摘要
国内外有关专家学者对γ谱数据处理的算法和应用开展了大量卓有成效的研究,但是,将全谱解析方法应用到能谱系统标定中的研究却鲜有见闻。能不能用更少的标准模型或者标准样品,以更简洁的方式,对航空γ谱仪测量系统进行可靠而精确的散射标定,并达到一定的精度,值得研究;新型国产航空γ谱仪研制后,其具体性能指标是人们所关心的,各项指标通过哪些切实可行、有效精确的方法进行测定,值得探讨;系统在有关试验中的响应情况如何,自然界中,陆域、水域和海域不同高度不同能量γ射线随高度的变化规律如何,值得分析。
本课题来源于于国家863计划资源与环境技术领域重大项目航空地球物理勘查技术系统的第七课题──航空伽玛能谱勘查系统研发。本文主要针对航空γ能谱仪主要性能测试、不同环境上空不同能量γ射线随高度的变化规律、系统的标定方法展开研究。论文首先介绍了航空γ能谱测量中主要的辐射源及其特征,并利用圆锥体模型对地表上空的γ照射量率的计算方法进行了分析和讨论;接着,对航空能谱测量常见天然原始谱、谱信号的形成过程及实测仪器谱的复杂化进行了深入分析;然后对论文的主要研究内容和成果进行了详细论述。
主要研究内容和成果有:
(1)分析谱仪的主要性能指标及其含义,研究重要指标的测试方法。在裸晶体和低本底两种条件下分别测定能量分辨率,对Cs源661KeV能量峰而言,两种条件下的单条探测器分辨率均小于8%,室内系统分辨率小于8.4%;利用U源、Th源的多特征峰及能量线性的公式求取能量起始阈小于23KeV、各条探测器和系统能量线性拟合度均大于0.9999,积分非线性小于0.2%,微分非线性小于1.0%,系统上限计数率达200K/sec;利用双源净计数法测定系统的死时间小于5μs;任意抽取稳定的室内环境24小时稳定性测试中的4小时数据进行分析,各窗计数率与均值相对误差均小于±10%,其中总道的相对误差为±6.29%;在温湿度随时间变化的室外环境进行48小时稳定性测试,结果表明计数率随地面湿度增大而减小;1024道模式下调偏16道,系统在90s后达到较好的稳谱效果。
(2)利用水、陆动态标定带数据,对谱仪系统在陆地、湖面上空300m范围内各能窗计数率随高度的变化规律进行分析,得到陆地和水域上低空范围不同能量γ射线随高度的变化规律;利用海上高高度标定数据,对各能窗计数率在海域上空1800m至3000m范围内随高度的变化规律进行分析,得到海域上空较高高度不同能量γ射线随高度的变化规律。
(3)在充分调研和分析的基础上,选择SINP和傅里叶变换相结合的方法对仪器谱进行精确本底扣除,然后利用直接解调方法进行全谱解析,并将该方法应用到系统标定上来。采用剥离系数法和航空标定模型对车载、Y-5飞机机载、Y-12飞机机载系统进行系统标定,其中谱漂严重的车载试验的标定结果明显错误,表明谱漂较严重时散射剥离将失去意义。将利用剥离系数和全谱解析法得到的换算系数,对混合模型含量进行反算、对比,两者与含量推荐值的相对误差相当,证明了全谱解析标定方法在航空伽γ能谱系统标定中的可行性和精确性。
(4)分别采用少量单点谱数据、所有数据参与全谱解析标定计算,结果表明采用更多谱数据参与计算,可有效抑制统计涨落影响;利用K、U、Th模型计算得到一组换算系数,利用混合模型计算得到另一组换算系数,比较两者的相对误差,结果表明两者相对误差不超过2.2%,所以可以利用一个标准饱和模型(或大面积饱和样品)得到换算系数,从而有效减少标定的工作量。
Fruitful research on gamma-ray data processing algorithm and application has done by experts and scholars in the domestic and foreign, however, will be the full spectrum of analytical method applied to the energy spectrum of research system calibration are rarely informed. Can or not use less of the standard model or standard sample for reliable and accurate scattering calibration of gamma-ray measuring system, with more concise way and a certain precision, is worth studying. When new aero-gamma spectrometer in domestic is developed, with the specific performance index is concerned, each index all need through the feasible and effective methods for precision measuring, this is worth discussing. In different testing, system how to respond, in different height range, the rule of different energy gamma rays with height change on waters, ground-launched and sea, all of this is worth researching.
This article comes from the national 863 Program, the seventh issue of major projects of resources and environment technoloygy "airborne geophysical exploration technique system"—"Department of airborne gamma spectrometry survey ECR&D" (No. 2006A06A207). This article launched research mainly on main performance testing of airborne gamma spectrometer, the rule of different energy gamma rays with height change in different environment, the calibration approach of system. It firstly introduces main radiation source and its characteristics of airborne gamma ray spectroscopy surve, and the calculation method of eminence above the earth's surface are analyzed and discussed by conical model. Then,deeply analyzes the common natural original spectrum of airline spectrum measurement, the forming process of the spectrum signal, and the complication of the measured instrument spectrum. Finally the paper's main research content and the results are discussed in detail
The main research contents and achievements are as follows:
(1) Analyze the main performance indexes and its meaning of spectral instrument. Research the test methods of key indicators In bare crystal and low background, measure the energy resolution under two conditions. In terms of 661KeV energy peaks of Cs source, all the resolutions of single detector in two conditions are less than 8%. Resolution of system is less than 8.4% in the indoor environment. Using many peaks of U and Th, and linear equation of energy, obtained the starting energy threshold which is less than 23KeV. Both the each detector and system’s degree of linear fitting of energy are more than 0.9999. The integral nonlinearity is less than 0.2%, and the differential nonlinearity is less than 1.0%. The maximum count rate of system reached 200K/sec. The dead time determination of system is less than 5μs by dual-source net count. Through arbitrary 4 hours data of 24 hours indoor stability testing, relative errors between count-rate of each window and the average count-rate are less than±10%. Among them, the count-rate of TC is less than±6.29%. For 48 hours stability testing, placed the system into outdoor environment where temperature and humidity changes with time, observations show that the count-rate decreases with the ground moisture. In 1024 mode, attune slants 16 channels, and the system will return to good spectrum-stabilizing effect in 90 seconds.
(2) Using the data over the water and the land dynamic calibration belt below 300 metres, analyze the count-rate of different energy windows, thereby getting the rule of gamma-ray distribution by enery in low altitude above land and water. Using the data over the sea between 1800 and 3000 meters, analyze the count-rate of different energy windows, thereby getting the rule of gamma-ray distribution by enery in higher altitude above sea.
(3) In full on the basis of investigation and analysis, select the method of combining SINP and Fourier transform into deducting the bottom of the spectrum instrument accurately. Then, use direct demodulation method for analyzing the full spectrum. This method is applied to system calibration. By stripping coefficient method and aviation calibration model, demarcate the system of on-board, on plane of Y-5, and on plane of Y-12. Among them spectrum drift seriously in the on-board test, there is a obvious mistake, when spectra drift show more serious, scattering detachment is meaningless. Comparing inverse calculation content of the hybrid model by the two methods, both the relative errors are similar with the recommended value. Demonstrate the full spectrum of analytical calibration gammaγenergy spectrum in the aviation system in the feasibility and accuracy of calibration. Proof the full spectrum analytical calibration method’s accuracy and feasibility in the calibration of aiborne gamma-ray spectrometer system
(4) Using the method of full spectrum analytical calibration with a single point spectrum and all the data respectively, the calculation results show that using more datas will benefit the inhibiting of statistical fluctuation. By the model of K, U, Th, get a group of conversion coefficient, and another group by the model of M, both a relative error less than 2.2%. So can use a saturated standard model or sample to get conversion coefficients, thus the full spectrum analytical calibration method can reduce the workload of calibration effectively.
引文
[1]周蓉生,∏.A.瓦岗诺夫.核方法原理及应用[M].北京:地质出版社,1994.
[2]刘艳阳,张志勇,刘庆成.我国航空伽玛能谱测量概述[J].铀矿冶,2007,26(2):79～83.
[3]李怀渊.航空放射性测量在环境检测中的应用[J].物探与化探,2004,28(6):515-517.
[4]韦中亚,徐素宁,邬伦.环境航空测量与评价系统的设计与实现[J].地理学与国土研究,2000,16(4):86-89.
[5]彭训才.航空伽玛能谱的找矿和地质研究潜力[J].物探与化探,2009,33(3):240-244.
[6]周锡华,乔广志.新一代航空伽玛能谱仪的引进和初步应用[J].物探与化探,2002,26(4):318-320.
[7]韦中亚,徐素宁,吴景双,等.土壤侵蚀调查中的航空137Cs测量方法初探[J].水土保持研究,2001,8(2):45-49.
[8] Technical report series.Airborne gamma ray spectrometer surveying international atomic energy agency[J]. Vienna, 1991.323.
[9] S.M.Wright, B. J. Howard, P. Strand, T. N ylen, M.A.K. Sickel. Prediction of 137Cs deposition from atmospheric nuclear weapons tests with in the artic[J]. Enviromental pollution 1999, 104: 131～143.
[10]王守坦.航空物探技术[J].地学前缘,1998,5(1～2):223～229.
[11]梁月明,黄旭钊,周道卿.航空物探在酸性岩岩性划分中的效果[J].物探与化探,2007, 31(6):520-525.
[12]陈树军,刘菁华,王祝文.航空伽玛能谱测量在浅覆盖区地质填图单元划分中的应用[J].物探与化探,2007,31(2):110-114.
[13] Gunn P J , Minty B R S , Milligan P R. The airborne gamma-ray spectrometric response over arid australian terranes. Meeting of―Exploration’97‖, Toronto (Canada) . Abstracts, 1997. 55.
[14] Minty,B.R.S Fundamentals of airborne gamma-ray spectrometry AGSO Journal of Australian Geology & Geophysics 17,02(1997)39～50.
[15]范正国,方迎尧,王懋基等.航空物探技术在1:25万区域地质调查中的应用[J].物探与化探,2007,31(6):504-509.
[16]倪卫冲,顾仁康.核应急航空监测方法[J].铀矿地质,2003,19(6):366～373.
[17]熊盛青.我国航空物探现状与展望[J].中国地质,1999,9:18-22.
[18]刘裕华,顾仁康,候振荣.航空放射性测量[J].物探与化探,2002,26(4):250-253.
[19]吴慧山.用航空γ能谱法普查铀矿[J].国外铀金地质,2001,18(4):227-231.
[20]沃罗比约夫.普查金属矿床的航空γ能谱测量方法.地质出版社,北京.1985.
[21]谷懿.航空伽玛能谱测量大气氡校正方法研究[D].成都理工大学,博士论文,2010.
[22]熊盛青.航空物探―九五‖进展综述[J].物探与化探,2002,26(1):1-5.
[23]郭良德.西方国家航空物探技术的若干进展[J].物探与化探,2000,24(5):340-345.
[24]线纪安.航空物探的技术现状及其应用[J].地质找矿纵论,2003,18(增刊):191-195.
[25]线纪安.冶金地质系统航空物探工作三十年[J].地质与勘探,2001,37(3):36-40.
[26]王怀武,韩长青.航空物探和航天遥感技术在环境评价中的应用现状[J].铀矿地质,17(2):125-128. [27] M. Matolin, B. Minty, LEVELLING AIRBORNE AND GROUND GAMMA-RAY SPECTROMETRIC DATA TO ASSIST URANIUM EXPLORATION. Environmental Issues, Vienna, Austria, 22-26 June 2009.
[28]葛良全,曾国强,赖万昌,等.航空数字γ能谱测量系统的研制[J].核技术,2011,34(2):156-159.
[29]吴永鹏,赖万昌,葛良全,等.多道γ能谱仪中的特征峰稳谱技术[J].物探与化探,2003,27(2):131-134.
[30]邱晓林,方国明,弟宇鸣,等.核辐射脉冲幅度分析的基线卡尔曼滤波估计[J].原子能科学技术,2007,41(3):375-377.
[31]曾国强,葛良全,熊盛青,等.卡尔曼滤波在航空γ能谱勘查系统自动稳谱中的应用[J].核电子学与探测技术,2010,30(5):698-702.
[32]李兵海,陈涛.小波分析在航空放射性谱数据处理中的应用[J].物探与化探,2006,30(4):334-337.
[33]张佳媚,师全林,白涛,等.小波分析方法对降低γ谱统计涨落的作用[J].原子能科学技术,2005,39(4):349-353.
[34]闫学昆,刘明健,张娜,等.基于小波变换的γ能谱分析[J].原子能科学技术,2007,41(4):505-508.
[35]于国梁,张一云,贺梁国.小波分析法检测γ谱特征峰[J].原子能科学技术,2008,42(11):984-987.
[36]于国梁,张一云,黎亚平,等.用小波分析方法提高γ谱弱峰检测能力的研究[J].四川大学学报(自然科学版),2005,42(2):334-339.
[37]葛良全.核辐射测量方法讲义.2006.
[38]庞巨丰.γ能谱数据分析[M].西安:陕西科学技术出版社,1990.
[39] Jens Hovgaard. A new processing technique for airborne gamma-ray spectrometer data(Noise adjusted singular value decomposition)[C]. In: Proceedings of American Nuclear Society Sixth Topical Meeting on Emergency Preparedness and Response, pp. 123–127.
[40] K. V. Mardia et al. Multivariate Analysis, Chap.8 &Appendix A[M]. London: Academic prsee,1994.
[41] B. H. Dickson, B. C. Bailey, and R. L. Grasty. Utilizingmulti-channel airborne gamma-ray spectra[J].Canadian Journal of Earth Sciences, 1981,18(12): 1793-1801.
[42] J. Hovgaard. A new approach to processing of airborne gamma-ray spectra. report, IAU, Technical Univesity of Denmark, December,1996.
[43] Hovgaard, J., and Grasty, R.L, Reducing Statistical Noise in Airborne Gamma-Ray Data Through Spectral Component Analysis[J]. Radiometric Methods and Remote Sensing,98:753-763.
[44] Grasty, R.L., and Hovgaard, J, The calibration of upward looking detectors in gamma-ray surveys: Proceedings 66th annual meeting of Society of Exploration Geophysicists. Denver, 1423-1425.
[45] Dickson, B.L., Taylor, G.F., Maximum noise fraction method reveals detail in aerial gamma-ray[J]. Exploration Geophysics,2000,31:73-77.
[46] Korsbech, U., Bargholz, K., Aage, H.K., Petersen, J. Simple calibration of spectral components based on airborne gamma-ray spectrometry data[C]. Notes for NKS PhD Course on Advanced Methods for Processing AGS and CGS and Similar Sets of Spectral Data. 2002, Available from http://server4. oersted.dtu.dk/ research/RI/AGSCGS/DKNASVD.pdf.
[47] Minty, B.R.S. Comments on:―Noise reduction of aerial gamma-ray surveys‖by Bruce Dickson, Geoffrey Taylor (Exploration Geophysics 29, 324–329). Exploration Geophysics,2001, 32, 129–130.
[48] Minty, B., McFadden, P. Improved NASVD smoothing of airborne gamma-ray spectra[J]. Exploration Geophysics,1998,29:516-523.
[49] Switzer, P., Green A.A. Min/Max Autocorrelation Factors for Multivariate Spatial Imagery[C]. Technical Report 6. Department of Statistics, Stanford University, Stanford, CA.1984.
[50] Tammenmaa, J., Grasty, R.L., Peltoniemi, M. The reduction of statistical noise in airborne radiometric data[J]. Canadian Journal of Earth Science, 1976, 13: 1351–1357.
[51] Bruce L. Dickson., Recent advances in aerial gamma-ray surveying[J]. Journal of environmental radioactivity, 2004, 76:225-236.
[52]刘建防,刘旭霞,宋健侃.峰面积法和逆矩阵法解析NaI(Tl)谱仪γ射线谱的比较[J].干旱环境监测,2004,18(1):12-15.
[53]李惕碚,吴枚.高能天文中成像和解谱的直接方法[J].天体物理学报,1993,17(3):263-270.
[54]李惕碚.能不能用低分辨率仪器实现高分辨率观测[J].大自然探索,1999,18(67).
[55]刘尊年,任爱阁,贾瑞皋.自然伽玛能谱测井谱解析方法研究[J].西南石油大学学报(自然科学版),2010,32(5):75-78.
[56]艾宪文.碲锌镉探测器性能分析及其γ谱解析方法研究[D].清华大学,博士论文,2005.
[57] East L V, et al. Body Burden analysis using a minicomputer based system.Canberra Paper Presented at the ANS Nuclear Technology Exhibit. Beijing, China. October 23,1981.
[58] Ewrro R J, Kennett T J, Prestwich W V. An automated background estimation procedure for gamma-ray spectra[J]. Nuclear Instrument and Metheds,1983, 216:205-207.
[59] Burgess D D,Terro R J. Background estimation for gamma-ray spectrometry[J]. Nuclear Instrument and Methods, 1983,214:431.
[60] Winter G. Continuum estimation and peak analysis for In-BEAM gamma-ray spectra. Nuclear Instrument and Methods in Physics Research,1987,A258:119.
[61]申成瑶,魏天佑,唐明华,等.NaI(Tl)整体测量γ谱的连续谱本底自动处理法[J].辐射防护,1994,14(2):148-153.
[62]田东风,龚健,伍钧,等.核材料γ特征谱的探测和分析技术[M].北京:国防工业出版社,2005.
[63]龚海宁,申华,黄惠忠,等.XPS中Tougaard法本底扣除初探[J].物理化学学报,2002,18(4):326-331.
[64]张庆贤.航空γ能谱特征和仪器谱解析方法研究[D].成都理工大学,博士论文,2010.
[65]王新建,葛良全,曾国强.小波多分辨率分析在X荧光谱线本底扣除中的应用研究[J].核电子学与探测技术,2008,28(4):853-856.
[66]尹旺明,刘宏章,汤彬.基于SNIP算法扣除γ能谱本底的探讨及应用[J].东华理工大学学报(自然科学版),2009,32(3):245-248.
[67] IAEA. Airborne gamma-ray spectrometer surveying [R]. IAEA Technical report, 1991,NO.323.
[68]孙健,张力军,来永芳,等.航空γ能谱监测系统的刻度方法[C].第十四届全国核电子学与探测技术学术年会论文集,2008,607-611.
[69]潘自强,郭明强,崔广志,等.中国天然辐射本底水平和居民剂量估算[J].辐射防护,1992,12(4):251-259.
[70]邱仁森.核能史话[M].长沙:湖南科技,2010.
[71]夏益华.关注人类活动引起天然照射的增加问题[J].辐射防护,2001,21(1):11-18.
[72]李广超.环境监测[M].北京:化学工业出版社,2010.
[73]李虎.环境自动连续监测技术[M].北京:化学工业出版社,2008.
[74]孙春宝.环境监测原理与技术[M].北京:机械工业出版社,2007.
[75]常用核辐射数据手册.北京:原子能出版社,1990.
[76]卢希庭.原子核物理[M].北京:原子能出版社,2000.
[77]成都地质学院三系.放射性测量方法[M].北京:原子能出版社,1978.
[78]吴慧山.核技术勘查[M].北京:原子能出版社,1994.
[79]程业勋,王南萍,侯胜利.核辐射场与放射性勘查[M].北京:地质出版社,2005.
[80]章晔,柴荣洲,石柏慎.放射性方法勘查[M].北京:原子能出版社,1990.
[81]邓新华.关于不同海拔高度宇宙射线吸收剂量率测量方法的探讨[J].四川环境,1990,9(3):39-42.
[82]蒋明.原子核物理导论[M].北京:原子能出版社,1983.
[83]丁洪林.核辐射探测器[M].哈尔滨:哈尔滨工程大学,2010.
[84]复旦大学,清华大学,北京大学合编.原子核物理实验方法[M].北京:原子能出版社,1985.
[85]钱建复,沈庭云.核辐射剂量学[M].北京:国防工业出版社,2009.
[86]赵天池.传感器和探测器的物理原理和应用[M].北京:科学出版社,2008.
[87]高鑫,何元金.LaBr3:Ce3+闪烁晶体研究进展[J].核电子学与探测技术,2010,30(1):5-11.
[88]中华人民共和国国家标准:EJ/T 4833-1997,多道脉冲幅度分析器主要性能、技术要求和测试方法,国家技术监督局,1997-10-14发布,1998-04-01实施.
[89]陈方强,葛良全,罗耀耀,等.双源净计数法测定航空γ能谱仪的死时间[J].核电子学与探测技术,2010,30(12):1555-1559.
[90]航空伽玛能谱勘查系统研发课题组.国家863计划重大项目“航空伽玛能谱勘查系统研发”子课题“航空伽玛能谱勘查系统的集成与测试”研究成果报告[R]. 2011.
[91]胡明考,蔡根庆,沈正新,等.应用航空伽玛能谱全谱信息预测铀成矿远景区[C].中国核科学技术进展报告,2009(1):160-163.
[92]中华人民共和国核行业标准:EJ/T 1032-2005,航空伽玛能谱测量规范,国防科学技术工业委员会,2005-04-11发布,2005-07-01实施.
[93]吴和喜,刘庆成,杨波,等. SNIP法在天然放射性核素γ能谱分析中的应用[J].核技术,2010,33(7):513-516.