Thesis Title : “ Evaluation of the Radiation Detection Properties of Synthetic

Aimed at improving the accuracy of dose determination in radiation medicine, this thesis explores the radiation detection properties of synthetic diamond crystals of various types and investigates the possibility of developing a single probe with synthetic diamond as sensor for the dosimetry of various beam types under large as well as small-field conditions. The study was conducted on two HPHT (high-pressure, high-temperature) and eight CVD (chemical vapor deposited) synthesized diamonds of optical grade (OG) and detector grade (DG) qualities of various dimensions. Various non-destructive techniques were employed to characterize the electrical quality and defect levels present within each of the samples. Detector performances were evaluated using a prototype probe housing constructed of tissueequivalent materials. The probe has features, which allow diamond crystals to be exposed in different exposure orientations (‘edge-on’ and ‘flat-on’) for impinging radiation without having first to re-orient the diamond sensor within its body. All dosimetric measurements taken with the synthetic diamond probe were from exposures to low-energy mammography X-rays (25-32 kVp), and megavoltage therapy electron (7-14 MeV) and photon (Co γ-ray, 6 and 15 MV X-ray) beams. The most important findings emphasized in this thesis include: (1) The main cause of the response instability of the examined crystals necessitating the often cited daily primimg procedure was isolated and ascribed to the presence of ambient light which has the effect of emptying trapping centres present within the diamond sensors. The percentage changes in response between measurements in light and dark conditions conducted over a period of three successive weeks were 2.8±1.2, 25.2±6.3 and 63.0±0.3% for HPHT, DG and OG CVD diamond detectors, respectively. For measurements under light conditions alone using the tested detectors, the difference in response was > 5%, whereas in dark conditions the difference in response was < 3%. This signifies that once the diamond sensors are properly shielded from ambient light and their response stabilized, daily priming is not necessary;