Room temperature CVD diamond X-ray and charged particle microdetectors

Hot filament chemical vapour deposition technique is particularly suitable for the realisation of diamond tip and wire detectors working in a coaxial geometry with a built-in internal metal electrode. By using tungsten wires of different diameters and by controlling the shape of the tip by an electrochemical etch, it is possible to obtain various kinds of microdetectors, with diameters ranging from 50 to 300 μm. The response of these diamond tip and wire detectors has been tested at low X-ray energies (50–250 keV) and at relatively high energies (6–15 MeV) both in terms of sensitivity (collected charge with respect to the absorbed dose) and of linearity as a function of X-ray fluence. Sensitivities larger than 2 nC/Gy are achieved, with a good linearity in the dose rate range used in applications. Such microprobes have been proved to be suitable as narrow X-ray beam profilers and as surface or in vivo microdosimeters for on-line monitoring of radiotherapy plans. Such detectors have also been used as nuclear micro detectors by measuring the response to alpha particles from an 241Am source and from a proton beam (2.4 MeV energy) produced by a van de Graaff accelerator. In this case the estimated collection efficiency is higher than 20% for wires and 50% for tips.