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Optimization of the effective light attenuation length of YAP:Ce and LYSO:Ce crystals for a novel geometrical PET concept

The effective light attenuation length in thin bars of YAP:Ce and LYSO:Ce crystals has been studied for different coatings of the lateral surfaces of the scintillators. This physical parameter plays a key role in a novel 3D PET concept based on axial arrays of long scintillator bars read out at both ends by Hybrid Photodetectors (HPD). The parameter influences the spatial, energy, and time resolutions of such a device. The expected resolutions let the novel concept appear competitive compared to existing traditional PET devices. In this paper we show that the effective light attenuation length can be tuned to the desired value by wrapping the lateral surfaces of the crystals or by coating them with layers of Cr or Au of different thickness. The studies have been carried out with long YAP and LYSO scintillator bars, read out by standard photomultiplier tubes. Even though the novel PET device is planned to use different scintillators and HPD readout, the results described here prove the feasibility of an important aspect of the concept and explore the potential resolution of the device.