铀尾矿库区稻田土中放射性核素的空间分布和放射性水平评价

Spatial Distribution and Radiation Evaluation of the Radionuclides in Paddy Soil of the Uranium Tailings Area

以我国南方某铀尾矿库下游稻田土壤为研究对象,通过现场取样与室内检测,对土壤中放射性核素238U、226Ra、232Th、40K的比活度进行空间分析。同时采用γ辐射吸收剂量率和年有效剂量法进行土壤环境放射性水平评价,得出土壤中所检测的4种典型核素放射性比活度差异较大。在土壤表层和剖面,226Ra和40K的均值、最大比活度和标准差均较高,232Th和238U较低。而226Ra含量超出当地背景值较多。剖面上4种放射性核素比活度均有随深度降低的趋势,高值出现在土壤浅层,这可能与土壤的有机质含量等有关。综合垂向和平面上的分布特征可知核素232Th、40K的迁移能力比238U、226Ra弱。放射性水平评价结果显示:研究区土壤年有效剂量率平均值小于联合国原子辐射效应科学委员会和全国年有效剂量率的推荐背景值,但是γ辐射吸收剂量率均值高出全国和世界平均水平的3倍。准确定量评价了尾矿库对居民造成的辐射影响,同时为放射性核素在周边稻田植物根系中的迁移机理研究提供基础资料。

The specific activity of radionuclide 238U,226Ra,232Th and 40K in the soil was analyzed by field sampling and laboratory test,taking the paddy soil in the lower reaches of a uranium tailings reservoir in the south of China as the research object.Meanwhile,the soil environmental radioactivity was evaluated by γ-radiation absorbed dose rate and annual effective dose method.It was concluded that the specific radioactivity of the four typical nuclides detected in the soil was quite different.There are higher values,maximum specific activities and standard deviations at 226Ra and 40K in soil surface and profile,while 232Th and 238U are lower in these areas.Besides,the content of 226Ra was higher than the local background value.Four specific activity of the radionuclides in the profile decreased with the depth,and the high values appeared in the shallow layer of the soil,which may be related to the content of organic matter in the soil.Combined with the vertical and plane distribution characteristics,the migration ability of nuclide 232Th and 40K are weaker than that of 238U and 226Ra.The results of radioactivity level evaluation show that the average annual effective dose rate of soil in the study area is less than the recommended background value of the UNSCEAR and the National annual effective value,while the average dose rate of γ-radiation absorption is three times higher than the national and world average.It accurately and quantitatively evaluates the radiation effect of tailing pool on residents and provides basic data for the study of radionuclide migration mechanism in the surrounding rice field plant roots.