Study On Synthesis And Purification Of TlBr Materials Used For Nuclear Radiation Detectors

Thallium bromide (TlBr) is a new promising material used for room-temperature nuclear radiation detectors due to its high atomic number (Tl:81, Br:35), high density (7.56 g/cm3), wide bandgap (2.68ev), simple cubic crystal structure (CsCl type), as well as relatively low melting point (460℃). As nuclear radiation detector, it exhibits high detection efficiency and good energy resolution when works at room temperature. However, stoichiometric proportion of TlBr powder and material purity are crucial to the quality of TlBr crystal and properties of detectors.In this paper, TlBr powder was synthesized by co-precipitation in solution. By studying reactants ratio, concentration of HBr and drying temperature of products with Pre-purified TlNO3 and HBr used as raw materials, a method of synthesis of powder in solution was obtained. X-ray fluorescence spectrometry (XRF) was used to detect elemental composition of synthesized TlBr powder, and the result showed that when reactants Ratio was 1, concentration of HBr was 0.09 mol / L, drying temperature of products was 80℃, stoichiometric ratio of synthesized powder was close to 1.Vacuum distillation (VD) was used to purify synthesized TlBr powder at 520-640℃, purification efficiency was obtained by ICP-MS since the concentration of impurities was detected. After process of vacuum distillation, the impurities of Ca,Al,Fe,Cr,Mn was obviously decreased, total impurities concentration was also decreased. The total concentration of impurities in synthesized powder was reduced from 26.409ppm to 3.925ppm under the pressure of 1mmHg and distillation condition of 520℃. Based on this condition, the combination of hydro-thermal re-crystallization (HR) and VD methods was studied and the concentration of impurities was further reduced, less than 1ppm.Melt-based method with vetical temperature gradient was used to grow crystal from synthesized powder, powder purified by HR, powder purified by VD, powder purified by the combination of HR and VD methods. Some characteristics of crystals such as X-ray diffraction analysis (XRD), resistivity, optical properties were detected. The results showed that the crystal grown from the combination of HR and VD methods possessed high resistivity of 1010?cm and avarage infrared transmittance of 59%.