Reproducibility of CVD diamond detectors for radiotherapy dosimetry

Three in-house X-ray detectors based on diamond chemical vapor deposition (CVD) from the same manufactured batch of single crystal films were investigated for their reproducibility. Leakage current, priming dose, response dynamics, dose linearity, dependence on dose rate and angular dependence were used to evaluate differences between detectors. Slight differences were seen in leakage currents before (<1.5 pA) and after (<12 pA) irradiation. A priming dose of ∼7 Gy and rise and fall times of 2 s were found for all three detectors. Sensitivities differed by up to 10%. Dependence on dose rate were similar (∆=0.92–0.94). Angular dependence was minimal (97–102% avg.). Differences in detector performance appeared to be primarily due to film thickness, which can significantly change sensitivities (nC Gy−1) and applied fields (V μm−1) for detectors with small sensitive volumes. Results suggest that preselection of CVD diamond films according to thickness in addition to material quality would be required to avoid individual calibration, which is performed for commercially available natural diamond detectors.