Speaker
Description
Recently, halide scintillators have been developed because of their high light yield which is originated from their narrow band gap. Thanks to great researchers’ efforts, some excellent scintillators have been found, such as Eu:SrI2 for high light yield, CeBr3 and Ce:LaBr3 for high light yield and fast decay time. In addition to these promising scintillators, new halide scintillator screening have been carried out for long time. For example, Ce doped AnREmXn+3m (A : Alkali metal, RE : Lanthanide, X : Cl, Br, I) and Ce doped A2A’REX6 (elpasolite structure, A : Alkali metal (large), A’ : Alkali metal (small) , RE : Lanthanide, X : Cl, Br, I) and Eu doped AnBmXn+2m (A : Alkali metal, B : Alkali earth metal, X : Cl, Br, I) have been studied a lot. But, except for few exception like CsI, most of halide scintillators are hygroscopic, therefore, scintillator materials which have both usability and good scintillation properties are required.
In this work, we focus on Ba2RECl7 (RE : Lanthanide). According to past references, Ba2RECl7 series are expected to be both moisture stable [1] and high light output [2] (for 10%Ce doped Ba2GdCl7 powder, light yield was estimated to be 30000 ph/MeV). In spite of their potential as a promising scintillator, only few research have been taken for Ba2RECl7. Therefore, we tried to grow single crystal of Ce doped Ba2RECl7 (RE = La, Gd, Lu and their combination) by Bridgman–Stockbarger (BS) method, and evaluated its scintillation properties.
Mixed powders were prepared as starting materials, and put them into quartz tube in glove box filled with Ar gas. Then, the quartz tube was evacuated with 250℃ heating for several hours to remove moisture and other impurities. After sealing, the quartz tube was heated up to the melting temperature of the compound by a high-frequency induction coil and carbon heater. Then, the crystal was grown by pulling down the quartz tube at 1 mm/h.
The grown crystals were cut and polished in a dry room using synthesis oil.
The phases of obtained crystals were confirmed by the X-ray powder diffraction (XRD) analysis. The scintillation properties of grown crystals were measured in dry room. In radioluminesence spectra, Ce3+ 5d-4f emissions were clearly observed. The pulse height spectra and decay time irradiated by radiation were also measured using PMT. 5%Ce doped Ba2GdCl7 was grown and evaluated its scintillation properties, light yield was about one third of CeBr3, and decay time was 33ns.
The phases of other grown crystals (Ce doped Ba2LuCl7, Ba2Lu0.5La0.5Cl7, Ba2Lu0.5Gd0.5Cl7) and difference of scintillation properties will be discussed.
References
[1] P. Egger, et al., Journal of Crystal Growth 200 (1999) 515 - 520.
[2] S. Derenzo, et al., Nucl Instr Meth A, 652 (2011) 247 - 250.
