【作者】 曾兵；

【导师】 葛良全；

【作者基本信息】 成都理工大学 ， 地球探测与信息技术， 2010， 博士

【摘要】 自1896年Becquerel发现天然放射性以来,充盈于人类生存、活动和获取资源场所上的核地球物理辐射场逐步被人们认识、了解与利用,它包括γ辐射场、β辐射场、中子辐射场、α辐射场、μ辐射场,以及其它粒子的宇宙射线场。其中,γ辐射场占有非常重要的地位。γ射线的作用空间称为核地球物理γ辐射场,一般以γ照射量率和γ射线能量来度量。γ场反应了γ射线在被研究介质中的空间分布。地-空界面上天然伽玛场的研究对于环境放射性评价、矿产资源勘查都具有重要的科学意义和实用价值。论文在研究成都平原的自然条件、地形地貌、地质特征、地球化学特征和土壤类型与分布的基础上,研究了天然放射性γ射线的来源、放射性衰变与积累及放射性系列平衡的建立,分析了天然γ场的测量原理,建立了无限大伽玛辐射体上方γ射线照射量率的正演数学表达式,并根据该表达式和土壤介质中铀、钍、钾元素含量与放射性比活度、距地面1m的高度处γ射线吸收剂量率之间的转换系数,从理论和实践上提出了成都平原铀-镭平衡系数、氡射气系数的校正方法,为成都平原原野放射性水平评价提供了理论依据和技术方法;根据氡在多孔介质中扩散和对流理论,论述了土壤介质中孔隙氡浓度和大气氡浓度的稳态正演数学模型,及其与土壤介质中铀含量之间关系的数学表达式,为成都平原原野氡潜势分布和室内氡浓度评价提供了理论依据。同时,论文广泛的收集和分析了成都平原自然地理、地质构造、地球化学和土壤类型的基础上,利用成都平原1:25万土壤地球化学取样的铀、钍、钾含量数据,以及在成都平原进行γ能谱测量、土壤氡浓度测量和室内空气氡浓度的测量成果,较系统的获得了成都平原地-空界面上天然伽玛能谱特征和辐射环境特征,并从地质构造和环境角度进行了科学解释:①、通过对成都市土壤取样进行化学分析和γ能谱测量的数据得到的铀-镭平衡系数进行统计分析,结果表明其频数大体呈正态分布,对成都平原的γ场进行测量和计算时可取土壤中的铀-镭平衡系数Kp = 1.92。②、成都平原放射性核素40K的比活度值在300.5~1273.9Bq/Kg之间,放射性核素40K的比活度值绝大部分都在350~800Bg/Kg区间,平均值为659.8Bq/Kg,略低于全国平均值;放射性核素232Th的比活度为18.5~127.2Bg/Kg,大体呈正态分布,均值为56.8Bg/Kg,均方差为15.5Bg/Kg,与全国的平均水平基本一致;放射性核素238U的比活度为11.6~84.8Bg/Kg,呈正态分布,均值为31.5Bg/Kg,均方差为7.3Bg/Kg,低于全国的平均水平。成都平原地质构造对放射性核素238U比活度有很大的影响,在褶皱断裂带地区放射性核素238U的比活度均较高。③、成都平原内照射指数为0.06~0.42,平均值为0.158;外照射指数为0.24~0.81平均值为0.461,内照射指数和外照射指数均低于国家强制性要求。成都平原γ辐射吸收剂量率为41.10~140.74nGy/h,均值为79.516nGy/h,均方差为13.7922nGy/h,与全国和世界的平均值基本一致,年有效剂量值为0.02~0.07mSv,均值为0.039mSv,均方差为0.0068mSv,远低于世界平均年有效外部剂量限值。④、成都平原共1800个取样点的土壤氡本底值范围为2.098×10~4Bq/m~3 ~ 15.332×10~4Bq/m~3,平均值为5.710×10~4Bq/m~3,标准差为1.329×10~4Bq/m~3。成都平原北部李家展、河清等地和南部地区如中兴场、青龙场等地的氡浓度稍高,达到了8.369×10~4Bq/m~3,极少数区域超过9.699×10~4Bq/m~3,但都在15.332×10~4Bq/m~3以下,绝大多数地区的氡浓度在5.710×10~4Bq/m~3以下。⑤、成都平原主体地区(成都市)的室内氡浓度范围为8~177Bq/m~3,平均值为39.~4Bq/m~3,均方差为22.9Bq/m~3,伽玛剂量率范围为75~169nSv/h,平均值为122.1 nSv/h,均方差为116.3nSv/h。室内氡浓度测量结果呈泊松分布,室内伽玛剂量率测量结果呈正态分布。温江、邛崃和成都高新区和彭州地区室内氡浓度要明显高于其他地区,其他地区室内氡浓度则基本处于一个水平范围,为35~45 Bq/m~3;而对于不同地区的伽玛剂量率除温江地区略低外,其他地区的伽玛剂量率则基本处于同一水平,范围在110~140 nSv/h之间。通过对成都平原地-空界面γ场及其引起的环境效应的研究,发现地质构造对成都平原的天然放射性核素的比活度有较大的影响。成都平原放射性水平分布情况和成都平原地质环境表明区域地质构造带对成都平原整体放射性水平的影响较大,断裂带区γ射线照射量率、内照射指数及外照射指数等放射性水平评价指标均高于其他地区。第四系冲洪积沉积物和地表水对元素的运移和富集作用对成都平原局部地区放射性水平也有较大的影响。本论文来源于国家基金项目“地空界面氡辐射场及其环境辐射效应研究”(40374051)、国家863计划“资源与环境技术”领域重大项目“航空地球物理勘查系统”中课题7“航空伽玛能谱勘查系统研发”(2006AA06A207)和中国地质调查局地质调查项目“四川省成都经济区城市生态地球化学评价”(200314200015)。更多还原

【Abstract】 Natural radioactivity when Becquerel discovered it in 1896,has been filling in human survival and the areas of nuclear geophysical radiation field. we know and use it day by day. it includesγradiation field,βradiation, neutron radiation field,αradiation field,μradiation field, as well as other particles in the cosmic ray field. Andγradiation field occupies a very important position.γradiation field was calledγfield in short. It Shows the the spatial distribution ofγray. When we need evaluate the environmental radioactivity or nuclear contamination caused by leakage evaluation, theγfield must be researched on ground. This way can obtained the content of natural radio nuclides include uranium, thorium and potassium, and the absorbed dose rate which caused by the natural radio nuclides.The paper studies the natural conditions, the topography, the geological features, the geochemistry, and the soil types and its distribution of the Chengdu Plain. It established the forward mathematical expression ofγ-ray exposure rate on over-infinite gamma radiation body. According to this expression,the content of soil medium uranium, thorium and potassium, the specific activity and the conversion factors ofγ-ray absorbed dose rate,which 1 m height from the ground, it presented the correction methods of Chengdu Plain uranium - radium equilibrium coefficient, radon emanation coefficient from the theory and practice. It provides the theoretical basis and technical approach for evaluating the radioactivity level for the Chengdu Plain Wilderness. According to the theory of diffusion and convection, It discusses the mathematical model of the radon concentration in soil pore medium and the steady-state radon concentration in the atmosphere and the mathematical expression between Uranium and the soil medium. It provides the theoretical evaluating basis of the Radon potential fields for the Chengdu Plain and the indoor radon concentration distribution.Meanwhile, the paper collection and analysis of a wide range of physical geography,geological structure, geochemistry and soil types of Chengdu Plain, use the Plain’s content data of 1:250 000 soil geochemical sampling of uranium, thorium and potassium and the measurement results ofγ-ray spectrometry of soil radon measurements and radon concentration in the Chengdu Plain,get the characteristics of the natural gamma radiation spectrum and environmental on ground-gas in the Chengdu Plain and make a explanation from the geological structure and the environment.①Through statistical analysising the soil samples’chemical analysis data and theγ-ray spectrometry data which obtained uranium - radium equilibrium coefficient, the paper showed that the frequency of large takes the shape of normal distribution. When we measure the Chengdu Plain’sγfield, we can take the uranium - radium equilibrium coefficient Kp = 1.92.②In Chengdu Plain, the radionuclide activity values of 40K is between 300.5 Bq/Kg and 1273.9Bq/Kg, the vast majority is between 350 Bq/Kg and 800Bq/Kg,and its average is 659.8Bq/Kg, lower than the national average.232Th is between 18.5Bq/Kg and 127.2Bq/Kg, distributing in normal and its average is 56.8Bq/Kg.The variance is 15.5Bg/Kg ,as the same as the national average.238U is between 11.6 Bq/Kg and 84.8Bq/Kg, distributing in normal and its average is 31.5Bq/Kg. The variance is 7.3Bg/Kg, lower than the national average. The geological structure is a great impact on the specific activity of radioactive 238U.The specific activity 238U in fault zones is higher than others.③In Chengdu Plain, the irradiation index is between 0.06 and 0.42, its average is 0.158.The external exposure index is between 0.24 and 0.81, its average is 0.461, all lower than the national mandatory requirements. Theγradiation absorption dose rate is between 41.10 nGy/h and 140.74 nGy/h, its average is 79.516 nGy/h, its square deviation is 13.7922 nGy/h, as the same as the national and the world. The annual effective dose is between 0.02 mSv and 0.07mSv, its average is 0.039mSv, its square deviation is 0.0068mSv,far lower than the world’s average annual effective external dose limits.④In Chengdu Plain,the soil radon measurement of the background value is between 2.098×10~4Bq/m~3 and 15.332×10~4Bq/m~3, the average is 5.710×10~4Bq/m~3, and the standard deviation is 1.329×10~4Bq/m~3. The radon content in the northern such as Lijiazhan, Heqing, etc. and the southern regions such as Zhongxinchang, Qinglongchang of the Chengdu Plain is higher than other places, reaching 8.369×10~4Bq/m~3, a handful of area of more than 9.699×10~4Bq/m~3, but all below in 15.332×10~4Bq/m~3,most areas of the radon concentration is lower than 5.710×10~4Bq/m~3.⑤In the main regions of the Chengdu Plain,the radon concentrations ranged from 8 ~ 177 Bq/m~3, average 39.4 Bq/m~3, MSE 22.9 Bq/m~3, gamma dose rate range of 75 ~ 169nSv / h, average to 122.1 nSv / h, the mean square 116.3nSv / h. the indoor’s radon concentration measurements were Poisson, the gama dose rate measurements were normally distributed,the indoor radon concentration of Wenjiang, Qionglai,Chengdu High-tech Zone and Pengzhou is higher than other areas, other’s level are 35~45 Bq/m~3 .Except Wenjiang, the gamma dose rate is between 110 nSv/hand140 nSv/h.The natural geological structure impacts the specific activity of radio nuclides greatly through studied theγfield and its environmental effects on the gas-ground interface in Chengdu Plain. The distribution of radioactivity showed that the regional geological structure of the Chengdu Plain impacts radiation levels greatly. The level of radioactivity, such as theγray exposure rate in fault zones, the internal and external exposure index ,were higher than other areas. The migration or enrichment of quaternary alluvial , flood sediment and surface water in Chengdu Plain also impact the radioactive level in some areas.The paper supported by the National Fund which is "The Research of Radon Radiation Field and Its Environmental Radiation Effects on Gas-ground Interface" (40374051) ,the 7th-project of the National 863 Program ,which is "The System of Air Geophysical Exploration" ,"The Research of airborne gamma spectrometry system" (2006AA06A207) in the field of Resources and Environment and the geological survey project of the Geological Survey Bureau which is " The Urban’s Evaluation of Eco-geochemical in Chengdu Economic Zone" (200314200015).更多还原