就地γ能谱中天然核素峰谷比随砂土容重的变化  

PVR's Variety with Soil-bulk Density in In-Situγ Spectra of Natural Radionuclides

作　　者：冯天成[1] 吴睿[1] 苏川英[1] 陈伟[1] 刘俊[1] 冯元举[1] 贾明雁[1] 程建平[2] 

机构地区：[1]西北核技术研究所,西安710024 [2]清华大学工程物理系,北京100084

出　　处：《核电子学与探测技术》2013年第4期417-424,共8页Nuclear Electronics & Detection Technology

摘　　要：对就地γ能谱中天然核素峰谷比与砂土容重的关系进行了理论推导、MC计算及实验研究。结果表明,对半空间无限大体源,峰谷比是一常数,不随砂土容重而改变;对有限体积体源,峰谷比将随砂土容重的增大而减小,体源尺度越小,这种变化越灵敏,但总体变化幅度不大。对半空间无限大均匀体源的就地γ谱仪测量工作,由于源的纵向厚度无法人为控制,且即便在探测器视野减小的情况下,峰谷比随源容重的变化幅度也很小,因此通过通常的峰谷比方法测量砂土容重不可行。研究也表明,对半空间无限大均匀体源,就地γ能谱中同一天然核素两不同能量γ射线计数率比值,亦不随砂土容重的变化而改变。研究结论修正了"利用天然核素的就地γ能谱峰谷比可确定土壤密度"的结论;同时揭示,"利用航空γ能谱全谱信息,…也能完成…地层密度的测定"的可行性,尚应进一步探究;也发现,利用峰谷比原理,应用铅准直器屏蔽探测视野,可测量确定一堵孤立物体(如墙壁)的质量厚度,厚度越小灵敏度越高。It presents the specific relationship between soil bulk density and peak - to - valley ratio （PVR） of natural radionuclides in situ γ spectra, by theoretical deduction, Monte Carlo simulation and experimental re- search. Results show that for an infinite half - space volume source, PVR is a constant independent of the di- verse soil bulk density. But for a limited - scale volume source, PVR would decrease slowly with an increase in soil bulk density, and the smaller the source scale, the larger the PVR variation with soil bulk density. Howev- er, the PVR variation with bulk density is very small in general. For field measurements, the volume source thickness is uncontrollable in practice, and the volume source radius should not be as small as needed for the limitation of low detection efficiency. Hence the soil bulk density could not be determined through the informa- tion from PVR of field in situ γ spectra. And the results reveal the conclusions of ＂soil bulk - density can be determined through the PVR informa- tion of natural in - situ γ spectra＂, and ＂study on the law of low - energy γ spectra discovers the relationships between the characteristics of shape and the effective atomic number and the density of the material＂, should be revised by the new theory established in the paper; But it is discovered also that the mass thickness of an ideal isolated wall can be determined by the PVR method, which is very sensitive when the wall~ mass thickness is not very large.

关 键 词：就地γ能谱 天然核素 峰谷比 砂土容重 

分 类 号：TL81[核科学技术—核技术及应用]