Systematic study of pre-irradiation effects in high efficiency CVD diamond nuclear particle detectors

Many outstanding properties of diamond can, in principle, lead to the development of radiation detectors with interesting capabilities. In particular, diamond-based nuclear particle detectors are good candidates to replace silicon-based detectors in several fields, e.g. in high-flux applications such as next generation particle-accelerator experiments or beam monitoring. However, the high concentration of defects (grain boundaries. impurities) in synthetic diamond films can strongly limit the detector's performance. A significant increase in the efficiency of CVD diamond detectors is achieved by means of pre-irradiation (pumping) with beta particles. We report here on a systematic study of the effects of pumping in high-quality microwave CVD diamond films. The efficiency (eta) and charge collection distance (CCD) of nuclear particle detectors based on these films depend on the methane content in the growth gas mixture and on the film thickness. Both efficiency and CCD behave in a markedly different way in the as-grown and pumped states. Experimental data are found to agree with a recently proposed model (Appl. Phys. Lett. 75 (1999) 3216) discussing how in-grain defects and grain boundaries affect the charge collection spectra of CVD diamond detectors, before and after pumping. The dependence of pumping effects at different operating temperatures of the detector is also reported. (C) 2002 Elsevier Science B.V. All rights reserved.