Position sensitive β⁻ detector based on p-terphenyl scintillator for medical applications

P-terphenyl crystals are high light yield organic scintillators characterised by a relatively short intrinsic light attenuation length. The effective value of this physical quantity depends on the actual design of the detector and can be tuned for a specific application with the appropriate combination of crystal size and shape, its bulk and superficial optical properties and the light sensor choice. In this paper we investigate the feasibility to use this feature to realize a simple, mono crystal, position sensitive, β⁻ particle counter able to identify both the presence and the position of a β⁻ point source located in close proximity of the detector. This simple design allows an integration of this detection technique into specific β⁻-RGS (Radio Guided Surgery) surgical devices of use in brain tumour-ectomy and in endoscopic applications, giving the surgeon a better guidance to spot the tumour localisation. We present the results obtained with two devices: a single channel particle counter built on a cylindrical crystal (ϕ=10 mm, h=10 mm) designed to probe and identify the position of a point β⁻ source located around the surface of the detector, and a four channels particle counter built on a smaller (ϕ=7 mm, h=3 mm), ring shaped, crystal designed to identify the position of a point β⁻ source placed just ahead of the detector. In both configurations we were able to clearly identify the presence and the position, relative to the detector, of a radio-active point source set off axis with respect to the crystal. The four channel detector shows an angular resolution of ±8 degree and an effective light absorption length of 4.2±0.1 mm. The single channel cylindrical crystal have a 8.0±0.5 mm effective light absorption length and the same discovery potential.