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Single photon avalanche diodes (SPADs) are highly sensitive solid-state photon detectors, and since their inception in 2003 into complementary metal oxide semiconductor (CMOS) technologies, have provided a platform of highly integrated and low-cost mass manufacture detectors, capable of rapid detection of single photons. The consequent commercial potential has led to the development and availability of a range of CMOS SPAD sensors and arrays. As a consequence of their mature development in advanced processes, detection sensitivity and timing capabilities, CMOS SPADs have found their way into multiple applications, most notably biomedical fluorescence lifetime imaging microscopy (FLIM), Light Detection and Ranging (LiDAR), Time-of-Flight (ToF) imaging, Single Photon Counting (SPC), high speed imaging, biological particle tracking and more recently visible light communications. Although, all current applications are constrained to the visible and near infrared spectrums. The advances and broad applications of CMOS SPADs has led to increased development towards further miniaturisation, performance improvements and developing highly integrated intelligent sensors. Therefore, the investigation of the application of SPADs in the detection of ionising radiation has significant commercial potential as an alternative technology to current detectors. The goal of this research is to explore the direct detection of ionising radiation with CMOS SPADs. The fundamental mechanism for detection is a depleted junction operated in Geiger mode, with an induced electric field that allows sensitive detection of generated electron-hole pairs as a result of incident radiation. Therefore, based on this principle it was hypothesised that SPADs can be applied beyond current photon specific detection applications into the detection of ionising radiation. Furthermore, high energy physics is transitioning towards CMOS processes with all the unprecedented advantages it provides. Therefore, it is believed that with SPAD advancement and maturity in CMOS technology, this parallel and continually developing technology may lend itself favourably towards progress and application in the detection of ionising radiation. This work reports on a 3D-stacked backside illuminated (BSI) CMOS SPAD image sensor for the detection of accelerated electrons, pions and X-rays, utilising a scanning electron microscope, synchrotron particle accelerators and X-ray tube sources respectively. For accelerated electron detection, electron energies from 5 to 30 keV were detected, and statistical significance was found that both SPAD excess bias voltage and/or incident accelerated electron energy result in a distinct output. Furthermore, the SPAD image sensor was able to achieve time-resolved imaging of the electron beam raster scan pattern. For X-ray detection, X-rays with peak photon energies from 30 to 160 keV were detectable using an X-ray tube, and it was found that an increase in either SPAD bias voltage, output beam voltage or beam intensity results in higher relative average counts per pixel, therefore demonstrating the potential application of SPAD image sensors in X-ray imaging. These results are the first demonstration and application of a CMOS SPAD in the detection of accelerated electrons and X-rays. Further investigation revealed that the attenuation of lower energy photons from an X-ray tube spectrum results in approximately 200 % increase in relative average counts. Furthermore, The BSI CMOS SPAD image sensor was irradiated with a high energy pion beam at 120 GeV, using the Super Proton Synchrotron (SPS) at CERN, and high energy electrons at 2.5 GeV, using an electron accelerator at ELSA. For the pion irradiation, pions were conclusively detected, and it was found that an increase in SPAD bias voltage results in higher relative average counts per pixel. No conclusive detection of higher energy electrons was observed as a result of low beam intensity. After the pion irradiation, radiation damage to the SPAD image sensor was observed. These results are the first demonstration and application of a CMOS SPAD in the detection of high energy charged particles.

In this work the design and implementation of an x-ray imager system is presented. The design features a direct x-ray detection scheme by making use of a hybrid pixel detector (Medipix3RX). Taking advantage of the capabilities of the Medipix3RX, such as a high resolution, zero dead-time, single photon detection, charge-sharing mode and colour mode. The imager has a better resolution and higher sensitivity compared to using traditional indirect detection schemes. A detailed description of the design process and implementation of the system is presented, which consists of a vacuum chamber containing the sensor, an electronic board for temperature management, conditioning and readout of the sensor and a data processing unit which also handles network connection and communication with clients by acting as a server. A field programmable gate array (FPGA) device is used to implement the readout protocol for the Medipix3RX. Apart from the readout, the FPGA can perform complex image processing functions such as histogram, profiling and image compression at high speeds. The temperature of the sensor is monitored and controlled through a PID algorithm making use of a Peltier cooler, improving the energy resolution and response stability of the sensor. Without implementing data compression techniques, the system is capable of transferring 680 profiles/s or 240 images/s in a continuous mode. A detailed analysis of equalization procedures and tests for all the operation modes of the sensor are presented in this work. Different equalization methods were tested, such as using electronic noise, injected pulses and x-ray photons to perform the equalization. The results of the trade-off of equalization time versus energy resolution are analysed and discussed. One of the tested applications of the system is as an x-ray beam position monitor (XBPM) device for synchrotron light source experiments. The XBPM allows a non-destructive real time measurement of the beam position, size and intensity. A Kapton foil is placed in the beam path scattering radiation towards a pinhole camera setup that allows the sensor to obtain an image of the beam. By using profiles of the synchrotron x-ray beam, high frequency movement of the beam position can be studied. Experiments testing the characteristics of the Medipix3RX are shown in this work. The colour mode capability and its limitations were tested and found to be able to recognize elements by their characteristic x-ray fluorescence. The Medipix3RX dependence to temperature was measured, showing the necessity of controlling the sensor's temperature.

Gamma-ray spectroscopy is undoubtedly the most effective tool for understanding the structure of the nucleus. In common with many other problems however, there is more information available that can be readily measured by standard experimental facilities. Therefore, this thesis investigates the potential for the use of a new detector material, CdZnTe, in nuclear physics applications. To evaluate the requirements of detection systems for nuclear physics applications, a y-ray spectroscopy experiment was performed to investigate neutron alignments in 100Mo, 104Ru and 108Pd using deep-inelastic reactions. This showed that a detector capable of detecting low energy (< 100 keV) X- rays without compromising y-ray detection efficiency could have significant benefit. A room temperature CdZnTe semiconductor detector could reasonably form part of a standard escape suppressed spectrometer. However, there is a substantially higher leakage current associated with room temperature semiconductor devices than standard cryogenically cooled semiconductor detectors. CdZnTe suffers from significant charge trapping, and therefore the rise time of the radiation induced pulses forms an important part of the signal analysis from such detectors. These two problems have implications on the design of preamplifier systems for CdZnTe detectors. For this reason, this thesis describes the design of optimised electronic systems for use with room-temperature operated CdZnTe detectors. Here, the focus is on the preamplifier design, and on practical ways of analysing noise performance of the preamplifier. A new preamplifier configuration with digital output has been developed, and a detailed signal-to-noise analysis performed. Such a circuit facilitates simultaneous measurement of both energy and pulse shape information.