Synthesis, Growth And Scintillation Properties Of CdWO₄ Single Crystal

Cadmium tungstate, CdWO4, is well-known as one of excellent scintillating materials with high X-ray absorption coefficient, high luminous efficiency, short afterglow time and strong irradiation damage resistance, which exhibits important application in the area of nuclear medical X- ray CT and the inspection system of container. As reported at home and abroad, CdWO4 single crystal was mainly grown by Czochralski method, but the typical problems are melt volatilization, cleavage along the(010) plane and crystal coloring. The thesis focuses on the research of CdWO4 single crystal and is arranged in three parts:Part I: Solid-state synthesis and liquid-state synthesis of CdWO4 polycrystalline material. CdWO4 polycrystalline material was synthesized by Solid-state and liquid-state reaction after optimizing the preparation process. This part focuses on the effect of pH in liquid-state reaction and the best reaction conditions was studied to synthesize high-purity CdWO4 polycrystalline material. The advantages and disadvantages of solid-state synthesis and liquid-state process were summarized.Part II: Research on growth and performance of CdWO4 single crystal. A transparent and almost colorless CdWO4 crystal with a size of φ15 mm×60 mm was successfully grown by improved Czochralski method, and the CdWO4 polycrystalline material was fabricated by liquidstate reaction. The macrodefects and growth conditions of CdWO4 single crystal were investigated. Crystal properties were analyzed, which were chemical etching, transparence curve, emission spectra, light output, energy resolution and decay time. The results show that the crystal has an absorption cut-off edge around 315 nm and optical transmittance of 70 % in the visible light region, and fluorescent peak at 473.8 nm. Furthermore, the crystal has an energy resolution of 7.8 %, absolute light yield of 20750 ± 375 photons/MeV and decay time of 1329.5 ns, 11501.5 ns. Compared with related literatures, the crystal quality is better than that literatures reported.Part III: Research on growth and performance of Cd1-xZnxWO4 solid solution crystals. Cd1-xZnxWO4(x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) polycrystalline materials were fabricated by solid-state reaction and X-ray diffraction results show that diffraction peaks present a trend from CdWO4 to ZnWO4. Cd1-xZnxWO4(x = 0, 0.057, 0.113, 0.416) crystals were successfully grown by improved Czochralski method. Crystal properties were analyzed, which were transparence curve, emission spectra, light output, energy resolution and decay time. The results show that the crystals has an absorption cut-off edge around 315 nm and optical transmittance of 65 % in the visible light region, and fluorescent peak has a red shift with increment of zinc content. Furthermore, Cd1-xZnxWO4 solid solution crystals present a trend that the energy resolution and decay time increases, absolute light yield decreases with increment of zinc content. Compared with relative literatures, the crystal quality is better than that literatures reported. In view of crystal properties and growth, Cd1-xZnxWO4(x < 0.1) crystals exhibit excellent scintillation properties after performance comparison.