Scintillator Geometrical Considerations for Detectors Based on Hexagonal SiPMs

A truncated icosahedron system with hexagonal detectors has been previously proposed as an approach to the ideal spherical PET scanner. In this work, we explore by Monte Carlo simulations, the role of hexagonal scintillator crystals in terms of light yield, scintillation pulse decay time and energy resolution by comparison with three geometries: square and triangular prisms and cylinder. The relevance of the reflector type (diffuse and specular) and finish (polished and rough) of the scintillation borders was also considered. The light yield for the hexagon is higher by approximately 2% and 4% depending on the finish and reflector type in comparison to the square. The energy resolution is between 0.2% and 1% better for the hexagon. Polished walls with specular reflector have the finest energy resolution. The difference in the pulse decay time among geometries is not determining. The light yield and energy resolution were validated experimentally for rough walls and diffuse reflector. A hexagonal scintillation array of 181 crystals of 1.25 mm of edge was finally manufactured. The flood field image read with four multiplexing channels is presented. The detector offers an excellent crystal identification with a mean peak-to-valley ratio over 13 and an energy resolution of 11.5%.