青岛城市规划区不同岩性氡浓度差异及其控制因素

BEDROCK RADON CONCENTRATION IN THE QINGDAO URBAN PLANNING AREA AND ITS BEARING ON LITHOLOGY

青岛是典型的花岗岩地区,通过分析青岛不同岩性的氡浓度探讨其差异和控制因素。结果表明:青岛不同岩芯的氡浓度变化范围为0.05~19.51 KBq/m3,平均值为2.56 KBq/m3(n=210),花岗岩氡浓度均值为1.54 KBq/m3,同其他岩性相比氡浓度较低。不同岩性样品氡浓度释放量平均值表现为粉质黏土>泥岩>砂质泥岩>泥质砂岩>闪长岩>粉土/填土>砂岩>正长花岗岩>粗砂>花岗岩>二长花岗质片麻岩。综合来看,土壤层中氡浓度最高,其次是沉积岩和岩浆岩,变质岩中氡浓度最低。不同岩性氡浓度与其铀含量和孔隙率有关,除花岗岩外,沉积岩和变质岩中铀含量越高所含氡浓度越高,沉积岩、岩浆岩以及变质岩的氡浓度和孔隙率大小呈正相关,沉积岩中氡浓度高于岩浆岩,推测与其所含的富水砂层有关;土壤的土质均匀疏松,孔隙度最高,氡在土壤中有大量的存储空间,故在所有岩性中所含的氡浓度最大。

The bedrock of the Qingdao area is dominated by granite. This paper is devoted to the radon concentrations in various bedrocks with different characteristics and influence factors. The results show that the radon concentrations the bedrocks of Qingdao change in a range from 0.05 to 19.51 KBq/m3, with an average of 2.56 KBq/m3(n=210), and the average is only 1.54 KBq/m3 for granite, which is much lower than that of other rocks. The average of radon in other samples reads as follows: silty clay>mudstone>sandy mudstone>argillaceous sandstone>diorite>silt/filled soil>sandstone>syenogranite>coarse sand>granite>monzonitic granitic gneiss. Highest radon concentration is found in consolidated soil, followed by sedimentary rock and magmatic rock, and the lowest remains with metamorphic rocks. It is observed that the radon concentrations in bedrocks is positively related to uranium content or porosity. The highest radon concentration observed in sedimentary rocks is not only related to its high porosity, but also the water-rich sandy interlayers in the sedimentary sequence. The unconsolidated soil is loose and porous, there is large space to keep radon-bearing water in the soil.