Dosimetric Characteristics of CVD Single Crystal Diamond Detectors in Radiotherapy Beams

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Dosimetric characteristics of a CVD single crystal diamond detector have been evaluated. Detector stability, linearity, optimal bias, temperature dependence, directional dependence, priming and pre-irradiation behaviour, depth dose curves and dose profiles were investigated.The optimal bias was determined to be 50 V. The detector stability measurement showed a too large variation for absolute dosimetry in a day to day measurement, but acceptable variation during one and the same day. The linearity constant, ?, in the relation between signal and dose rate, (Fowler 1966), was determined to 0.978 and 0.953 for two detectors. The sub-linearity was also observed in the depth dose curves and could be eliminated with a correction method. The diamond detector showed smaller temperature dependence than the EFD silicon diode. The directional dependency was, <1 %, up to at least ± 15° and therefore no angular correction is needed. A priming dose of 0.6 Gy was determined, which is considerably smaller than for existing detectors on the market. After pre-irradiation with electrons (8 and 18 MeV) a large and permanent desensitization of up to 31 % / 500 Gy was detected. This is in contradiction to what previous published articles claim. 15 MV photons also reduced the sensitivity of the detector, but no evidence that 5 MV photons do has been found. A 50 Gy dose of 180 MeV protons did not reduce the sensitivity either. The detector dose rate linearity was improved by electron pre-ir...