Development and Characterization of Tb-Doped Borate Scintillators, and Study for Radiography Applications = Tb 도핑 붕산염 섬광체 개발 및 특성 분석, 그리고 방사선 촬영 응용 분야 연구

다국어 초록 (Multilingual Abstract)

This dissertation presents an integrated investigation of Tb-doped borate scintillators and the development of a cost-effective X-ray imaging device, establishing a comprehensive platform for advanced radiation imaging and monitoring applications. Two complementary classes of terbium-doped borate materials were investigated to address distinct radiation imaging requirements. Firstly, LaB3O6:Tb was systematically studied in both crystalline and amorphous glass forms as a candidate material for X-ray scintillation screens. Despite identical chemical composition, the two phases exhibited dramatically different optical characteristics. The crystalline phase exhibited intrinsic host luminescence, peaking in the ultraviolet range (310-320 nm), coupled with characteristic visible emissions of Tb3+. Synchrotron photoluminescence measurements confirmed highly efficient energy transfer from the LaB3O6 host to Tb3+ ions, identifying novel excitation bands (≈ 60 nm) critical to the scintillation mechanism. The structure-dependent scintillation behavior demonstrates that atomic organization independently controls luminescence efficiency. Crucially, the material exhibits a high effective atomic number (Zeff ≈ 44), establishing LaB3O6:Tb as suitable for advanced X- ray imaging screen applications. Secondly, insightful research explores the fabrication and characterization of terbium- doped lithium borate (LBO(Tb)) glasses, positioning them as a promising material for real- time dose monitoring, a critical safety component in X-ray imaging and medical radiation facilities was conducted. The study indicated that the incorporation of terbium (Tb3+) ions significantly enhances the material's luminescence and scintillation properties. A key advantage is the ability to tune the effective atomic number by adjusting the lithium content, which allows the material to be engineered as a tissue-equivalent dosimeter. Through thermoluminescence investigations, an optimal composition of 30 % Li2O and 1 % Tb4O7 was identified. This formulation combines a low effective atomic number with a relatively fast decay time, making it ideal for real-time applications and suggesting its potential for neutron imaging. However, the observed fading effect suggests that further material refinement is needed to improve long-term stability and ensure reliable performance. Finally, a cost-effective X-ray imaging system by integrating a Raspberry Pi component in an indirect conversion configuration was developed. It’s a High-Quality camera, a custom optical assembly, and a Gd2O2S:Tb (GOS:Tb) scintillator. Systematic evaluation demonstrated that the system achieves a spatial resolution of 68 lp/mm under ambient light and 25 lp/mm under X-ray exposure. By analyzing both camera parameters and exposure settings, we established a practical methodology for optimizing contrast, signal-to-noise ratio, and spatial resolution, thereby reaffirming the fundamental principles of radiographic imaging within an accessible framework. The primary outcome of this study is the validation of a low-cost, modular platform that lowers barriers to digital radiography, including both X-ray, proton, and neutron imaging. Beyond technical feasibility, the system demonstrates versatility across multiple domains. It serves as an effective hands-on tool for teaching the complete imaging chain and reinforcing theoretical concepts in education. It provides an affordable solution for non-destructive testing, including electronics inspection and material defect detection. Moreover, its customizable design supports integration with alternative scintillators, sensors, or software to accommodate a wide range of applications. By broadening access to digital radiography, this work promotes wider adoption in cost-sensitive settings, fostering innovation and enhancing both educational and scientific research capabilities. Overall, this work demonstrates a comprehensive approach that combines advanced luminescent materials with affordable hardware to realize versatile X-ray imaging and monitoring systems. The findings provide both technological and material insights, paving the way for cost-effective applications in research, education, non-destructive testing, radiation detection, and medical diagnostics.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1 Scintillation materials 1
• 1.2 Terbium-doped borate materials 2
• 1.3 Research objectives and motivations 3
• Chapter 2. Fundamental concepts 5
• 2.1 Interaction of radiation with matter 5
• 2.1.1 X-ray/gamma ray interactions 5
• 2.1.2 Neutron interactions 8
• 2.1.3 Charge particle interactions 9
• 2.2 Luminescence and scintillation mechanisms 9
• 2.2.1 Scintillation processes 9
• 2.2.2 Activator Role: Terbium (Tb³⁺) characteristics 10
• 2.3 Crystalline and amorphous scintillators 10
• 2.4 Borate-based scintillation materials 11
• 2.5 Thermoluminescence (TL) and tissue-equivalent dosimetry 12
• 2.6 Fundamentals of X-ray radiography 13
• Chapter 3. Sample preparation and characterization techniques 15
• 3.1 Solid-state reaction and melt-quenching methods 15
• 3.1.1 Preparation of LaB3O6:Tb 16
• 3.1.2 Preparation of LBO(Tb) glass 17
• 3.2 Characterization techniques 19
• 3.2.1 Phase structure analysis 19
• 3.2.2 UV-Vis measurements 20
• 3.2.3 X-ray luminescence 20
• 3.2.4 Photoluminescence and VUV photoluminescence measurements 21
• 3.2.5 Thermoluminescence 22
• 3.2.5 Decay time measurement 23
• Chapter 4. Development of an X-ray imaging device 25
• 4.1 Instrument configuration 25
• 4.2 Measurement method 28
• 4.2.1 Readout noise measurement. 30
• 4.2.2 Image contrast and effect of ISO-exposure time setting 30
• 4.2.3 Modulation Transfer Function 31
• 4.2.4 Signal to Noise Ratio (SNR) 34
• Chapter 5. Results and Discussions 35
• 5.1 Properties of Tb-doped lanthanum borate material 35
• 5.1.1 Phase structure of LaB3O6:Tb samples 35
• 5.1.2 X-ray Luminescence 36
• 5.1.3 UV-Vis spectroscopy 38
• 5.1.4 Photoluminescence 39
• 5.1.5 VUV photoluminescence studies at UVSOR facility 40
• 5.1.6 Decay time 44
• 5.2 Properties of Tb-doped lithium borate glass 46
• 5.2.1 Optimal composition of LBO(Tb) for TL measurement 46
• 5.2.2 X-ray luminescence 48
• 5.2.3 UV-Vis transmission 49
• 5.2.4 Photoluminescence 49
• 5.2.5 Thermoluminescence 51
• 5.2.6 Dose response and reproducibility 54
• 5.2.7 Decay time and thermal fading 56
• 5.2.8 Effective atomic number (Zeff) and usability for neutron imaging 56
• 5.3 Performance of X-ray imaging system 57
• 5.3.1 Performance of the imaging system under ambient light 57
• 5.3.2 Readout noise property 58
• 5.3.3 Effect of ISO and exposure time setting. 59
• 5.3.4 Modulation Transfer Function 62
• 5.3.5 Image contrast and Signal to Noise Ratio 64
• 5.3.6 Preliminary results in proton and neutron imaging. 66
• 5.3.7 Cost consideration. 67
• Chapter 6. Summary and Conclusions 69
• References 71
• (초 록) 83