geant4

\author S. Incerti (a, *), , H. Tran (a, *), V. Ivantchenko (b), M. Karamitros\n a. LP2i, IN2P3 / CNRS / Bordeaux 1 University, 33175 Gradignan, France \n b. G4AI Ltd., UK

e-mail: incerti@lp2ib.in2p3.fr or tran@lp2ib.in2p3.fr \n

INTRODUCTION.

The dnaphysics example shows how to simulate track structures in liquid water using the Geant4-DNA physics processes and models.

The Geant4-DNA processes and models are further described at: http://geant4-dna.org

Any report or published results obtained using the Geant4-DNA software shall cite the following Geant4-DNA collaboration publications: \n Med. Phys. 51 (2024) 5873–5889 \n Med. Phys. 45 (2018) e722-e739 \n Phys. Med. 31 (2015) 861-874 \n Med. Phys. 37 (2010) 4692-4708 \n Int. J. Model. Simul. Sci. Comput. 1 (2010) 157–178

GEOMETRY SET-UP

The geometry is a 100-micron side cube (World) made of liquid water (G4_WATER material). Particles are shot from the center of the volume. The World size can be changed directly in the dnaphysics.in macro file.

The variable density feature of materials is illustrated in DetectorConstruction. The material density can be changed directly in the dnaphysics.in macro file.

SET-UP

Make sure $G4LEDATA points to the low energy electromagnetic data files.

HOW TO RUN THE EXAMPLE

In interactive mode, run:

./dnaphysics

In batch, the macro dnaphysics.in can be used. It shows how to shoot different particle types and how to use Geant4-DNA Physics constructors.

The deexcitation.in macro can be used to simulate the energy spectrum of deexcitation products.

The radioactive.in macro can be used to simulate some radioactive nuclei.

PHYSICS

The PhysicsList uses Geant4-DNA Physics constructors and other electromagnetic physics constructors.

Geant4-DNA Physics constructors can be selected using the command:

/dna/test/addPhysics DNA_OptX

where X is 0 to 8 (2, 4 or 6 are recommended).

In addition, to also enable radioactive decay, one can use:

/dna/test/addPhysics raddecay

Warning regarding ions: when the incident particle type is ion (/gun/particle ion), specified with Z and A numbers (/gun/ion A Z), the Rudd ionisation extended model is used. The particles are tracked by default down to 0.5 MeV/u and undergo below a capture process. This tracking cut can be bypassed using:

/dna/test/addIonsTrackingCut false

SIMULATION OUTPUT AND RESULT ANALYSIS

The output results consists in a dna.root file, containing two ntuples, named "step" and "track", respectively:

1) for each simulation step:

the type of particle for the current step
the type of process for the current step
the step PostStepPoint coordinates (in nm)
the energy deposit along the current step (in eV)
the step length (in nm)
the total energy loss along the current step (in eV)
the kinetic energy at PreStepPoint (in eV)
the cos of the scattering angle
the event ID
the track ID
the parent track ID
the step number

This information is extracted from the SteppingAction class.

The ROOT file can be easily analyzed using for example the provided ROOT macro file plot.C; to do so :

be sure to have ROOT installed on your machine
be sure to be in the directory containing the ROOT files created by dnaphysics
copy plot.C into this directory
from there, launch ROOT by typing root
under your ROOT session, type in : .X plot.C to execute the macro file
alternatively you can type directly under your session : root plot.C

The plotDeexcitation.C ROOT macro file can be used to plot results of deexcitation.in.

The plotRadioactive.C ROOT macro file can be used to plot results of radioactive.in.

The plotElastic.C ROOT macro file can be used to show distribution of elastic scattering angles of the elastic process obtained with elastic.in. This macro also illustrates the usage of a dedicated UI command :

/step/recordOnlyFirstStep value

where value is 0 or 1. Setting value to 1 only records the first step and then kills the track and its secondaries.

The naming scheme for particles and processes on the displayed ROOT plots adopts a local numbering, as follows (see SteppingAction.cc):

particles: \n gamma: 0 \n e-: 1 \n proton: 2 \n hydrogen: 3 \n alpha: 4 \n alpha+: 5 \n helium: 6 \n GenericIon (above helium): 7\n \n
processes: \n

Capture: 1

RadioactiveDecay: 2

e-_G4DNAElectronSolvation: 10 \n e-_G4DNAElastic: 11 \n e-_G4DNAExcitation: 12 \n e-_G4DNAIonisation: 13 \n e-_G4DNAAttachment: 14 \n e-_G4DNAVibExcitation: 15 \n msc: 110 \n CoulombScat: 120 \n eIoni: 130 \n \n

proton_G4DNAElastic: 21 \n proton_G4DNAExcitation: 22 \n proton_G4DNAIonisation: 23 \n proton_G4DNAChargeDecrease: 24 \n msc: 210 \n CoulombScat: 220 \n hIoni: 230 \n nuclearStopping: 240 \n \n

hydrogen_G4DNAElastic: 31 \n hydrogen_G4DNAExcitation: 32 \n hydrogen_G4DNAIonisation: 33 \n hydrogen_G4DNAChargeIncrease: 35 \n \n

alpha_G4DNAElastic: 41 \n alpha_G4DNAExcitation: 42 \n alpha_G4DNAIonisation: 43 \n alpha_G4DNAChargeDecrease: 44 \n msc: 410 \n CoulombScat: 420 \n ionIoni: 430 \n nuclearStopping: 440 \n \n

alpha+_G4DNAElastic: 51 \n alpha+_G4DNAExcitation: 52 \n alpha+_G4DNAIonisation: 53 \n alpha+_G4DNAChargeDecrease: 54 \n alpha+_G4DNAChargeIncrease: 55 \n msc: 510 \n CoulombScat: 520 \n hIoni: 530 \n nuclearStopping: 540 \n

helium_G4DNAElastic: 61 \n helium_G4DNAExcitation: 62 \n helium_G4DNAIonisation: 63 \n helium_G4DNAChargeIncrease: 65 \n \n

GenericIon_G4DNAIonisation: 73 \n msc: 710 \n CoulombScat: 720 \n ionIoni: 730 \n nuclearStopping: 740 \n \n

phot: 81 \n compt: 82 \n conv: 83 \n Rayl: 84 \n

2) for each simulation track:

the type of particle for the current track (see 1))
the track position (in nm)
the track momentum direction
the track kinetic energy (in eV)
the track ID
the parent track ID

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