中国内地地区表层土壤和陆生植物的^(137)Cs水平分析

Level of^(137)Cs in Chinese terrestrial surface soils and plants

为评估当前中国地表环境人工放射性水平,用反康普顿HPGeγ能谱无损分析了我国陆地表层土壤和陆生植物中^(137)Cs的含量,采用蒙特卡洛方法对样品几何形状因子和密度差异进行校正.分析结果表明:中国内地表层土壤人工放射性水平最高的是西北部的哈密地区,^(137)Cs的比活度为29.9Bq/kg,其次为东北部的罕乌拉地区,^(137)Cs的比活度为24.6Bq/kg;高值带是从哈密到罕乌拉的一条长约3000km,宽约200km的区域,与20世纪上风向核试验场的大气层核试验放射性烟云的传输沉降带基本一致,其他地区土壤中^(137)Cs含量较低,但所有样品的^(137)Cs含量均在全球沉降本底范围以内,最可几比活度为1.74Bq/kg;陆生植物样品中^(137)Cs的含量整体上很低,大多数低于1.5Bq/kg的水平,云南和河南两个地区的植物中^(137)Cs出现了一些高值,这与该地区中土壤样品可交换态的^(137)Cs含量较高有可能相关.

In order to assess the artificial radioactivity level in China,^(137)Cs contents in soil and plant samples were analysed by anti-Compton HPGeγspectrometry,with Monte-Carlo method used to correct the detection efficiency for samples with different geometry and density.The analysis results showed that the highest artificial radioactivity of soil samples was observed for Hami region in the northwest with a specific activity of 29.9Bq/kg,followed by the Hanwula region in the northeast with a specific activity of 24.6Bq/kg;The relatively high level zone was a band of about 3000km long and 200km wide from Hami to Hanwula,basically same as the transporting route of the radioactive clouds from the atmospheric nuclear tests in the upwind test sites in the last century.Beyond this band,the^(137)Cs level of the soil was very low.However,the^(137)Cs content in all the soil samples lies in the range of the global fallout with the most probable specific activity was 1.74Bq/kg.The^(137)Cs level in plant samples was very low overall,most of which was lower than 1.5Bq/kg.A few high values were observed for Yunnan,Henan Province,where the exchangeable^(137)Cs content of soil samples are probably rather high.