【作者】 张庆贤；

【导师】 葛良全； 熊盛青；

【作者基本信息】 成都理工大学 ， 核资源与核勘查工程， 2010， 博士

【摘要】 航空γ能谱测量是将γ能谱仪安装在飞机上探测陆地介质放出的γ射线,进而确定地表介质中U、Th、K的含量。航空γ能谱测量在矿产资源勘查尤其是放射性矿产资源勘查、辐射环境调查、核应急等领域得到广泛应用。航空γ能谱特征和仪器谱的解析是提高U、Th、K含量测量精度的关键问题。目前基于仪器谱或核素放出离散谱对航空γ能谱特征进行研究,而对于通过地质体作用后的原始能谱分布研究不多;采用剥离系数法进行仪器谱的解析,对于全谱的解析研究较少。同时航空γ能谱测量影响因素是进行测量结果反演的关键问题,但目前国内缺少该方面的研究。针对目前航空γ能谱测量研究不足,本文在空中γ能谱特征和仪器谱解析等方面展开研究。1、本文通过理论分析与蒙特卡罗(MC)数值模拟相结合的方法,获得了地-空界面大气中天然γ能谱的原始谱分布特征。地空界面上空γ能谱是连续谱,由特征γ射线和连续散射本底两部分组成。γ能谱分布特征尤其是低能散射峰同地表介质成分相关。在考虑大气扰动因素下,对单一元素介质、花岗岩、石灰岩、砂岩和玄武岩上空γ能谱的分布特征进行研究,结果表明利用S1/S2的方法可以定性判别岩石的有效原子序数,进而区分岩石性质。地表γ能谱测量受到地质体中水分含量的影响。当土壤水分增加的时候,地表γ射线注量率降低。论文通过理论分析建立了土壤中水分校正模型,通过MC方法求解了校正模型的参数。通过实验表明,该模型可以有效校正水分的影响,校正后误差小于2%。2、本文深入分析了地形对航空γ能谱测量的影响机理,提出了航空γ能谱测量有限元地形校正方法。采用数值积分的方法,实现航空γ能谱测量地形校正,并实现了相关代码。在论文中计算了凹方锥、凸方锥、凸平台、凹平台、凹圆锥、凸圆锥、凹条带、凸条带和阶梯等9种典型地形情况下航空γ能谱测量的地形校正系数,为航空γ能谱测量地形校正提供了新的方法技术。3、针对NaI(Tl)晶体的能量分辨率不足、康普顿散射对航空γ能谱测量的干扰难题和传统剥离系数法标定的不足,提出并实现了γ能谱解析方法。①首先文中采用傅里叶变换本底逐步逼近法,对航空γ能谱散射本底进行扣除,得到由全能峰组成的特征γ射线谱线。有效扣除散射本底,可以采用简单的高斯函数建立响应函数矩阵,降低谱线解析过程中响应函数建立的难度,达到全谱解析方法的实用化。通过模拟谱线验证,本底扣除误差小于15%。②文中采用响应函数矩阵的思想,建立了仪器谱和输入谱之间的关系。采用极大似然方法和直接解调方法实现了谱线重构,有效分离了峰位相差为一个半高宽的重叠峰,峰面积变化小于10%。③将谱线解析算法应用于γ能谱仪的标定,建立特征γ射线净峰面积同U、Th、K之间的关系,简化能谱仪的标定过程。经地面γ能谱仪在饱和基准放射性模型实验表明:在混合基准模型上,传统的剥离系数法计算放射性元素含量和谱线解析法计算放射性元素含量相对于模型推荐值之间的相对误差分别为:K,9.74%和8.73%;U,-8.25%和-0.96%;Th,10.51%和-3.13%。④采用谱线解析方法,讨论了NaI(Tl)晶体探测器测量137Cs方法。实验表明,通过谱线解析NaI(Tl)晶体探测器可以有效测量137Cs的活度,测量137Cs的净峰面积同活度之间关系的判定系数为0.99。本研究提高U、Th、K含量的测量精度,简化仪器刻度的过程,为航空γ应用于找矿地质解释提供依据,具有实用价值和科学意义,同时拓宽了航空γ能谱测量的应用范围。更多还原

【Abstract】 Airborne gamma-ray spectrometry survey is detecting the gamma-ray spectrum released form the terrene which the airborne gamma-ray detecor is fixed in airplane. It can get U, Th and K contents of the terrene directly when the airplane flying. Airborne gamma-ray spectrometry survey is widely applied, such as mineralization exposure, environment radiation evaluation and nucleus emergency. The gamma-ray spectrum characteristics and spectrum analysis is the key of improving the precision of U, Th, K content measurement. At present, the researchers pay attention to the spectrum measured by instrument and radionuclides released, hardly consider the sperctrum disturbution which effected by geologic body. As for the spectrum analysis, the conventional method is the tripping-ratio, few regarding the full spectrum analysis. Influencing factor of the airborne gamma-ray spectrometry survey is the key of the survey result inversion. In view of the research insufficiency the airborne gamma-ray spectrum, airborne gamma-ray spectrum characteristic and spectrum analysis have been studied in this paper.In the paper, the author gets the characteristic of airborne gamma-ray spectrometry by theoretic analysis and Monte Carlo method. The character such as:①The gamma-ray spectrometry in the air is consecutive, it is different from the gamma-ray spectrometry from the the radioactive nuclear. The gamma-ray spectrometry construct of charactertic gamma-ray and the baseline of Compton Scattering.②The character of gamma-ray spectrometry in air, especially the Compton Scattering peak, is relationship to medium composition. In the paper, the character of gamma-ray spectrometry is studied upon the simplex element medium, granite, gritstone, limestone and basalt. We can use the variable of S1/S2 to distinguish the effective atom number so we can distinguish the lithology.③The effect of water in the soil on the gamma-ray spectrometry measuring on the surfer of ground. With the increase of the water content, the flux of gama-ray decrease on the surfer of ground. In the paper, author established the correction model of wate content in the soil. By the Monte Carlo simulation, the parameters of the correction model had been acquired. Moreover, the model can correct the influence of water by experimentation test and the error is less than 2%.In the thesis, the influence mechanism of landform to the airborne gamma-ray spectrometry survey has been analysised, and the micro elment landform correction method has been put forwarded. Based on the numerical calculation, the landform correction on the airborne gamma-ray sepectrometry survey has been achieved; furthermore, the program code has been completed. There are nine typical landform had bed considerated and corresponding correction factors has been calculated. As a consequence, there is the new method for the landform correction of airborne gamma-ray sepectrometry survey.For the unsatisfactory energy resolution of the NaI(Tl) crystal, the problem of scattered rays in airborne gamma-ray sepectrometry and the defect of conventional tripping-ratio method, Author put forward the analysis mehod of gamma-ray spectrum for airborne gamma-ray spectrometry.①The method of fourier transform approach background by step (FTABS) is been adopted to estimate the scattered rays background for airborne spectrum. FTABS can estimate the scattered rays effectively only by the response function matrix which is established by gaussian function. Using this method, the response function is simpler and has higher practicality in full spectrum analysis. By the simulation spectrum test, the error of background estimation is less than 15%.②Profits from the concept of response function matrix, author establish the relation between spectrometry and input spectrum. The spectrum have been restructured by maximum likelihood method and direct demodulate method. A FWHM-discrepant overlapping peak has been separated by the spectrum restructured technology, and the area of peaks maintains invariable.③The spectrum analysis algorithm is applied to gamma-ray spectrometry calibration, the relation between net peak area of characteristic gamma-ray and the content of U, Th and K has been established. Using spectrum analysis algorithm, spectrometer calibration process can be simplified. In the experiment of content calibration processing prove that the spectrum analysis algorithm can effectively improve the precision of element content calibration. Calibrating on the saturated gamma model, the mixed model content by measurement described as fellow: comparing with conventional tripping-ratio method, the error of K element content from 9.74% reduces to 8.73%, the error of U element content from -8.25% reduces to -0.96% and the error of Th element content from 10.51% reduces to -3.13%.④The 137Cs measurement which detected by NaI(Tl) crystal using spectrum analysis algorithm has been discussed. Experiment proves that NaI(Tl) crystal detector can measure the activity of 137Cs by spectrum analysis. The determination coefficient between the net area and activity of 137Cs is 0.99.For the rearch in the thesis, measuring accuracy of U, Th and K content has been improved and calibration process has been simplified. The rearch provides the basis of geologic interpretation of prospecting by airborne gamma-ray spectrometry survey, which have high practical value and scientific significance and expanded application scope.更多还原