氡-220体积活度参考标准的建立

Development of standard reference of ^(220)Rn activity concentration

氡-220体积活度参考标准是氡-220测量装置刻度校准的基本要件。国内急需建立一个特性良好的氡-220体积活度参考标准。用存放40年以上的硝酸钍通过离子交换法制备钍射气源;设计制作温湿度及气流可调控的内源式钍射气室,保证稳定性与均匀性;通过更换不同232Th活度的钍射气源来调节钍射气室内220Rn的体积活度水平;研制闪烁室探测器测量装置,以模拟计算和国际比对刻度结果确定其探测效率;钍射气室内220Rn的体积活度值经闪烁室探测器定值,作为氡-220体积活度参考标准。实验结果显示,该参考标准的短时间稳定性(2天以上)与长时间稳定性(约半年)均很好;其空间不均匀程度不超过5.5%;其活度浓度在500–20 000 Bq·m-3范围内可逐级调节;闪烁室探测器刻度系数为53.02 Bq·m-3·min。该研究建立了一个体积活度量值准确、稳定、均匀,浓度可调的氡-220体积活度参考标准,可用于氡-220测量装置的刻度与校准。

Standard reference of 220Rn activity concentration is essential for 220Rn measuring device calibration. Purpose： A well performance standard reference of ：220Rn activity concentration is imperative for 220Rn measurement device calibration in China. Methods： For this purpose, analytically pure Th（NO3）4-4H20 which had been preserved for more than 40 years was used for producing 220Rn source with stable exhalation rate. An inner source 220Rn chamber was designed and constructed with temperature, humidity and airflow control system to ensure the stability and homogeneity. The 220Rn activity concentration was adjustable through changing different activity 220Rn sources. A measuring device using Lucas scintillation cell whose calibration coefficient was determined by both theoretical method and calibration test in PTB was developed to determine the 220Rn activity concentration in the chamber. Results： It was shown that both the short-term （more than two days） and long-term （half a year） stability of our standard reference performed very well. The heterogeneity of our standard reference in the chamber was less than 5.5%. By changing different 220Rn sources, the adjustable range of our standard reference was 500-20 000 Bq＇m 3. The calibration coefficient of the Lucas scintillation cell was confirmed as 53.02 Bq＇m-3＂min in PTB calibration test. Conclusion： A standard reference of 220Rn activity concentration which is accurate, stable, uniformly distributed and concentration adjustable is established in this study.