Institute of Radiation Medicine, Fudan University, Shanghai, 200032, China.
Shanghai Institute of Measurement and Testing Technology, Shanghai, 201203, China.
J Environ Radioact. 2020 Dec;225:106427. doi: 10.1016/j.jenvrad.2020.106427. Epub 2020 Sep 25.
For more efficient and accurate determination of airborne tritium in the environment, the procedure optimization, performance test and uncertainty analysis of a commercially available low-background liquid scintillation counting (LSC) system with 100-ml counting vials were studied in this work. The results showed that 50 ml water sample mixed with 50 ml scintillation cocktail (Ultima Gold uLLT, PE) could achieve the optimal counting condition after a dark adaption time longer than 1440 min. The minimum detectable activity (MDA) of the 100-ml vial system was estimated to be 0.18 Bq·L in a continuous counting time of 3600 min, which was approximately 3.5 times lower than that of 20-ml vial system, and its determination uncertainty was also generally lower provided the collected samples was more than 15 ml. It indicates that the LSC system with 100-ml counting vials is preferable for environmental tritium determination. However, for more accurate determination, the electrolytic enrichment is still needed for the sample with the specific activity lower than 0.4 Bq·L. On the other hand, considering the cost and potential environmental impact of present available cocktails, the system with 20-ml vials is recommended for determining the sample with the specific activity higher than 2 Bq·L.
为了更高效、更准确地测定环境中的氚气，本工作对一款商用的、配备 100ml 计数瓶的低本底液体闪烁计数（LSC）系统进行了程序优化、性能测试和不确定度分析。结果表明，水样和闪烁液（Ultima Gold uLLT，PE）以 50:50 的比例混合，在暗适应时间大于 1440min 后可达到最佳计数条件。在连续计数 3600min 的情况下，100ml 计数瓶系统的最小可探测活度（MDA）估计为 0.18Bq·L，约为 20ml 计数瓶系统的 1/3.5，其测定不确定度通常也更低，前提是采集的样本量大于 15ml。这表明，对于环境氚的测定，配备 100ml 计数瓶的 LSC 系统更为适用。然而，对于比活度低于 0.4Bq·L 的样品，仍需采用电解浓缩的方法以提高测定的准确性。另一方面，鉴于目前可用的闪烁液的成本和潜在环境影响，建议对于比活度高于 2Bq·L 的样品，使用配备 20ml 计数瓶的系统。
