基于NaI(Tl)谱仪实现气载放射性碘制备产率的连续测量系统

Development of a successive yield measurement system for airborne radioiodine generation using NaI(Tl) spectrometer

气载放射性碘的制备过程中,利用串联的收集容器同时收集制备的气载放射性碘,并用NaI(Tl)谱仪实时监测收集容器内131Ⅰ活度变化情况,实现气载放射性碘制备产率的连续测量。该系统可一次性测量气载放射性碘制备技术的产率随时间变化函数Y(t),同时适用于气态单质碘、有机碘、颗粒碘三种形态的气载放射性碘的产率测量。其测量周期任意可调,测量周期取20s时,可兼顾测量频率与单次测量的不确定度。在典型工况下,当产率Y期望值为90%时,其单次测量结果的扩展不确定度为2.5%(k=2)。该产率连续测量系统可用于观察气载放射性碘制备的动态过程,将为气载放射性碘制备技术的优化提供有力工具。

[Background]Environment airborne radioiodine monitoring is important for the operation of nuclear power plants and public nuclear safety.The airborne radioiodine generation technique is essential for airborne radioiodine research,including its measurement technology and behavior characteristics.Although many airborne radioiodine generation techniques have been developed,little attention has been paid to higher performance generation techniques and detailed understanding of the generation process.[Purpose]This study aims to develop a successive airborne radioiodine generation measurement system.[Methods]Two series-connected collection containers,two NaI(Tl)spectrometers,and one computer with self-developed software,were employed for the composition of this successive yield measurement system.In the process of airborne radioiodine generation,the series-connected collection containers were connected with the generation container for continuous airborne radioiodine collection whilst the NaI(Tl)spectrometers monitored radioiodine in the collection containers and generation container in real time.Meanwhile,the measured spectrum was sent to the computer and analyzed by selfdeveloped software.Hence the change of yield with time during the generation of the airborne radioiodine could be reflected by the software.The major influences in the measurement were also discussed theoretically and experimentally,including interference of measurements between radioiodine in different containers and inconsistencies between radioiodine collection containers.Finally,the uncertainty analysis of this measurement result under typical working conditions was performed.[Results]This measurement system was applicable to various airborne radioiodine generation techniques including inorganic iodine,organic iodine and aerosol iodine.The measurement period was adjustable.Considering the measurement frequency and uncertainty,the recommended measurement period was 20 s.Under typical working conditions,the expanded uncertainty of the measured yield was 2.5%(k=2)while yield was 90%.[Conclusions]This successive yield measurement system could be used to observe the detailed process of airborne radioiodine generation,and provide a powerful tool for the optimization of airborne radioiodine generation techniques.