Speaker
Description
Bismuth germanate (Bi₄Ge₃O₁₂, BGO) scintillation crystals, owing to their high density (7.13 g/cm³) and high effective atomic number (74), offer significant advantages in detection efficiency and energy resolution for high-energy rays. They are widely used in high-energy physics, nuclear physics, space physics, industrial measurement and control, environmental monitoring, and security inspection.
Our BGO project R&D team of Xiamen Tungsten Co., Ltd. has focused on the preparation technology for large cross section BGO crystals required by neutron activation analyzer development projects—such as Prompt Gamma Neutron Activation Analysis (PGNAA) and Pulsed Fast Thermal Neutron Activation Analysis (PFTNA)—and for long size BGO crystals needed for the CEPC (Circular Electron Positron Collider) large scale scientific project. By fully leveraging the strengths of both the Kyropoulos and Bridgman methods, our team systematically conducted research on thermal field regulation, melt convection control, and growth process innovations to address the technical bottlenecks of large size BGO crystals, such as coloration, poor uniformity, and cracking during growth. After four years of efforts, we successfully overcame the challenges in preparing large size, high quality BGO crystals.
To meet the CEPC’s demand for ultra long BGO crystals up to 24 m³ in total volume, our team adopted the Bridgman method for growth. The core difficulty in growing ultra long crystals lies in uneven heat dissipation during the mid-to-late stages of growth, which leads to continuous accumulation of thermal stress and easy cracking. To solve this, our team independently developed a precise thermal field control and dynamic temperature compensation technology. We established a thermal field system with independently adjustable axial and radial gradients, combined with a dynamic temperature compensation mechanism, to suppress thermal stress and prevent crystal cracking. With this technology, we successfully resolved the cracking issue and produced BGO crystal boules with dimensions of 55×55×440 mm³, 66×88×430 mm³, and 108×108×400 mm³. For the 55×55×440 mm³ boule, each furnace run yields 90 finished crystals. For the 66×88×430 mm³ boule, each run yields 160 finished crystals. For the largest 108×108×400 mm³ boule, each run produces 216 finished crystals. This greatly improves production efficiency and material utilization, providing stable, reliable mass production capability for the CEPC project.
To address the demand for large cross section BGO crystals with diameters of 6 to 8 inches for PGNAA/PFTNA neutron activation analyzers, our team explored both the Kyropoulos and Bridgman methods. Large cross section crystals face challenges such as intense melt convection, difficult thermal conduction control, and the inability to simultaneously achieve large size and high performance. Our team overcame these challenges through two key technological innovations. First, we developed a wide‑plate BGO melt convection control technology. This technology optimizes melt convection to enhance impurity removal capability and significantly improves crystal uniformity. Second, we established a Kyropoulos‑method growth process for large‑size BGO crystals. Drawing on experience from sapphire growth, we systematically optimized crucible geometry, thermal field, and growth parameters to successfully overcome coloration and deformation defects caused by composition deviation, and produced BGO crystals with diameters of 6 to 8 inches—a size not previously reporte. Performance tests show that the crystal energy resolution is stable at 10%–12% (Cs‑137 @ 662 keV), fully meeting actual application requirement and filling the gap in the international market.
