食品和饮用水放射性监测时测量时间与探测限关系初步研究

目的 比较不同测量时间食品和饮用水中放射性核素的探测限值,为应对核与辐射突发事件提供参考。方法 使用同一台γ谱仪分别测量水、牛奶和菠菜的马林杯样品,每种样品测量的活时间分别为2、4、8、12、24、72 h,将分析得到的探测限值与国际原子能机构(IAEA)推荐的操作干预水平以及世界卫生组织(WHO)推荐的饮用水水质标准进行比较。结果 饮用水和牛奶样品2~72小时¹³¹I、¹³⁷Cs和¹³⁴Cs测量结果范围分别为0.04~0.30 Bq/kg,0.05~0.34 Bq/kg和0.05~0.36 Bq/kg,新鲜菠菜样品的探测限略高于饮用水和牛奶样品。三种样品2~72 h测量结果均符合相关标准要求,但所得探测限值均随测量时间延长而减小。结论 在时间许可的条件下,尽量采用较长的探测时间可以增强检测能力,提高样品的检出率,但在应急情况下,应当进行代价利益分析,选择与可探测到的最低活度匹配的最佳测量时间。

A Preliminary Study on the Relationship between Measured Time and the Minimum Detectable Concentration (MDC) of Samples during Radioactivity Measurement of Food and Drinking-water

Objective To compare the MDC of radionuclides in food and drinking-water achieved by different measured time, and to provide reference material to deal with a nuclear or radiological emergency.Methods Measuring the MDC of radionuclides in Marinelli backer filled with samples which are drinking-water, milk and fresh spinach by the measured live time 2 hours, 4, 8, 12, 24 and 72 hours, respectively, then comparing the results with the values of operational intervention level 6 (OIL6) recommended by International Atomic Energy Agency (IAEA) and the guidelines for drinking-water quality recommended by World Health Organization (WHO).Results The MDC of the samples of drinking-water and milk are in the range of 0.04~0.30 Bq/kg, 0.05~0.34 Bq/kg and 0.05~0.36 Bq/kg for the ¹³¹I, ¹³⁷Cs and ¹³⁴Cs if measure them from 2 to 72 hours, but the MDC of the sample of fresh spinach is a little higher than that of drinking-water and milk. All the MDC we got are in conformity with the relevant standards, and the longer time we spent in measuring samples, the smaller MDC we would get.Conclusion In the condition of time permitting, we could take a longer measured time to improve the detectability, but in an emergency a cost-benefit analysis to choose the most suitable time to match the MDC is necessary.