【作者】 徐宏坤；

【导师】 方方；

【作者基本信息】 成都理工大学 ， 核技术及应用， 2011， 博士

【摘要】 月球表面物质的原子或原子核在受到宇宙线粒子轰击时,会激发产生特征γ射线;此外,一些天然放射性元素也可以自发产生γ射线。不同元素释放出的γ谱线具有不同的特征能量,因此我们可以通过γ射线谱仪测量这些特征γ谱线的能量和通量,从而推算月表物质元素的种类和丰度。开展嫦娥月球探测工程是我国向宇宙深空探测迈出的第一步,实现了我国航天深空探测零的突破。目前月球科学已成为国际科学研究的焦点,月球具有可供人类开发和利用的各种独特资源,其特有的矿产和能源,是对地球资源的重要补充和储备,对人类社会的可持续发展具有重要的意义。本文围绕月表主要放射性元素的特征分布问题,通过对嫦娥一号伽玛射线谱仪在一年内的科学探测数据开展分析研究;并综合对比国内外绕月伽玛能谱探测与数据处理情况,开展了以下研究。1、通过对2C级数据中5,449,778条伽玛探测谱线的筛选校正、元素分布数据检查,发现异常高值现象,因此对经过该经纬度范围的所有2C级谱线文件进行经纬度做图检查,注意到伽玛探测过程中太阳粒子事件的对探测器的影响,将对应异常探测数据剔除,有效地消除了元素特征分布图中的异常条带现象,保证了生成3C级伽玛数据文件的准确性。2、针对放射性探测中的统计涨落现象,进行正交小波分解,利用其能量守恒的特性,确保了小波逆变换时不扩大噪声在小波域中的能量,引入非线性阈值函数,设置对于无偏估计门限,在保证计数值稳定的情况下,重构得出平滑的能谱曲线,有效降低了伽玛谱线数据的噪声波动,这对准确计算月表元素含量的特征分布具有重要的意义。3、在分析国内外本底处理方法的基础上,本文提出趋势线峰形加强本底扣除(TPSBE)方法。首先,将伽玛射线能谱从频域上看做低频本底和高频特征峰的叠加,滤除特征峰和杂波,得到能谱趋势线,通过趋势线计算,将能谱特征峰峰形加强。之后,利用双正交小波具有线性相位的特性,通过细节系数与零值的交界情况逐次迭代逼近峰位和波谷,并增加判断机制对结果进行筛选和校正。最后,差值构造出特征峰本底曲线。结果表明该方法分析低能段重叠峰和弱峰时具有较好的效果。4、对谱线中特征能量相近元素所形成的重叠峰,按均方误差极小构造各自特征峰曲线,采用高斯函数进行拟合解析。并以等面积分布图、等值线图、球面3D分布图三种形式清晰展示全月元素特征分布情况。5、根据对全月U、Th、K元素结果数据成图分析,三种元素的分布具有显著的相关性,主要分布于月球正月面北部,由西经70°,北纬50°;西经20°,南纬30°;东经50°,北纬70°三点组成的三角区域中,尤其在南部的云海、湿海、风暴洋区域,具有显著的高值点;在此正月面三角形区域之外及背月面,三种放射性元素的分布普遍偏低,其中在南极艾肯盆地附近有相对高值区域出现,但远低于正月面北部的三角形区域。6、通过对比分析嫦娥一号伽玛谱仪与阿波罗号伽玛谱仪、月球勘察者号伽玛谱仪、月亮女神号伽玛谱仪对月球放射性探测的成图结果,虽然在探月任务中探测卫星的运行轨道不同、探测时间不同、探测仪器不同,然而,数据处理结果中U、Th、K三种放射性元素的总体分布呈现出较高的一致性,能够客观反映出月球主要放射性元素的组成和分布特征。更多还原

【Abstract】 When the nuclei of Lunar surface material bombarded by cosmic ray particles, it will produce its characteristicγ-ray excitation; besides, a number of natural radioactive elements can also spontaneously produceγ-rays. Different elements can produce gamma-ray spectra with different energy. Therefore, by measuring the energy and flux of these characteristics spectra, we can get the composition and abundance of lunar surface materials.China Lunar Exploration Program was the first step of deep space exploration, its successful implementation was breakthrough of China’s aerospace exploration. At present, lunar has become the focus of scientists in many countries, there are a variety of unique mineral and energy resources on the moon for human development, and is an important complement and reserves to the Earth’s resources, also it has a profound impact in human society for sustainable development.This paper focused on getting the radioactive composition and abundance of lunar surface materials, analyzed the data of gamma ray spectrometer on the Chang’E-1 during one year scientific exploration. After compared with other analyzing result of lunar detection mission, following conclusions can be drawn.1, After selection and calibration for 5,449,778 spectra of 2C level data, we checked the overall distribution map of elements, and found that there was some abnormally high value band shape distribution. So we extracted the latitude, longitude, measuring status and time parameters of Chang’E-1 satellite from documents, map the latitude and longitude of abnormal 2C-level files, found the possible causes, and removed the abnormal orbit data, then effectively eliminating the abnormal high counts band shape distribution in the results.2, In order to decreasing the statistical fluctuation in radioactive detection, we take Daubechies-4 for wavelet orthogonal decomposition. By its energy conservation characteristic, we can ensure it doesn’t increase noise energy in inverse wavelet transform. After setting the unbiased estimation threshold by non-linear threshold function, we reconstructed the smoothing spectrum with stability of count value, which was of great significance for the accuracy of quantitative element analysis.3, Based on analyzing of some background estimation methods, we proposed the Trend line Peak Strengthening for Background Estimation (TPSBE) method, decomposited the spectrum in frequency domain, get the trend line and enhanced the characteristic peaks. Then, we found the position of peaks and valleys by biorthogonal wavelet decomposition. After correction of the result, we estimated the background by interpolation. Using this method, we can well extract the information of elemental characteristic peaks, especially for the low energy band section in which the weak peaks information were submerged in high background counts.4, For the overlapping peaks in the spectra, such as the characteristic peaks of potassium and magnesium, we decomposited them by Gaussian function fitting method according to minimum mean square error principle. The result of lunar radioactive elements distribution was clearly shown by equal-area map, contour map, spherical 3D map.5, According to the distribution map of U, Th, K elements, there was a significant correlation-ship, all of them were mainly distributed in the northern near side of lunar, within an big triangular region constituted by west longitude 70°, north latitude 50°; West longitude 20°, south latitude 30°; east longitude 50°, north latitude 70°north latitude. Particularly in the south of the Mare Nubium, Mare Humorum, the Oceanus procellarum, were significant high-value distribution. Outside the big triangular region the counts were generally low. While in the Antarctic Aiken Basin there was a relatively high value area, but much lower than that in the big triangular region.6, Comparing Chang’E-1 GRS’s result with that of Apollo, Lunar Prospector, and Kaguya, although different mission with different detecting devices, in different satellite orbit, during different time, the data processing result for three radioactive elements of Uranium, thorium, potassium presented high consistency in distribution map, which could objectively reflect the main radioactive element composition and distribution on the moon,.更多还原