CVD diamond dosimeters for heavy ion beams

Abstract

Studies on dosimeters based on diamond grown by Chemical Vapour Deposition CVD for hadron therapy [G. Kraft, Nucl. Inst. and Meth. in Phys. Res. A 454 (2000) 1.] are presented. Online beam monitoring and non-integrating dosimetry by particle counting as well as passive thermoluminescence dosimetry is the aim of this work. Experiments have been performed with high-energy carbon beams (88–430 MeV/u) as well as low-energy (11.4 MeV/u) heavy charged-particles from 12C up to 238U. In order to benefit from its excellent signal-to-noise ratio single-crystal CVD samples have been used to count single-primary particles. The electronics is based on an ASIC and processed the current signals obtained from the detectors during the passage of every single particle in a bipolar readout configuration. The results have been compared with those obtained with broadband amplifiers. The counting efficiency has been measured to be 100% with an error of 7% for therapeutic carbon ions as well as for low energetic uranium ions. The thermoluminescence (TL) response of a batch of commercially available ‘mechanical grade’ polycrystalline CVD detectors has been studied. We found the TL signals of the dosimeters tested to be very reproducible and stable [M. Rębisz, A. Martemiyanov, E. Berdermann, M. Pomorski, B. Marczewska and B. Voss, Diamond Relat. Mater. 15 (2006) 822.]. In this paper the first measurements of the depth–dose distribution in specially prepared PMMA phantoms are presented.