radioprotection

Introduction

This example has been provided to illustrate radiation monitoring solutions within a space radiation environment. It features a diamond based microdosimeter [1] with an active sensitive volume (SV) to record energy depositions and plot them into a pre-assigned histogram. The diamond microdosimeter was designed by Prof. Anatoly Rosenfeld, Centre For Medical Radiation Physics, University of Wollongong, and collaborators and documented in [1]. This example also allows you to plot the spectral energy fluence of the primary particles. Lastly, this example records the kinetic energy, charge and atomic mass of all secondaries within the active SV and stores this information within an ntuple. This feature allows users to monitor secondaries and compare relative contributions to dose. The radiation field is composed of Galactic Cosmic Ray (GCR) protons directed isotropically inwards from a sphere towards the microdosimeter design. GCR protons make up approximately 85% of the total GCR flux. Energy spectral fluence has been sourced from Creme96 [2]. This application was designed and implemented at the Centre for Medical Radiation Physics by Dr. Susanna Guatelli and Mr. Jeremy Davis for microdosimetric applications within space environments.

Authors:
Susanna Guatelli
Jeremy Davis

Example components

The radioprotection example encompasses components, that have different responsibilities and cooperate to achieve the goals of the application defined in the User Requirement Documents.

Primary particles

As aforementioned, the examples models protons typical of GCR protons with energy spanning from 1 MeV up to 100GeV (see Fig. 1). Particles are modelled using General Particle Source (GPS). Particles are generated from a sphere with radius 0.2m using a cosine distribution as this has been recognised to produce best agreement for an isotropic field. A limiting angle has been implemented in order maximise particles which might cross the device structure thereby reducing computing time and thus increase the overall efficiency. All of the particle and field parameters can be located in Primary.mac macro which is implemented within the run.mac script in the example.

CREME96_H_He_3.png
Fig1: GCR protons sourced from CREME96 [2]

Experimental set-up

The device features four SV structures composed of diamond “embedded” within a diamond substrate. In this example only one SV has been made active, its co-ordinates relative to the origin are (-45, 105, Z?) and has dimensions of 150x150x1.38 µm3. The substrate itself is a slab of diamond with dimensions µm3. On top of the device is an aluminium contact layer which covers all four of the SV structures. This has been placed within a vacuum block (daughter of the diamond substrate). This design method allows for medium continuity without succumbing to overlapping geometries. Below the SV structures is a boron doped layer to provide a resistive path to the back contact; a gold cylinder made up of three separate gold cylinders in order to overcome overlapping volumes.

side_device.png
Fig 2: Device profile

top_device.png
Fig. 3: Top view of Device

Physics

The physics component has the responsibility of the activation of Geant4 physics processes. It is modularised in sub-components: each component controls the activation of the processes for a given particle type. The user can activate both electromagnetic and hadronic physics processes.

Stepping

This component manages information regarding the steps of particles in the experimental set-up. The user can retrieve the information about the type of a particle, its energy, its initial energy, etc..

Visualisation

The application is interfaced to external visualisation tools to visualise the experimental set-up and the particle tracks. The user can use OpenGL, DAWN, VRML as graphics tools. A macro is provided as example of visualisation using OpenGL: vis.mac

Analysis

The output is radioprotection.root, containing 3 ntuples
  • An ntuple with the energy spectrum (in MeV) of primary particles (h10)
  • An ntuple with the energy deposition per event(in keV) in the SV.
  • An ntuple with the A, Z, and energy of the secondary particles originated in the diamond microdosimeters.

LoadPlot_Ntuple.C is provided to plot any stored events within the ntuple in the radioprotection.root file. If the user intends to use these macros, ROOT must be installed (http://root.cern.ch/).

Set-up

A standard Geant4 example CMakeLists.txt is provided. Setup for analysis: By default, the example has no analysis component.T o compile and use the application with the analysis on, build the example with the following command:
cmake -DWITH_ANALYSIS_USE=ON -DGeant4_DIR=/path/to/Geant4_installation /path/to/radioprotection example

How to run the example

Batch mode:
./radioprotection run.mac
Interactive mode:
./radioprotection
vis.mac is the default macro, executed in interactive mode.

References:

[1] J. A. Davis et al. IEEE Trans. Nucl. Sci., Vol. 59 (6), 2012
[2] A J. Tylka, et al. IEEE Trans. Nucl. Sci., Vol. 44 (6), 1997.

UowCmrpPms.PNG

-- LucianoPandola - 22 Oct 2014

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Topic revision: r2 - 2015-01-07 - SusannaGuatelli
 
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