青岛市地表天然放射性水平及其主控因素特征

Characteristics and controlling factors of natural ground radioactivity in Qingdao City

通过对青岛市1 500 km2范围内大密度土壤放射性核素(238U、232Th和40K)和地表γ辐射测量,系统深入地研究了其放射性特征、分布规律及其影响因素。结果表明,青岛市土壤中核素232Th和40K的放射性比活度偏高,而238U偏低。地表γ辐射吸收剂量率(平均值91.87 nGy.h-1)略高于全国和世界平均值,研究发现地表93.14%的γ辐射来自地面放射性核素238U、232Th和40K的γ辐射,其中232Th和40K的贡献占81.21%,是主要的贡献者。地质背景是影响地面γ辐射吸收剂量率的主要因素,燕山期各类花岗岩是导致青岛市区—王哥庄一带γ辐射吸收剂量率偏高的主要原因;同时环境因素(路面材料、地貌景观)对地表γ辐射吸收剂量率也存在一定影响。虽然研究区的γ辐射吸收剂量率较高,但其年有效剂量(0.56 mSv)远低于公众照射年剂量当量限值1.0 mSv,人居环境基本不受影响。

Based on a large density measurements of soil radionuclides （^238U、^232Th,^40K） and surface gamma radiation within 1 500 km^2 in Qingdao City, a systematic in-depth study of its radioactive characteristics, distribution and influencing factors are conducted. The results reveal that the radioactive of nuclides ^232Th and ^40K in soils of Qingdao City are with high specific activity, while ^238U is low. Surface gamma radiation absorbed dose rate （mean value： 91.87 nGy/h） is slightly higher than the national and world mean values. The study found that 93.14% of the surface gamma radiation comes from radionuclides ^238U,^232Th and ^40K, meanwhile ^232Th and ^40K are the main radioactive elements which accounted for 81.21% of the contribution. The geological background is the main factor which effect the gamma radiation absorbed dose rate of the surface soil, the high gamma radiation from Qingdao to Wanggezhuang could be mainly resulted from the various types of granite and fault structure of Yanshannian, in the meantime, environmental factors （paving, landscape, etc.） contributed the gamma radiation absorbed dose rate to a certain level as well. Although the gamma radiation absorbed dose rate in the study area is a little higher, the annual effective dose （0.56 mSv） is far below the public exposure dose limits 1.0 mSv, cause no harm to living environment.