Abstract—

The results of the field radiometric survey of the mined monazite Vasil’evka placer in southern Yakutia are presented. It is shown that the natural background radioactivity of soils of the surveyed area mainly depends on the features of its geological structure and, to some extent, on landscape-geocryological conditions. The rate of equivalent dose of gamma radiation on the soil surface of the studied plot varies in a wide range (from 0.04 to 0.50 µSv/h or more), depending on changes in the concentrations of ⁴⁰K, ²³⁸U, and ²³²Th in soils. Radiogeochemical features of soils in the studied area are well displayed on radiometric maps by isolines of the dose rate and radionuclide contents. The concentrations of ⁴⁰K, ²³⁸U, and ²³²Th are minimal in a peat-bog soil and a high moor on the interfluves composed of crystalline schists and gneisses and are maximal in podburs and alluvial soils formed on the products of weathering of granitoid rocks and monazite-bearing alluvial deposits in the Vasil’evka River valley. The studied soils are characterized by low mean concentrations of ⁴⁰K and ²³⁸U, corresponding to their background values in soils of Yakutia. The mean concentration of ²³²Th in the studied soils is increased as compared to the geochemical background. In addition to the composition of soil-forming rocks, the content and distribution of radionuclides in soils are significantly affected by soil-forming processes, chemical properties of elements, and technogenic impact. According to the effective specific activity of radionuclides, the studied soils correspond to the first, second, and third classes of building materials. Soils and enriched sands in some parts of technogenic landscapes are assigned to low-radioactive industrial waste according to the specific activity of thorium and require disposal. Their use as building materials from the identified areas of natural thorium concentration in alluvial deposits has serious limitations.

中文翻译：

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雅库特南部独居石砂矿土壤和沙子的放射性地球化学

摘要-

介绍了在雅库特南部开采的独居石 Vasil'evka 砂矿的现场辐射测量结果。结果表明，调查区土壤的自然本底放射性主要取决于其地质结构特征，在一定程度上还取决于景观-地质条件。研究地块土壤表面伽马辐射等效剂量率在很大范围内变化（从 0.04 到 0.50 µSv/h 或更多），这取决于⁴⁰ K、²³⁸ U 和²³² Th浓度的变化土壤。研究区土壤的放射地球化学特征通过剂量率和放射性核素含量的等值线在辐射图上得到很好的显示。浓度为⁴⁰ K, ²³⁸U 和²³² Th 在泥炭沼泽土壤和由结晶片岩和片麻岩组成的河道上的高沼泽地中最小，在 podburs 和冲积土中最大，这些土壤是由花岗岩风化产物和含独居石的冲积沉积物形成的瓦西里耶夫卡河谷。所研究的土壤的特征是⁴⁰ K 和²³⁸ U的低平均浓度，对应于它们在雅库特土壤中的背景值。平均浓度²³²与地球化学背景相比，所研究土壤中的 Th 增加。除了成土岩石的组成外，土壤中放射性核素的含量和分布还受到成土过程、元素化学性质和技术影响的显着影响。根据放射性核素的有效比活度，所研究的土壤分别对应于第一、二、三类建筑材料。根据钍的特定活性，技术景观某些部分的土壤和富集沙被归为低放射性工业废物并需要处置。将它们用作冲积矿床中确定的天然钍浓度区域的建筑材料具有严重的局限性。