Development and Evaluations of Apatite Crystal Scintillators

Five apatite crystal scintillators, which have chemical compositions of Ce 0.5%: Gd_9.33(SiO₄)₆O₂, Ce 0.5%: (Gd₈Sr₂)(SiO₄)₆O₂, Ce 5%:(Gd₈Sr₂) (SiO₄)₆O₂, Yb 0.5%:(Gd₈Sr₂) (SiO₄)₆ O₂ and Yb 3%:(Gd₈Sr₂) (SiO₄)₆ O₂ were grown by the micro-pulling down method. After cut and polishing processes, optical and radiation properties were evaluated. In a transmittance measurement, Ce doped crystals showed an absorption feature at approximately 300 nm and Yb doped ones 220 nm, respectively. When Ce-doped ones were excited by 340 nm photons, the emission peak appeared at approximately 400 and 440 nm, due to Ce³⁺ 5d-4f transitions. In Yb-doped series, 270 nm excitation caused emission peaking around 300 nm. The photoluminescence decay time kinetics of Ce-doped series were investigated. The Ce 0.5% doped (Gd₈Sr₂) (SiO₄)₆ O₂ showed about 23 ns decay constants, and the 5% doped one showed 14 ns. When coupled with Si-APD and irradiated by ²⁴¹Am α-ray, Ce doped scintillators showed 300-500 photons/5.5 MeV as α light yield.