Example jetcounter

Author

M. Pietrzak (*), M. Mietelska, A. Bancer, A. Rucinski and B. Brzozowska
e-mail:marci.nosp@m.n.pi.nosp@m.etrza.nosp@m.k@fu.nosp@m.w.edu.nosp@m..pl or marci.nosp@m.n.pi.nosp@m.etrza.nosp@m.k@nc.nosp@m.bj.go.nosp@m.v.pl
This example is provided by the Geant4-DNA collaboration
Any report or published results obtained using the Geant4-DNA software

shall cite the following Geant4-DNA collaboration publications:
[1] Med. Phys. 37 (2010) 4692-4708
[2] Phys. Med. 31 (2015) 861-874
In addition, for this example, please cite:
[3] M. Pietrzak et al 2021 Phys. Med. Biol. 66 225008 (doi: 10.1088/1361-6560/ac33eb).

INTRODUCTION

The jetcounter example provides a setup for simulation of a typical experiment with the Jet Counter nanodosemeter.

This example allows the calculation of the ionisation cluster size distribution (ICSD) (the number of ionisations per projectile) in a real sized cylindrical interaction volume (IV) of the Jet Counter device.

The results of each of the simulation are provided in the plain text format. Each thread produces its own output file.

Each row in the output file consist information from a single event, where single primary particle (projectile) was generated. Each row contains 4 numbers (columns):

1. Ionisation cluster size.
2. Initial energy of the projectile.
3. Interaction energy of the projectile.
4. Final energy of the projectile.

Geometry visualization is available through vis.mac file.

Script written in Python is provided for visualization of the results.

GEOMETRY SET-UP

• The height of the interaction volume (IV) is equal to 20 mm and its diameter is equal to 10 mm.
• The beam axis enters the IV perpendicularly to its axis of rotation, 5 mm from the top.
• The IV is filled with liquid water material (G4_WATER), but its density is set to 0.45 µg/cm³, which corresponds to the nitrogen gas density in real experimental conditions. For details see [3].
• The beam divergence is restricted by a cylindrical collimator (3 mm in diameter, 23 mm in length) adjacent to the source.
• There is a wall around the IV in the form of a cylinder opened on both ends. The wall thickness is 0.98 mg/cm² (7 µm).
• The wall is composed of two layers: outer layer is made of Mylar, 0.96 mg/cm² in thickness; inner layer is made of liquid water (G4_WATER), 0.02 mg/cm² in thickness.
• There is a silicon (trigger) detector in the form of a thin disk placed behind the IV.

PRIMARY PARTICLES

If the beam energy is set to any positive value, the beam is mono-energetic with the given energy. If the beam energy is set to -1 (default value), the energy spectrum file is used. The energy spectrum of the beam is based on experimental data. Its mean energy is 4.6 MeV, which is the energy of alpha particles from gold-plated americium (241-Am) source. This source is chosen in the primaries.in macro file.

PHYSICS LIST

The PhysicsList used in this example show how to combine Geant4-DNA physics and standard physics in different regions using the G4EmDNAPhysicsActivator.

1. G4EmDNAPhysics is active in the IV and inner layer of the wall (both made of G4_WATER).
2. G4EmLivermorePhysics is active in other parts of the setup.

The G4DNAPhysics_option is chosen in the init_phys.in macro file. Hence, it can be changed without the need of recompilation.

SET UP

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

HOW TO RUN THE EXAMPLE

For the visualization:

./jetcounter vis

For the complete simulation:

./jetcounter run

In run.mac macro file will read init_phys.in and primaries.in.

However, it is recommended to first increase the number of simulated events in the run.mac file to at least 4000.

To produce figures from simulation results (requires numpy and matplotlib Python libraries):

 python3 plot.py