Year

2015

Degree Name

Doctor of Philosophy

Department

School of Engineering Physics

Abstract

The harsh space radiation environment, imposes a significant risk, to both biological and non-biological matter. Radiation Induced Damage (RID), depends upon the type and energy of radiation and the material properties of the interacting medium. The similarities between microelectronics and biological cells in relation to RID then, are such that a common methodology of measuring radiation dose might be used. Microdosimetry, being a technique that allows for the measurement of stochastic energy deposition distributions within micron size sensitive volume (SV), is a methodology well suited to act as dose monitoring system for biological and non-biological matter.

A number of restrictions are placed upon device operation within the space radiation environment,that must be addressed when considering the viability of a detector. The cost of deployment, necessitates that the size, weight and power usage of the device be minimal. Spatial resolution, tissue equivalence and radiation hardness, especially for long term biological applications are concerned, are also vital. Solid state microdosimetry is well suited to address these issues and requirements, given the appropriate selection of materials such as diamond, which is both tissue equivalent and radiation hard.

A variety of different device structures based upon different fabrication technologies were developed and investigated with respect to applicability to microdosimetry. The behaviour of each device, was studied using both experimental and simulation based techniques. Experimental characterisation was performed to determine the electrical and charge collection properties of each device and validate charge confinement to the desired SV region. Simulation studies, to support experimental results, utilised two different simulations package suites; Geant4 and Sentaurus TCAD. Geant4 was used to investigate the effect of contact thickness upon energy deposition in addition to determining a tissue equivalence correction, to convert the energy deposition response in diamond to that in water. TCAD was used to model device structures and characterising the electric field structures and response to heavy ion strikes. TCAD modelling enabled a pre-fabrication assessment tool for device design and optimisation.

The results presented, demonstrate the viability of diamond along with a variety of different fabrication techniques, employed to produce structures, for solid state microdosimetry. Provided certain recommendations are followed, this work will certainly lead to the eventual realisation and commercialisation of diamond based devices for microdosimetric applications in space.

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