Preparation And Properties Of Large Size Thallium Doped Sodium Iodide Crystals

NaI(Tl)crystals have received much attention for their small self-absorption,high luminescence efficiency,easy production and good energy resolution for X and γ rays,while large-size NaI(Tl)crystals are favored by industry for their high material utilization and low production cost.In this thesis,NaI(Tl)crystals of Φ75 mm and Φ115 mm were prepared by the Bridgman method,and large-sized NaI(Tl)crystals of Φ155 mm × 300 mm were prepared by the temperature field design and process optimization of crystal growth,and square NaI(Tl)crystals of 100 mm × 50 mm × 400 mm were further obtained by forging,cutting,grinding,polishing,and encapsulation.NaI(Tl)crystals with a volume of 100 mm × 50 mm × 400 mm were further obtained by forging,cutting,grinding,polishing,and encapsulation,and their properties were tested to meet the requirements of scintillation crystal radiation detectors.The research in this paper is as follows:First,the research background of the radiation detector,the properties of NaI(Tl)crystals and the research significance of large-size NaI(Tl)crystals are explained,while the crystal energy conservation theory,the stability theory of the crystal growth interface and the crystal nucleation theory are analyzed in detail to provide theoretical guidance for the subsequent preparation of NaI(Tl)crystals.Secondly,the effects of heater position,length and heat insulation screen on the temperature field distribution in the growth environment of NaI(Tl)crystals were analyzed by simulations with the multi-physics field coupling software COMSOL Multiphysics in conjunction with the crystal growth theory.Again,NaI(Tl)crystals of Φ75 mm and Φ115 mm were grown by the Bridgman method,and test samples of NaI(Tl)crystals were prepared by forging,cutting,grinding,polishing,and encapsulation,etc.The samples were analyzed by X-ray powder diffraction(XRD),ultraviolet-visible near-infrared transmission spectrometer(UV-VIS-NIR),inductively coupled plasma emission spectrometer(ICP-OES)to test and characterize the crystal structure,transmittance,and Tl ion concentration of the samples,and the performance tests such as energy resolution and relative optical output of the relevant devices were performed by multi-channel energy spectrometer(MCA).Finally,based on the results of numerical simulation analysis,a large-size crystal growth furnace was designed and fabricated,and NaI(Tl)crystals of Φ155 mm were successfully grown by adjusting and optimizing the process parameters,and square NaI(Tl)crystals of 100 mm × 50 mm × 400 mm were prepared by the above processing procedures,and were tested and characterized by XRD,UV-VIS-NIR,and ICP-OES.The square NaI(Tl)crystals were tested and characterized by XRD,UV-VIS-NIR,ICP-OES,and the energy resolution and relative optical output of the square crystal devices were tested by MCA.The test results show that the energy resolution and relative light output of square NaI(Tl)crystals meet the industry standard for NaI(Tl)crystal radiation detectors,and the study is of guidance for the practical production of large-size NaI(Tl)crystals.