Measurement of radioactivity in water by vacuum rotary evaporation
ZHANG Guojie1, LIANG Manchun1, HE Shuijun1, XU Limei2, YANG Dandan2, DU Xiaochuang1, FU Qi1, SHEN Hongmin2
1. Institute of Public Safety Research, Department of Engineering Physics, Tsinghua University, Beijing 100084, China; 2. Beijing Global Safety Technology Co., Ltd., Beijing 100094, China
Abstract：[Objective] The measurement of radioactivity in water samples with low activity by direct sampling is unreliable and inaccurate. We designed an automatic concentration method based on the vacuum rotary evaporation process to increase the ease and accuracy of such measurements.[Methods] In this method, the water samples were first evaporated to dryness by vacuum rotary evaporation and then washed with dilute nitric acid. The used nitric acid was then sampled and measured by a liquid scintillation spectrometer. An automatic concentration device was designed for these measurements. The optimum water bath temperature for concentrating the samples was determined experimentally. The relationship between the volume of dilute nitric acid used and the proportion of nuclides recovered was studied to improve the yield of the cleaning process. Given that a portion of the residues is likely to adhere to the inner wall of the container during the evaporation process, an experiment was designed to study the efficacy of our procedure to clean these residues using 12mL of 0.05mol/L nitric acid by determining the number of repeated cleanings required for the container to return to the normal background level after evaporating solutions containing 241Am and 90Sr with activitiy concentrations of 20, 5, and 1 Bq/L. After the water samples were automatically concentrated, they were measured using a liquid scintillation spectrometer, and the recovery rates of the two nuclides were calculated at different activity concentrations.[Results] Using vacuum rotary evaporation with a vacuum of 2.0-4.0 kPa, a condenser temperature of -5℃-0℃, a rotation speed of 50 r/min, and an initial water bath temperature of 50℃, which was raised to 60℃ after 50min, it took about 70min to concentrate 1 L of the water sample. To reduce the post-cleaning residue and avoid contaminating subsequent water samples, the evaporation should be washed with 12 mL of 0.05 mol/L dilute nitric acid before washing with pure water. After evaporating a 1 L water sample with a total activity of less than 5 Bq, two to three cleaning operations were needed, while after evaporating a 1 L water sample with a total activity of 20 Bq, about five cleaning operations were needed. Using 12mL 0.05mol/L nitric acid for elution could get satisfactory elution effects. The average yield of 241Am by the automatic concentration method reached more than 70%, and the average recovery rate of 90Sr reached about 80%.[Conclusions] This paper proposes an automatic concentration method based on the vacuum rotary evaporation process, which has not only a quick turnaround time but also high yield.
张国杰, 梁漫春, 何水军, 徐立梅, 杨丹丹, 杜晓闯, 付起, 沈红敏. 利用减压旋蒸技术测量水样放射性活度[J]. 清华大学学报（自然科学版）, 2023, 63(6): 987-993.
ZHANG Guojie, LIANG Manchun, HE Shuijun, XU Limei, YANG Dandan, DU Xiaochuang, FU Qi, SHEN Hongmin. Measurement of radioactivity in water by vacuum rotary evaporation. Journal of Tsinghua University(Science and Technology), 2023, 63(6): 987-993.
[1] 刘波.低放废水和环境水体中痕量Pu、U、Am、Th和Sr的快速分析方法研究[D].兰州:兰州大学, 2016. LIU B. Study on the rapid analysis of trace amount of Pu, U, Am, Th and Sr in LLW and environmental water[D]. Lanzhou:Lanzhou University, 2016.(in Chinese) [2] 何敬涛,梁漫春,陈安滢,等.利用脱气膜技术检测水中14C[J].清华大学学报(自然科学版), 2020, 60(4):341-347. HE J T, LIANG M C, CHEN A Y, et al. Degassing membrane for 14C detection in water[J]. Journal of Tsinghua University (Science and Technology), 2020, 60(4):341-347.(in Chinese) [3] 汪向伟,梁漫春,李钢,等.水中铀的分离富集方法综述[J].清华大学学报(自然科学版), 2021, 61(1):64-69. WANG, LIANG M C, LI G, et al. Review of uranium separation and enrichment methods in water[J]. Journal of Tsinghua University (Science and Technology), 2021, 61(1):64-69.(in Chinese) [4] L'AN-NUNZIATA M F. Handbook of radioactivity analysis[M]. 2nd ed. New York:Academic Press, 2003. [5] 杨永钦,王洋洋.关于辐射环境及个人剂量探测下限讨论[J].四川环境, 2016, 35(3):135-140. YANG Y Q, WANG Y Y. Discussion on minimum detection limit of the radiation environment and individual dose detection[J]. Sichuan Environment, 2016, 35(3):135-140.(in Chinese) [6] 汪向伟,梁漫春,吴飞,等.水中铀的分析方法研究进展[J].工业水处理, 2021, 41(5):1-8. WANG, LIANG M C, WU F, et al. Research progress of determination methods of uranium in water[J]. Industrial Water Treatment, 2021, 41(5):1-8.(in Chinese) [7] LI G, LIANG M C, HE S J, et al. RO film-based pretreatment method for tritium determination by LSC[J]. Applied Radiation and Isotopes, 2020, 166:109343. [8] 郑琦.旋转蒸发工艺制备氮化硅空心微球的特性分析[D].景德镇:景德镇陶瓷大学, 2021. ZHENG Q. Characteristics analysis of silicon nitride hollow microspheres prepared by rotary evaporation process[D]. Jingdezhen:Jingdezhen Ceramic University, 2021.(in Chinese) [9] CHATTERJEE S, SUGILAL G, PRABHU S V. Heat transfer in a partially filled rotary evaporator[J]. International Journal of Thermal Sciences, 2019, 142:407-421. [10] PLECAS I, DIMOVIC S, SMICIKLAS I. Utilization of bentonite and zeolite in cementation of dry radioactive evaporator concentrate[J]. Progress in Nuclear Energy, 2006, 48(6):495-503. [11] SUN Q, HU J, WANG J L. Optimization of composite admixtures used in cementation formula for radioactive evaporator concentrates[J]. Progress in Nuclear Energy, 2014, 70:1-5. [12] GROSSMANN R, MAIER H J, FRIEBEL H U, et al. Preparation of radioactive targets for tandem accelerator experiments by high vacuum evaporation-condensation[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2002, 480(1):209-213. [13] 王铁健,崔建勇,胡小华,等.液体闪烁法测定水中总α、总β活度的影响因素研究[J].世界核地质科学, 2015, 32(2):96-100. WANG T J, CUI J Y, HU X H, et al. Study on influential factors of gross α and gross β activities determination in water by liquid scintillation counting method[J]. World Nuclear Geoscience, 2015, 32(2):96-100.(in Chinese) [14] 王海山,陈璞,梁漫春,等.甘肃饮用水源地水体辐射环境在线自动监测系统总体设计[J].核电子学与探测技术, 2021, 41(1):62-67. WANG H S, CHEN P, LIANG M C, et al. Overall design ideas of on-line automatic monitoring system for water radiation environment of drinking water source in Gansu Province[J]. Nuclear Electronics&Detection Technology, 2021, 41(1):62-67.(in Chinese) [15] HE S J, HE J T, LIANG M C, et al. Application of low-temperature vacuum concentration in automated on-line monitoring of gross alpha and beta in water[C]//Proceedings of the 27th International Conference on Nuclear Engineering. Ibaraki, Japan:ICONE, 2019:ICONE 27-1258. [16] OFORIWAA P O, LIANG M C, SU G F. System modelling approach of radionuclide soil-to-plant transfer for nuclear emergencies decision; case study-China[C/OL]//28th International Conference on Nuclear Engineering. Virtual, Online:American Society of Mechanical Engineers, 2021.
2023, Vol. 63 
