Development and Evaluations of Apatite Crystal Scintillators

Five apatite crystal scintillators, which have chemical compositions of Ce 0.5%: Gd
_9.33
(SiO
₄
)
₆
O
₂
, Ce 0.5%: (Gd
₈
Sr
₂
)(SiO
₄
)
₆
O
₂
, Ce 5%:(Gd
₈
Sr
₂
) (SiO
₄
)
₆
O
₂
, Yb 0.5%:(Gd
₈
Sr
₂
) (SiO
₄
)
₆
O
₂
and Yb 3%:(Gd
₈
Sr
₂
) (SiO
₄
)
₆
O
₂
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 Ce
³⁺
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 (Gd
₈
Sr
₂
) (SiO
₄
)
₆
O
₂
showed about 23 ns decay constants, and the 5% doped one showed 14 ns. When coupled with Si-APD and irradiated by
²⁴¹
Am α-ray, Ce doped scintillators showed 300-500 photons/5.5 MeV as α light yield.