Hydrothermal Preparation Of Uranium Fluoride Single Crystal And Its X-ray Response

As a kind of single crystal with special optical properties,scintillators are very sensitive to X-ray.The rapid development of scintillators brings hope to nuclear medical imaging and high-energy physics.As an excellent scintillator,X-ray response performance has a huge impact on its luminescence properties.The high atomic number、dense structure and high density of uranium fluoride single crystal have the potential to become scintillator single crystal matrices,which has attracted wide attention of researchers.In this thesis,single crystals of binary uranium fluoride(U₃F₁₂（H₂O）,ternary uranium fluoride（LiUF₅,KU₂F₉,RbUF₅）and quaternary uranium fluoride(Na₄CoU₆F₃₀,Na₄Cu₆U₆F₃₀)were prepared by a hydrothermal method,using UO₂（CH₃CO₂）₂·H2O as uranium source、CH₃COO^—as reducing agent and copper as catalyst to promote crystal growth.（1）The structure of U₃F₁₂（H₂O）was determined by SXRD.The optical properties,thermal properties and microstructures of U₃F₁₂（H₂O）were tested and analyzed by FT-IR,UV-vis,TG-DTA and SEM and the response of U₃F₁₂（H₂O）to X-ray was tested.The results show that U₃F₁₂（H₂O）is a green acicular crystal with a length of about 1 mm and has a complex three-dimensional structure.Moreover,the intensity of the current of U₃F₁₂（H₂O）exposed to X-ray is 70 times stronger than not exposed to X-ray.（2）The structures of three uranium fluorides（LiUF₅,KU₂F₉ and RbUF₅）were determined by SXRD.The optical properties and microstructures of these three uranium fluorides（LiUF₅,KU₂F₉ and RbUF₅）were tested and analyzed by FT-IR,UV-vis and（SEM）.The X-ray responses of the three uranium fluorides（LiUF₅,KU₂F₉ and RbUF₅）were also tested.The results show that all three uranium fluorides（LiUF₅,KU₂F₉ and RbUF₅）are green needle-like crystals with millimeter-sized lengths and complex three-dimensional structures,and the three uranium fluorides（LiUF₅,KU₂F₉ and RbUF₅）single crystals have obvious response to X-ray,and the intensity of the current of three uranium fluorides exposed to X-ray is 60-90 times stronger than not exposed to X-ray.（3）The structures of two kinds of quaternary uranium fluorides(Na₄CoU₆F₃₀ and Na₄CuU₆F₃₀)were determined by SXRD.The optical properties and microstructures of the two kinds of quaternary uranium fluorides(Na₄CoU₆F₃₀ and Na₄CuU₆F₃₀)were tested and analyzed by FT-IR,UV-vis and SEM.The X-ray responses of the two kinds of quaternary uranium fluorides(Na₄CoU₆F₃₀ and Na₄CuU₆F₃₀)were also tested.The results show that two kinds of quaternary uranium fluorides(Na₄CoU₆F₃₀ and Na₄CuU₆F₃₀)are green hexagonal crystals with a length of about 100 um and complex three-dimensional structure,and two kinds of quaternary uranium fluorides(Na₄CoU₆F₃₀ and Na₄CuU₆F₃₀)have obvious response to X-ray,and the intensity of the current of two kinds of quaternary uranium fluorides exposed to X-ray is 120times stronger than not exposed to X-ray.In summary,all six kinds of single crystals have obvious response to X-ray.Among the three types of single crystals,quaternary uranium fluoride is the most sensitive to X-ray,followed by ternary uranium fluoride,and finally U₃F₁₂（H₂O）.It is sensitive for uranium fluorides single crystal to X-ray due to the existence of isolated 5f electrons in U（IV）.Because of the transition of f-f in U（IV）,the internal structure of the sample changes and the resistance of the sample decreases sharply under the irradiation of X-ray,which leads to the increase of the passing current.It can be used to detect the intensity of X-ray in the environment by transforming the electrical signal into other signals.Because of the sensitivity of X-ray to energetic particles,it has the potential to become a single crystal matrix for scintillators,and can be used in the detection of high-energy particles,nuclear medicine imaging and industrial non-destructive testing etc.