Energy in MeV

The available output parameters are:

• int nEvents: number of events run in the simulation
• int event: event number of the recorded step
• int pid: particle ID of the particle making the step
• int trackID: track ID for the recorded step
• int parentID: parent track ID of the track being recorded
• int step: current step number
• double KE: kinetic energy at the start (step=0) or end (step>0) of the step
• double Edep: energy deposited along the step
• double x: global x coordinate of the pre- (step=0) or post- (step>0) step position
• double y: global y coordinate of the pre- (step=0) or post- (step>0) step position
• double z: global z coordinate of the pre- (step=0) or post- (step>0) step position
• double lx: local x coordinate of the pre- (step=0) or post- (step>0) step position
• double ly: local y coordinate of the pre- (step=0) or post- (step>0) step position
• double lz: local z coordinate of the pre- (step=0) or post- (step>0) step position
• double pdx: global x component of the pre- (step=0) or post- (step>0) step momentum
• double pdy: global x component of the pre- (step=0) or post- (step>0) step momentum
• double pdz: global x component of the pre- (step=0) or post- (step>0) step momentum
• double t: global time of the pre- (step=0) or post- (step>0) step point
• int volID: the ID of the volume being traversed (user-defined) (see example run.mac)
• int iRep: the replica number of the volume being traversed

You can turn on and off different output fields using the macro silenceOutput/addOutput macro commands (see examples in run.mac).

Note: Each pair of rows in the output corresponds to the pre- and post-step point of the corresponding step, with the step number, Edep, and volume traversed for the step recorded along with the post-step. Note that this means that volume ID changes occur at the first step point inside a volume, not at the point recorded on the boundary. This may be counter-intuitive for those familiar with G4, where the step point on the boundary is marked as being "in" the volume being entered.

For every energy-depositing particle traversing a sensitive volume, the g4simple output will include the step info for the first step point in the volume. If the previous volume was not a sensitive volume, that step will have Edep = 0.

See Also

Similar project by Jing Liu at https://github.com/jintonic/gears