东北黑土中^(137)Cs背景值研究

Study on Reference Cesium-137 Inventory of Black Soil in Northeast China

通过测定东北黑土背景点样品中137Cs活度,探讨了土壤剖面中137Cs的分布特征,对因风蚀造成背景点土壤表层137Cs的沉积进行了校正,得出了黑土的137Cs背景值,为水蚀风蚀两相侵蚀地区土壤137Cs背景值的确定提供了新思路。结果表明:黑土背景点土壤剖面中137Cs比活度的分布呈指数型,其拟合方程为Cs=76.744e-0.2566h,相关系数达到0.994。剖面中75.7%的137Cs分布在0～5cm的表层中,92.5%的137Cs分布在0～10cm的土壤上层;黑土的137Cs背景值为2463.64Bq/m2,与平坦黑土耕地中137Cs的沉降总量接近,可以利用该背景值进行黑土侵蚀速率的估算。

A background profile which located at Jiutai county, Jilin province was selected.The profile soil samples were sampled in 5 cm depth increment and cesium-137 activities of samples were determined by hyper-pure germanium (γ-ray energy spectrometry. The distribution type of cesium-137 activities in the profile was analyzed. Because there is stronger wind erosion in the region of black boil, cesium-137 activities in the surface layer of 0~5 cm at vegetated reference site could be disturbed due to sedimentation of soil particles from near farmland. That is, there are a phenomena that soil particles will be preferentially accumulated at vegetated sites and preferentially eroded at bare sites. The dust was found to be cesium-137 enriched. So, cesium-137 activities in the background profile should be emendated. This paper gives a new method for determine reference()^(137)cesium inventory of soil in the region where there are both water erosion and wind erosion.The reference inventory in black soil was contradistinguished against those in other sites all over the world. Finally, the reliability of reference inventory was tested by comparing with the inventories in the flat farmlands nearby the background site. The results show that the depth distribution of cesium-137 activities in the background site fits exponential type remarkably. The equation is Cs=76.744e^(-0.2566h). 75.7% and 92.5% cesium-137 falloutsare are in the layer 0~5 cm, 0~10 cm,respectively. The reference is 2 463.64 Bq/m^2, which is reliable and may be used to estimate the loss rate of black soil.