Year

2012

Degree Name

Doctor of Philosophy

Department

Centre for Medical Radiation Physics

Abstract

There are many types of semiconductor detectors used in radiation detection and dosimetry. A common problem of these detectors under a wide energy spectrum is that their response in a radiation field depends on energy. In radiation protection-applications, gamma and neutron are the most common primary radiation. Other forms of radiation, such as hadronic particles, are important in space applications, but are not included in the scope of this study because they deserve a separate examination. This study mainly focuses on the development of semiconductor dosimeters for mixed gamma-neutron, with an improved energy response achieved by an innovative design and packaging that can adjust the energy response of the detector for each application. Two detectors – were the metal-oxide-semiconductor field-effect transistor (MOSFET) for gamma dosimetry and the pixelated silicon diode detector, Medipix2 [1] for fast neutron dosimetry – were modelled using a Monte Carlo simulation developed in the GEometry ANd Tracking (GEANT4) application toolkit to improve their energy response.

Since the MOSFET was introduced to the field of radiation detection, its packaging has undergone many evolutions to satisfy its intended working conditions. This study focuses on the optimisation of MOSFET packaging to adjust its energy response for personnel dosimeter applications. The aim of this optimisation was to reduce its tendency to over-respond at photon energy less than 100 keV.

Medipix2 was first developed as a tracker of high-energy charged particles in HEP applications; it subsequently found a use as an X-ray imaging detector. In later developments Medipix2 demonstrated its ability in neutron imaging and detection [2], thereby showing its potential as a neutron dosimeter. This research proposed and developed a structured hydrogen-rich neutron converter coupled with Medipix2 to achieve an independent energy response. The converter was designed to allow Medipix2 to measure the ambient dose equivalent of neutrons [3]. The GEANT4 simulation results were then compared to the preliminary experimental results on fastneutron sources. These promising results will help pave the way for future development of a novel fast-neutron detector.

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