【公開日：2023.07.31】【最終更新日：2023.05.13】

課題データ / Project Data

課題番号 / Project Issue Number

22UT0165

利用課題名 / Title

光導波型シンチレータに関する研究

利用した実施機関 / Support Institute

東京大学 / Tokyo Univ.

機関外・機関内の利用 / External or Internal Use

外部利用/External Use

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）計測・分析/Advanced Characterization（副 / Sub）-

【重要技術領域 / Important Technology Area】（主 / Main）高度なデバイス機能の発現を可能とするマテリアル/Materials allowing high-level device functions to be performed（副 / Sub）-

キーワード / Keywords

電子顕微鏡/Electron microscopy,光導波路/ Optical waveguide

利用者と利用形態 / User and Support Type

利用者名（課題申請者）/ User Name (Project Applicant)

鎌田 圭

所属名 / Affiliation

東北大

共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes

矢島隆雅,佐々木玲

ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes

利用形態 / Support Type

（主 / Main）機器利用/Equipment Utilization（副 / Sub）-

利用した主な設備 / Equipment Used in This Project

UT-102：高分解能走査型分析電子顕微鏡

報告書データ / Report

概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)

The demand for thermal neutron detectors is increasing for application in the medical sector, as well as to non-destructive inspection, structural analysis, astronomical observation, water imaging in plants, and resource exploration. In an environment using a neutron detector, radiation in the form of γ-rays exists in addition to neutrons, making it necessary to efficiently distinguish neutron rays. Therefore, a scintillator with high sensitivity to neutron rays and low sensitivity to γ-rays is required. Thermal neutron detectors are composed of gas, liquid, and solid scintillators containing ³He, ⁶Li, ¹⁰B, and ¹⁵⁷Gd, which offer a large neutron capture cross-section. Recently, solid scintillators for detecting thermal neutrons have been developed and applied to replace conventional ³He gas detectors, the resources for which are depleting. In recent years, scintillation detectors using inorganic solid scintillators containing ⁶Li have been increasingly employed owing to their ease of handling and radiation resistivity. In these detectors, the scintillators absorb the α-rays generated by the ⁶Li (n, α) ³H reaction and convert them into visible light. In the past decade, inorganic solid scintillators containing Li, such as Ce or Eu:LiCaAlF₆ (LiCAF) [1] and Ce:Cs₂LiYCl₆ (CLYC) [2], have been developed in addition to the traditional 20Al(PO₃)₃-80LiF (Li-glass) scintillator for thermal neutron detection. To improve the performance of a thermal neutron detector, it is necessary to develop novel scintillators containing ⁶Li at a higher concentration for high neutron sensitivity and a low density for low γ-ray sensitivity. In compound crystals, the Li content is limited by the chemical composition. In contrast, eutectic scintillators containing a high concentration of Li, such as LiF/CaF₂, LiF/SrF₂, LiF/LiGdF₄, LiSrI₃/LiI, LiF/BaCl₂, Li₃AlF₆/CaF₂, LiF/LaF₃, and LiF/CaF₂/LiBaF₃ [3,4] have been reported. Eutectics are composed of neutron-capturing phases containing Li and scintillator phases. As a result, a much higher ⁶Li content and higher neutron sensitivity can be achieved compared to single-crystal scintillators such as CLYC and LiCAF. In addition, scintillators must offer a high light yield and be transparent to the generated scintillation. A higher transparency can be achieved by combining crystal phases with closer refractive indices. At the point view of scintillation properties, high light yield scintillators such SrCl₂, BaCl₂, LaCl₃, CeCl₃, BaBr₂, LaBr₃, CeBr₃ with Eu²⁺ or Ce³⁺ doping were selected as the scintillator phase (Table 1). We searched the phase diagram of each scintillator material and Li-containing halides and systematically examined possible combinations that could constitute eutectics.

実験 / Experimental

In this research, eutectics with the combination of  LiBr/(BaBr₂, LaBr₃, CeBr₃), LiCl/(BaCl₂, SrCl₂) and ternary eutectics of LiCl/SrCl₂/LaCl₃, LiCl/CaCl₂/CeCl₃ were fabricated. Each powder material at the corresponding eutectic compositions were set in the quartz amples after baking process at 100°C under high vacuum (~10^-4 Pa) to eliminate water and oxygen, and the quartz ampoules was sealed in a quartz tube with an inner diameter of 4 mm. The eutectics were prepared by the vertical Bridgman method at a pull-down rate of 0.1-0.2 mm/min. Figure 1 shows photographs, backscattered electron images (BEIs) and refractive index values of each eutectic. It can be seen that the transparency of the wafer changes due to the difference in refractive indices of each crystal phase in each eutectic. Powder XRD and BEI observations confirmed the expected crystal phases in each eutectic. 

結果と考察 / Results and Discussion

 In binary eutectic, the closer the refractive indices of the coexisting crystalline phases are, the higher the transparency. On the other hand, in the ternary eutectic, the scintillator phase had a higher refractive index than the other two phases, but the wafer was slightly transparent.　 The light yield was determined based on the energy spectra under α-ray (²⁴¹Am) and thermal neutron (²⁵²Cf) excitation using a PMT (R7600U-200, Hamamatsu). The decay time was measured using the same setup as for the PMT and a digital oscilloscope. Table 1 shows the physical properties and performance of the eutectics in this study, reported eutectics, and common scintillators. Among of the eutectics, ⁶LiBr/Ce:LaBr and LiCl/SrCl₂/Ce:LaCl₃ showed high light yields of 74,000 and 30,000 photons/neutron under ²⁵²Cf neutron irradiation, respectively . The LiCl/SrCl₂/Ce:LaCl₃ sample wafer showed transparency. Details of eutectic growth, structure, scintillation properties and neutron responses will be also reported in the presentation.

図・表・数式 / Figures, Tables and Equations

Table 1. The selected scintillators and their scintillation properties.

Fig.1 The photographs, BEIs and refractive index values of the fabricated eutectics

Table 2. The physical properties and performance of the eutectics in this study, reported eutectics, and common scintillators.

その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)

References[1]      A. Yoshikawa, et al., Single crystal growth, optical properties and neutron response of Ce³⁺-doped LiCaAlF₆, IEEE Trans. Nucl. Sci. 56 (2009) 3796–3799, [2]      J. Glodo, et al., Development of Cs₂LiYCl₆ scintillator, J. Cryst. Growth, 379 (2013) 73–78, [3]      T. Yanagida, et al., Eu-doped ⁶ LiF-SrF₂ eutectic scintillators for neutron detection, Opt. Mater. 34 (2012) 868–871, [4]      K. Kamada, et al., Growth and scintillation properties of Tb-doped LiGdF₄/LiF eutectic scintillator. Opt. Mater. 61 (2016) 134–138,

成果発表・成果利用 / Publication and Patents

論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)

1. Rei Sasaki, Fabrication of CeCl3/LiCl/CaCl2 Ternary Eutectic Scintillator for Thermal Neutron Detection, Crystals, 12, 1760(2022).
   DOI: 10.3390/cryst12121760
   
2. Ryuga Yajima, Fabrication and Characterization of K2CeCl5/6LiCl and CeCl3/SrCl2/6LiCl Eutectics for Thermal Neutron Detection, Crystals, 12, 1795(2022).
   DOI: 10.3390/cryst12121795
   

口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.

1. 矢島隆雅，鎌田圭, 佐々木玲, 沓澤直子, 村上力輝斗，堀合毅彦，Kyoung Jin Kim，吉野将生，山路晃広，黒澤俊介，横田有為，佐藤浩樹，豊田智史，大橋雄二，花田貴，Vladimir Kochurikhin，吉川彰, “発光特性を考慮した6Li含有中性子用共晶体シンチレータの開発”, 第16回日本フラックス成長研究発表会, 令和4年12月16日
2. 佐々木玲，鎌田圭，矢島隆雅，吉野将生，堀合毅彦，村上力輝斗，Kyoung Jin Kim， 山路晃広，黒澤俊介，横田有為，佐藤浩樹，豊田智史，大橋雄二，花田貴，Vladimir. V. Kochurikhin，吉川彰, “シンチレータ応用を目的としたCsI-LiBr系状態図の検討と共晶体作成・評価”, 第16回日本フラックス成長研究発表会, 令和4年12月16日．
3. 佐々木 玲, 鎌田 圭, 矢島 隆雅, 吉野 将生, 堀合 毅彦, 村上 力輝斗, Kyoung Jin Kim, 山路 晃広, 黒澤 俊介, 横田 有為, 佐藤 浩樹 豊田 智史, 大橋 雄二, 花田 貴, 吉川 彰, “中性子検出用Ce1%LaCl3 /6LiClとCe1%LaCl3 /6LiCl / SrCl2シンチレータの育成と特性評価”, 第83回応用物理学会秋季学術講演会, 令和4年9月22日
4. Ryuga Yajima, Kei Kamada, Masao Yoshino, Rikito Murakami, Takahiko Horiai , Naoko Kutsuzawa , Kyoung Jin Kim, Akihiro Yamaji , Shunsuke Kurosawa, Yuui Yokota, Hiroki Sato, Satoshi Toyoda, Yuji Ohashi, Takashi Hanada, Vladimir. Kochurikhin, Akira Yoshikawa,“Growth and scintillation properties of a novel K2CeCl5/LiCl eutectic for thermal neutron detection”, The 6th International Conference on the Physics of Optical Materials and Devices & The 5th International Workshop of Persistent and Photostimulable Phosphors, 令和4年9月1日．

特許 / Patents

特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件