Improving the Performance of HPHT-diamond Detectors for Pulsed X-ray Dosimetry using the Synchronous Detection Technique

A single-crystal diamond sample grown by highpressure high temperature (HPHT) technique was used for the fabrication of a metal-semiconductor-metal photoconductor. The sample quality was evaluated by means of spectral photocurrent measurements highlighting the presence of a significant density of defect states within the diamond bandgap, responsible for trapmediated conduction mechanisms. The photoconductor was fully characterized under 6 MeV pulsed X-rays, sourced by a medical linear accelerator, in the 0.05 – 10 Gy and 1 – 6 Gy/min dose and dose-rate ranges, respectively. Photocurrent measurements performed with a conventional precision electrometer showed that the detector performance is strongly affected by charge-trapping phenomena, resulting in a sub-linear dependence with the doserate (power-law dependence with an exponent of 0.86). Measurements were repeated in the same experimental conditions by coupling the detector to a specifically developed gatedintegrator, allowing for a synchronous integration of photocurrent pulses (limited to 40 μs) centered on each impinging X-ray pulse. In this case, the detector photoresponse showed an excellent linearity with both the dose and the dose-rate (power-law dependence with 1.0009 ± 0.0004 and 1.009 ± 0.005 exponents, respectively). Significantly, the proposed synchronous integration technique is then able to mitigate the detrimental effect that defects have on detector performance. The proposed method paves therefore the way to the exploitation of HPHT-diamond as a lowcost alternative to single-crystal CVD-diamond for the fabrication of accurate and linear X-ray dosimeters.